Changes since v2 [1]: * Rather than have an IS_IOMAP_IMMUTABLE() check in xfs_alloc_file_space(), place one centrally in xfs_bmapi_write() to catch all attempts to write the block allocation map. (Dave) * Make sealing an already sealed file, or unsealing an already unsealed file return success (Darrick) * Set S_IOMAP_IMMUTABLE along with the transaction that sets XFS_DIFLAG2_IOMAP_IMMUTABLE (Darrick) * Round the range of the allocation and extent conversion performed by FALLOC_FL_SEAL_BLOCK_MAP up to the filesystem block size. * Add a proof-of-concept patch for the use of immutable files with swap. [1]: https://lkml.org/lkml/2017/8/3/996 --- The ability to make the physical block-allocation map of a file immutable is a powerful mechanism that allows userspace to have predictable dax-fault latencies, flush dax mappings to persistent memory without a syscall, and otherwise enable access to storage directly without ongoing mediation from the filesystem. This last aspect of direct storage addressability has been called a "horrible abuse" [2], but the reality is quite the reverse. Enabling files to be block-map immutable allows applications that would otherwise need to rely on dangerous raw device access to instead use a filesystem. Security, naming, re-provisioning capacity between usages are all better supported with safe semantics in a filesystem compared to a device file. It is time to "give up the idea that only the filesystem can access the storage underlying the filesystem" [3] to enable a better / safer alternative to using a raw device for userpace block servers, dax hypervisors, and peer-to-peer transfers to name a few use cases. [2]: https://lkml.org/lkml/2017/8/5/56 [3]: https://lkml.org/lkml/2017/8/6/299 --- Dan Williams (6): fs, xfs: introduce S_IOMAP_IMMUTABLE fs, xfs: introduce FALLOC_FL_SEAL_BLOCK_MAP fs, xfs: introduce FALLOC_FL_UNSEAL_BLOCK_MAP xfs: introduce XFS_DIFLAG2_IOMAP_IMMUTABLE xfs: toggle XFS_DIFLAG2_IOMAP_IMMUTABLE in response to fallocate mm, xfs: protect swapfile contents with immutable + unwritten extents fs/attr.c | 10 +++ fs/nfs/file.c | 7 ++ fs/open.c | 24 +++++++ fs/read_write.c | 3 + fs/xfs/libxfs/xfs_bmap.c | 6 ++ fs/xfs/libxfs/xfs_bmap.h | 12 +++- fs/xfs/libxfs/xfs_format.h | 5 +- fs/xfs/xfs_aops.c | 54 ++++++++++++++++ fs/xfs/xfs_bmap_util.c | 142 +++++++++++++++++++++++++++++++++++++++++++ fs/xfs/xfs_bmap_util.h | 5 ++ fs/xfs/xfs_file.c | 16 ++++- fs/xfs/xfs_inode.c | 2 + fs/xfs/xfs_ioctl.c | 7 ++ fs/xfs/xfs_iops.c | 8 ++ include/linux/falloc.h | 4 + include/linux/fs.h | 2 + include/uapi/linux/falloc.h | 18 +++++ include/uapi/linux/fs.h | 1 mm/filemap.c | 5 ++ mm/page_io.c | 1 mm/swapfile.c | 20 ++---- 21 files changed, 328 insertions(+), 24 deletions(-)
