On Tue, Jun 07, 2016 at 05:50:49AM +0100, Sitsofe Wheeler wrote: > On Mon, Jun 06, 2016 at 03:33:58PM -0700, Shaohua Li wrote: > > blkdev_issue_zeroout try discard/writesame first, if they fail, zeroout > > fallback to regular write. The problem is discard/writesame doesn't > > return error for -EOPNOTSUPP, then zeroout can't do fallback and leave > > disk data not changed. zeroout should have guaranteed zero-fill > > behavior. > > > > https://bugzilla.kernel.org/show_bug.cgi?id=118581 > > > > V2: move the return value policy to blkdev_issue_discard and > > delete the policy for blkdev_issue_write_same (Martin) > > > > Cc: Sitsofe Wheeler <sits...@yahoo.com> > > Cc: Mike Snitzer <snit...@redhat.com> > > Cc: Jens Axboe <ax...@fb.com> > > Cc: Martin K. Petersen <martin.peter...@oracle.com> > > Signed-off-by: Shaohua Li <s...@fb.com> > > --- > > block/blk-lib.c | 49 +++++++++++++++++++++++++++++++------------------ > > 1 file changed, 31 insertions(+), 18 deletions(-) > > > > diff --git a/block/blk-lib.c b/block/blk-lib.c > > index 23d7f30..a3a26c8 100644 > > --- a/block/blk-lib.c > > +++ b/block/blk-lib.c > > @@ -84,6 +84,28 @@ int __blkdev_issue_discard(struct block_device *bdev, > > sector_t sector, > > } > > EXPORT_SYMBOL(__blkdev_issue_discard); > > > > +static int do_blkdev_issue_discard(struct block_device *bdev, sector_t > > sector, > > + sector_t nr_sects, gfp_t gfp_mask, unsigned long flags, > > + int *io_err) > > +{ > > + int type = REQ_WRITE | REQ_DISCARD; > > + struct bio *bio = NULL; > > + struct blk_plug plug; > > + int ret; > > + > > + if (flags & BLKDEV_DISCARD_SECURE) > > + type |= REQ_SECURE; > > + > > + blk_start_plug(&plug); > > + ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, type, > > + &bio); > > + if (!ret && bio) > > + *io_err = submit_bio_wait(type, bio); > > + blk_finish_plug(&plug); > > + > > + return ret; > > +} > > + > > /** > > * blkdev_issue_discard - queue a discard > > * @bdev: blockdev to issue discard for > > @@ -98,23 +120,12 @@ EXPORT_SYMBOL(__blkdev_issue_discard); > > int blkdev_issue_discard(struct block_device *bdev, sector_t sector, > > sector_t nr_sects, gfp_t gfp_mask, unsigned long flags) > > { > > - int type = REQ_WRITE | REQ_DISCARD; > > - struct bio *bio = NULL; > > - struct blk_plug plug; > > - int ret; > > + int ret, io_err; > > > > - if (flags & BLKDEV_DISCARD_SECURE) > > - type |= REQ_SECURE; > > - > > - blk_start_plug(&plug); > > - ret = __blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, type, > > - &bio); > > - if (!ret && bio) { > > - ret = submit_bio_wait(type, bio); > > - if (ret == -EOPNOTSUPP) > > - ret = 0; > > - } > > - blk_finish_plug(&plug); > > + ret = do_blkdev_issue_discard(bdev, sector, nr_sects, gfp_mask, > > + flags, &io_err); > > + if (!ret && io_err != -EOPNOTSUPP) > > + ret = io_err; > > Because io_err is always consulted if ret is not true shouldn't it be > explicitly initialized to 0 before the call to do_blkdev_issue_discard > (as do_blkdev_issue_discard will only set io_err if bio returned true)? > > Perhaps there's an argument that do_blkdev_issue_discard should always > set io_err on all its paths rather than just on errors in case the > caller hasn't initialized it - is there an existing kernel pattern for > this)?
I didn't follow. io_err is only and always set when ret == 0. io_err is meanless if ret != 0, because that means the disk doesn't support discard and we don't dispatch discard IO. why should we initialized io_err to 0?
