From: "J. Bruce Fields" <bfields@fieldses.org>
To: Pavel Shilovsky <piastry@etersoft.ru>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-cifs@vger.kernel.org, linux-nfs@vger.kernel.org,
wine-devel@winehq.org
Subject: Re: [PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open syscall
Date: Thu, 7 Feb 2013 11:19:48 -0500 [thread overview]
Message-ID: <20130207161948.GG3222@fieldses.org> (raw)
In-Reply-To: <CAKywueShbPd9b+WmJwnfwPR_vzk_atBVRBZNTf-HpS7N2CK+AA@mail.gmail.com>
On Thu, Feb 07, 2013 at 08:00:13PM +0400, Pavel Shilovsky wrote:
> 2013/2/7 J. Bruce Fields <bfields@fieldses.org>:
> > On Thu, Feb 07, 2013 at 06:32:38PM +0400, Pavel Shilovsky wrote:
> >> 2013/2/7 J. Bruce Fields <bfields@fieldses.org>:
> >> > On Thu, Feb 07, 2013 at 01:53:46PM +0400, Pavel Shilovsky wrote:
> >> >> Nothing prevents it. If somebody grabbed a share mode lock on a file
> >> >> before we call deny_lock_file, we simply close this file and return
> >> >> -ETXTBSY.
> >> >
> >> > But leave the newly-created file there--ugh.
> >> >
> >> >> We can't grab it before atomic_open because we don't have an
> >> >> inode there.
> >> >
> >> > If you can get the lock while still holding the directory i_mutex can't
> >> > you prevent anyone else from looking up the new file until you've gotten
> >> > the lock?
> >> >
> >>
> >> Hm..., seems you are right, I missed this part:
> >> mutex_lock
> >> lookup_open -> atomic_open -> deny_lock_file
> >> mutex_unlock
> >>
> >> that means that nobody can open and of course set flock on the newly
> >> created file (because flock is done through file descriptor). So, it
> >> should be fine to call flock after f_ops->atomic_open in atomic_open
> >> function. Thanks.
> >
> > Whether that works may also depend on how the new dentry is set up? If
> > it's hashed before you call flock then I suppose it's already visible to
> > others.
>
> It seems it should be hashed in f_ops->atomic_open() (at least cifs
> and nfs do it this way). In do_last when we do an ordinary open, we
> don't hit parent i_mutex if lookup is succeeded through lookup_fast.
> lookup_fast can catch newly created dentry and set it's share mode
> before atomic_open codepath hits deny_lock_file.
>
> Also, I noted that: atomic open does f_ops->atomic_open and then it
> processes may_open check; if may_open fails, the file is closed and
> open returns with a error code (but file is created anyway).
That would be a bug, I think. E.g. "man 3posix open":
No files shall be created or modified if the function returns
-1.
Looking at the code... See the references to FILE_CREATED in
atomic_open--looks like that's trying to prevent may_open from failing
in this case.
> I think
> there is no difference between this case and the situation with
> deny_lock_file there.
Looks to me like it would be a bug in either case.
--b.
next prev parent reply other threads:[~2013-02-07 16:19 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-17 16:52 [PATCH v2 1/8] locks: make flock_lock_file take is_conflict callback parm Pavel Shilovsky
2013-01-17 16:52 ` [PATCH v2 2/8] fcntl: Introduce new O_DENY* open flags Pavel Shilovsky
2013-01-17 16:52 ` [PATCH v2 3/8] vfs: Add O_DENYREAD/WRITE flags support for open syscall Pavel Shilovsky
2013-01-30 22:16 ` J. Bruce Fields
2013-02-05 11:45 ` Pavel Shilovsky
2013-02-05 14:35 ` J. Bruce Fields
2013-02-07 9:53 ` Pavel Shilovsky
2013-02-07 14:18 ` J. Bruce Fields
2013-02-07 14:32 ` Pavel Shilovsky
2013-02-07 14:41 ` J. Bruce Fields
2013-02-07 16:00 ` Pavel Shilovsky
2013-02-07 16:19 ` J. Bruce Fields [this message]
2013-02-07 16:50 ` Pavel Shilovsky
2013-02-07 17:03 ` J. Bruce Fields
2013-01-17 16:53 ` [PATCH v2 4/8] CIFS: Add O_DENY* open flags support Pavel Shilovsky
2013-01-30 22:16 ` J. Bruce Fields
2013-02-05 11:54 ` Pavel Shilovsky
2013-01-17 16:53 ` [PATCH v2 5/8] CIFS: Use NT_CREATE_ANDX command for forcemand mounts Pavel Shilovsky
2013-01-17 16:53 ` [PATCH v2 6/8] CIFS: Translate SHARING_VIOLATION to -ETXTBSY error code for SMB2 Pavel Shilovsky
2013-01-17 16:53 ` [PATCH v2 7/8] NFSv4: Add O_DENY* open flags support Pavel Shilovsky
2013-01-17 16:53 ` [PATCH v2 8/8] NFSD: Pass share reservations flags to VFS Pavel Shilovsky
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