[PATCH v2] perf/probe: Report permission error for tracefs access

[Masami Hiramatsu]

Report permission error for the tracefs open and rewrite
whole the error message code around it.
You'll see a hint according to what you want to do with
perf probe as below.

  $ perf probe -l
  No permission to read tracefs.
  Please try 'sudo mount -o remount,mode=755 /sys/kernel/tracing/'
    Error: Failed to show event list.

  $ perf probe -d \*
  No permission to write tracefs.
  Please run this command again with sudo.
    Error: Failed to delete events.

This also fixes -ENOTSUP checking for mounting tracefs/debugfs.
Actually open returns -ENOENT in that case and we have to check
it with current mount point list. If we unmount debugfs and tracefs
perf probe shows correct message as below.

  $ perf probe -l
  Debugfs or tracefs is not mounted
  Please try 'sudo mount -t tracefs nodev /sys/kernel/tracing/'
    Error: Failed to show event list.


Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
 Changes in v2:
  - Rewrite whole the error message for the tracefs access.
---
 tools/perf/util/probe-file.c |   95 +++++++++++++++++++++++++++++-------------
 1 file changed, 65 insertions(+), 30 deletions(-)

diff --git a/tools/perf/util/probe-file.c b/tools/perf/util/probe-file.c
index 52273542e6ef..f9a6cbcd6415 100644
--- a/tools/perf/util/probe-file.c
+++ b/tools/perf/util/probe-file.c
@@ -22,6 +22,7 @@
 #include "symbol.h"
 #include "strbuf.h"
 #include <api/fs/tracing_path.h>
+#include <api/fs/fs.h>
 #include "probe-event.h"
 #include "probe-file.h"
 #include "session.h"
@@ -31,44 +32,78 @@
 /* 4096 - 2 ('\n' + '\0') */
 #define MAX_CMDLEN 4094
 
-static void print_open_warning(int err, bool uprobe)
+static bool print_common_warning(int err, bool readwrite)
 {
-	char sbuf[STRERR_BUFSIZE];
+	if (err == -EACCES)
+		pr_warning("No permission to %s tracefs.\nPlease %s\n",
+			   readwrite ? "write" : "read",
+			   readwrite ? "run this command again with sudo." :
+				       "try 'sudo mount -o remount,mode=755 /sys/kernel/tracing/'");
+	else
+		return false;
 
-	if (err == -ENOENT) {
-		const char *config;
+	return true;
+}
 
-		if (uprobe)
-			config = "CONFIG_UPROBE_EVENTS";
-		else
-			config = "CONFIG_KPROBE_EVENTS";
+static bool print_configure_probe_event(int kerr, int uerr)
+{
+	const char *config, *file;
+
+	if (kerr == -ENOENT && uerr == -ENOENT) {
+		file = "{k,u}probe_events";
+		config = "CONFIG_KPROBE_EVENTS=y and CONFIG_UPROBE_EVENTS=y";
+	} else if (kerr == -ENOENT) {
+		file = "kprobe_events";
+		config = "CONFIG_KPROBE_EVENTS=y";
+	} else if (uerr == -ENOENT) {
+		file = "uprobe_events";
+		config = "CONFIG_UPROBE_EVENTS=y";
+	} else
+		return false;
 
-		pr_warning("%cprobe_events file does not exist"
-			   " - please rebuild kernel with %s.\n",
-			   uprobe ? 'u' : 'k', config);
-	} else if (err == -ENOTSUP)
-		pr_warning("Tracefs or debugfs is not mounted.\n");
+	if (!debugfs__configured() && !tracefs__configured())
+		pr_warning("Debugfs or tracefs is not mounted\n"
+			   "Please try 'sudo mount -t tracefs nodev /sys/kernel/tracing/'\n");
 	else
-		pr_warning("Failed to open %cprobe_events: %s\n",
-			   uprobe ? 'u' : 'k',
-			   str_error_r(-err, sbuf, sizeof(sbuf)));
+		pr_warning("%s/%s does not exist.\nPlease rebuild kernel with %s.\n",
+			   tracing_path_mount(), file, config);
+
+	return true;
+}
+
+static void print_open_warning(int err, bool uprobe, bool readwrite)
+{
+	char sbuf[STRERR_BUFSIZE];
+
+	if (print_common_warning(err, readwrite))
+		return;
+
+	if (print_configure_probe_event(uprobe ? 0 : err, uprobe ? err : 0))
+		return;
+
+	pr_warning("Failed to open %s/%cprobe_events: %s\n",
+		   tracing_path_mount(), uprobe ? 'u' : 'k',
+		   str_error_r(-err, sbuf, sizeof(sbuf)));
 }
 
-static void print_both_open_warning(int kerr, int uerr)
+static void print_both_open_warning(int kerr, int uerr, bool readwrite)
 {
-	/* Both kprobes and uprobes are disabled, warn it. */
-	if (kerr == -ENOTSUP && uerr == -ENOTSUP)
-		pr_warning("Tracefs or debugfs is not mounted.\n");
-	else if (kerr == -ENOENT && uerr == -ENOENT)
-		pr_warning("Please rebuild kernel with CONFIG_KPROBE_EVENTS "
-			   "or/and CONFIG_UPROBE_EVENTS.\n");
-	else {
-		char sbuf[STRERR_BUFSIZE];
-		pr_warning("Failed to open kprobe events: %s.\n",
+	char sbuf[STRERR_BUFSIZE];
+
+	if (kerr == uerr && print_common_warning(kerr, readwrite))
+		return;
+
+	if (print_configure_probe_event(kerr, uerr))
+		return;
+
+	if (kerr < 0)
+		pr_warning("Failed to open %s/kprobe_events: %s.\n",
+			   tracing_path_mount(),
 			   str_error_r(-kerr, sbuf, sizeof(sbuf)));
-		pr_warning("Failed to open uprobe events: %s.\n",
+	if (uerr < 0)
+		pr_warning("Failed to open %s/uprobe_events: %s.\n",
+			   tracing_path_mount(),
 			   str_error_r(-uerr, sbuf, sizeof(sbuf)));
-	}
 }
 
 int open_trace_file(const char *trace_file, bool readwrite)
@@ -109,7 +144,7 @@ int probe_file__open(int flag)
 	else
 		fd = open_kprobe_events(flag & PF_FL_RW);
 	if (fd < 0)
-		print_open_warning(fd, flag & PF_FL_UPROBE);
+		print_open_warning(fd, flag & PF_FL_UPROBE, flag & PF_FL_RW);
 
 	return fd;
 }
@@ -122,7 +157,7 @@ int probe_file__open_both(int *kfd, int *ufd, int flag)
 	*kfd = open_kprobe_events(flag & PF_FL_RW);
 	*ufd = open_uprobe_events(flag & PF_FL_RW);
 	if (*kfd < 0 && *ufd < 0) {
-		print_both_open_warning(*kfd, *ufd);
+		print_both_open_warning(*kfd, *ufd, flag & PF_FL_RW);
 		return *kfd;
 	}