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Date:   Thu, 11 Feb 2021 10:20:18 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Jiri Olsa <jolsa@kernel.org>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Ingo Molnar <mingo@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Namhyung Kim <namhyung@kernel.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Michael Petlan <mpetlan@redhat.com>,
        Ian Rogers <irogers@google.com>,
        Alexei Budankov <abudankov@huawei.com>
Subject: Re: [PATCH 13/24] perf daemon: Allow only one daemon over base
 directory
Message-ID: <20210211132018.GE1131885@kernel.org>
References: <20210208200908.1019149-1-jolsa@kernel.org>
 <20210208200908.1019149-14-jolsa@kernel.org>
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Em Mon, Feb 08, 2021 at 09:08:57PM +0100, Jiri Olsa escreveu:
> Add 'lock' file under daemon base and flock it, so only one
> perf daemon can run on top of it.
> 
> Each daemon tries to create and lock BASE/lock file, if it's
> successful we are sure we're the only daemon running over
> the BASE.
> 
> Once daemon is finished, file descriptor to lock file is
> closed and lock is released.
> 
> Example:
> 
>   # cat ~/.perfconfig
>   [daemon]
>   base=/opt/perfdata
> 
>   [session-cycles]
>   run = -m 10M -e cycles --overwrite --switch-output -a
> 
>   [session-sched]
>   run = -m 20M -e sched:* --overwrite --switch-output -a
> 
> Starting the daemon:
> 
>   # perf daemon start
> 
> And try once more:
> 
>   # perf daemon start
>   failed: another perf daemon (pid 775594) owns /opt/perfdata
> 
> will end up with an error, because there's already one running
> on top of /opt/perfdata.

Had to add this:

Committer notes:

Provide lockf(F_TLOCK) when not available, i.e. transform:

  lockf(fd, F_TLOCK, 0);

into:

  flock(fd, LOCK_EX | LOCK_NB);

Which should be equivalent.

Noticed when cross building to some odd Android NDK.

------

Patch:

[acme@five perf]$ git diff
diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
index 1c17c9e10ca6a656..2890573540f7d027 100644
--- a/tools/perf/builtin-daemon.c
+++ b/tools/perf/builtin-daemon.c
@@ -914,6 +914,20 @@ static int setup_config(struct daemon *daemon)
        return daemon->config_real ? 0 : -1;
 }
 
+#ifndef F_TLOCK
+#define F_TLOCK 2
+
+#include <sys/file.h>
+
+static int lockf(int fd, int cmd, off_t len)
+{
+       if (cmd != F_TLOCK || len != 0)
+               return -1;
+
+       return flock(fd, LOCK_EX | LOCK_NB);
+}
+#endif // F_TLOCK
+
 /*
  * Each daemon tries to create and lock BASE/lock file,
  * if it's successful we are sure we're the only daemon
[acme@five perf]$