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path: root/fs/overlayfs/overlayfs.h
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2017-02-07ovl: introduce copy up waitqueueAmir Goldstein
The overlay sb 'copyup_wq' and overlay inode 'copying' condition variable are about to replace the upper sb rename_lock, as finer grained synchronization objects for concurrent copy up. Suggested-by: Miklos Szeredi <miklos@szeredi.hu> Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2017-02-07ovl: check if upperdir fs supports O_TMPFILEAmir Goldstein
This is needed for choosing between concurrent copyup using O_TMPFILE and legacy copyup using workdir+rename. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: clean up kstat usageAl Viro
FWIW, there's a bit of abuse of struct kstat in overlayfs object creation paths - for one thing, it ends up with a very small subset of struct kstat (mode + rdev), for another it also needs link in case of symlinks and ends up passing it separately. IMO it would be better to introduce a separate object for that. In principle, we might even lift that thing into general API and switch ->mkdir()/->mknod()/->symlink() to identical calling conventions. Hell knows, perhaps ->create() as well... Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: fold ovl_copy_up_truncate() into ovl_copy_up()Amir Goldstein
This removes code duplication. Signed-off-by: Amir Goldstein <amir73il@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: opaque cleanupMiklos Szeredi
oe->opaque is set for a) whiteouts b) directories having the "trusted.overlay.opaque" xattr Case b can be simplified, since setting the xattr always implies setting oe->opaque. Also once set, the opaque flag is never cleared. Don't need to set opaque flag for non-directories. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: redirect on rename-dirMiklos Szeredi
Current code returns EXDEV when a directory would need to be copied up to move. We could copy up the directory tree in this case, but there's another, simpler solution: point to old lower directory from moved upper directory. This is achieved with a "trusted.overlay.redirect" xattr storing the path relative to the root of the overlay. After such attribute has been set, the directory can be moved without further actions required. This is a backward incompatible feature, old kernels won't be able to correctly mount an overlay containing redirected directories. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: lookup redirectsMiklos Szeredi
If a directory has the "trusted.overlay.redirect" xattr, it means that the value of the xattr should be used to find the underlying directory on the next lower layer. The redirect may be relative or absolute. Absolute redirects begin with a slash. A relative redirect means: instead of the current dentry's name use the value of the redirect to find the directory in the next lower layer. Relative redirects must not contain a slash. An absolute redirect means: look up the directory relative to the root of the overlay using the value of the redirect in the next lower layer. Redirects work on lower layers as well. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: split super.cMiklos Szeredi
fs/overlayfs/super.c is the biggest of the overlayfs source files and it contains various utility functions as well as the rather complicated lookup code. Split these parts out to separate files. Before: 1446 fs/overlayfs/super.c After: 919 fs/overlayfs/super.c 267 fs/overlayfs/namei.c 235 fs/overlayfs/util.c 51 fs/overlayfs/ovl_entry.h Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: rename: simplify handling of lower/merged directoryMiklos Szeredi
d_is_dir() is safe to call on a negative dentry. Use this fact to simplify handling of the lower or merged directories. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: get rid of PURE typeMiklos Szeredi
The remainging uses of __OVL_PATH_PURE can be replaced by ovl_dentry_is_opaque(). Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: check lower existence when removingMiklos Szeredi
Currently ovl_lookup() checks existence of lower file even if there's a non-directory on upper (which is always opaque). This is done so that remove can decide whether a whiteout is needed or not. It would be better to defer this check to unlink, since most of the time the gathered information about opaqueness will be unused. This adds a helper ovl_lower_positive() that checks if there's anything on the lower layer(s). The following patches also introduce changes to how the "opaque" attribute is updated on directories: this attribute is added when the directory is creted or moved over a whiteout or object covering something on the lower layer. However following changes will allow the attribute to remain on the directory after being moved, even if the new location doesn't cover anything. Because of this, we need to check lower layers even for opaque directories, so that whiteout is only created when necessary. This function will later be also used to decide about marking a directory opaque, so deal with negative dentries as well. When dealing with negative, it's enough to check for being a whiteout If the dentry is positive but not upper then it also obviously needs whiteout/opaque. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: add ovl_dentry_is_whiteout()Miklos Szeredi
And use it instead of ovl_dentry_is_opaque() where appropriate. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-12-16ovl: treat special files like a regular fsMiklos Szeredi
No sense in opening special files on the underlying layers, they work just as well if opened on the overlay. Side effect is that it's no longer possible to connect one side of a pipe opened on overlayfs with the other side opened on the underlying layer. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-09-27fs: rename "rename2" i_op to "rename"Miklos Szeredi
Generated patch: sed -i "s/\.rename2\t/\.rename\t\t/" `git grep -wl rename2` sed -i "s/\brename2\b/rename/g" `git grep -wl rename2` Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-09-01ovl: Switch to generic_getxattrAndreas Gruenbacher
Now that overlayfs has xattr handlers for iop->{set,remove}xattr, use those same handlers for iop->getxattr as well. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-09-01ovl: Switch to generic_removexattrAndreas Gruenbacher
Commit d837a49bd57f ("ovl: fix POSIX ACL setting") switches from iop->setxattr from ovl_setxattr to generic_setxattr, so switch from ovl_removexattr to generic_removexattr as well. As far as permission checking goes, the same rules should apply in either case. While doing that, rename ovl_setxattr to ovl_xattr_set to indicate that this is not an iop->setxattr implementation and remove the unused inode argument. Move ovl_other_xattr_set above ovl_own_xattr_set so that they match the order of handlers in ovl_xattr_handlers. Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Fixes: d837a49bd57f ("ovl: fix POSIX ACL setting") Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-09-01ovl: Fix OVL_XATTR_PREFIXAndreas Gruenbacher
Make sure ovl_own_xattr_handler only matches attribute names starting with "overlay.", not "overlayXXX". Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com> Fixes: d837a49bd57f ("ovl: fix POSIX ACL setting") Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-09-01ovl: proper cleanup of workdirMiklos Szeredi
When mounting overlayfs it needs a clean "work" directory under the supplied workdir. Previously the mount code removed this directory if it already existed and created a new one. If the removal failed (e.g. directory was not empty) then it fell back to a read-only mount not using the workdir. While this has never been reported, it is possible to get a non-empty "work" dir from a previous mount of overlayfs in case of crash in the middle of an operation using the work directory. In this case the left over state should be discarded and the overlay filesystem will be consistent, guaranteed by the atomicity of operations on moving to/from the workdir to the upper layer. This patch implements cleaning out any files left in workdir. It is implemented using real recursion for simplicity, but the depth is limited to 2, because the worst case is that of a directory containing whiteouts under "work". Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Cc: <stable@vger.kernel.org>
2016-08-08ovl: don't copy up opaquenessMiklos Szeredi
When a copy up of a directory occurs which has the opaque xattr set, the xattr remains in the upper directory. The immediate behavior with overlayfs is that the upper directory is not treated as opaque, however after a remount the opaque flag is used and upper directory is treated as opaque. This causes files created in the lower layer to be hidden when using multiple lower directories. Fix by not copying up the opaque flag. To reproduce: ----8<---------8<---------8<---------8<---------8<---------8<---- mkdir -p l/d/s u v w mnt mount -t overlay overlay -olowerdir=l,upperdir=u,workdir=w mnt rm -rf mnt/d/ mkdir -p mnt/d/n umount mnt mount -t overlay overlay -olowerdir=u:l,upperdir=v,workdir=w mnt touch mnt/d/foo umount mnt mount -t overlay overlay -olowerdir=u:l,upperdir=v,workdir=w mnt ls mnt/d ----8<---------8<---------8<---------8<---------8<---------8<---- output should be: "foo n" Reported-by: Derek McGowan <dmcg@drizz.net> Link: https://bugzilla.kernel.org/show_bug.cgi?id=151291 Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Cc: <stable@vger.kernel.org>
2016-07-29ovl: fix POSIX ACL settingMiklos Szeredi
Setting POSIX ACL needs special handling: 1) Some permission checks are done by ->setxattr() which now uses mounter's creds ("ovl: do operations on underlying file system in mounter's context"). These permission checks need to be done with current cred as well. 2) Setting ACL can fail for various reasons. We do not need to copy up in these cases. In the mean time switch to using generic_setxattr. [Arnd Bergmann] Fix link error without POSIX ACL. posix_acl_from_xattr() doesn't have a 'static inline' implementation when CONFIG_FS_POSIX_ACL is disabled, and I could not come up with an obvious way to do it. This instead avoids the link error by defining two sets of ACL operations and letting the compiler drop one of the two at compile time depending on CONFIG_FS_POSIX_ACL. This avoids all references to the ACL code, also leading to smaller code. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-29ovl: share inode for hard linkMiklos Szeredi
Inode attributes are copied up to overlay inode (uid, gid, mode, atime, mtime, ctime) so generic code using these fields works correcty. If a hard link is created in overlayfs separate inodes are allocated for each link. If chmod/chown/etc. is performed on one of the links then the inode belonging to the other ones won't be updated. This patch attempts to fix this by sharing inodes for hard links. Use inode hash (with real inode pointer as a key) to make sure overlay inodes are shared for hard links on upper. Hard links on lower are still split (which is not user observable until the copy-up happens, see Documentation/filesystems/overlayfs.txt under "Non-standard behavior"). The inode is only inserted in the hash if it is non-directoy and upper. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-29ovl: store real inode pointer in ->i_privateMiklos Szeredi
To get from overlay inode to real inode we currently use 'struct ovl_entry', which has lifetime connected to overlay dentry. This is okay, since each overlay dentry had a new overlay inode allocated. Following patch will break that assumption, so need to leave out ovl_entry. This patch stores the real inode directly in i_private, with the lowest bit used to indicate whether the inode is upper or lower. Lifetime rules remain, using ovl_inode_real() must only be done while caller holds ref on overlay dentry (and hence on real dentry), or within RCU protected regions. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-29ovl: update atime on upperMiklos Szeredi
Fix atime update logic in overlayfs. This patch adds an i_op->update_time() handler to overlayfs inodes. This forwards atime updates to the upper layer only. No atime updates are done on lower layers. Remove implicit atime updates to underlying files and directories with O_NOATIME. Remove explicit atime update in ovl_readlink(). Clear atime related mnt flags from cloned upper mount. This means atime updates are controlled purely by overlayfs mount options. Reported-by: Konstantin Khlebnikov <koct9i@gmail.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-29ovl: simplify permission checkingMiklos Szeredi
The fact that we always do permission checking on the overlay inode and clear MAY_WRITE for checking access to the lower inode allows cruft to be removed from ovl_permission(). 1) "default_permissions" option effectively did generic_permission() on the overlay inode with i_mode, i_uid and i_gid updated from underlying filesystem. This is what we do by default now. It did the update using vfs_getattr() but that's only needed if the underlying filesystem can change (which is not allowed). We may later introduce a "paranoia_mode" that verifies that mode/uid/gid are not changed. 2) splitting out the IS_RDONLY() check from inode_permission() also becomes unnecessary once we remove the MAY_WRITE from the lower inode check. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-29ovl: define ->get_acl() for overlay inodesVivek Goyal
Now we are planning to do DAC permission checks on overlay inode itself. And to make it work, we will need to make sure we can get acls from underlying inode. So define ->get_acl() for overlay inodes and this in turn calls into underlying filesystem to get acls, if any. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-07-27Merge branch 'd_real' into overlayfs-nextMiklos Szeredi
2016-07-04ovl: Copy up underlying inode's ->i_mode to overlay inodeVivek Goyal
Right now when a new overlay inode is created, we initialize overlay inode's ->i_mode from underlying inode ->i_mode but we retain only file type bits (S_IFMT) and discard permission bits. This patch changes it and retains permission bits too. This should allow overlay to do permission checks on overlay inode itself in task context. [SzM] It also fixes clearing suid/sgid bits on write. Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Reported-by: Eryu Guan <eguan@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com> Fixes: 4bacc9c9234c ("overlayfs: Make f_path always point to the overlay and f_inode to the underlay") Cc: <stable@vger.kernel.org>
2016-06-30vfs: merge .d_select_inode() into .d_real()Miklos Szeredi
The two methods essentially do the same: find the real dentry/inode belonging to an overlay dentry. The difference is in the usage: vfs_open() uses ->d_select_inode() and expects the function to perform copy-up if necessary based on the open flags argument. file_dentry() uses ->d_real() passing in the overlay dentry as well as the underlying inode. vfs_rename() uses ->d_select_inode() but passes zero flags. ->d_real() with a zero inode would have worked just as well here. This patch merges the functionality of ->d_select_inode() into ->d_real() by adding an 'open_flags' argument to the latter. [Al Viro] Make the signature of d_real() match that of ->d_real() again. And constify the inode argument, while we are at it. Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-05-27Merge branch 'for-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs Pull vfs fixes from Al Viro: "Followups to the parallel lookup work: - update docs - restore killability of the places that used to take ->i_mutex killably now that we have down_write_killable() merged - Additionally, it turns out that I missed a prerequisite for security_d_instantiate() stuff - ->getxattr() wasn't the only thing that could be called before dentry is attached to inode; with smack we needed the same treatment applied to ->setxattr() as well" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: switch ->setxattr() to passing dentry and inode separately switch xattr_handler->set() to passing dentry and inode separately restore killability of old mutex_lock_killable(&inode->i_mutex) users add down_write_killable_nested() update D/f/directory-locking
2016-05-27switch ->setxattr() to passing dentry and inode separatelyAl Viro
smack ->d_instantiate() uses ->setxattr(), so to be able to call it before we'd hashed the new dentry and attached it to inode, we need ->setxattr() instances getting the inode as an explicit argument rather than obtaining it from dentry. Similar change for ->getxattr() had been done in commit ce23e64. Unlike ->getxattr() (which is used by both selinux and smack instances of ->d_instantiate()) ->setxattr() is used only by smack one and unfortunately it got missed back then. Reported-by: Seung-Woo Kim <sw0312.kim@samsung.com> Tested-by: Casey Schaufler <casey@schaufler-ca.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-05-27Merge branch 'overlayfs-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs Pull overlayfs update from Miklos Szeredi: "The meat of this is a change to use the mounter's credentials for operations that require elevated privileges (such as whiteout creation). This fixes behavior under user namespaces as well as being a nice cleanup" * 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs: ovl: Do d_type check only if work dir creation was successful ovl: update documentation ovl: override creds with the ones from the superblock mounter
2016-05-27ovl: override creds with the ones from the superblock mounterAntonio Murdaca
In user namespace the whiteout creation fails with -EPERM because the current process isn't capable(CAP_SYS_ADMIN) when setting xattr. A simple reproducer: $ mkdir upper lower work merged lower/dir $ sudo mount -t overlay overlay -olowerdir=lower,upperdir=upper,workdir=work merged $ unshare -m -p -f -U -r bash Now as root in the user namespace: \# touch merged/dir/{1,2,3} # this will force a copy up of lower/dir \# rm -fR merged/* This ends up failing with -EPERM after the files in dir has been correctly deleted: unlinkat(4, "2", 0) = 0 unlinkat(4, "1", 0) = 0 unlinkat(4, "3", 0) = 0 close(4) = 0 unlinkat(AT_FDCWD, "merged/dir", AT_REMOVEDIR) = -1 EPERM (Operation not permitted) Interestingly, if you don't place files in merged/dir you can remove it, meaning if upper/dir does not exist, creating the char device file works properly in that same location. This patch uses ovl_sb_creator_cred() to get the cred struct from the superblock mounter and override the old cred with these new ones so that the whiteout creation is possible because overlay is wrong in assuming that the creds it will get with prepare_creds will be in the initial user namespace. The old cap_raise game is removed in favor of just overriding the old cred struct. This patch also drops from ovl_copy_up_one() the following two lines: override_cred->fsuid = stat->uid; override_cred->fsgid = stat->gid; This is because the correct uid and gid are taken directly with the stat struct and correctly set with ovl_set_attr(). Signed-off-by: Antonio Murdaca <runcom@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-04-11->getxattr(): pass dentry and inode as separate argumentsAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2016-03-21ovl: Ensure upper filesystem supports d_typeVivek Goyal
In some instances xfs has been created with ftype=0 and there if a file on lower fs is removed, overlay leaves a whiteout in upper fs but that whiteout does not get filtered out and is visible to overlayfs users. And reason it does not get filtered out because upper filesystem does not report file type of whiteout as DT_CHR during iterate_dir(). So it seems to be a requirement that upper filesystem support d_type for overlayfs to work properly. Do this check during mount and fail if d_type is not supported. Suggested-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Vivek Goyal <vgoyal@redhat.com> Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
2016-01-21Merge branch 'overlayfs-linus' of ↵Linus Torvalds
git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs Pull overlayfs updates from Miklos Szeredi: "This contains several bug fixes and a new mount option 'default_permissions' that allows read-only exported NFS filesystems to be used as lower layer" * 'overlayfs-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs: ovl: check dentry positiveness in ovl_cleanup_whiteouts() ovl: setattr: check permissions before copy-up ovl: root: copy attr ovl: move super block magic number to magic.h ovl: use a minimal buffer in ovl_copy_xattr ovl: allow zero size xattr ovl: default permissions
2015-12-06ovl: get rid of the dead code left from broken (and disabled) optimizationsAl Viro
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2015-10-12ovl: default permissionsMiklos Szeredi
Add mount option "default_permissions" to alter the way permissions are calculated. Without this option and prior to this patch permissions were calculated by underlying lower or upper filesystem. With this option the permissions are calculated by overlayfs based on the file owner, group and mode bits. This has significance for example when a read-only exported NFS filesystem is used as a lower layer. In this case the underlying NFS filesystem will reply with EROFS, in which case all we know is that the filesystem is read-only. But that's not what we are interested in, we are interested in whether the access would be allowed if the filesystem wasn't read-only; the server doesn't tell us that, and would need updating at various levels, which doesn't seem practicable. Signed-off-by: Miklos Szeredi <miklos@szeredi.hu>
2015-06-19overlayfs: Make f_path always point to the overlay and f_inode to the underlayDavid Howells
Make file->f_path always point to the overlay dentry so that the path in /proc/pid/fd is correct and to ensure that label-based LSMs have access to the overlay as well as the underlay (path-based LSMs probably don't need it). Using my union testsuite to set things up, before the patch I see: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:38 5 -> /a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 13381 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 13381 Links: 1 ... After the patch: [root@andromeda union-testsuite]# bash 5</mnt/a/foo107 [root@andromeda union-testsuite]# ls -l /proc/$$/fd/ ... lr-x------. 1 root root 64 Jun 5 14:22 5 -> /mnt/a/foo107 [root@andromeda union-testsuite]# stat /mnt/a/foo107 ... Device: 23h/35d Inode: 40346 Links: 1 ... [root@andromeda union-testsuite]# stat -L /proc/$$/fd/5 ... Device: 23h/35d Inode: 40346 Links: 1 ... Note the change in where /proc/$$/fd/5 points to in the ls command. It was pointing to /a/foo107 (which doesn't exist) and now points to /mnt/a/foo107 (which is correct). The inode accessed, however, is the lower layer. The union layer is on device 25h/37d and the upper layer on 24h/36d. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
2014-12-13ovl: Use macros to present ovl_xattrhujianyang
This patch adds two macros: OVL_XATTR_PRE_NAME and OVL_XATTR_PRE_LEN to present ovl_xattr name prefix and its length. Also, a new macro OVL_XATTR_OPAQUE is introduced to replace old *ovl_opaque_xattr*. Fix the length of "trusted.overlay." to *16*. Signed-off-by: hujianyang <hujianyang@huawei.com> Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
2014-12-13ovl: helper to iterate layersMiklos Szeredi
Add helper to iterate through all the layers, starting from the upper layer (if exists) and continuing down through the lower layers. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
2014-12-13ovl: make path-type a bitmapMiklos Szeredi
OVL_PATH_PURE_UPPER -> __OVL_PATH_UPPER | __OVL_PATH_PURE OVL_PATH_UPPER -> __OVL_PATH_UPPER OVL_PATH_MERGE -> __OVL_PATH_UPPER | __OVL_PATH_MERGE OVL_PATH_LOWER -> 0 Multiple R/O layers will allow __OVL_PATH_MERGE without __OVL_PATH_UPPER. Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
2014-10-24overlay filesystemMiklos Szeredi
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>