On 01/27/12 07:36, Stefan Hajnoczi wrote:
On Thu, Jan 26, 2012 at 10:36:41PM +0100, Laszlo Ersek wrote:
The lockf() call in qemu_create_pidfile() aims at ensuring mutual
exclusion. We shouldn't close the pidfile on success, because that drops
the lock as well [1]:
"File locks shall be released on first close by the locking process
of any file descriptor for the file."
Coverity may complain again about the leaked file descriptor; let's
worry about that later.
[1] http://pubs.opengroup.org/onlinepubs/9699919799/functions/lockf.html
Signed-off-by: Laszlo Ersek<ler...@redhat.com>
---
Isn't the normal way to do pidfiles O_CREAT | O_EXCL?
Yes, it is.
It may not work
on all NFS versions but putting the pidfile on NFS doesn't really make
sense.
Then we can drop the lockf(3) completely.
When you rely on O_EXCL to ensure mutual exclusion, and an abruptly
terminated process leaves the lockfile lying around, then the user has
to clean it up manually before starting the next instance (and double
check if the pid file is in fact stale or not). I'm personally OK with
that, but I reckoned the qemu code tried to avoid that intentionally.
Record locks can't remain stale when the process dies.
Laszlo
