Date: Tue, 25 Aug 2020 22:06:22 -0400 From: J David <j.david.lists@gmail.com> To: freebsd-hackers@freebsd.org Subject: pidfile_open() usage in "mount" Message-ID: <CABXB=RRM7YusQL1gGVGD4s9xi9AB4F5AR5-Jqbp4G1WTZWWA%2BQ@mail.gmail.com>
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It looks like the "mount" program creates /var/run/mountd.pid every
time it runs, if mountd is not itself running.
This code appears in sbin/mount/mount.c:
static void
restart_mountd(void)
{
struct pidfh *pfh;
pid_t mountdpid;
mountdpid = 0;
pfh = pidfile_open(_PATH_MOUNTDPID, 0600, &mountdpid);
if (pfh != NULL) {
/* Mountd is not running. */
pidfile_remove(pfh);
return;
}
pidfile_open(3) *creates* /var/run/mountd.pid if it doesn't already
exist, hence the need to delete it if the call actually succeeds.
This leads to a race condition when multiple mounts occur at the same
time. That case is handled later in the code:
/*
* Refuse to send broadcast or group signals, this has
* happened due to the bugs in pidfile(3).
*/
if (mountdpid <= 0) {
warnx("mountd pid %d, refusing to send SIGHUP", mountdpid);
return;
}
"mount" is not "mountd." It seems inappropriate for it to, under any
circumstances, create mountd's pid file. The multiple workarounds for
the problems that causes don't seem like the optimal approach.
This is something I'd be willing to open a bug and submit a patch for,
but so as not to do work that stands no chance of being accepted, I'd
like to understand first if the preferred approach would be to change
mount.c not to use pidfile library calls at all, or if it would be
better to add a function to the pidfile library similar to
pidfile_open() designed for "consumer" use that would never create the
file, leaving pidfile_open() for "producer" use?
Thanks!
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