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From: Miklos Szeredi <miklos@szeredi.hu>
To: NeilBrown <neilb@suse.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	Josef Bacik <josef@toxicpanda.com>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	Chuck Lever <chuck.lever@oracle.com>, Chris Mason <clm@fb.com>,
	David Sterba <dsterba@suse.com>,
	linux-fsdevel@vger.kernel.org,
	Linux NFS list <linux-nfs@vger.kernel.org>,
	Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Subject: Re: [PATCH 01/11] VFS: show correct dev num in mountinfo
Date: Fri, 30 Jul 2021 07:54:33 +0200	[thread overview]
Message-ID: <CAJfpegsR1qvWAKNmdjLfOewUeQy-b6YBK4pcHf7JBExAqqUvvg@mail.gmail.com> (raw)
In-Reply-To: <162762290067.21659.4783063641244045179@noble.neil.brown.name>

On Fri, 30 Jul 2021 at 07:28, NeilBrown <neilb@suse.de> wrote:
>
> On Fri, 30 Jul 2021, Al Viro wrote:
> > On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:
> > > /proc/$PID/mountinfo contains a field for the device number of the
> > > filesystem at each mount.
> > >
> > > This is taken from the superblock ->s_dev field, which is correct for
> > > every filesystem except btrfs.  A btrfs filesystem can contain multiple
> > > subvols which each have a different device number.  If (a directory
> > > within) one of these subvols is mounted, the device number reported in
> > > mountinfo will be different from the device number reported by stat().
> > >
> > > This confuses some libraries and tools such as, historically, findmnt.
> > > Current findmnt seems to cope with the strangeness.
> > >
> > > So instead of using ->s_dev, call vfs_getattr_nosec() and use the ->dev
> > > provided.  As there is no STATX flag to ask for the device number, we
> > > pass a request mask for zero, and also ask the filesystem to avoid
> > > syncing with any remote service.
> >
> > Hard NAK.  You are putting IO (potentially - network IO, with no upper
> > limit on the completion time) under namespace_sem.
>
> Why would IO be generated? The inode must already be in cache because it
> is mounted, and STATX_DONT_SYNC is passed.  If a filesystem did IO in
> those circumstances, it would be broken.

STATX_DONT_SYNC is a hint, and while some network fs do honor it, not all do.

Thanks,
Miklos

  reply	other threads:[~2021-07-30  5:54 UTC|newest]

Thread overview: 127+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-27 22:37 [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly NeilBrown
2021-07-27 22:37 ` [PATCH 07/11] exportfs: Allow filehandle lookup to cross internal mount points NeilBrown
2021-07-28 10:13   ` Amir Goldstein
2021-07-29  0:28     ` NeilBrown
2021-07-29  5:27       ` Amir Goldstein
2021-08-06  7:52         ` Miklos Szeredi
2021-08-06  8:08           ` Amir Goldstein
2021-08-06  8:18             ` Miklos Szeredi
2021-07-28 19:17   ` J. Bruce Fields
2021-07-28 22:25     ` NeilBrown
2021-07-27 22:37 ` [PATCH 04/11] VFS: export lookup_mnt() NeilBrown
2021-07-30  0:31   ` Al Viro
2021-07-30  5:33     ` NeilBrown
2021-07-27 22:37 ` [PATCH 01/11] VFS: show correct dev num in mountinfo NeilBrown
2021-07-30  0:25   ` Al Viro
2021-07-30  5:28     ` NeilBrown
2021-07-30  5:54       ` Miklos Szeredi [this message]
2021-07-30  6:13         ` NeilBrown
2021-07-30  7:18           ` Miklos Szeredi
2021-07-30  7:33             ` NeilBrown
2021-07-30  7:59               ` Miklos Szeredi
2021-08-02  4:18                 ` A Third perspective on BTRFS nfsd subvol dev/inode number issues NeilBrown
2021-08-02  5:25                   ` Al Viro
2021-08-02  5:40                     ` NeilBrown
2021-08-02  7:54                       ` Amir Goldstein
2021-08-02 13:53                         ` Josef Bacik
2021-08-03 22:29                           ` Qu Wenruo
2021-08-02 14:47                         ` Frank Filz
2021-08-02 21:24                         ` NeilBrown
2021-08-02  7:15                   ` Martin Steigerwald
2021-08-02 21:40                     ` NeilBrown
2021-08-02 12:39                   ` J. Bruce Fields
2021-08-02 20:32                     ` Patrick Goetz
2021-08-02 20:41                       ` J. Bruce Fields
2021-08-02 21:10                     ` NeilBrown
2021-08-02 21:50                       ` J. Bruce Fields
2021-08-02 21:59                         ` NeilBrown
2021-08-02 22:14                           ` J. Bruce Fields
2021-08-02 22:36                             ` NeilBrown
2021-08-03  0:15                               ` J. Bruce Fields
2021-07-27 22:37 ` [PATCH 03/11] VFS: pass lookup_flags into follow_down() NeilBrown
2021-07-27 22:37 ` [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots NeilBrown
2021-07-28  8:37   ` kernel test robot
2021-07-28  8:37     ` kernel test robot
2021-07-28  8:37   ` [RFC PATCH] btrfs: btrfs_mountpoint_expiry_timeout can be static kernel test robot
2021-07-28  8:37     ` kernel test robot
2021-07-28 13:12   ` [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots Christian Brauner
2021-07-29  0:43     ` NeilBrown
2021-07-29 14:38       ` Christian Brauner
2021-07-31  6:25   ` [btrfs] 5874902268: xfstests.btrfs.202.fail kernel test robot
2021-07-31  6:25     ` kernel test robot
2021-07-27 22:37 ` [PATCH 06/11] nfsd: include a vfsmount in struct svc_fh NeilBrown
2021-07-27 22:37 ` [PATCH 10/11] btrfs: introduce mapping function from location to inum NeilBrown
2021-07-27 22:37 ` [PATCH 02/11] VFS: allow d_automount to create in-place bind-mount NeilBrown
2021-07-27 22:37 ` [PATCH 09/11] nfsd: Allow filehandle lookup to cross internal mount points NeilBrown
2021-07-28 19:15   ` J. Bruce Fields
2021-07-28 22:29     ` NeilBrown
2021-07-30  0:42   ` Al Viro
2021-07-30  5:43     ` NeilBrown
2021-07-27 22:37 ` [PATCH 08/11] nfsd: change get_parent_attributes() to nfsd_get_mounted_on() NeilBrown
2021-07-27 22:37 ` [PATCH 05/11] VFS: new function: mount_is_internal() NeilBrown
2021-07-28  2:16   ` Al Viro
2021-07-28  3:32     ` NeilBrown
2021-07-30  0:34       ` Al Viro
2021-07-28  2:19 ` [PATCH/RFC 00/11] expose btrfs subvols in mount table correctly Al Viro
2021-07-28  4:58 ` Wang Yugui
2021-07-28  6:04   ` Wang Yugui
2021-07-28  7:01     ` NeilBrown
2021-07-28 12:26       ` Neal Gompa
2021-07-28 19:14         ` J. Bruce Fields
2021-07-29  1:29           ` Zygo Blaxell
2021-07-29  1:43             ` NeilBrown
2021-07-29 23:20               ` Zygo Blaxell
2021-07-28 22:50         ` NeilBrown
2021-07-29  2:37           ` Zygo Blaxell
2021-07-29  3:36             ` NeilBrown
2021-07-29 23:20               ` Zygo Blaxell
2021-07-30  2:36                 ` NeilBrown
2021-07-30  5:25                   ` Qu Wenruo
2021-07-30  5:31                     ` Qu Wenruo
2021-07-30  5:53                       ` Amir Goldstein
2021-07-30  6:00                       ` NeilBrown
2021-07-30  6:09                         ` Qu Wenruo
2021-07-30  5:58                     ` NeilBrown
2021-07-30  6:23                       ` Qu Wenruo
2021-07-30  6:53                         ` NeilBrown
2021-07-30  7:09                           ` Qu Wenruo
2021-07-30 18:15                             ` Zygo Blaxell
2021-07-30 15:17                         ` J. Bruce Fields
2021-07-30 15:48                           ` Josef Bacik
2021-07-30 16:25                             ` Forza
2021-07-30 17:43                             ` Zygo Blaxell
2021-07-30  5:28                   ` Amir Goldstein
2021-07-28 13:43       ` g.btrfs
2021-07-29  1:39         ` NeilBrown
2021-07-29  9:28           ` Graham Cobb
2021-07-28  7:06   ` NeilBrown
2021-07-28  9:36     ` Wang Yugui
2021-07-28 19:35 ` J. Bruce Fields
2021-07-28 21:30   ` Josef Bacik
2021-07-30  0:13     ` Al Viro
2021-07-30  6:08       ` NeilBrown
2021-08-13  1:45 ` [PATCH] VFS/BTRFS/NFSD: provide more unique inode number for btrfs export NeilBrown
2021-08-13 14:55   ` Josef Bacik
2021-08-15  7:39   ` Goffredo Baroncelli
2021-08-15 19:35     ` Roman Mamedov
2021-08-15 21:03       ` Goffredo Baroncelli
2021-08-15 21:53         ` NeilBrown
2021-08-17 19:34           ` Goffredo Baroncelli
2021-08-17 21:39             ` NeilBrown
2021-08-18 17:24               ` Goffredo Baroncelli
2021-08-15 22:17       ` NeilBrown
2021-08-19  8:01         ` Amir Goldstein
2021-08-20  3:21           ` NeilBrown
2021-08-20  6:23             ` Amir Goldstein
2021-08-23  4:05         ` [PATCH v2] BTRFS/NFSD: " NeilBrown
2021-08-23  8:17           ` kernel test robot
2021-08-23  8:17             ` kernel test robot
2021-08-18 14:54   ` [PATCH] VFS/BTRFS/NFSD: " Wang Yugui
2021-08-18 21:46     ` NeilBrown
2021-08-19  2:19       ` Zygo Blaxell
2021-08-20  2:54         ` NeilBrown
2021-08-22 19:29           ` Zygo Blaxell
2021-08-23  5:51             ` NeilBrown
2021-08-23 23:22             ` NeilBrown
2021-08-25  2:06               ` Zygo Blaxell
2021-08-23  0:57         ` Wang Yugui

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