v3 is a resend of v2 [2] with no code or commit-message changes; the v2 posting went out with malformed To/Cc headers, so most recipients did not get a direct copy.
Extending a fuse file past a non-page-aligned EOF does not zero the tail of the old last page. When that page is cached and has been mmap-dirtied beyond the old EOF, the now in-bounds tail is served to later reads as stale data rather than zeros, which violates POSIX file-extension semantics. Some file systems get this zeroing automatically at writeback time (block_write_full_folio() / iomap_writeback_handle_eof() zero the tail of the folio straddling i_size). A non-writeback caching fuse file system uses neither path, so it has to zero the tail itself from the size-extending paths, like XFS (xfs_file_write_zero_eof()) and ext4 (ext4_block_zero_eof()) do. pagecache_isize_extended() cannot be reused: it is a no-op when i_blocksize() >= PAGE_SIZE, and would increase the work in that function for use cases that don't need it, if changed to support this situation. Patch 1 adds fuse_zero_partial_eof_folio() and calls it up front from the three paths that extend a file: buffered write, setattr, and fallocate. Patch 2 adds a self-contained raw /dev/fuse selftest covering each path. Tested by booting the patched kernel under User-Mode Linux and running the new selftest, and reproduced against libfuse's passthrough_ll example daemon. Changes since v1 [1]: - Miklos and Jan Kara discussed whether there was a better pattern with less duplication between file systems. Jan confirmed that other file systems do this zeroing themselves from their write/setattr paths (e.g. XFS xfs_file_write_zero_eof(), ext4 ext4_block_zero_eof()), because the block / iomap writeback that would otherwise zero the straddling folio does not run on this path. File systems currently implement this separately. It is beyond me to pursue unifying it. Restructure to match the pattern in other file systems: zero [old EOF, write start) up front from fuse_perform_write() rather than after the fact from fuse_write_update_attr(), keyed on the write starting beyond EOF. - This keeps the zeroed range disjoint from the written data, so a write that lands inside the old EOF folio is preserved by construction; the v1 "pos - written" arithmetic and the fallocate double-call are gone. - fuse_write_update_attr() goes back to being a pure attr update; the setattr/truncate call in fuse_do_setattr() is unchanged. - The selftest is unchanged from v1. [1] https://lore.kernel.org/all/[email protected]/ [2] https://lore.kernel.org/all/[email protected]/ Jimmy Zuber (2): fuse: zero the partial EOF page when extending a file selftests/fuse: test post-EOF page zeroing when a file is extended fs/fuse/dir.c | 3 + fs/fuse/file.c | 56 +++ fs/fuse/fuse_i.h | 1 + .../selftests/filesystems/fuse/.gitignore | 1 + .../selftests/filesystems/fuse/Makefile | 3 + .../filesystems/fuse/write_extend_eof_test.c | 368 ++++++++++++++++++ 6 files changed, 432 insertions(+) create mode 100644 tools/testing/selftests/filesystems/fuse/write_extend_eof_test.c base-commit: 7d87a5a284bb34edb3f4e7e312ef403b3385a7b7 -- 2.50.1
