diff options
Diffstat (limited to 'Documentation/filesystems')
| -rw-r--r-- | Documentation/filesystems/overlayfs.txt | 34 | ||||
| -rw-r--r-- | Documentation/filesystems/proc.txt | 6 |
2 files changed, 39 insertions, 1 deletions
diff --git a/Documentation/filesystems/overlayfs.txt b/Documentation/filesystems/overlayfs.txt index c9e884b52698..36f528a7fdd6 100644 --- a/Documentation/filesystems/overlayfs.txt +++ b/Documentation/filesystems/overlayfs.txt @@ -201,6 +201,40 @@ rightmost one and going left. In the above example lower1 will be the top, lower2 the middle and lower3 the bottom layer. +Sharing and copying layers +-------------------------- + +Lower layers may be shared among several overlay mounts and that is indeed +a very common practice. An overlay mount may use the same lower layer +path as another overlay mount and it may use a lower layer path that is +beneath or above the path of another overlay lower layer path. + +Using an upper layer path and/or a workdir path that are already used by +another overlay mount is not allowed and will fail with EBUSY. Using +partially overlapping paths is not allowed but will not fail with EBUSY. + +Mounting an overlay using an upper layer path, where the upper layer path +was previously used by another mounted overlay in combination with a +different lower layer path, is allowed, unless the "inodes index" feature +is enabled. + +With the "inodes index" feature, on the first time mount, an NFS file +handle of the lower layer root directory, along with the UUID of the lower +filesystem, are encoded and stored in the "trusted.overlay.origin" extended +attribute on the upper layer root directory. On subsequent mount attempts, +the lower root directory file handle and lower filesystem UUID are compared +to the stored origin in upper root directory. On failure to verify the +lower root origin, mount will fail with ESTALE. An overlayfs mount with +"inodes index" enabled will fail with EOPNOTSUPP if the lower filesystem +does not support NFS export, lower filesystem does not have a valid UUID or +if the upper filesystem does not support extended attributes. + +It is quite a common practice to copy overlay layers to a different +directory tree on the same or different underlying filesystem, and even +to a different machine. With the "inodes index" feature, trying to mount +the copied layers will fail the verification of the lower root file handle. + + Non-standard behavior --------------------- diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt index 4cddbce85ac9..adba21b5ada7 100644 --- a/Documentation/filesystems/proc.txt +++ b/Documentation/filesystems/proc.txt @@ -1786,12 +1786,16 @@ pair provide additional information particular to the objects they represent. pos: 0 flags: 02 mnt_id: 9 - tfd: 5 events: 1d data: ffffffffffffffff + tfd: 5 events: 1d data: ffffffffffffffff pos:0 ino:61af sdev:7 where 'tfd' is a target file descriptor number in decimal form, 'events' is events mask being watched and the 'data' is data associated with a target [see epoll(7) for more details]. + The 'pos' is current offset of the target file in decimal form + [see lseek(2)], 'ino' and 'sdev' are inode and device numbers + where target file resides, all in hex format. + Fsnotify files ~~~~~~~~~~~~~~ For inotify files the format is the following |
