From: Omar Sandoval <osan...@fb.com> Hello,
This series adds a way to write compressed data directly to Btrfs. The intended use case is making send/receive on compressed file systems more efficient; however, the interface is general enough that it could be used in other scenarios. Patch 5 is the main change; see that for more details. Patches 1-3 are small fixes/cleanups that I ran into while implementing this; they should go in regardless of the remainder of the series. Patch 4 exports a required VFS interface. An example program and test case are available at [1]. To preemptively address a few concerns: - Writing arbitrary, untrusted data which we feed to the decompression algorithm can be a security risk. For that reason, the ioctl is restricted to CAP_SYS_ADMIN. The Btrfs code is properly hardened against invalid compressed data/incorrect lengths, and the compression libraries are mature, but better safe than sorry for now. - If the user is writing their own compressed data rather than just blindly feeding in something from btrfs send, they need to know some implementation details about the compression format. For zlib, there are no special requirements. For zstd, a non-default compression parameter must be used. For lzo, we have our own wrapper format since lzo doesn't have a standard wrapper format. It feels a little wrong to expose these details, but they are part of the on-disk format, so they must be stable regardless. - The permissions checks duplicated from the VFS code are fairly minimal. This series is based on misc-next. This is an RFC, so please, comment away. Thanks! 1: https://github.com/osandov/xfstests/tree/btrfs-compressed-write Omar Sandoval (5): Btrfs: use correct count in btrfs_file_write_iter() Btrfs: treat RWF_{,D}SYNC writes as sync for CRCs Btrfs: stop clearing EXTENT_DIRTY in inode I/O tree fs: export rw_verify_area() Btrfs: add ioctl for directly writing compressed data fs/btrfs/compression.c | 6 +- fs/btrfs/compression.h | 14 +-- fs/btrfs/ctree.h | 12 ++ fs/btrfs/extent_io.c | 6 +- fs/btrfs/file.c | 22 ++-- fs/btrfs/free-space-cache.c | 9 +- fs/btrfs/inode.c | 232 +++++++++++++++++++++++++++++++---- fs/btrfs/ioctl.c | 101 ++++++++++++++- fs/btrfs/tests/inode-tests.c | 12 +- fs/internal.h | 5 - fs/read_write.c | 1 + include/linux/fs.h | 1 + include/uapi/linux/btrfs.h | 63 ++++++++++ 13 files changed, 415 insertions(+), 69 deletions(-) -- 2.17.1
