On Mon, Nov 11, 2019 at 10:50:28AM -0800, Evan Green wrote: > This series addresses some errors seen when using the loop > device directly backed by a block device. The first change plumbs > out the correct error message, and the second change prevents the > error from occurring in many cases. > > The errors look like this: > [ 90.880875] print_req_error: I/O error, dev loop5, sector 0 > > The errors occur when trying to do a discard or write zeroes operation > on a loop device backed by a block device that does not support write zeroes. > Firstly, the error itself is incorrectly reported as I/O error, but is > actually EOPNOTSUPP. The first patch plumbs out EOPNOTSUPP to properly > report the error. > > The second patch prevents these errors from occurring by mirroring the > zeroing capabilities of the underlying block device into the loop device. > Before this change, discard was always reported as being supported, and > the loop device simply turns around and does an fallocate operation on the > backing device. After this change, backing block devices that do support > zeroing will continue to work as before, and continue to get all the > benefits of doing that. Backing devices that do not support zeroing will > fail earlier, avoiding hitting the loop device at all and ultimately > avoiding this error in the logs. > > I can also confirm that this fixes test block/003 in the blktests, when > running blktests on a loop device backed by a block device. > > Darrick, I see you've got a related change in linux-next. I'm not sure what > the status of that is, so I didn't base my latest spin on top of yours. AFAIK the patch you reference changes NOUNMAP requests to use FALLOC_FL_ZERO_RANGE and is queued for 5.5, which means patch #2 will clash with it. It sort of looks like patch #2 reimplements the patch that Jens already pulled for 5.5, so you probably want to rebase this series atop his for-next tree.... but you should really ask Jens. --D > Changes in v6: > - Updated tags > > Changes in v5: > - Don't mirror discard if lo_encrypt_key_size is non-zero (Gwendal) > > Changes in v4: > - Mirror blkdev's write_zeroes into loopdev's discard_sectors. > > Changes in v3: > - Updated tags > - Updated commit description > > Changes in v2: > - Unnested error if statement (Bart) > > Evan Green (2): > loop: Report EOPNOTSUPP properly > loop: Better discard support for block devices > > drivers/block/loop.c | 66 +++++++++++++++++++++++++++++--------------- > 1 file changed, 44 insertions(+), 22 deletions(-) > > -- > 2.21.0 >
