Hi Chandan, Please pull this branch with changes for xfs for 6.10-rc1. As usual, I did a test-merge with the main upstream branch as of a few minutes ago, and didn't see any conflicts. Please let me know if you encounter any problems. --D The following changes since commit 15f78aa3eb07645e7bef15a53b4ae1c757907d2c: xfs: constify xfs_bmap_is_written_extent (2024-04-15 14:54:12 -0700) are available in the Git repository at: https://git.kernel.org/pub/scm/linux/kernel/git/djwong/xfs-linux.git tags/atomic-file-updates-6.10_2024-04-15 for you to fetch changes up to 0730e8d8ba1d1507f1d7fd719e1f835ce69961fe: xfs: enable logged file mapping exchange feature (2024-04-15 14:54:26 -0700) ---------------------------------------------------------------- xfs: atomic file content exchanges [v30.3 03/16] This series creates a new XFS_IOC_EXCHANGE_RANGE ioctl to exchange ranges of bytes between two files atomically. This new functionality enables data storage programs to stage and commit file updates such that reader programs will see either the old contents or the new contents in their entirety, with no chance of torn writes. A successful call completion guarantees that the new contents will be seen even if the system fails. The ability to exchange file fork mappings between files in this manner is critical to supporting online filesystem repair, which is built upon the strategy of constructing a clean copy of a damaged structure and committing the new structure into the metadata file atomically. The ioctls exist to facilitate testing of the new functionality and to enable future application program designs. User programs will be able to update files atomically by opening an O_TMPFILE, reflinking the source file to it, making whatever updates they want to make, and exchange the relevant ranges of the temp file with the original file. If the updates are aligned with the file block size, a new (since v2) flag provides for exchanging only the written areas. Note that application software must quiesce writes to the file while it stages an atomic update. This will be addressed by a subsequent series. This mechanism solves the clunkiness of two existing atomic file update mechanisms: for O_TRUNC + rewrite, this eliminates the brief period where other programs can see an empty file. For create tempfile + rename, the need to copy file attributes and extended attributes for each file update is eliminated. However, this method introduces its own awkwardness -- any program initiating an exchange now needs to have a way to signal to other programs that the file contents have changed. For file access mediated via read and write, fanotify or inotify are probably sufficient. For mmaped files, that may not be fast enough. Here is the proposed manual page: IOCTL-XFS-EXCHANGE-RANGE(2System Calls ManuIOCTL-XFS-EXCHANGE-RANGE(2) NAME ioctl_xfs_exchange_range - exchange the contents of parts of two files SYNOPSIS #include <sys/ioctl.h> #include <xfs/xfs_fs.h> int ioctl(int file2_fd, XFS_IOC_EXCHANGE_RANGE, struct xfs_ex‐ change_range *arg); DESCRIPTION Given a range of bytes in a first file file1_fd and a second range of bytes in a second file file2_fd, this ioctl(2) ex‐ changes the contents of the two ranges. Exchanges are atomic with regards to concurrent file opera‐ tions. Implementations must guarantee that readers see either the old contents or the new contents in their entirety, even if the system fails. The system call parameters are conveyed in structures of the following form: struct xfs_exchange_range { __s32 file1_fd; __u32 pad; __u64 file1_offset; __u64 file2_offset; __u64 length; __u64 flags; }; The field pad must be zero. The fields file1_fd, file1_offset, and length define the first range of bytes to be exchanged. The fields file2_fd, file2_offset, and length define the second range of bytes to be exchanged. Both files must be from the same filesystem mount. If the two file descriptors represent the same file, the byte ranges must not overlap. Most disk-based filesystems require that the starts of both ranges must be aligned to the file block size. If this is the case, the ends of the ranges must also be so aligned unless the XFS_EXCHANGE_RANGE_TO_EOF flag is set. The field flags control the behavior of the exchange operation. XFS_EXCHANGE_RANGE_TO_EOF Ignore the length parameter. All bytes in file1_fd from file1_offset to EOF are moved to file2_fd, and file2's size is set to (file2_offset+(file1_length- file1_offset)). Meanwhile, all bytes in file2 from file2_offset to EOF are moved to file1 and file1's size is set to (file1_offset+(file2_length- file2_offset)). XFS_EXCHANGE_RANGE_DSYNC Ensure that all modified in-core data in both file ranges and all metadata updates pertaining to the exchange operation are flushed to persistent storage before the call returns. Opening either file de‐ scriptor with O_SYNC or O_DSYNC will have the same effect. XFS_EXCHANGE_RANGE_FILE1_WRITTEN Only exchange sub-ranges of file1_fd that are known to contain data written by application software. Each sub-range may be expanded (both upwards and downwards) to align with the file allocation unit. For files on the data device, this is one filesystem block. For files on the realtime device, this is the realtime extent size. This facility can be used to implement fast atomic scatter-gather writes of any complexity for software-defined storage targets if all writes are aligned to the file allocation unit. XFS_EXCHANGE_RANGE_DRY_RUN Check the parameters and the feasibility of the op‐ eration, but do not change anything. RETURN VALUE On error, -1 is returned, and errno is set to indicate the er‐ ror. ERRORS Error codes can be one of, but are not limited to, the follow‐ ing: EBADF file1_fd is not open for reading and writing or is open for append-only writes; or file2_fd is not open for reading and writing or is open for append-only writes. EINVAL The parameters are not correct for these files. This error can also appear if either file descriptor repre‐ sents a device, FIFO, or socket. Disk filesystems gen‐ erally require the offset and length arguments to be aligned to the fundamental block sizes of both files. EIO An I/O error occurred. EISDIR One of the files is a directory. ENOMEM The kernel was unable to allocate sufficient memory to perform the operation. ENOSPC There is not enough free space in the filesystem ex‐ change the contents safely. EOPNOTSUPP The filesystem does not support exchanging bytes between the two files. EPERM file1_fd or file2_fd are immutable. ETXTBSY One of the files is a swap file. EUCLEAN The filesystem is corrupt. EXDEV file1_fd and file2_fd are not on the same mounted filesystem. CONFORMING TO This API is XFS-specific. USE CASES Several use cases are imagined for this system call. In all cases, application software must coordinate updates to the file because the exchange is performed unconditionally. The first is a data storage program that wants to commit non- contiguous updates to a file atomically and coordinates write access to that file. This can be done by creating a temporary file, calling FICLONE(2) to share the contents, and staging the updates into the temporary file. The FULL_FILES flag is recom‐ mended for this purpose. The temporary file can be deleted or punched out afterwards. An example program might look like this: int fd = open("/some/file", O_RDWR); int temp_fd = open("/some", O_TMPFILE | O_RDWR); ioctl(temp_fd, FICLONE, fd); /* append 1MB of records */ lseek(temp_fd, 0, SEEK_END); write(temp_fd, data1, 1000000); /* update record index */ pwrite(temp_fd, data1, 600, 98765); pwrite(temp_fd, data2, 320, 54321); pwrite(temp_fd, data2, 15, 0); /* commit the entire update */ struct xfs_exchange_range args = { .file1_fd = temp_fd, .flags = XFS_EXCHANGE_RANGE_TO_EOF, }; ioctl(fd, XFS_IOC_EXCHANGE_RANGE, &args); The second is a software-defined storage host (e.g. a disk jukebox) which implements an atomic scatter-gather write com‐ mand. Provided the exported disk's logical block size matches the file's allocation unit size, this can be done by creating a temporary file and writing the data at the appropriate offsets. It is recommended that the temporary file be truncated to the size of the regular file before any writes are staged to the temporary file to avoid issues with zeroing during EOF exten‐ sion. Use this call with the FILE1_WRITTEN flag to exchange only the file allocation units involved in the emulated de‐ vice's write command. The temporary file should be truncated or punched out completely before being reused to stage another write. An example program might look like this: int fd = open("/some/file", O_RDWR); int temp_fd = open("/some", O_TMPFILE | O_RDWR); struct stat sb; int blksz; fstat(fd, &sb); blksz = sb.st_blksize; /* land scatter gather writes between 100fsb and 500fsb */ pwrite(temp_fd, data1, blksz * 2, blksz * 100); pwrite(temp_fd, data2, blksz * 20, blksz * 480); pwrite(temp_fd, data3, blksz * 7, blksz * 257); /* commit the entire update */ struct xfs_exchange_range args = { .file1_fd = temp_fd, .file1_offset = blksz * 100, .file2_offset = blksz * 100, .length = blksz * 400, .flags = XFS_EXCHANGE_RANGE_FILE1_WRITTEN | XFS_EXCHANGE_RANGE_FILE1_DSYNC, }; ioctl(fd, XFS_IOC_EXCHANGE_RANGE, &args); NOTES Some filesystems may limit the amount of data or the number of extents that can be exchanged in a single call. SEE ALSO ioctl(2) XFS 2024-02-10 IOCTL-XFS-EXCHANGE-RANGE(2) The reference implementation in XFS creates a new log incompat feature and log intent items to track high level progress of swapping ranges of two files and finish interrupted work if the system goes down. Sample code can be found in the corresponding changes to xfs_io to exercise the use case mentioned above. Note that this function is /not/ the O_DIRECT atomic untorn file writes concept that has also been floating around for years. It is also not the RWF_ATOMIC patchset that has been shared. This RFC is constructed entirely in software, which means that there are no limitations other than the general filesystem limits. As a side note, the original motivation behind the kernel functionality is online repair of file-based metadata. The atomic file content exchange is implemented as an atomic exchange of file fork mappings, which means that we can implement online reconstruction of extended attributes and directories by building a new one in another inode and exchanging the contents. Subsequent patchsets adapt the online filesystem repair code to use atomic file exchanges. This enables repair functions to construct a clean copy of a directory, xattr information, symbolic links, realtime bitmaps, and realtime summary information in a temporary inode. If this completes successfully, the new contents can be committed atomically into the inode being repaired. This is essential to avoid making corruption problems worse if the system goes down in the middle of running repair. For userspace, this series also includes the userspace pieces needed to test the new functionality, and a sample implementation of atomic file updates. This has been running on the djcloud for months with no problems. Enjoy! Signed-off-by: Darrick J. Wong <djwong@xxxxxxxxxx> ---------------------------------------------------------------- Darrick J. Wong (15): vfs: export remap and write check helpers xfs: introduce new file range exchange ioctl xfs: create a incompat flag for atomic file mapping exchanges xfs: introduce a file mapping exchange log intent item xfs: create deferred log items for file mapping exchanges xfs: bind together the front and back ends of the file range exchange code xfs: add error injection to test file mapping exchange recovery xfs: condense extended attributes after a mapping exchange operation xfs: condense directories after a mapping exchange operation xfs: condense symbolic links after a mapping exchange operation xfs: make file range exchange support realtime files xfs: support non-power-of-two rtextsize with exchange-range xfs: capture inode generation numbers in the ondisk exchmaps log item docs: update swapext -> exchmaps language xfs: enable logged file mapping exchange feature .../filesystems/xfs/xfs-online-fsck-design.rst | 259 ++-- fs/read_write.c | 1 + fs/remap_range.c | 4 +- fs/xfs/Makefile | 3 + fs/xfs/libxfs/xfs_defer.c | 6 + fs/xfs/libxfs/xfs_defer.h | 2 +- fs/xfs/libxfs/xfs_errortag.h | 4 +- fs/xfs/libxfs/xfs_exchmaps.c | 1237 ++++++++++++++++++++ fs/xfs/libxfs/xfs_exchmaps.h | 123 ++ fs/xfs/libxfs/xfs_format.h | 26 +- fs/xfs/libxfs/xfs_fs.h | 42 + fs/xfs/libxfs/xfs_log_format.h | 66 +- fs/xfs/libxfs/xfs_log_recover.h | 4 + fs/xfs/libxfs/xfs_sb.c | 5 + fs/xfs/libxfs/xfs_symlink_remote.c | 47 + fs/xfs/libxfs/xfs_symlink_remote.h | 1 + fs/xfs/libxfs/xfs_trans_space.h | 4 + fs/xfs/xfs_error.c | 3 + fs/xfs/xfs_exchmaps_item.c | 614 ++++++++++ fs/xfs/xfs_exchmaps_item.h | 64 + fs/xfs/xfs_exchrange.c | 804 +++++++++++++ fs/xfs/xfs_exchrange.h | 38 + fs/xfs/xfs_ioctl.c | 4 + fs/xfs/xfs_log_recover.c | 33 + fs/xfs/xfs_mount.h | 2 + fs/xfs/xfs_super.c | 23 + fs/xfs/xfs_symlink.c | 49 +- fs/xfs/xfs_trace.c | 2 + fs/xfs/xfs_trace.h | 327 ++++++ include/linux/fs.h | 1 + 30 files changed, 3613 insertions(+), 185 deletions(-) create mode 100644 fs/xfs/libxfs/xfs_exchmaps.c create mode 100644 fs/xfs/libxfs/xfs_exchmaps.h create mode 100644 fs/xfs/xfs_exchmaps_item.c create mode 100644 fs/xfs/xfs_exchmaps_item.h create mode 100644 fs/xfs/xfs_exchrange.c create mode 100644 fs/xfs/xfs_exchrange.h
