| Message ID | 20230719192057.172560-1-brgl@bgdev.pl |
|---|---|
| Headers | show |
| Series | core: provide information about the parent chip in line requests | expand |
On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > While working on the DBus API, it occurred to me that while we can obtain > the list of requested offsets from a line request, this information lacks > context if we cannot get any information about the parent chip on which > the request was made. > > We cannot reference the chip in any way as its lifetime is disconnected > from the request but we can at least provide the path to the character > device used to open it as a way of providing some context for the offsets. > No problem with this conceptually, the only question I have is which one of these should be stored: - requested path e.g. 'a_symlink_to_my_favorite_chip' - canonicalised path e.g. '/dev/gpiochip0' - chip name e.g. 'gpiochip0' - chip number e.g. 0 In this patch we get the requested path, right? Cheers, Kent. > This series adds a new getter for struct gpiod_line_request and wrappers > for it for all bindings. This will be used in the upcoming DBus GPIO > manager code. > > Bartosz Golaszewski (5): > core: provide gpiod_line_request_get_chip_path() > tests: add a test-case for gpiod_line_request_get_chip_path() > bindings: cxx: provide line_request::chip_path() > bindings: python: provide the chip_path property in line_request > bindings: rust: provide LineRequest::chip_path() > > bindings/cxx/gpiodcxx/line-request.hpp | 7 +++++++ > bindings/cxx/line-request.cpp | 10 +++++++++- > bindings/cxx/tests/tests-line-request.cpp | 6 ++++-- > bindings/python/gpiod/chip.py | 1 + > bindings/python/gpiod/line_request.py | 12 +++++++++-- > bindings/python/tests/tests_line_request.py | 13 +++++++----- > bindings/rust/libgpiod/src/line_request.rs | 12 +++++++++++ > bindings/rust/libgpiod/tests/line_request.rs | 13 ++++++++++++ > include/gpiod.h | 9 +++++++++ > lib/chip.c | 2 +- > lib/internal.h | 3 ++- > lib/line-request.c | 20 ++++++++++++++++++- > tests/tests-line-request.c | 21 ++++++++++++++++++++ > 13 files changed, 116 insertions(+), 13 deletions(-) > > -- > 2.39.2 >
On Wed Jul 19, 2023 at 9:20 PM CEST, Bartosz Golaszewski wrote: > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > Provide a wrapper around gpiod_line_request_get_chip_path() for Rust > bindings and add a test-case. > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > --- [...] > diff --git a/bindings/rust/libgpiod/src/line_request.rs b/bindings/rust/libgpiod/src/line_request.rs > index 1140aa9..2caab14 100644 > --- a/bindings/rust/libgpiod/src/line_request.rs > +++ b/bindings/rust/libgpiod/src/line_request.rs [...] > @@ -25,6 +26,17 @@ impl Request { > Ok(Self { request }) > } > > + pub fn chip_path(&self) -> Result<&str> { A rustdoc comment `/// <explanation>` on the function may be helpful. The other functions have some (though those could probably also be a little longer...). More importantly, _if_ this function is returning a file path, then I would consider to return a Path [1]. The conversion from &str -> Path is "0-cost" and makes the API more explicit. `Sim::dev_path()` also returns a PathBuf so the conversion in the test would become a little easier. > + // SAFETY: The string returned by libgpiod is guaranteed to live as long > + // as the `struct LineRequest`. > + let path = unsafe { gpiod::gpiod_line_request_get_chip_path(self.request) }; The SAFETY comment should explain why the following `unsafe` block is safe. For this block, the lifetime of the string does not matter for safety. Instead, it should explain why self.request is valid and safe to use. Maybe like this? + // SAFETY: The `gpiod_line_request` is guaranteed to be live as long + // as `&self` > + // SAFETY: The string is guaranteed to be valid here by the C API. > + unsafe { CStr::from_ptr(path) } > + .to_str() > + .map_err(Error::StringNotUtf8) > + } Here the lifetime of the string is important then! Checking the Cstr::from_ptr doc [2], one needs to ensure that: - The memory pointed to by ptr must contain a valid nul terminator at the end of the string. - ptr must be valid for reads of bytes up to and including the null terminator. - The memory referenced by the returned CStr must not be mutated for the duration of lifetime 'a. The SAFETY comment should explain why these three requirements are satisfied. Suggestion: + // SAFETY: The string is guaranteed to be valid, non-null and immutable + // by the C API for the lifetime of the `gpiod_line_request`. The + // `gpiod_line_request` is living as long as `&self`. The string is + // returned read-only with a lifetime of `&self`. [1] https://doc.rust-lang.org/stable/std/path/struct.Path.html [2] https://doc.rust-lang.org/std/ffi/struct.CStr.html#method.from_ptr [...] LGTM otherwise. - Erik
On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > While working on the DBus API, it occurred to me that while we can obtain > > the list of requested offsets from a line request, this information lacks > > context if we cannot get any information about the parent chip on which > > the request was made. > > > > We cannot reference the chip in any way as its lifetime is disconnected > > from the request but we can at least provide the path to the character > > device used to open it as a way of providing some context for the offsets. > > > > No problem with this conceptually, the only question I have is which > one of these should be stored: > - requested path e.g. 'a_symlink_to_my_favorite_chip' > - canonicalised path e.g. '/dev/gpiochip0' > - chip name e.g. 'gpiochip0' > - chip number e.g. 0 > > In this patch we get the requested path, right? > Yes, I think we should just use whatever filesystem path was used to create the chip as it would be the one allowing the caller to reopen the same chip. Bart > Cheers, > Kent. > > > This series adds a new getter for struct gpiod_line_request and wrappers > > for it for all bindings. This will be used in the upcoming DBus GPIO > > manager code. > > > > Bartosz Golaszewski (5): > > core: provide gpiod_line_request_get_chip_path() > > tests: add a test-case for gpiod_line_request_get_chip_path() > > bindings: cxx: provide line_request::chip_path() > > bindings: python: provide the chip_path property in line_request > > bindings: rust: provide LineRequest::chip_path() > > > > bindings/cxx/gpiodcxx/line-request.hpp | 7 +++++++ > > bindings/cxx/line-request.cpp | 10 +++++++++- > > bindings/cxx/tests/tests-line-request.cpp | 6 ++++-- > > bindings/python/gpiod/chip.py | 1 + > > bindings/python/gpiod/line_request.py | 12 +++++++++-- > > bindings/python/tests/tests_line_request.py | 13 +++++++----- > > bindings/rust/libgpiod/src/line_request.rs | 12 +++++++++++ > > bindings/rust/libgpiod/tests/line_request.rs | 13 ++++++++++++ > > include/gpiod.h | 9 +++++++++ > > lib/chip.c | 2 +- > > lib/internal.h | 3 ++- > > lib/line-request.c | 20 ++++++++++++++++++- > > tests/tests-line-request.c | 21 ++++++++++++++++++++ > > 13 files changed, 116 insertions(+), 13 deletions(-) > > > > -- > > 2.39.2 > >
On Thu, Jul 20, 2023 at 7:04 AM Erik Schilling <erik.schilling@linaro.org> wrote: > > On Wed Jul 19, 2023 at 9:20 PM CEST, Bartosz Golaszewski wrote: > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > Provide a wrapper around gpiod_line_request_get_chip_path() for Rust > > bindings and add a test-case. > > > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > --- > [...] > > diff --git a/bindings/rust/libgpiod/src/line_request.rs b/bindings/rust/libgpiod/src/line_request.rs > > index 1140aa9..2caab14 100644 > > --- a/bindings/rust/libgpiod/src/line_request.rs > > +++ b/bindings/rust/libgpiod/src/line_request.rs > [...] > > @@ -25,6 +26,17 @@ impl Request { > > Ok(Self { request }) > > } > > > > + pub fn chip_path(&self) -> Result<&str> { > > A rustdoc comment `/// <explanation>` on the function may be helpful. > The other functions have some (though those could probably also be a > little longer...). > > More importantly, _if_ this function is returning a file path, then I > would consider to return a Path [1]. The conversion from &str -> Path is > "0-cost" and makes the API more explicit. `Sim::dev_path()` also returns > a PathBuf so the conversion in the test would become a little easier. > I wanted to stay in line with chip's path() getter which also returns Result<&str>. As you're saying - the user can convert it at 0 cost if needed. Bart > > + // SAFETY: The string returned by libgpiod is guaranteed to live as long > > + // as the `struct LineRequest`. > > + let path = unsafe { gpiod::gpiod_line_request_get_chip_path(self.request) }; > > The SAFETY comment should explain why the following `unsafe` block is > safe. For this block, the lifetime of the string does not matter for > safety. Instead, it should explain why self.request is valid and safe > to use. > > Maybe like this? > > + // SAFETY: The `gpiod_line_request` is guaranteed to be live as long > + // as `&self` > > > > + // SAFETY: The string is guaranteed to be valid here by the C API. > > + unsafe { CStr::from_ptr(path) } > > + .to_str() > > + .map_err(Error::StringNotUtf8) > > + } > > Here the lifetime of the string is important then! Checking the > Cstr::from_ptr doc [2], one needs to ensure that: > > - The memory pointed to by ptr must contain a valid nul terminator at > the end of the string. > - ptr must be valid for reads of bytes up to and including the null > terminator. > - The memory referenced by the returned CStr must not be mutated for the > duration of lifetime 'a. > > The SAFETY comment should explain why these three requirements are > satisfied. > > Suggestion: > > + // SAFETY: The string is guaranteed to be valid, non-null and immutable > + // by the C API for the lifetime of the `gpiod_line_request`. The > + // `gpiod_line_request` is living as long as `&self`. The string is > + // returned read-only with a lifetime of `&self`. > I'll take the suggestions verbatim, thanks! Bart > [1] https://doc.rust-lang.org/stable/std/path/struct.Path.html > [2] https://doc.rust-lang.org/std/ffi/struct.CStr.html#method.from_ptr > > [...] > > LGTM otherwise. > > - Erik
On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > the list of requested offsets from a line request, this information lacks > > > context if we cannot get any information about the parent chip on which > > > the request was made. > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > from the request but we can at least provide the path to the character > > > device used to open it as a way of providing some context for the offsets. > > > > > > > No problem with this conceptually, the only question I have is which > > one of these should be stored: > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > - canonicalised path e.g. '/dev/gpiochip0' > > - chip name e.g. 'gpiochip0' > > - chip number e.g. 0 > > > > In this patch we get the requested path, right? > > > > Yes, I think we should just use whatever filesystem path was used to > create the chip as it would be the one allowing the caller to reopen > the same chip. > So there are instances where those four don't map to the same thing? Cheers, Kent.
On Thu Jul 20, 2023 at 10:04 AM CEST, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 7:04 AM Erik Schilling > <erik.schilling@linaro.org> wrote: > > > > On Wed Jul 19, 2023 at 9:20 PM CEST, Bartosz Golaszewski wrote: > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > Provide a wrapper around gpiod_line_request_get_chip_path() for Rust > > > bindings and add a test-case. > > > > > > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > --- > > [...] > > > diff --git a/bindings/rust/libgpiod/src/line_request.rs b/bindings/rust/libgpiod/src/line_request.rs > > > index 1140aa9..2caab14 100644 > > > --- a/bindings/rust/libgpiod/src/line_request.rs > > > +++ b/bindings/rust/libgpiod/src/line_request.rs > > [...] > > > @@ -25,6 +26,17 @@ impl Request { > > > Ok(Self { request }) > > > } > > > > > > + pub fn chip_path(&self) -> Result<&str> { [...] > > More importantly, _if_ this function is returning a file path, then I > > would consider to return a Path [1]. The conversion from &str -> Path is > > "0-cost" and makes the API more explicit. `Sim::dev_path()` also returns > > a PathBuf so the conversion in the test would become a little easier. > > > > I wanted to stay in line with chip's path() getter which also returns > Result<&str>. As you're saying - the user can convert it at 0 cost if > needed. Makes sense. Did not notice that it is used as &str elsewhere. - Erik
On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > the list of requested offsets from a line request, this information lacks > > > > context if we cannot get any information about the parent chip on which > > > > the request was made. > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > from the request but we can at least provide the path to the character > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > one of these should be stored: > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > - canonicalised path e.g. '/dev/gpiochip0' > > > - chip name e.g. 'gpiochip0' > > > - chip number e.g. 0 > > > > > > In this patch we get the requested path, right? > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > create the chip as it would be the one allowing the caller to reopen > > the same chip. > > > > So there are instances where those four don't map to the same thing? > Not in a typical situation, it can happen if the chip was removed and another one took its place which is very unlikely. I just think that we cannot have any "hard data" as in: a programmatic reference to the chip in the request (their lifetimes are not connected), so the next best thing is the filesystem path. Bart
On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > the list of requested offsets from a line request, this information lacks > > > > > context if we cannot get any information about the parent chip on which > > > > > the request was made. > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > from the request but we can at least provide the path to the character > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > one of these should be stored: > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > - chip name e.g. 'gpiochip0' > > > > - chip number e.g. 0 > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > create the chip as it would be the one allowing the caller to reopen > > > the same chip. > > > > > > > So there are instances where those four don't map to the same thing? > > > > Not in a typical situation, it can happen if the chip was removed and > another one took its place which is very unlikely. > And a symlink could get changed as well. > I just think that we cannot have any "hard data" as in: a programmatic > reference to the chip in the request (their lifetimes are not > connected), so the next best thing is the filesystem path. > Indeed - the chip fd used to request the line is out of scope. But the number of possible requested paths is many, whereas the other three options produce a unique and comparable identifier, in a searching sense. On a related point, does the DBus API allow a client to access lines requested by another client? And if so, how can they be sure they have the right line? Cheers, Kent.
On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: ... > as it would be the one allowing the caller to reopen the same chip. Since you do not control the lifetime of the files, the above may not be guaranteed. So, this path is just an arbitrary information from the past. It _was_ consistent with the request, but it does _not_ mean it still is. I would rely on the chip name, which is provided by the DT/driver, if possible.
On Thu, Jul 20, 2023 at 10:39 AM Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > > the list of requested offsets from a line request, this information lacks > > > > > > context if we cannot get any information about the parent chip on which > > > > > > the request was made. > > > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > > from the request but we can at least provide the path to the character > > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > > one of these should be stored: > > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > > - chip name e.g. 'gpiochip0' > > > > > - chip number e.g. 0 > > > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > > create the chip as it would be the one allowing the caller to reopen > > > > the same chip. > > > > > > > > > > So there are instances where those four don't map to the same thing? > > > > > > > Not in a typical situation, it can happen if the chip was removed and > > another one took its place which is very unlikely. > > > > And a symlink could get changed as well. > > > I just think that we cannot have any "hard data" as in: a programmatic > > reference to the chip in the request (their lifetimes are not > > connected), so the next best thing is the filesystem path. > > > > Indeed - the chip fd used to request the line is out of scope. > > But the number of possible requested paths is many, whereas the other > three options produce a unique and comparable identifier, in a searching > sense. > So which one do you suggest? > On a related point, does the DBus API allow a client to access lines > requested by another client? And if so, how can they be sure they have > the right line? > Sure they can but various user permissions as configured in the relevant .conf file may apply. So what I've got so far in dbus (and feel free to check out the WiP[1]) is this: There's an /io/gpiod1/gpiochipX object per chip implementing the io.gpiod1.Chip interface. For each line there's a separate object as well: /io/gpiod1/gpiochip0 /io/gpiod1/gpiochip0/0 /io/gpiod1/gpiochip0/1 /io/gpiod1/gpiochip0/2 /io/gpiod1/gpiochip0/3 Line objects implement the io.gpiod1.Line interface and the daemon emits a PropertiesChanged signal for any status changes. You can call io.gpiod1.Chip.RequestLines() method on a chip object which will return the object path to the new request. /io/gpiod1/gpiochip0 /io/gpiod1/gpiochip0/0 /io/gpiod1/gpiochip0/1 /io/gpiod1/gpiochip0/2 /io/gpiod1/gpiochip0/3 /io/gpiod1/request0 The request will reference the chip object from which it was created as well as the lines it controls. Bart > Cheers, > Kent. [1] https://github.com/brgl/libgpiod-private/tree/topic/dbus/
On Thu, Jul 20, 2023 at 10:49:46AM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 10:39 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > > > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > > > the list of requested offsets from a line request, this information lacks > > > > > > > context if we cannot get any information about the parent chip on which > > > > > > > the request was made. > > > > > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > > > from the request but we can at least provide the path to the character > > > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > > > one of these should be stored: > > > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > > > - chip name e.g. 'gpiochip0' > > > > > > - chip number e.g. 0 > > > > > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > > > create the chip as it would be the one allowing the caller to reopen > > > > > the same chip. > > > > > > > > > > > > > So there are instances where those four don't map to the same thing? > > > > > > > > > > Not in a typical situation, it can happen if the chip was removed and > > > another one took its place which is very unlikely. > > > > > > > And a symlink could get changed as well. > > > > > I just think that we cannot have any "hard data" as in: a programmatic > > > reference to the chip in the request (their lifetimes are not > > > connected), so the next best thing is the filesystem path. > > > > > > > Indeed - the chip fd used to request the line is out of scope. > > > > But the number of possible requested paths is many, whereas the other > > three options produce a unique and comparable identifier, in a searching > > sense. > > > > So which one do you suggest? > Any of the latter three are equivlent, so you can use whichever is most convenient. I've used canonical path in my Rust library, and chip name in my Go library. IIRC in Rust I had the canonical path handy and it was easier to keep it as is than to break it down to name or number. Why I went with name in the Go is lost in the mists of time. I do recall toying with going with number but I wasn't sure if gpiochips were guaranteed to be named 'gpiochipN'. Given what you have below for DBus, name looks the most natural to me. > > On a related point, does the DBus API allow a client to access lines > > requested by another client? And if so, how can they be sure they have > > the right line? > > > > Sure they can but various user permissions as configured in the > relevant .conf file may apply. > So setting up the dbus-daemon security policy for the objects? > So what I've got so far in dbus (and feel free to check out the WiP[1]) is this: > I have had a quick look at it, but so far only a quick look and I'm not familiar with DBus so there is a lot of background to fill in. > There's an /io/gpiod1/gpiochipX object per chip implementing the > io.gpiod1.Chip interface. For each line there's a separate object as > well: > > /io/gpiod1/gpiochip0 > /io/gpiod1/gpiochip0/0 > /io/gpiod1/gpiochip0/1 > /io/gpiod1/gpiochip0/2 > /io/gpiod1/gpiochip0/3 > > Line objects implement the io.gpiod1.Line interface and the daemon > emits a PropertiesChanged signal for any status changes. > Can the client select which of those signals it sees? > You can call io.gpiod1.Chip.RequestLines() method on a chip object > which will return the object path to the new request. > > /io/gpiod1/gpiochip0 > /io/gpiod1/gpiochip0/0 > /io/gpiod1/gpiochip0/1 > /io/gpiod1/gpiochip0/2 > /io/gpiod1/gpiochip0/3 > /io/gpiod1/request0 > > The request will reference the chip object from which it was created > as well as the lines it controls. > What about the reverse mapping? Where do edge events fit in there? Cheers, Kent.
On Thu, Jul 20, 2023 at 11:16 AM Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Jul 20, 2023 at 10:49:46AM +0200, Bartosz Golaszewski wrote: > > On Thu, Jul 20, 2023 at 10:39 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > > > > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > > > > the list of requested offsets from a line request, this information lacks > > > > > > > > context if we cannot get any information about the parent chip on which > > > > > > > > the request was made. > > > > > > > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > > > > from the request but we can at least provide the path to the character > > > > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > > > > one of these should be stored: > > > > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > > > > - chip name e.g. 'gpiochip0' > > > > > > > - chip number e.g. 0 > > > > > > > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > > > > create the chip as it would be the one allowing the caller to reopen > > > > > > the same chip. > > > > > > > > > > > > > > > > So there are instances where those four don't map to the same thing? > > > > > > > > > > > > > Not in a typical situation, it can happen if the chip was removed and > > > > another one took its place which is very unlikely. > > > > > > > > > > And a symlink could get changed as well. > > > > > > > I just think that we cannot have any "hard data" as in: a programmatic > > > > reference to the chip in the request (their lifetimes are not > > > > connected), so the next best thing is the filesystem path. > > > > > > > > > > Indeed - the chip fd used to request the line is out of scope. > > > > > > But the number of possible requested paths is many, whereas the other > > > three options produce a unique and comparable identifier, in a searching > > > sense. > > > > > > > So which one do you suggest? > > > > Any of the latter three are equivlent, so you can use whichever is most > convenient. I've used canonical path in my Rust library, and chip name > in my Go library. IIRC in Rust I had the canonical path handy and it > was easier to keep it as is than to break it down to name or number. > Why I went with name in the Go is lost in the mists of time. > I do recall toying with going with number but I wasn't sure if gpiochips > were guaranteed to be named 'gpiochipN'. > > Given what you have below for DBus, name looks the most natural to me. > > > > On a related point, does the DBus API allow a client to access lines > > > requested by another client? And if so, how can they be sure they have > > > the right line? > > > > > > > Sure they can but various user permissions as configured in the > > relevant .conf file may apply. > > > > So setting up the dbus-daemon security policy for the objects? > Not per-object unfortunately, I don't think this is possible with the standard dbus-daemon or dbus-broker. May be possible in the daemon itself if we can get the UID of the peer (we can get credentials of peers in pure DBus but I'm not sure if we can do it when passing through a bus daemon). > > So what I've got so far in dbus (and feel free to check out the WiP[1]) is this: > > > > I have had a quick look at it, but so far only a quick look and I'm not > familiar with DBus so there is a lot of background to fill in. > > > There's an /io/gpiod1/gpiochipX object per chip implementing the > > io.gpiod1.Chip interface. For each line there's a separate object as > > well: > > > > /io/gpiod1/gpiochip0 > > /io/gpiod1/gpiochip0/0 > > /io/gpiod1/gpiochip0/1 > > /io/gpiod1/gpiochip0/2 > > /io/gpiod1/gpiochip0/3 > > > > Line objects implement the io.gpiod1.Line interface and the daemon > > emits a PropertiesChanged signal for any status changes. > > > > Can the client select which of those signals it sees? > They can listen for PropertiesChanged on a single line but will get an event on any change and will have to filter out the unwanted themselves. > > You can call io.gpiod1.Chip.RequestLines() method on a chip object > > which will return the object path to the new request. > > > > /io/gpiod1/gpiochip0 > > /io/gpiod1/gpiochip0/0 > > /io/gpiod1/gpiochip0/1 > > /io/gpiod1/gpiochip0/2 > > /io/gpiod1/gpiochip0/3 > > /io/gpiod1/request0 > > > > The request will reference the chip object from which it was created > > as well as the lines it controls. > > > > What about the reverse mapping? > As in: line-to-request? Not sure this is needed? I want the io.gpiod1.Line interface to expose GetValue/SetValue methods and let the daemon figure out the mapping logic internally. These methods would fail if the line is not part of any request controlled by the daemon. > > Where do edge events fit in there? > It's a signal exposed by the io.gpiod1.Line interface. Bart > Cheers, > Kent.
On Thu, Jul 20, 2023 at 11:38:19AM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 11:16 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > On Thu, Jul 20, 2023 at 10:49:46AM +0200, Bartosz Golaszewski wrote: > > > On Thu, Jul 20, 2023 at 10:39 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > > > > > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > > > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > > > > > the list of requested offsets from a line request, this information lacks > > > > > > > > > context if we cannot get any information about the parent chip on which > > > > > > > > > the request was made. > > > > > > > > > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > > > > > from the request but we can at least provide the path to the character > > > > > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > > > > > one of these should be stored: > > > > > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > > > > > - chip name e.g. 'gpiochip0' > > > > > > > > - chip number e.g. 0 > > > > > > > > > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > > > > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > > > > > create the chip as it would be the one allowing the caller to reopen > > > > > > > the same chip. > > > > > > > > > > > > > > > > > > > So there are instances where those four don't map to the same thing? > > > > > > > > > > > > > > > > Not in a typical situation, it can happen if the chip was removed and > > > > > another one took its place which is very unlikely. > > > > > > > > > > > > > And a symlink could get changed as well. > > > > > > > > > I just think that we cannot have any "hard data" as in: a programmatic > > > > > reference to the chip in the request (their lifetimes are not > > > > > connected), so the next best thing is the filesystem path. > > > > > > > > > > > > > Indeed - the chip fd used to request the line is out of scope. > > > > > > > > But the number of possible requested paths is many, whereas the other > > > > three options produce a unique and comparable identifier, in a searching > > > > sense. > > > > > > > > > > So which one do you suggest? > > > > > > > Any of the latter three are equivlent, so you can use whichever is most > > convenient. I've used canonical path in my Rust library, and chip name > > in my Go library. IIRC in Rust I had the canonical path handy and it > > was easier to keep it as is than to break it down to name or number. > > Why I went with name in the Go is lost in the mists of time. > > I do recall toying with going with number but I wasn't sure if gpiochips > > were guaranteed to be named 'gpiochipN'. > > > > Given what you have below for DBus, name looks the most natural to me. > > > > > > On a related point, does the DBus API allow a client to access lines > > > > requested by another client? And if so, how can they be sure they have > > > > the right line? > > > > > > > > > > Sure they can but various user permissions as configured in the > > > relevant .conf file may apply. > > > > > > > So setting up the dbus-daemon security policy for the objects? > > > > Not per-object unfortunately, I don't think this is possible with the > standard dbus-daemon or dbus-broker. May be possible in the daemon > itself if we can get the UID of the peer (we can get credentials of > peers in pure DBus but I'm not sure if we can do it when passing > through a bus daemon). > > > > So what I've got so far in dbus (and feel free to check out the WiP[1]) is this: > > > > > > > I have had a quick look at it, but so far only a quick look and I'm not > > familiar with DBus so there is a lot of background to fill in. > > > > > There's an /io/gpiod1/gpiochipX object per chip implementing the > > > io.gpiod1.Chip interface. For each line there's a separate object as > > > well: > > > > > > /io/gpiod1/gpiochip0 > > > /io/gpiod1/gpiochip0/0 > > > /io/gpiod1/gpiochip0/1 > > > /io/gpiod1/gpiochip0/2 > > > /io/gpiod1/gpiochip0/3 > > > > > > Line objects implement the io.gpiod1.Line interface and the daemon > > > emits a PropertiesChanged signal for any status changes. > > > > > > > Can the client select which of those signals it sees? > > > > They can listen for PropertiesChanged on a single line but will get an > event on any change and will have to filter out the unwanted > themselves. > > > > You can call io.gpiod1.Chip.RequestLines() method on a chip object > > > which will return the object path to the new request. > > > > > > /io/gpiod1/gpiochip0 > > > /io/gpiod1/gpiochip0/0 > > > /io/gpiod1/gpiochip0/1 > > > /io/gpiod1/gpiochip0/2 > > > /io/gpiod1/gpiochip0/3 > > > /io/gpiod1/request0 > > > > > > The request will reference the chip object from which it was created > > > as well as the lines it controls. > > > > > > > What about the reverse mapping? > > > > As in: line-to-request? Not sure this is needed? I want the > io.gpiod1.Line interface to expose GetValue/SetValue methods and let > the daemon figure out the mapping logic internally. These methods > would fail if the line is not part of any request controlled by the > daemon. > The case I was thinking of was wanting to release a line, and if you don't know which request you will have to walk the request objects. And what of lines that are requested directly by apps other than the gpio-manager? > > > > Where do edge events fit in there? > > > > It's a signal exposed by the io.gpiod1.Line interface. But separate from the PropertiesChanged? I am also wondering if the tools can be extended with the option to perform their ops using the gpio-manager, particularly get/set/mon that currently require exclusive access. Cheers, Kent.
On Thu, Jul 20, 2023 at 11:52 AM Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Jul 20, 2023 at 11:38:19AM +0200, Bartosz Golaszewski wrote: > > On Thu, Jul 20, 2023 at 11:16 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > On Thu, Jul 20, 2023 at 10:49:46AM +0200, Bartosz Golaszewski wrote: > > > > On Thu, Jul 20, 2023 at 10:39 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > On Thu, Jul 20, 2023 at 10:25:14AM +0200, Bartosz Golaszewski wrote: > > > > > > On Thu, Jul 20, 2023 at 10:05 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > > > On Thu, Jul 20, 2023 at 09:59:00AM +0200, Bartosz Golaszewski wrote: > > > > > > > > On Thu, Jul 20, 2023 at 5:27 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > > > > > > > On Wed, Jul 19, 2023 at 09:20:52PM +0200, Bartosz Golaszewski wrote: > > > > > > > > > > From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> > > > > > > > > > > > > > > > > > > > > While working on the DBus API, it occurred to me that while we can obtain > > > > > > > > > > the list of requested offsets from a line request, this information lacks > > > > > > > > > > context if we cannot get any information about the parent chip on which > > > > > > > > > > the request was made. > > > > > > > > > > > > > > > > > > > > We cannot reference the chip in any way as its lifetime is disconnected > > > > > > > > > > from the request but we can at least provide the path to the character > > > > > > > > > > device used to open it as a way of providing some context for the offsets. > > > > > > > > > > > > > > > > > > > > > > > > > > > > No problem with this conceptually, the only question I have is which > > > > > > > > > one of these should be stored: > > > > > > > > > - requested path e.g. 'a_symlink_to_my_favorite_chip' > > > > > > > > > - canonicalised path e.g. '/dev/gpiochip0' > > > > > > > > > - chip name e.g. 'gpiochip0' > > > > > > > > > - chip number e.g. 0 > > > > > > > > > > > > > > > > > > In this patch we get the requested path, right? > > > > > > > > > > > > > > > > > > > > > > > > > Yes, I think we should just use whatever filesystem path was used to > > > > > > > > create the chip as it would be the one allowing the caller to reopen > > > > > > > > the same chip. > > > > > > > > > > > > > > > > > > > > > > So there are instances where those four don't map to the same thing? > > > > > > > > > > > > > > > > > > > Not in a typical situation, it can happen if the chip was removed and > > > > > > another one took its place which is very unlikely. > > > > > > > > > > > > > > > > And a symlink could get changed as well. > > > > > > > > > > > I just think that we cannot have any "hard data" as in: a programmatic > > > > > > reference to the chip in the request (their lifetimes are not > > > > > > connected), so the next best thing is the filesystem path. > > > > > > > > > > > > > > > > Indeed - the chip fd used to request the line is out of scope. > > > > > > > > > > But the number of possible requested paths is many, whereas the other > > > > > three options produce a unique and comparable identifier, in a searching > > > > > sense. > > > > > > > > > > > > > So which one do you suggest? > > > > > > > > > > Any of the latter three are equivlent, so you can use whichever is most > > > convenient. I've used canonical path in my Rust library, and chip name > > > in my Go library. IIRC in Rust I had the canonical path handy and it > > > was easier to keep it as is than to break it down to name or number. > > > Why I went with name in the Go is lost in the mists of time. > > > I do recall toying with going with number but I wasn't sure if gpiochips > > > were guaranteed to be named 'gpiochipN'. > > > > > > Given what you have below for DBus, name looks the most natural to me. > > > > > > > > On a related point, does the DBus API allow a client to access lines > > > > > requested by another client? And if so, how can they be sure they have > > > > > the right line? > > > > > > > > > > > > > Sure they can but various user permissions as configured in the > > > > relevant .conf file may apply. > > > > > > > > > > So setting up the dbus-daemon security policy for the objects? > > > > > > > Not per-object unfortunately, I don't think this is possible with the > > standard dbus-daemon or dbus-broker. May be possible in the daemon > > itself if we can get the UID of the peer (we can get credentials of > > peers in pure DBus but I'm not sure if we can do it when passing > > through a bus daemon). > > > > > > So what I've got so far in dbus (and feel free to check out the WiP[1]) is this: > > > > > > > > > > I have had a quick look at it, but so far only a quick look and I'm not > > > familiar with DBus so there is a lot of background to fill in. > > > > > > > There's an /io/gpiod1/gpiochipX object per chip implementing the > > > > io.gpiod1.Chip interface. For each line there's a separate object as > > > > well: > > > > > > > > /io/gpiod1/gpiochip0 > > > > /io/gpiod1/gpiochip0/0 > > > > /io/gpiod1/gpiochip0/1 > > > > /io/gpiod1/gpiochip0/2 > > > > /io/gpiod1/gpiochip0/3 > > > > > > > > Line objects implement the io.gpiod1.Line interface and the daemon > > > > emits a PropertiesChanged signal for any status changes. > > > > > > > > > > Can the client select which of those signals it sees? > > > > > > > They can listen for PropertiesChanged on a single line but will get an > > event on any change and will have to filter out the unwanted > > themselves. > > > > > > You can call io.gpiod1.Chip.RequestLines() method on a chip object > > > > which will return the object path to the new request. > > > > > > > > /io/gpiod1/gpiochip0 > > > > /io/gpiod1/gpiochip0/0 > > > > /io/gpiod1/gpiochip0/1 > > > > /io/gpiod1/gpiochip0/2 > > > > /io/gpiod1/gpiochip0/3 > > > > /io/gpiod1/request0 > > > > > > > > The request will reference the chip object from which it was created > > > > as well as the lines it controls. > > > > > > > > > > What about the reverse mapping? > > > > > > > As in: line-to-request? Not sure this is needed? I want the > > io.gpiod1.Line interface to expose GetValue/SetValue methods and let > > the daemon figure out the mapping logic internally. These methods > > would fail if the line is not part of any request controlled by the > > daemon. > > > > The case I was thinking of was wanting to release a line, and if you > don't know which request you will have to walk the request objects. > You cannot release a single line if it's part of a wider request though. > And what of lines that are requested directly by apps other than the > gpio-manager? > You can tell they're used but cannot request them just like with any other user of the cdev. > > > > > > Where do edge events fit in there? > > > > > > > It's a signal exposed by the io.gpiod1.Line interface. > > But separate from the PropertiesChanged? > Yes. PropertiesChanged is emitted on changes in properties (direction, edge, all reported by gpionotify) while EdgeEvent is for edges exclusively. > > I am also wondering if the tools can be extended with the option to > perform their ops using the gpio-manager, particularly get/set/mon that > currently require exclusive access. > There's a client app already functional in my WiP branch. Think nmcli for NetworkManager. It doesn't link against libgpiod - only uses the DBus API. You can do something like this (not all of this is implemented yet): $ # Wait for a chip with a particular label to appear $ gpiocli wait --chip="foobar" --timeout=10s $ # Request a line for edge events $ gpiocli request --input --rising-edge --falling-edge foo request0 $ # List available requests $ gpiocli requests request0 (gpiochip0) offsets: [4] $ # Wait for edge events: $ gpiocli monitor foo Offset: 4 RISING EDGE Timestamp: 3425234234 $ # Release the request $ gpiocli release request0 This way the user can easily use bash scripts, command line or even any DBus library out there while we still use the character device in the daemon and ditch sysfs. Bart > Cheers, > Kent. >
On Thu, Jul 20, 2023 at 02:30:45PM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 11:52 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > The case I was thinking of was wanting to release a line, and if you > > don't know which request you will have to walk the request objects. > > > > You cannot release a single line if it's part of a wider request though. > Of course. Unless we were to extend the uAPI to allow that. > > And what of lines that are requested directly by apps other than the > > gpio-manager? > > > > You can tell they're used but cannot request them just like with any > other user of the cdev. > This is going to be a pain point - the concept of "used" is getting muddy. Say two processes want to get a line. So both need to request it before they can get it? Or only one does the request and both can get? The latter case is painful to use. The former requires request being idempotent or at least to return an error that distiguishes a line already held by gpio-manager and a line already held but not by gpio-manager. > > > > > > > > Where do edge events fit in there? > > > > > > > > > > It's a signal exposed by the io.gpiod1.Line interface. > > > > But separate from the PropertiesChanged? > > > > Yes. PropertiesChanged is emitted on changes in properties (direction, > edge, all reported by gpionotify) while EdgeEvent is for edges > exclusively. > > > > > I am also wondering if the tools can be extended with the option to > > perform their ops using the gpio-manager, particularly get/set/mon that > > currently require exclusive access. > > > > There's a client app already functional in my WiP branch. Think nmcli > for NetworkManager. It doesn't link against libgpiod - only uses the > DBus API. > Sure - doesn't mean other tools can't use the DBus API too. My thinking was existing users of GPIO tools could just add an option, say -D, to their scripts to switch over to gpio-manager. > You can do something like this (not all of this is implemented yet): > > $ # Wait for a chip with a particular label to appear > $ gpiocli wait --chip="foobar" --timeout=10s > $ # Request a line for edge events > $ gpiocli request --input --rising-edge --falling-edge foo > request0 Will that support multiple lines, possibly spanning multiple chips? > $ # List available requests > $ gpiocli requests > request0 (gpiochip0) offsets: [4] But that will only return the requests made by gpio-manager, right? > $ # Wait for edge events: > $ gpiocli monitor foo > Offset: 4 RISING EDGE Timestamp: 3425234234 > $ # Release the request > $ gpiocli release request0 > > This way the user can easily use bash scripts, command line or even > any DBus library out there while we still use the character device in > the daemon and ditch sysfs. > Agreed. As covered earlier, access control needs to be fleshed out, but other than that I don't see any obvious deal breakers. Cheers, Kent.
On Thu, Jul 20, 2023 at 3:37 PM Kent Gibson <warthog618@gmail.com> wrote: > > On Thu, Jul 20, 2023 at 02:30:45PM +0200, Bartosz Golaszewski wrote: > > On Thu, Jul 20, 2023 at 11:52 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > The case I was thinking of was wanting to release a line, and if you > > > don't know which request you will have to walk the request objects. > > > > > > > You cannot release a single line if it's part of a wider request though. > > > > Of course. Unless we were to extend the uAPI to allow that. > > > > And what of lines that are requested directly by apps other than the > > > gpio-manager? > > > > > > > You can tell they're used but cannot request them just like with any > > other user of the cdev. > > > > This is going to be a pain point - the concept of "used" is getting > muddy. > > Say two processes want to get a line. > So both need to request it before they can get it? > Or only one does the request and both can get? I think I badly worded the previous answer. The GPIO manager has no notion of a user. It just receives a message from the bus. It's the daemon that filters the users (e.g. only users in "gpio" group can request and set/get GPIOs). So the answer is: one user can in fact request a line, it stays requested by the manager and then another user can set it or even release it as long as it's got the permissions to do so. This is similar to how sysfs works. > > The latter case is painful to use. > The former requires request being idempotent or at least to return an > error that distiguishes a line already held by gpio-manager and a line > already held but not by gpio-manager. > This should be fine. The manager knows if it's the one controlling a line. It's just a matter of distinct error codes. > > > > > > > > > > Where do edge events fit in there? > > > > > > > > > > > > > It's a signal exposed by the io.gpiod1.Line interface. > > > > > > But separate from the PropertiesChanged? > > > > > > > Yes. PropertiesChanged is emitted on changes in properties (direction, > > edge, all reported by gpionotify) while EdgeEvent is for edges > > exclusively. > > > > > > > > I am also wondering if the tools can be extended with the option to > > > perform their ops using the gpio-manager, particularly get/set/mon that > > > currently require exclusive access. > > > > > > > There's a client app already functional in my WiP branch. Think nmcli > > for NetworkManager. It doesn't link against libgpiod - only uses the > > DBus API. > > > > Sure - doesn't mean other tools can't use the DBus API too. > My thinking was existing users of GPIO tools could just add > an option, say -D, to their scripts to switch over to gpio-manager. > The functionality of the DBus API doesn't have a full overlap with using the library. I don't see why we would want to do this. It would introduce a lot of overhead for no reason. I think a separate client that doesn't use any libgpiod APIs at all is what's needed. > > You can do something like this (not all of this is implemented yet): > > > > $ # Wait for a chip with a particular label to appear > > $ gpiocli wait --chip="foobar" --timeout=10s > > $ # Request a line for edge events > > $ gpiocli request --input --rising-edge --falling-edge foo > > request0 > > Will that support multiple lines, possibly spanning multiple chips? Multiple lines, sure. Spanning multiple chips: I don't think so. Why would we need this? > > > $ # List available requests > > $ gpiocli requests > > request0 (gpiochip0) offsets: [4] > > But that will only return the requests made by gpio-manager, right? Yes. Bart > > > $ # Wait for edge events: > > $ gpiocli monitor foo > > Offset: 4 RISING EDGE Timestamp: 3425234234 > > $ # Release the request > > $ gpiocli release request0 > > > > This way the user can easily use bash scripts, command line or even > > any DBus library out there while we still use the character device in > > the daemon and ditch sysfs. > > > > Agreed. As covered earlier, access control needs to be fleshed out, but > other than that I don't see any obvious deal breakers. > > Cheers, > Kent.
On Thu, Jul 20, 2023 at 05:01:09PM +0200, Bartosz Golaszewski wrote: > On Thu, Jul 20, 2023 at 3:37 PM Kent Gibson <warthog618@gmail.com> wrote: > > > > On Thu, Jul 20, 2023 at 02:30:45PM +0200, Bartosz Golaszewski wrote: > > > On Thu, Jul 20, 2023 at 11:52 AM Kent Gibson <warthog618@gmail.com> wrote: > > > > > > > > > > > > The case I was thinking of was wanting to release a line, and if you > > > > don't know which request you will have to walk the request objects. > > > > > > > > > > You cannot release a single line if it's part of a wider request though. > > > > > > > Of course. Unless we were to extend the uAPI to allow that. > > > > > > And what of lines that are requested directly by apps other than the > > > > gpio-manager? > > > > > > > > > > You can tell they're used but cannot request them just like with any > > > other user of the cdev. > > > > > > > This is going to be a pain point - the concept of "used" is getting > > muddy. > > > > Say two processes want to get a line. > > So both need to request it before they can get it? > > Or only one does the request and both can get? > > I think I badly worded the previous answer. The GPIO manager has no > notion of a user. It just receives a message from the bus. It's the > daemon that filters the users (e.g. only users in "gpio" group can > request and set/get GPIOs). So the answer is: one user can in fact > request a line, it stays requested by the manager and then another > user can set it or even release it as long as it's got the permissions > to do so. This is similar to how sysfs works. > Sure. The point I was trying to make is how does the user determine if they can release the line via gpio-manager? Currently they have to walk the requests looking for the line - and they might not find it. This is only a minor pain point - in practice the processes will most likely all be using gpio-manager. > > > > The latter case is painful to use. > > The former requires request being idempotent or at least to return an > > error that distiguishes a line already held by gpio-manager and a line > > already held but not by gpio-manager. > > > > This should be fine. The manager knows if it's the one controlling a > line. It's just a matter of distinct error codes. > > > > > > > > > > > > > Where do edge events fit in there? > > > > > > > > > > > > > > > > It's a signal exposed by the io.gpiod1.Line interface. > > > > > > > > But separate from the PropertiesChanged? > > > > > > > > > > Yes. PropertiesChanged is emitted on changes in properties (direction, > > > edge, all reported by gpionotify) while EdgeEvent is for edges > > > exclusively. > > > > > > > > > > > I am also wondering if the tools can be extended with the option to > > > > perform their ops using the gpio-manager, particularly get/set/mon that > > > > currently require exclusive access. > > > > > > > > > > There's a client app already functional in my WiP branch. Think nmcli > > > for NetworkManager. It doesn't link against libgpiod - only uses the > > > DBus API. > > > > > > > Sure - doesn't mean other tools can't use the DBus API too. > > My thinking was existing users of GPIO tools could just add > > an option, say -D, to their scripts to switch over to gpio-manager. > > > > The functionality of the DBus API doesn't have a full overlap with > using the library. I don't see why we would want to do this. It would > introduce a lot of overhead for no reason. I think a separate client > that doesn't use any libgpiod APIs at all is what's needed. > Fair enough. That works for me. > > > You can do something like this (not all of this is implemented yet): > > > > > > $ # Wait for a chip with a particular label to appear > > > $ gpiocli wait --chip="foobar" --timeout=10s > > > $ # Request a line for edge events > > > $ gpiocli request --input --rising-edge --falling-edge foo > > > request0 > > > > Will that support multiple lines, possibly spanning multiple chips? > > Multiple lines, sure. Spanning multiple chips: I don't think so. Why > would we need this? > There is no need - the user can make multiple requests as they are now persistant. Just wondering what the API looks like to the user. Cheers, Kent.
From: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> While working on the DBus API, it occurred to me that while we can obtain the list of requested offsets from a line request, this information lacks context if we cannot get any information about the parent chip on which the request was made. We cannot reference the chip in any way as its lifetime is disconnected from the request but we can at least provide the path to the character device used to open it as a way of providing some context for the offsets. This series adds a new getter for struct gpiod_line_request and wrappers for it for all bindings. This will be used in the upcoming DBus GPIO manager code. Bartosz Golaszewski (5): core: provide gpiod_line_request_get_chip_path() tests: add a test-case for gpiod_line_request_get_chip_path() bindings: cxx: provide line_request::chip_path() bindings: python: provide the chip_path property in line_request bindings: rust: provide LineRequest::chip_path() bindings/cxx/gpiodcxx/line-request.hpp | 7 +++++++ bindings/cxx/line-request.cpp | 10 +++++++++- bindings/cxx/tests/tests-line-request.cpp | 6 ++++-- bindings/python/gpiod/chip.py | 1 + bindings/python/gpiod/line_request.py | 12 +++++++++-- bindings/python/tests/tests_line_request.py | 13 +++++++----- bindings/rust/libgpiod/src/line_request.rs | 12 +++++++++++ bindings/rust/libgpiod/tests/line_request.rs | 13 ++++++++++++ include/gpiod.h | 9 +++++++++ lib/chip.c | 2 +- lib/internal.h | 3 ++- lib/line-request.c | 20 ++++++++++++++++++- tests/tests-line-request.c | 21 ++++++++++++++++++++ 13 files changed, 116 insertions(+), 13 deletions(-)