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linux-sg2042/Documentation/filesystems
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Sargun Dhillon 335d3fc579 ovl: implement volatile-specific fsync error behaviour 
Overlayfs's volatile option allows the user to bypass all forced sync calls
to the upperdir filesystem. This comes at the cost of safety. We can never
ensure that the user's data is intact, but we can make a best effort to
expose whether or not the data is likely to be in a bad state.

The best way to handle this in the time being is that if an overlayfs's
upperdir experiences an error after a volatile mount occurs, that error
will be returned on fsync, fdatasync, sync, and syncfs. This is
contradictory to the traditional behaviour of VFS which fails the call
once, and only raises an error if a subsequent fsync error has occurred,
and been raised by the filesystem.

One awkward aspect of the patch is that we have to manually set the
superblock's errseq_t after the sync_fs callback as opposed to just
returning an error from syncfs. This is because the call chain looks
something like this:

sys_syncfs ->
	sync_filesystem ->
		__sync_filesystem ->
			/* The return value is ignored here
			sb->s_op->sync_fs(sb)
			_sync_blockdev
		/* Where the VFS fetches the error to raise to userspace */
		errseq_check_and_advance

Because of this we call errseq_set every time the sync_fs callback occurs.
Due to the nature of this seen / unseen dichotomy, if the upperdir is an
inconsistent state at the initial mount time, overlayfs will refuse to
mount, as overlayfs cannot get a snapshot of the upperdir's errseq that
will increment on error until the user calls syncfs.

Signed-off-by: Sargun Dhillon <sargun@sargun.me>
Suggested-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Fixes: c86243b090 ("ovl: provide a mount option "volatile"")
Cc: stable@vger.kernel.org
Reviewed-by: Vivek Goyal <vgoyal@redhat.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
 		2021-01-28 10:22:48 +01:00
..
caching docs: filesystems: Replace HTTP links with HTTPS ones 2020-07-13 09:33:22 -06:00
cifs docs: filesystems: convert cifs/cifsroot.txt to ReST 2020-05-05 09:22:21 -06:00
ext4 ext4: add docs about fast commit idempotence 2020-12-17 13:30:44 -05:00
nfs nfsd: close cached files prior to a REMOVE or RENAME that would replace target 2020-12-09 09:39:38 -05:00
spufs docs: filesystems: convert spufs/spu_run.txt to ReST 2020-05-05 09:22:24 -06:00
9p.rst Replace HTTP links with HTTPS ones: 9P FILE SYSTEM 2020-07-13 11:28:12 -06:00
adfs.rst docs: filesystems: convert adfs.txt to ReST 2020-03-02 13:58:44 -07:00
affs.rst affs: fix basic permission bits to actually work 2020-08-31 12:20:31 +02:00
afs.rst Replace HTTP links with HTTPS ones: AFS FILESYSTEM 2020-07-13 11:25:29 -06:00
api-summary.rst docs: fs: api-summary.rst: get rid of kernel-doc include 2020-10-28 11:41:15 -06:00
autofs-mount-control.rst Documentation: filesystems: autofs-mount-control: drop doubled words 2020-07-05 14:44:29 -06:00
autofs.rst docs: filesystems: Add mount map description in Content 2019-11-18 12:19:59 -07:00
automount-support.rst docs: filesystems: convert automount-support.txt to ReST 2020-05-05 09:22:21 -06:00
befs.rst docs: filesystems: convert befs.txt to ReST 2020-03-02 14:01:25 -07:00
bfs.rst docs: filesystems: convert bfs.txt to ReST 2020-03-02 14:01:26 -07:00
btrfs.rst docs: filesystems: convert btrfs.txt to ReST 2020-03-02 14:01:28 -07:00
ceph.rst libceph, rbd, ceph: "blacklist" -> "blocklist" 2020-10-12 15:29:26 +02:00
coda.rst Documentation: coda: annotate duplicated words 2020-07-13 10:02:32 -06:00
configfs.rst Documentation: filesystems: configfs: drop doubled word 2020-07-05 14:44:29 -06:00
cramfs.rst docs: filesystems: convert cramfs.txt to ReST 2020-03-02 14:02:07 -07:00
dax.txt This is the second round of ext4 commits for 5.8 merge window. It 2020-06-15 09:32:10 -07:00
debugfs.rst debugfs: remove return value of debugfs_create_devm_seqfile() 2020-10-30 08:37:39 +01:00
devpts.rst docs: filesystems: convert devpts.txt to ReST 2020-05-05 09:22:21 -06:00
directory-locking.rst Documentation: filesystems: directory-locking: drop doubled word 2020-07-05 14:44:29 -06:00
dlmfs.rst ocfs2: replace HTTP links with HTTPS ones 2020-08-07 11:33:22 -07:00
dnotify.rst docs: filesystems: convert dnotify.txt to ReST 2020-05-05 09:22:22 -06:00
ecryptfs.rst docs: prevent warnings due to autosectionlabel 2020-03-20 17:01:29 -06:00
efivarfs.rst docs: filesystems: add info about efivars content 2020-05-25 18:59:59 -06:00
erofs.rst docs: filesystems: convert erofs.txt to ReST 2020-03-02 14:02:57 -07:00
ext2.rst docs: filesystems: Reduce ext2.rst to one top-level heading 2020-11-09 15:33:54 +01:00
ext3.rst docs: filesystems: convert ext3.txt to ReST 2020-03-02 14:03:16 -07:00
f2fs.rst f2fs: add compress_mode mount option 2020-12-03 00:11:57 -08:00
fiemap.rst A lot of bug fixes and cleanups for ext4, including: 2020-06-05 16:19:28 -07:00
files.rst file: Rename fcheck lookup_fd_rcu 2020-12-10 12:40:07 -06:00
fscrypt.rst docs: fs: fscrypt.rst: get rid of :c:type: tags 2020-10-15 07:49:42 +02:00
fsverity.rst fs-verity: move structs needed for file signing to UAPI header 2020-11-23 19:30:14 -08:00
fuse-io.rst docs: filesystems: convert fuse-io.txt to ReST 2020-05-05 09:22:22 -06:00
fuse.rst fuse: update project homepage 2020-09-04 11:32:10 +02:00
gfs2-glocks.rst docs: filesystems: convert gfs2-glocks.txt to ReST 2020-06-02 19:45:05 +02:00
gfs2-uevents.rst docs: filesystems: convert gfs2-uevents.txt to ReST 2020-03-02 14:03:35 -07:00
gfs2.rst Documentation: Update filesystems/gfs2.rst 2020-12-01 00:25:20 +01:00
hfs.rst Replace HTTP links with HTTPS ones: Documentation/filesystems 2020-06-26 11:14:12 -06:00
hfsplus.rst docs: filesystems: convert hfsplus.txt to ReST 2020-03-02 14:03:47 -07:00
hpfs.rst Replace HTTP links with HTTPS ones: Documentation/filesystems 2020-06-26 11:14:12 -06:00
index.rst docs: filesystems: link ubifs-authentication.rst without .rst extension 2020-11-13 15:07:47 -07:00
inotify.rst docs: filesystems: convert inotify.txt to ReST 2020-03-02 14:03:55 -07:00
isofs.rst docs: filesystems: convert isofs.txt to ReST 2020-03-02 14:04:06 -07:00
journalling.rst jbd2: drop jbd2_fc_init documentation 2020-11-06 23:01:03 -05:00
locking.rst Documentation/filesystems/locking.rst: remove an incorrect sentence 2020-09-02 07:59:59 -06:00
locks.rst docs: filesystems: convert mandatory-locking.txt to ReST 2020-05-05 09:22:22 -06:00
mandatory-locking.rst docs: filesystems: convert mandatory-locking.txt to ReST 2020-05-05 09:22:22 -06:00
mount_api.rst Documentation: mount_api: change kernel log wording 2020-12-03 15:53:13 -07:00
nilfs2.rst docs: filesystems: convert nilfs2.txt to ReST 2020-03-02 14:04:06 -07:00
ntfs.rst docs: filesystems: convert ntfs.txt to ReST 2020-03-02 14:04:06 -07:00
ocfs2-online-filecheck.rst docs: filesystems: convert ocfs2-online-filecheck.txt to ReST 2020-03-02 14:04:06 -07:00
ocfs2.rst ocfs2: replace HTTP links with HTTPS ones 2020-08-07 11:33:22 -07:00
omfs.rst Replace HTTP links with HTTPS ones: OMFS 2020-07-13 11:24:43 -06:00
orangefs.rst docs: orangefs: fix pvfs2tab literal block 2020-04-28 12:35:47 -06:00
overlayfs.rst ovl: implement volatile-specific fsync error behaviour 2021-01-28 10:22:48 +01:00
path-lookup.rst docs: path-lookup: markup fixes for emphasis 2020-07-27 16:14:13 -06:00
path-lookup.txt Replace HTTP links with HTTPS ones: documentation 2020-06-08 09:30:19 -06:00
porting.rst ovl: make private mounts longterm 2020-06-04 10:48:19 +02:00
proc.rst proc: provide details on indirect branch speculation 2020-12-15 22:46:15 -08:00
qnx6.rst docs: filesystems: fix typo in qnx6.rst 2020-04-07 13:20:56 -06:00
quota.rst quota: Fixup http links in quota doc 2020-07-09 08:14:01 +02:00
ramfs-rootfs-initramfs.rst Replace HTTP links with HTTPS ones: Documentation/filesystems 2020-06-26 11:14:12 -06:00
relay.rst docs: filesystems: convert relay.txt to ReST 2020-03-02 14:04:41 -07:00
romfs.rst docs: filesystems: convert romfs.txt to ReST 2020-03-02 14:04:41 -07:00
seq_file.rst doc: seq_file: clarify role of *pos in ->next() 2020-09-28 15:19:44 -06:00
sharedsubtree.rst docs: filesystems: convert sharedsubtree.txt to ReST 2020-05-05 09:22:23 -06:00
splice.rst docs: Bring some order to filesystem documentation 2019-03-06 09:46:10 -07:00
squashfs.rst docs: filesystems: convert squashfs.txt to ReST 2020-03-02 14:04:41 -07:00
sysfs.rst Driver Core patches for 5.10-rc1 2020-10-14 16:09:32 -07:00
sysv-fs.rst docs: filesystems: convert sysv-fs.txt to ReST 2020-03-02 14:04:41 -07:00
tmpfs.rst tmpfs: fix Documentation nits 2020-12-15 12:13:39 -08:00
ubifs-authentication.rst docs: ubifs-authentication: Add a top-level heading 2020-09-09 11:53:33 -06:00
ubifs.rst docs: filesystems: convert ubifs.txt to ReST 2020-03-02 14:04:41 -07:00
udf.rst udf: Replace HTTP links with HTTPS ones 2020-07-14 14:37:39 +02:00
vfat.rst Documentation: filesystems: convert vfat.txt to RST 2020-01-10 10:58:45 -07:00
vfs.rst docs: filesystems: vfs: correct flag name 2020-07-27 16:19:51 -06:00
virtiofs.rst virtiofs: Add mount option and atime behavior to the doc 2020-04-20 17:01:34 +02:00
xfs-delayed-logging-design.rst docs: filesystems: convert xfs-delayed-logging-design.txt to ReST 2020-05-05 09:22:24 -06:00
xfs-self-describing-metadata.rst New code for 5.8: 2020-06-02 19:21:40 -07:00
zonefs.rst zonefs: document the explicit-open mount option 2020-09-15 18:32:58 +09:00