• Cyril Hrubis's avatar
    loop: Disable fallocate() zero and discard if not supported · 5f75e081
    Cyril Hrubis authored
    If fallcate is implemented but zero and discard operations are not
    supported by the filesystem the backing file is on we continue to fill
    dmesg with errors from the blk_mq_end_request() since each time we call
    fallocate() on the loop device the EOPNOTSUPP error from lo_fallocate()
    ends up propagated into the block layer. In the end syscall succeeds
    since the blkdev_issue_zeroout() falls back to writing zeroes which
    makes the errors even more misleading and confusing.
    
    How to reproduce:
    
    1. make sure /tmp is mounted as tmpfs
    2. dd if=/dev/zero of=/tmp/disk.img bs=1M count=100
    3. losetup /dev/loop0 /tmp/disk.img
    4. mkfs.ext2 /dev/loop0
    5. dmesg |tail
    
    [710690.898214] operation not supported error, dev loop0, sector 204672 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898279] operation not supported error, dev loop0, sector 522 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898603] operation not supported error, dev loop0, sector 16906 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.898917] operation not supported error, dev loop0, sector 32774 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899218] operation not supported error, dev loop0, sector 49674 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899484] operation not supported error, dev loop0, sector 65542 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.899743] operation not supported error, dev loop0, sector 82442 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900015] operation not supported error, dev loop0, sector 98310 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900276] operation not supported error, dev loop0, sector 115210 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    [710690.900546] operation not supported error, dev loop0, sector 131078 op 0x9:(WRITE_ZEROES) flags 0x8000800 phys_seg 0 prio class 0
    
    This patch changes the lo_fallocate() to clear the flags for zero and
    discard operations if we get EOPNOTSUPP from the backing file fallocate
    callback, that way we at least stop spewing errors after the first
    unsuccessful try.
    
    CC: Jan Kara <jack@suse.cz>
    Signed-off-by: default avatarCyril Hrubis <chrubis@suse.cz>
    Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
    Reviewed-by: default avatarJan Kara <jack@suse.cz>
    Link: https://lore.kernel.org/r/20240613163817.22640-1-chrubis@suse.czSigned-off-by: default avatarJens Axboe <axboe@kernel.dk>
    5f75e081
loop.c 58.4 KB