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plugins: pidfile: tricky zebra doesn't close its pid file

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This patch fixes a few really hard problems wrt PID files:

 1. Listening for IN_CREATE events means we get notified immediately by
    the kernel when someone calls open()/fopen() on a PID file.  Reading
    the contents returns 0, thank you atoi() ... so we drop IN_CREATE
    and instead look for IN_CLOSE_WRITE, there fixed it!  Not quite ...

 2. Some programs, like Zebra, and other Quagga/Frr daemons, don't
    close() their PID files after creation.  Instead they ftruncate()
    and keep them open, and locked.  Presumably to get a mechanism to
    detect already running instances -- messes life up a bit for the
    rest of us though.  So we need to read files after IN_MODIFY too.

 3. We also want to track IN_DELETE so we can deassert conditions when
    services exit gracefully and clean up their PID files

The rest fo the commit is debug instrumentation changes.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>
This commit is contained in:
Joachim Wiberg
2021-03-11 11:44:23 +01:00
parent 05ac9c18c9
commit 2711b27971
2 changed files with 8 additions and 13 deletions
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plugins/pidfile.c
+5 -12
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@@ -58,7 +58,7 @@ static int pidfile_add_path(struct iwatch *iw, char *path)
}
}
return iwatch_add(iw, path, IN_ONLYDIR);
return iwatch_add(iw, path, IN_ONLYDIR | IN_CLOSE_WRITE);
}
static void pidfile_update_conds(char *dir, char *name, uint32_t mask)
@@ -68,11 +68,11 @@ static void pidfile_update_conds(char *dir, char *name, uint32_t mask)
svc_t *svc;
paste(fn, sizeof(fn), dir, name);
_d("path: %s, mask: %08x", fn, mask);
if (fnmatch("*\\.pid", fn, 0) && fnmatch("*/pid", fn, 0))
return;
_d("path: %s, mask: %08x", fn, mask);
svc = svc_find_by_pidfile(fn);
if (!svc) {
_d("No matching svc for %s", fn);
@@ -82,7 +82,7 @@ static void pidfile_update_conds(char *dir, char *name, uint32_t mask)
_d("Found svc %s for %s with pid %d", svc->name, fn, svc->pid);
mkcond(svc, cond, sizeof(cond));
if (mask & (IN_CREATE | IN_ATTRIB | IN_MODIFY | IN_MOVED_TO)) {
if (mask & (IN_CLOSE_WRITE | IN_ATTRIB | IN_MODIFY | IN_MOVED_TO)) {
svc_started(svc);
if (svc_is_forking(svc)) {
pid_t pid;
@@ -174,8 +174,6 @@ static void pidfile_callback(void *arg, int fd, int events)
if (!ev->mask)
continue;
_d("name %s, event: 0x%08x", ev->name, ev->mask);
/* Find base path for this event */
iwp = iwatch_find_by_wd(&iw_pidfile, ev->wd);
if (!iwp)
@@ -186,12 +184,7 @@ static void pidfile_callback(void *arg, int fd, int events)
continue;
}
if (ev->mask & IN_DELETE) {
_d("pidfile %s/%s removed ...", iwp->path, ev->name);
continue;
}
if (ev->mask & (IN_CREATE | IN_ATTRIB | IN_MODIFY | IN_MOVED_TO))
if (ev->mask & (IN_CLOSE_WRITE | IN_DELETE | IN_ATTRIB | IN_MODIFY | IN_MOVED_TO))
pidfile_update_conds(iwp->path, ev->name, ev->mask);
}
}