diff options
| author | Miklos Szeredi <mszeredi@suse.cz> | 2012-05-14 13:06:13 +0200 |
|---|---|---|
| committer | John Rigby <john.rigby@linaro.org> | 2012-06-25 15:04:09 -0600 |
| commit | e0ad3dc399aa8f76943c3b30ef52d36d62c207e4 (patch) | |
| tree | 81bc6a8e78a71b47af482764ea7a05ca4538c8c3 /fs/Makefile | |
| parent | dfafba2935e27a9080cd106e66a67b6ba77be954 (diff) | |
UBUNTU: ubuntu: overlayfs -- overlay filesystem
Overlayfs allows one, usually read-write, directory tree to be
overlaid onto another, read-only directory tree. All modifications
go to the upper, writable layer.
This type of mechanism is most often used for live CDs but there's a
wide variety of other uses.
The implementation differs from other "union filesystem"
implementations in that after a file is opened all operations go
directly to the underlying, lower or upper, filesystems. This
simplifies the implementation and allows native performance in these
cases.
The dentry tree is duplicated from the underlying filesystems, this
enables fast cached lookups without adding special support into the
VFS. This uses slightly more memory than union mounts, but dentries
are relatively small.
Currently inodes are duplicated as well, but it is a possible
optimization to share inodes for non-directories.
Opening non directories results in the open forwarded to the
underlying filesystem. This makes the behavior very similar to union
mounts (with the same limitations vs. fchmod/fchown on O_RDONLY file
descriptors).
Usage:
mount -t overlay -olowerdir=/lower,upperdir=/upper overlay /mnt
Supported:
- all operations
Missing:
- Currently a crash in the middle of copy-up, rename, unlink, rmdir or create
over a whiteout may result in filesystem corruption on the overlay level.
IOW these operations need to become atomic or at least the corruption needs
to be detected.
The following cotributions have been folded into this patch:
Neil Brown <neilb@suse.de>:
- minimal remount support
- use correct seek function for directories
- initialise is_real before use
- rename ovl_fill_cache to ovl_dir_read
Felix Fietkau <nbd@openwrt.org>:
- fix a deadlock in ovl_dir_read_merged
- fix a deadlock in ovl_remove_whiteouts
Erez Zadok <ezk@fsl.cs.sunysb.edu>
- fix cleanup after WARN_ON
Sedat Dilek <sedat.dilek@googlemail.com>
- fix up permission to confirm to new API
Also thanks to the following people for testing and reporting bugs:
Jordi Pujol <jordipujolp@gmail.com>
Andy Whitcroft <apw@canonical.com>
Michal Suchanek <hramrach@centrum.cz>
Felix Fietkau <nbd@openwrt.org>
Erez Zadok <ezk@fsl.cs.sunysb.edu>
Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Diffstat (limited to 'fs/Makefile')
| -rw-r--r-- | fs/Makefile | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/fs/Makefile b/fs/Makefile index 2fb97793467..fcd9788adfb 100644 --- a/fs/Makefile +++ b/fs/Makefile @@ -106,6 +106,7 @@ obj-$(CONFIG_QNX6FS_FS) += qnx6/ obj-$(CONFIG_AUTOFS4_FS) += autofs4/ obj-$(CONFIG_ADFS_FS) += adfs/ obj-$(CONFIG_FUSE_FS) += fuse/ +obj-$(CONFIG_OVERLAYFS_FS) += overlayfs/ obj-$(CONFIG_UDF_FS) += udf/ obj-$(CONFIG_SUN_OPENPROMFS) += openpromfs/ obj-$(CONFIG_OMFS_FS) += omfs/ |