linux/fs/overlayfs/Kconfig

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# SPDX-License-Identifier: GPL-2.0-only
config OVERLAY_FS
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 overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay 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 Robin Dong <hao.bigrat@gmail.com> - fix possible leak in ovl_new_inode - create new inode in ovl_link Andy Whitcroft <apw@canonical.com> - switch to __inode_permission() - copy up i_uid/i_gid from the underlying inode AV: - ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits - ovl_clear_empty() - one failure exit forgetting to do unlock_rename(), lack of check for udir being the parent of upper, dropping and regaining the lock on udir (which would require _another_ check for parent being right). - bogus d_drop() in copyup and rename [fix from your mail] - copyup/remove and copyup/rename races [fix from your mail] - ovl_dir_fsync() leaving ERR_PTR() in ->realfile - ovl_entry_free() is pointless - it's just a kfree_rcu() - fold ovl_do_lookup() into ovl_lookup() - manually assigning ->d_op is wrong. Just use ->s_d_op. [patches picked from Miklos]: * copyup/remove and copyup/rename races * bogus d_drop() in copyup and rename 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>
2014-10-23 22:14:38 +00:00
tristate "Overlay filesystem support"
select EXPORTFS
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 overlayfs overlayfs -olowerdir=/lower,upperdir=/upper/upper,workdir=/upper/work /overlay 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 Robin Dong <hao.bigrat@gmail.com> - fix possible leak in ovl_new_inode - create new inode in ovl_link Andy Whitcroft <apw@canonical.com> - switch to __inode_permission() - copy up i_uid/i_gid from the underlying inode AV: - ovl_copy_up_locked() - dput(ERR_PTR(...)) on two failure exits - ovl_clear_empty() - one failure exit forgetting to do unlock_rename(), lack of check for udir being the parent of upper, dropping and regaining the lock on udir (which would require _another_ check for parent being right). - bogus d_drop() in copyup and rename [fix from your mail] - copyup/remove and copyup/rename races [fix from your mail] - ovl_dir_fsync() leaving ERR_PTR() in ->realfile - ovl_entry_free() is pointless - it's just a kfree_rcu() - fold ovl_do_lookup() into ovl_lookup() - manually assigning ->d_op is wrong. Just use ->s_d_op. [patches picked from Miklos]: * copyup/remove and copyup/rename races * bogus d_drop() in copyup and rename 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>
2014-10-23 22:14:38 +00:00
help
An overlay filesystem combines two filesystems - an 'upper' filesystem
and a 'lower' filesystem. When a name exists in both filesystems, the
object in the 'upper' filesystem is visible while the object in the
'lower' filesystem is either hidden or, in the case of directories,
merged with the 'upper' object.
For more information see Documentation/filesystems/overlayfs.rst
config OVERLAY_FS_REDIRECT_DIR
bool "Overlayfs: turn on redirect directory feature by default"
depends on OVERLAY_FS
help
If this config option is enabled then overlay filesystems will use
redirects when renaming directories by default. In this case it is
still possible to turn off redirects globally with the
"redirect_dir=off" module option or on a filesystem instance basis
with the "redirect_dir=off" mount option.
Note, that redirects are not backward compatible. That is, mounting
an overlay which has redirects on a kernel that doesn't support this
feature will have unexpected results.
If unsure, say N.
config OVERLAY_FS_REDIRECT_ALWAYS_FOLLOW
bool "Overlayfs: follow redirects even if redirects are turned off"
default y
depends on OVERLAY_FS
help
Disable this to get a possibly more secure configuration, but that
might not be backward compatible with previous kernels.
If backward compatibility is not an issue, then it is safe and
recommended to say N here.
For more information, see Documentation/filesystems/overlayfs.rst
If unsure, say Y.
config OVERLAY_FS_INDEX
bool "Overlayfs: turn on inodes index feature by default"
depends on OVERLAY_FS
help
If this config option is enabled then overlay filesystems will use
the index directory to map lower inodes to upper inodes by default.
In this case it is still possible to turn off index globally with the
"index=off" module option or on a filesystem instance basis with the
"index=off" mount option.
The inodes index feature prevents breaking of lower hardlinks on copy
up.
Note, that the inodes index feature is not backward compatible.
That is, mounting an overlay which has an inodes index on a kernel
that doesn't support this feature will have unexpected results.
If unsure, say N.
config OVERLAY_FS_NFS_EXPORT
bool "Overlayfs: turn on NFS export feature by default"
depends on OVERLAY_FS
depends on OVERLAY_FS_INDEX
depends on !OVERLAY_FS_METACOPY
help
If this config option is enabled then overlay filesystems will use
the index directory to decode overlay NFS file handles by default.
In this case, it is still possible to turn off NFS export support
globally with the "nfs_export=off" module option or on a filesystem
instance basis with the "nfs_export=off" mount option.
The NFS export feature creates an index on copy up of every file and
directory. This full index is used to detect overlay filesystems
inconsistencies on lookup, like redirect from multiple upper dirs to
the same lower dir. The full index may incur some overhead on mount
time, especially when verifying that directory file handles are not
stale.
Note, that the NFS export feature is not backward compatible.
That is, mounting an overlay which has a full index on a kernel
that doesn't support this feature will have unexpected results.
Most users should say N here and enable this feature on a case-by-
case basis with the "nfs_export=on" mount option.
Say N unless you fully understand the consequences.
ovl: add support for "xino" mount and config options With mount option "xino=on", mounter declares that there are enough free high bits in underlying fs to hold the layer fsid. If overlayfs does encounter underlying inodes using the high xino bits reserved for layer fsid, a warning will be emitted and the original inode number will be used. The mount option name "xino" goes after a similar meaning mount option of aufs, but in overlayfs case, the mapping is stateless. An example for a use case of "xino=on" is when upper/lower is on an xfs filesystem. xfs uses 64bit inode numbers, but it currently never uses the upper 8bit for inode numbers exposed via stat(2) and that is not likely to change in the future without user opting-in for a new xfs feature. The actual number of unused upper bit is much larger and determined by the xfs filesystem geometry (64 - agno_log - agblklog - inopblog). That means that for all practical purpose, there are enough unused bits in xfs inode numbers for more than OVL_MAX_STACK unique fsid's. Another use case of "xino=on" is when upper/lower is on tmpfs. tmpfs inode numbers are allocated sequentially since boot, so they will practially never use the high inode number bits. For compatibility with applications that expect 32bit inodes, the feature can be disabled with "xino=off". The option "xino=auto" automatically detects underlying filesystem that use 32bit inodes and enables the feature. The Kconfig option OVERLAY_FS_XINO_AUTO and module parameter of the same name, determine if the default mode for overlayfs mount is "xino=auto" or "xino=off". Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-03-29 06:08:18 +00:00
config OVERLAY_FS_XINO_AUTO
bool "Overlayfs: auto enable inode number mapping"
default n
depends on OVERLAY_FS
depends on 64BIT
ovl: add support for "xino" mount and config options With mount option "xino=on", mounter declares that there are enough free high bits in underlying fs to hold the layer fsid. If overlayfs does encounter underlying inodes using the high xino bits reserved for layer fsid, a warning will be emitted and the original inode number will be used. The mount option name "xino" goes after a similar meaning mount option of aufs, but in overlayfs case, the mapping is stateless. An example for a use case of "xino=on" is when upper/lower is on an xfs filesystem. xfs uses 64bit inode numbers, but it currently never uses the upper 8bit for inode numbers exposed via stat(2) and that is not likely to change in the future without user opting-in for a new xfs feature. The actual number of unused upper bit is much larger and determined by the xfs filesystem geometry (64 - agno_log - agblklog - inopblog). That means that for all practical purpose, there are enough unused bits in xfs inode numbers for more than OVL_MAX_STACK unique fsid's. Another use case of "xino=on" is when upper/lower is on tmpfs. tmpfs inode numbers are allocated sequentially since boot, so they will practially never use the high inode number bits. For compatibility with applications that expect 32bit inodes, the feature can be disabled with "xino=off". The option "xino=auto" automatically detects underlying filesystem that use 32bit inodes and enables the feature. The Kconfig option OVERLAY_FS_XINO_AUTO and module parameter of the same name, determine if the default mode for overlayfs mount is "xino=auto" or "xino=off". Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-03-29 06:08:18 +00:00
help
If this config option is enabled then overlay filesystems will use
unused high bits in undelying filesystem inode numbers to map all
inodes to a unified address space. The mapped 64bit inode numbers
might not be compatible with applications that expect 32bit inodes.
If compatibility with applications that expect 32bit inodes is not an
issue, then it is safe and recommended to say Y here.
For more information, see Documentation/filesystems/overlayfs.rst
ovl: add support for "xino" mount and config options With mount option "xino=on", mounter declares that there are enough free high bits in underlying fs to hold the layer fsid. If overlayfs does encounter underlying inodes using the high xino bits reserved for layer fsid, a warning will be emitted and the original inode number will be used. The mount option name "xino" goes after a similar meaning mount option of aufs, but in overlayfs case, the mapping is stateless. An example for a use case of "xino=on" is when upper/lower is on an xfs filesystem. xfs uses 64bit inode numbers, but it currently never uses the upper 8bit for inode numbers exposed via stat(2) and that is not likely to change in the future without user opting-in for a new xfs feature. The actual number of unused upper bit is much larger and determined by the xfs filesystem geometry (64 - agno_log - agblklog - inopblog). That means that for all practical purpose, there are enough unused bits in xfs inode numbers for more than OVL_MAX_STACK unique fsid's. Another use case of "xino=on" is when upper/lower is on tmpfs. tmpfs inode numbers are allocated sequentially since boot, so they will practially never use the high inode number bits. For compatibility with applications that expect 32bit inodes, the feature can be disabled with "xino=off". The option "xino=auto" automatically detects underlying filesystem that use 32bit inodes and enables the feature. The Kconfig option OVERLAY_FS_XINO_AUTO and module parameter of the same name, determine if the default mode for overlayfs mount is "xino=auto" or "xino=off". Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2018-03-29 06:08:18 +00:00
If unsure, say N.
config OVERLAY_FS_METACOPY
bool "Overlayfs: turn on metadata only copy up feature by default"
depends on OVERLAY_FS
select OVERLAY_FS_REDIRECT_DIR
help
If this config option is enabled then overlay filesystems will
copy up only metadata where appropriate and data copy up will
happen when a file is opened for WRITE operation. It is still
possible to turn off this feature globally with the "metacopy=off"
module option or on a filesystem instance basis with the
"metacopy=off" mount option.
Note, that this feature is not backward compatible. That is,
mounting an overlay which has metacopy only inodes on a kernel
that doesn't support this feature will have unexpected results.
If unsure, say N.