Here is another post of the VFS based union mount implementation. Traditionally the mount operation is opaque, which means that the content of the mount point, the directory where the file system is mounted on, is hidden by the content of the mounted file system's root directory until the file system is unmounted again. Unlike the traditional UNIX mount mechanism, that hides the contents of the mount point, a union mount presents a view as if both filesystems are merged together. Although only the topmost layer of the mount stack can be altered, it appears as if transparent file system mounts allow any file to be created, modified or deleted. Most people know the concepts and features of union mounts from other operating systems like Sun's Translucent Filesystem, Plan9 or BSD. For an in-depth review of union mounts and other unioning file systems, see: http://lwn.net/Articles/324291/ http://lwn.net/Articles/325369/ http://lwn.net/Articles/327738/ Here are the key features of this implementation: - completely VFS based - does not change the namespace stacking - directory listings have duplicate entries removed in the kernel - writable unions: only the topmost file system layer may be writable - writable unions: new whiteout filetype handled inside the kernel Major changes since last post: - Updated the whiteout patches: - DCACHE_WHITEOUT flag set on a negative dentry - uses filetype instead of reserved inode number on EXT2 - Copy-up directories during lookup - Implemented fallthru support for in-kernel readdir() as proposed by Valerie Aurora (Henson) - Bugfixes Valerie updated the HOWTO page and the UML disk image. You can find her instruction how to testdrive the code here: http://valerieaurora.org/union/ The following patches apply on 2.6.29. Comments are welcome! Cheers, Jan Jan Blunck (26): atomic: Only take lock when the counter drops to zero on UP as well VFS: BUG() if somebody tries to rehash an already hashed dentry VFS: propagate mnt_flags into do_loopback VFS: Make lookup_hash() return a struct path VFS: Remove unnecessary micro-optimization in cached_lookup() VFS: Make real_lookup() return a struct path VFS: Introduce dput() variant that maintains a kill-list whiteout: Don't return information about whiteouts to userspace whiteout: Add vfs_whiteout() and whiteout inode operation whiteout: Set S_OPAQUE inode flag when creating directories whiteout: Add whiteout support to tmpfs whiteout: Split of ext2_append_link() from ext2_add_link() whiteout: Add whiteout support to ext2 whiteout: Add path_whiteout() helper union-mount: Documentation union-mount: Introduce MNT_UNION and MS_UNION flags union-mount: Introduce union_mount structure union-mount: Drive the union cache via dcache union-mount: Some checks during namespace changes union-mount: Changes to the namespace handling union-mount: Make lookup work for union-mounted file systems union-mount: stop lookup when directory has S_OPAQUE flag set union-mount: stop lookup when finding a whiteout union-mount: in-kernel file copy between union mounted filesystems union-mount: check for logically empty directory (FIXME) union-mount: call do_whiteout() on unlink and rmdir Valerie Aurora (Henson) (6): union-mount: Always create topmost directory on open union-mount: Basic fallthru definitions union mount: Support for fallthru entries in union mount lookup union mount: ext2 fallthru support union-mount: tmpfs fallthru support union-mount: Copy up directory entries on first readdir() Documentation/filesystems/union-mounts.txt | 187 +++++ fs/Kconfig | 8 + fs/Makefile | 2 + fs/compat.c | 9 + fs/dcache.c | 143 ++++- fs/ext2/dir.c | 242 ++++++- fs/ext2/ext2.h | 4 + fs/ext2/inode.c | 11 +- fs/ext2/namei.c | 85 +++- fs/ext2/super.c | 8 + fs/libfs.c | 18 +- fs/namei.c | 1009 +++++++++++++++++++++++++--- fs/namespace.c | 54 ++- fs/nfsd/nfs3xdr.c | 5 + fs/nfsd/nfs4xdr.c | 2 +- fs/nfsd/nfsxdr.c | 4 + fs/readdir.c | 25 + fs/union.c | 948 ++++++++++++++++++++++++++ include/linux/dcache.h | 30 +- include/linux/ext2_fs.h | 5 + include/linux/fs.h | 7 + include/linux/mount.h | 4 + include/linux/namei.h | 6 + include/linux/union.h | 82 +++ lib/dec_and_lock.c | 3 +- mm/shmem.c | 195 +++++- 26 files changed, 2927 insertions(+), 169 deletions(-) create mode 100644 Documentation/filesystems/union-mounts.txt create mode 100644 fs/union.c create mode 100644 include/linux/union.h -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
