Re: [PATCH 13/24] perf daemon: Allow only one daemon over base directory

[Jiri Olsa <jolsa@redhat.com>]

On Thu, Feb 11, 2021 at 10:20:18AM -0300, Arnaldo Carvalho de Melo wrote:
> 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]$
> 

nice, thanks

jirka