[v2,03/14] perf: Add persistent event facilities

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 6fddac1..d2a42b7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -518,6 +518,13 @@  struct perf_output_handle {
 	int				page;
 };
 
+struct pers_event_desc {
+	struct perf_event_attr *attr;
+	struct perf_event *event;
+	struct list_head plist;
+	int fd;
+};
+
 #ifdef CONFIG_PERF_EVENTS
 
 extern int perf_pmu_register(struct pmu *pmu, char *name, int type);
@@ -750,7 +757,9 @@  extern void perf_event_enable(struct perf_event *event);
 extern void perf_event_disable(struct perf_event *event);
 extern int __perf_event_disable(void *info);
 extern void perf_event_task_tick(void);
-#else
+extern int perf_add_persistent_event(struct perf_event_attr *, unsigned);
+extern int perf_add_persistent_event_by_id(int id);
+#else /* !CONFIG_PERF_EVENTS */
 static inline void
 perf_event_task_sched_in(struct task_struct *prev,
 			 struct task_struct *task)			{ }
@@ -790,7 +799,10 @@  static inline void perf_event_enable(struct perf_event *event)		{ }
 static inline void perf_event_disable(struct perf_event *event)		{ }
 static inline int __perf_event_disable(void *info)			{ return -1; }
 static inline void perf_event_task_tick(void)				{ }
-#endif
+static inline int perf_add_persistent_event(struct perf_event_attr *attr,
+					    unsigned nr_pages)		{ return -EINVAL; }
+static inline int perf_add_persistent_event_by_id(int id)		{ return -EINVAL; }
+#endif /* !CONFIG_PERF_EVENTS */
 
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_NO_HZ_FULL)
 extern bool perf_event_can_stop_tick(void);
diff --git a/kernel/events/Makefile b/kernel/events/Makefile
index 103f5d1..70990d5 100644
--- a/kernel/events/Makefile
+++ b/kernel/events/Makefile
@@ -2,7 +2,7 @@  ifdef CONFIG_FUNCTION_TRACER
 CFLAGS_REMOVE_core.o = -pg
 endif
 
-obj-y := core.o ring_buffer.o callchain.o
+obj-y := core.o ring_buffer.o callchain.o persistent.o
 
 obj-$(CONFIG_HAVE_HW_BREAKPOINT) += hw_breakpoint.o
 obj-$(CONFIG_UPROBES) += uprobes.o
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a13e457..a9b6470 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3021,8 +3021,6 @@  static void free_event_rcu(struct rcu_head *head)
 	kfree(event);
 }
 
-static void rb_put(struct ring_buffer *rb);
-
 static void free_event(struct perf_event *event)
 {
 	irq_work_sync(&event->pending);
@@ -3398,8 +3396,6 @@  unlock:
 	return ret;
 }
 
-static const struct file_operations perf_fops;
-
 static inline int perf_fget_light(int fd, struct fd *p)
 {
 	struct fd f = fdget(fd);
@@ -3684,7 +3680,7 @@  static struct ring_buffer *rb_get(struct perf_event *event)
 	return rb;
 }
 
-static void rb_put(struct ring_buffer *rb)
+void rb_put(struct ring_buffer *rb)
 {
 	struct perf_event *event, *n;
 	unsigned long flags;
@@ -3866,7 +3862,7 @@  static int perf_fasync(int fd, struct file *filp, int on)
 	return 0;
 }
 
-static const struct file_operations perf_fops = {
+const struct file_operations perf_fops = {
 	.llseek			= no_llseek,
 	.release		= perf_release,
 	.read			= perf_read,
@@ -6623,6 +6619,9 @@  SYSCALL_DEFINE5(perf_event_open,
 	if (err)
 		return err;
 
+	if (attr.persistent)
+		return perf_get_persistent_event_fd(cpu, &attr);
+
 	if (!attr.exclude_kernel) {
 		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
 			return -EACCES;
@@ -7579,6 +7578,8 @@  void __init perf_event_init(void)
 	 */
 	BUILD_BUG_ON((offsetof(struct perf_event_mmap_page, data_head))
 		     != 1024);
+
+	persistent_events_init();
 }
 
 static int __init perf_event_sysfs_init(void)
diff --git a/kernel/events/internal.h b/kernel/events/internal.h
index eb675c4..3b481be 100644
--- a/kernel/events/internal.h
+++ b/kernel/events/internal.h
@@ -38,6 +38,7 @@  struct ring_buffer {
 extern void rb_free(struct ring_buffer *rb);
 extern struct ring_buffer *
 rb_alloc(int nr_pages, long watermark, int cpu, int flags);
+extern void rb_put(struct ring_buffer *rb);
 extern void perf_event_wakeup(struct perf_event *event);
 
 extern void
@@ -174,4 +175,7 @@  static inline bool arch_perf_have_user_stack_dump(void)
 #define perf_user_stack_pointer(regs) 0
 #endif /* CONFIG_HAVE_PERF_USER_STACK_DUMP */
 
+extern const struct file_operations perf_fops;
+extern int perf_get_persistent_event_fd(unsigned cpu, struct perf_event_attr *attr);
+extern void __init persistent_events_init(void);
 #endif /* _KERNEL_EVENTS_INTERNAL_H */
diff --git a/kernel/events/persistent.c b/kernel/events/persistent.c
new file mode 100644
index 0000000..53411b4
--- /dev/null
+++ b/kernel/events/persistent.c
@@ -0,0 +1,181 @@ 
+#include <linux/slab.h>
+#include <linux/file.h>
+#include <linux/perf_event.h>
+#include <linux/anon_inodes.h>
+
+#include "internal.h"
+
+/* 512 kiB: default perf tools memory size, see perf_evlist__mmap() */
+#define CPU_BUFFER_NR_PAGES	((512 * 1024) / PAGE_SIZE)
+
+static DEFINE_PER_CPU(struct list_head, pers_events);
+
+static struct perf_event *
+add_persistent_event_on_cpu(unsigned int cpu, struct perf_event_attr *attr,
+			    unsigned nr_pages)
+{
+	struct perf_event *event = ERR_PTR(-ENOMEM);
+	struct pers_event_desc *desc;
+	struct ring_buffer *buf;
+
+	desc = kzalloc(sizeof(*desc), GFP_KERNEL);
+	if (!desc)
+		goto out;
+
+	buf = rb_alloc(nr_pages, 0, cpu, 0);
+	if (!buf)
+		goto err_rb;
+
+	event = perf_event_create_kernel_counter(attr, cpu, NULL, NULL, NULL);
+	if (IS_ERR(event))
+		goto err_event;
+
+	rcu_assign_pointer(event->rb, buf);
+
+	desc->event = event;
+	desc->attr  = attr;
+
+	INIT_LIST_HEAD(&desc->plist);
+	list_add_tail(&desc->plist, &per_cpu(pers_events, cpu));
+
+	/* All workie, enable event now */
+	perf_event_enable(event);
+
+	goto out;
+
+ err_event:
+	rb_put(buf);
+
+ err_rb:
+	kfree(desc);
+
+ out:
+	return event;
+}
+
+static void del_persistent_event(int cpu, struct perf_event_attr *attr)
+{
+	struct pers_event_desc *desc, *tmp;
+	struct perf_event *event = NULL;
+
+	list_for_each_entry_safe(desc, tmp, &per_cpu(pers_events, cpu), plist) {
+		if (desc->attr->config == attr->config) {
+			event = desc->event;
+			break;
+		}
+	}
+
+	if (!event)
+		return;
+
+	list_del(&desc->plist);
+
+	perf_event_disable(event);
+	if (event->rb) {
+		rb_put(event->rb);
+		rcu_assign_pointer(event->rb, NULL);
+	}
+
+	perf_event_release_kernel(event);
+	put_unused_fd(desc->fd);
+	kfree(desc->attr);
+	kfree(desc);
+}
+
+static int __alloc_persistent_event_fd(struct pers_event_desc *desc)
+{
+	struct file *event_file = NULL;
+	int event_fd = -1;
+
+	event_fd = get_unused_fd();
+	if (event_fd < 0)
+		goto out;
+
+	event_file = anon_inode_getfile("[pers_event]", &perf_fops,
+					desc->event, O_RDONLY);
+	if (IS_ERR(event_file))
+		goto err_event_file;
+
+	desc->fd = event_fd;
+	fd_install(event_fd, event_file);
+
+	goto out;
+
+
+ err_event_file:
+	put_unused_fd(event_fd);
+
+ out:
+	return event_fd;
+}
+
+/*
+ * Create and enable the persistent version of the perf event described by
+ * @attr.
+ *
+ * @attr: perf event descriptor
+ * @nr_pages: size in pages
+ */
+int perf_add_persistent_event(struct perf_event_attr *attr, unsigned nr_pages)
+{
+	struct perf_event *event;
+	int i;
+
+	for_each_possible_cpu(i) {
+		event = add_persistent_event_on_cpu(i, attr, nr_pages);
+		if (IS_ERR(event))
+			goto unwind;
+	}
+	return 0;
+
+unwind:
+	pr_err("%s: Error adding persistent event on cpu %d: %ld\n",
+		__func__, i, PTR_ERR(event));
+
+	while (--i >= 0)
+		del_persistent_event(i, attr);
+
+	return PTR_ERR(event);
+}
+
+int perf_add_persistent_event_by_id(int id)
+{
+	struct perf_event_attr *attr;
+
+	attr = kzalloc(sizeof(*attr), GFP_KERNEL);
+	if (!attr)
+		return -ENOMEM;
+
+	attr->sample_period	= 1;
+	attr->wakeup_events	= 1;
+	attr->sample_type	= PERF_SAMPLE_RAW;
+	attr->persistent	= 1;
+	attr->config		= id;
+	attr->type		= PERF_TYPE_TRACEPOINT;
+	attr->size		= sizeof(*attr);
+
+	return perf_add_persistent_event(attr, CPU_BUFFER_NR_PAGES);
+}
+
+int perf_get_persistent_event_fd(unsigned cpu, struct perf_event_attr *attr)
+{
+	struct pers_event_desc *desc;
+
+	if (cpu >= (unsigned)nr_cpu_ids)
+		return -EINVAL;
+
+	list_for_each_entry(desc, &per_cpu(pers_events, cpu), plist)
+		if (desc->attr->config == attr->config)
+			return __alloc_persistent_event_fd(desc);
+
+	return -ENODEV;
+}
+
+
+void __init persistent_events_init(void)
+{
+	int i;
+
+	for_each_possible_cpu(i)
+		INIT_LIST_HEAD(&per_cpu(pers_events, i));
+}