[PATCH RFC v1 3/4] perf: Annotate some of the error codes with perf_err()

[Alexander Shishkin <alexander.shishkin@linux.intel.com>]

This patch annotates a few semi-random error paths in perf core to
illustrate the extended error reporting facility. Most of them can
be triggered from perf tools.

NYet-Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
---
 kernel/events/core.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4ff09fdc67..e1d9fe6f23 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3367,10 +3367,10 @@ find_lively_task_by_vpid(pid_t vpid)
 	rcu_read_unlock();
 
 	if (!task)
-		return ERR_PTR(-ESRCH);
+		return PERF_ERR_PTR(-ESRCH, "task not found");
 
 	/* Reuse ptrace permission checks for now. */
-	err = -EACCES;
+	err = perf_err(-EACCES, "insufficient permissions for tracing this task");
 	if (!ptrace_may_access(task, PTRACE_MODE_READ))
 		goto errout;
 
@@ -3398,7 +3398,8 @@ find_get_context(struct pmu *pmu, struct task_struct *task,
 	if (!task) {
 		/* Must be root to operate on a CPU event: */
 		if (perf_paranoid_cpu() && !capable(CAP_SYS_ADMIN))
-			return ERR_PTR(-EACCES);
+			return PERF_ERR_PTR(-EACCES,
+					    "must be root to operate on a CPU event");
 
 		/*
 		 * We could be clever and allow to attach a event to an
@@ -3406,7 +3407,7 @@ find_get_context(struct pmu *pmu, struct task_struct *task,
 		 * that's for later.
 		 */
 		if (!cpu_online(cpu))
-			return ERR_PTR(-ENODEV);
+			return PERF_ERR_PTR(-ENODEV, "cpu is offline");
 
 		cpuctx = per_cpu_ptr(pmu->pmu_cpu_context, cpu);
 		ctx = &cpuctx->ctx;
@@ -7985,15 +7986,16 @@ SYSCALL_DEFINE5(perf_event_open,
 
 	if (!attr.exclude_kernel) {
 		if (perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
-			return -EACCES;
+			return perf_err_sync(&attr, -EACCES,
+					     "kernel tracing forbidden for the unprivileged");
 	}
 
 	if (attr.freq) {
 		if (attr.sample_freq > sysctl_perf_event_sample_rate)
-			return -EINVAL;
+			return perf_err_sync(&attr, -EINVAL, "sample_freq too high");
 	} else {
 		if (attr.sample_period & (1ULL << 63))
-			return -EINVAL;
+			return perf_err_sync(&attr, -EINVAL, "sample_period too high");
 	}
 
 	/*
@@ -8003,14 +8005,14 @@ SYSCALL_DEFINE5(perf_event_open,
 	 * cgroup.
 	 */
 	if ((flags & PERF_FLAG_PID_CGROUP) && (pid == -1 || cpu == -1))
-		return -EINVAL;
+		return perf_err_sync(&attr, -EINVAL, "pid and cpu need to be set in cgroup mode");
 
 	if (flags & PERF_FLAG_FD_CLOEXEC)
 		f_flags |= O_CLOEXEC;
 
 	event_fd = get_unused_fd_flags(f_flags);
 	if (event_fd < 0)
-		return event_fd;
+		return perf_err_sync(&attr, event_fd, "can't obtain a file descriptor");
 
 	if (group_fd != -1) {
 		err = perf_fget_light(group_fd, &group);
-- 
2.1.4