From: Christian Brauner <christian.brauner@ubuntu.com>
To: NeilBrown <neilb@suse.de>
Cc: 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>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-btrfs@vger.kernel.org
Subject: Re: [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots.
Date: Wed, 28 Jul 2021 15:12:13 +0200 [thread overview]
Message-ID: <20210728131213.pgu3r4m4ulozrcav@wittgenstein> (raw)
In-Reply-To: <162742546558.32498.1901201501617899416.stgit@noble.brown>
On Wed, Jul 28, 2021 at 08:37:45AM +1000, NeilBrown wrote:
> All subvol roots are now marked as automounts. If the d_automount()
> function determines that the dentry is not the root of the vfsmount, it
> creates a simple loop-back mount of the dentry onto itself. If it
> determines that it IS the root of the vfsmount, it returns -EISDIR so
> that no further automounting is attempted.
>
> btrfs_getattr pays special attention to these automount dentries.
> If it is NOT the root of the vfsmount:
> - the ->dev is reported as that for the rest of the vfsmount
> - the ->ino is reported as the subvol objectid, suitable transformed
> to avoid collision.
>
> This way the same inode appear to be different depending on which mount
> it is in.
>
> automounted vfsmounts are kept on a list and timeout after 500 to 1000
> seconds of last use. This is configurable via a module parameter.
> The tracking and timeout of automounts is copied from NFS.
>
> Link: https://lore.kernel.org/r/162742546558.32498.1901201501617899416.stgit@noble.brown
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: NeilBrown <neilb@suse.de>
> ---
> fs/btrfs/btrfs_inode.h | 2 +
> fs/btrfs/inode.c | 108 ++++++++++++++++++++++++++++++++++++++++++++++++
> fs/btrfs/super.c | 1
> 3 files changed, 111 insertions(+)
>
> diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
> index a4b5f38196e6..f03056cacc4a 100644
> --- a/fs/btrfs/btrfs_inode.h
> +++ b/fs/btrfs/btrfs_inode.h
> @@ -387,4 +387,6 @@ static inline void btrfs_print_data_csum_error(struct btrfs_inode *inode,
> mirror_num);
> }
>
> +void btrfs_release_automount_timer(void);
> +
> #endif
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 02537c1a9763..a5f46545fb38 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -31,6 +31,7 @@
> #include <linux/migrate.h>
> #include <linux/sched/mm.h>
> #include <linux/iomap.h>
> +#include <linux/fs_context.h>
> #include <asm/unaligned.h>
> #include "misc.h"
> #include "ctree.h"
> @@ -5782,6 +5783,8 @@ static int btrfs_init_locked_inode(struct inode *inode, void *p)
> struct btrfs_iget_args *args = p;
>
> inode->i_ino = args->ino;
> + if (args->ino == BTRFS_FIRST_FREE_OBJECTID)
> + inode->i_flags |= S_AUTOMOUNT;
> BTRFS_I(inode)->location.objectid = args->ino;
> BTRFS_I(inode)->location.type = BTRFS_INODE_ITEM_KEY;
> BTRFS_I(inode)->location.offset = 0;
> @@ -5985,6 +5988,101 @@ static int btrfs_dentry_delete(const struct dentry *dentry)
> return 0;
> }
>
> +static void btrfs_expire_automounts(struct work_struct *work);
> +static LIST_HEAD(btrfs_automount_list);
> +static DECLARE_DELAYED_WORK(btrfs_automount_task, btrfs_expire_automounts);
> +int btrfs_mountpoint_expiry_timeout = 500 * HZ;
> +static void btrfs_expire_automounts(struct work_struct *work)
> +{
> + struct list_head *list = &btrfs_automount_list;
> + int timeout = READ_ONCE(btrfs_mountpoint_expiry_timeout);
> +
> + mark_mounts_for_expiry(list);
> + if (!list_empty(list) && timeout > 0)
> + schedule_delayed_work(&btrfs_automount_task, timeout);
> +}
> +
> +void btrfs_release_automount_timer(void)
> +{
> + if (list_empty(&btrfs_automount_list))
> + cancel_delayed_work(&btrfs_automount_task);
> +}
> +
> +static struct vfsmount *btrfs_automount(struct path *path)
> +{
> + struct fs_context fc;
> + struct vfsmount *mnt;
> + int timeout = READ_ONCE(btrfs_mountpoint_expiry_timeout);
> +
> + if (path->dentry == path->mnt->mnt_root)
> + /* dentry is root of the vfsmount,
> + * so skip automount processing
> + */
> + return ERR_PTR(-EISDIR);
> + /* Create a bind-mount to expose the subvol in the mount table */
> + fc.root = path->dentry;
> + fc.sb_flags = 0;
> + fc.source = "btrfs-automount";
> + mnt = vfs_create_mount(&fc);
> + if (IS_ERR(mnt))
> + return mnt;
Hey Neil,
Sorry if this is a stupid question but wouldn't you want to copy the
mount properties from path->mnt here? Couldn't you otherwise use this to
e.g. suddenly expose a dentry on a read-only mount as read-write?
Christian
next prev parent reply other threads:[~2021-07-28 13:12 UTC|newest]
Thread overview: 122+ 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
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 ` [RFC PATCH] btrfs: btrfs_mountpoint_expiry_timeout can be static kernel test robot
2021-07-28 13:12 ` Christian Brauner [this message]
2021-07-29 0:43 ` [PATCH 11/11] btrfs: use automount to bind-mount all subvol roots NeilBrown
2021-07-29 14:38 ` Christian Brauner
2021-07-31 6:25 ` [btrfs] 5874902268: xfstests.btrfs.202.fail 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
2021-08-18 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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