linux-kernel - Re: [PATCH] tools lib api fs: Store tracing mountpoint for better error message

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Date:	Sat, 19 Sep 2015 11:23:53 -0400
From:	Raphaël Beamonte <raphael.beamonte@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Matt Fleming <matt@...eblueprint.co.uk>
Subject: Re: [PATCH] tools lib api fs: Store tracing mountpoint for better
 error message

2015-09-19 11:00 GMT-04:00 Jiri Olsa <jolsa@...hat.com>:
> On Sat, Sep 19, 2015 at 08:50:19AM -0600, David Ahern wrote:
>> On 9/19/15 8:47 AM, Jiri Olsa wrote:
>>
>> >diff --git a/tools/lib/api/fs/tracing_path.c b/tools/lib/api/fs/tracing_path.c
>> >index 38aca2dd1946..0406a7d5c891 100644
>> >--- a/tools/lib/api/fs/tracing_path.c
>> >+++ b/tools/lib/api/fs/tracing_path.c
>> >@@ -12,12 +12,14 @@
>> >  #include "tracing_path.h"
>> >
>> >
>> >+char tracing_mnt[PATH_MAX + 1]         = "/sys/kernel/debug";
>> >  char tracing_path[PATH_MAX + 1]        = "/sys/kernel/debug/tracing";
>> >  char tracing_events_path[PATH_MAX + 1] = "/sys/kernel/debug/tracing/events";
>>
>> why all the +1s? null terminator has to fit within PATH_MAX as well.
>
> good question.. can't see a reason ATM

It is quite weird actually, it seems there is multiple occurrences of
that, without any comment to explain why that +1, even if the #define
of PATH_MAX in limits.h specify that that size also counts nul.
Most of these occurrences are linked to perf though, but there's also
fs/ocfs2/aops.c, scripts/docproc.c and usr/gen_init_cpio.c.
Perhaps a mistake that started somewhere and that was propagated
looking at the original mistake?

> jirka
>
>>
>> >
>> >
>> >  static void __tracing_path_set(const char *tracing, const char *mountpoint)
>> >  {
>> >+    snprintf(tracing_mnt, sizeof(tracing_mnt), "%s", mountpoint);
>> >     snprintf(tracing_path, sizeof(tracing_path), "%s/%s",
>> >              mountpoint, tracing);
>> >     snprintf(tracing_events_path, sizeof(tracing_events_path), "%s/%s%s",
>> >@@ -109,19 +111,10 @@ static int strerror_open(int err, char *buf, size_t size, const char *filename)
>> >                      "Hint:\tTry 'sudo mount -t debugfs nodev /sys/kernel/debug'");
>> >             break;
>> >     case EACCES: {
>> >-            const char *mountpoint = debugfs__mountpoint();
>> >-
>> >-            if (!access(mountpoint, R_OK) && strncmp(filename, "tracing/", 8) == 0) {
>> >-                    const char *tracefs_mntpoint = tracefs__mountpoint();
>> >-
>> >-                    if (tracefs_mntpoint)
>> >-                            mountpoint = tracefs__mountpoint();
>> >-            }
>> >-
>> >             snprintf(buf, size,
>> >                      "Error:\tNo permissions to read %s/%s\n"
>> >                      "Hint:\tTry 'sudo mount -o remount,mode=755 %s'\n",
>> >-                     tracing_events_path, filename, mountpoint);
>> >+                     tracing_events_path, filename, tracing_mnt);
>> >     }
>> >             break;
>> >     default:
>> >
>>
>> LGTM.
>>
>> David
--
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