On Mon, 19.01.15 13:24, Pablo Neira Ayuso (pablo@xxxxxxxxxxxxx) wrote:
> On Sun, Jan 18, 2015 at 10:28:32PM +0100, Jan Engelhardt wrote:
> > On Sunday 2015-01-18 22:13, Pablo Neira Ayuso wrote:
> >
> > >This patch introduces a semaphore
> > >index b18022e..80eed2c 100644
> > >--- a/iptables/xshared.c
> > >+++ b/iptables/xshared.c
> > >+static int xtables_check_owner(int semid)
> > >+{
> > >+ int ret;
> > >+ struct semid_ds ds;
> > >+
> > >+ ret = semctl(semid, 0, IPC_STAT, &ds);
> >
> > Is there a particular reason you are not using the POSIX semaphores?
> > [sem_open/shm_open as per sem_overview(7)].
>
> Please, read the patch description:
>
> "This patch introduces a semaphore that is identified by the path to
> the iptables binary, it also relies on SEM_UNDO so the kernel performs
> the up() operation at process exit to avoid races with signals. This
> also avoids file locks that require a writable filesystem."
/run is always writable. /dev/shm too. And BSD file locks are robust
too (i.e. are automatically unlocked on exit). And you can have that
for POSIX locks too.
Lennart
--
Lennart Poettering, Red Hat
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