Date: Mon, 12 Jun 2006 05:48:41 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Kris Kennaway <kris@obsecurity.org> Cc: current@FreeBSD.org Subject: Re: FILEDESC_LOCK() implementation Message-ID: <33721.1150091321@critter.freebsd.dk> In-Reply-To: Your message of "Mon, 12 Jun 2006 01:41:15 -0400." <20060612054115.GA42379@xor.obsecurity.org>
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In message <20060612054115.GA42379@xor.obsecurity.org>, Kris Kennaway writes:
>I wonder if something better can be done with the funky home-grown
>locking in FILEDESC_LOCK() (see <sys/filedesc.h>) to make it more
>light-weight?
It probably can.
What's needed is a combined short/long lock, where you can either
grab lock for sleepable locking (like for instance sxlocks) or only
grab a quick version (like a mutex) for lightweight operations.
See vfs_syscalls.c for examples like:
FILEDESC_LOCK(fdp);
if (chroot_allow_open_directories == 0 ||
(chroot_allow_open_directories == 1 && fdp->fd_rdir != rootvnode)) {
error = chroot_refuse_vdir_fds(fdp);
if (error) {
FILEDESC_UNLOCK(fdp);
return (error);
}
}
oldvp = fdp->fd_rdir;
fdp->fd_rdir = vp;
VREF(fdp->fd_rdir);
if (!fdp->fd_jdir) {
fdp->fd_jdir = vp;
VREF(fdp->fd_jdir);
}
FILEDESC_UNLOCK(fdp);
and
FILEDESC_LOCK_FAST(fdp);
vp = fdp->fd_cdir;
fdp->fd_cdir = nd.ni_vp;
FILEDESC_UNLOCK_FAST(fdp);
respectively
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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