| Message ID | 20201118170738.324226-1-toke@redhat.com |
|---|---|
| State | New |
| Headers | show |
| Series | [bpf-next] libbpf: Add libbpf_version() function to get library version at runtime | expand |
On Wed, 18 Nov 2020 09:43:25 -0800, Alexei Starovoitov wrote: > Just like the kernel doesn't add features for out-of-tree modules > libbpf doesn't add features for projects where libbpf is optional. A more fitting comparison would be the kernel refusing to add a new uAPI call because some application refuses to bundle the kernel. A libbpf equivalent of a kernel module would be some kind of libbpf plugin (which does not exist), asking for an internal libbpf API to be added. Alexei, could you please start cooperating with others and actually listening to others' needs? I know you started eBPF but you're not the only user anymore and as much convinced you may be about your view, people have reasons for what they're doing. It would help greatly if you could listen to these reasons. Jiri
diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile index 5f9abed3e226..c9999e09a0c8 100644 --- a/tools/lib/bpf/Makefile +++ b/tools/lib/bpf/Makefile @@ -107,6 +107,7 @@ override CFLAGS += -Werror -Wall override CFLAGS += $(INCLUDES) override CFLAGS += -fvisibility=hidden override CFLAGS += -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64 +override CFLAGS += -DLIBBPF_VERSION="$(LIBBPF_VERSION)" # flags specific for shared library SHLIB_FLAGS := -DSHARED -fPIC diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 313034117070..dc7bb3001fa6 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -136,6 +136,18 @@ static void pr_perm_msg(int err) #define STRERR_BUFSIZE 128 +#ifndef LIBBPF_VERSION +#define LIBBPF_VERSION unset +#endif +#define __str(s) #s +#define _str(s) __str(s) +static const char *_libbpf_version = _str(LIBBPF_VERSION); + +const char *libbpf_version(void) +{ + return _libbpf_version; +} + /* Copied from tools/perf/util/util.h */ #ifndef zfree # define zfree(ptr) ({ free(*ptr); *ptr = NULL; }) diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h index 6909ee81113a..d8256bc1e02e 100644 --- a/tools/lib/bpf/libbpf.h +++ b/tools/lib/bpf/libbpf.h @@ -45,6 +45,7 @@ enum libbpf_errno { }; LIBBPF_API int libbpf_strerror(int err, char *buf, size_t size); +LIBBPF_API const char *libbpf_version(void); enum libbpf_print_level { LIBBPF_WARN, diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map index 29ff4807b909..5f931bf1b5b0 100644 --- a/tools/lib/bpf/libbpf.map +++ b/tools/lib/bpf/libbpf.map @@ -345,4 +345,5 @@ LIBBPF_0.3.0 { btf__parse_split; btf__new_empty_split; btf__new_split; + libbpf_version; } LIBBPF_0.2.0;
As a response to patches adding libbpf support to iproute2, an extensive discussion ensued about libbpf version visibility and enforcement in tools using the library[0]. In particular, two problems came to light: 1. If a tool is statically linked against libbpf, there is no way for a user to discover which version of libbpf the tool is using, unless the tool takes particular care to embed the library version at build time and print it. 2. If a tool is dynamically linked against libbpf, but doesn't use any symbols from the latest library version, the library version used at runtime can be older than the one used at compile time, and the application has no way to verify the version at runtime. To make progress on resolving this, let's add a libbpf_version() function that will simply return a version string which is embedded into the library at compile time. This makes it possible for applications to unambiguously get the library version at runtime, resolving (2.) above, and as an added bonus makes it easy for applications to print the library version, which should help with (1.). [0] https://lore.kernel.org/bpf/20201109070802.3638167-1-haliu@redhat.com/T/#t Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com> --- tools/lib/bpf/Makefile | 1 + tools/lib/bpf/libbpf.c | 12 ++++++++++++ tools/lib/bpf/libbpf.h | 1 + tools/lib/bpf/libbpf.map | 1 + 4 files changed, 15 insertions(+)