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Date:   Fri, 6 Oct 2023 18:29:44 -0700
From:   Sarthak Kukreti <sarthakkukreti@...omium.org>
To:     "Darrick J. Wong" <djwong@...nel.org>
Cc:     dm-devel@...hat.com, linux-block@...r.kernel.org,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Brian Foster <bfoster@...hat.com>,
        "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Bart Van Assche <bvanassche@...gle.com>
Subject: Re: [PATCH v7 5/5] loop: Add support for provision requests

On Mon, May 22, 2023 at 6:22 PM Darrick J. Wong <djwong@...nel.org> wrote:
>
> On Mon, May 22, 2023 at 03:09:55PM -0700, Sarthak Kukreti wrote:
> > On Mon, May 22, 2023 at 9:37 AM Darrick J. Wong <djwong@...nel.org> wrote:
> > >
> > > If someone calls fallocate(UNSHARE_RANGE) on a loop bdev, shouldn't
> > > there be a way to pass that through to the fallocate call to the backing
> > > file?
> > >
> > > --D
> > >
> >
> > Yeah, I think we could add a REQ_UNSHARE bit (similar to REQ_NOUNMAP) to pass down the intent to the backing file (and possibly beyond...).
> >
> > I took a stab at implementing it as a follow up patch so that there's
> > less review churn on the current series. If it looks good, I can add
> > it to the end of the series (or incorporate this into the existing
> > block and loop patches):
>
> It looks like a reasonable addition to the end of the series, assuming
> that filling holes in thinp devices is cheap but unsharing snapshot
> blocks is not.
>
> > From: Sarthak Kukreti <sarthakkukreti@...omium.org>
> > Date: Mon, 22 May 2023 14:18:15 -0700
> > Subject: [PATCH] block: Pass unshare intent via REQ_OP_PROVISION
> >
> > Allow REQ_OP_PROVISION to pass in an extra REQ_UNSHARE bit to
> > annotate unshare requests to underlying layers. Layers that support
> > FALLOC_FL_UNSHARE will be able to use this as an indicator of which
> > fallocate() mode to use.
>
> > Signed-off-by: Sarthak Kukreti <sarthakkukreti@...omium.org>
> > ---
> >  block/blk-lib.c           |  6 +++++-
> >  block/fops.c              |  6 +++++-
> >  drivers/block/loop.c      | 35 +++++++++++++++++++++++++++++------
> >  include/linux/blk_types.h |  3 +++
> >  include/linux/blkdev.h    |  3 ++-
> >  5 files changed, 44 insertions(+), 9 deletions(-)
> >
> > diff --git a/block/blk-lib.c b/block/blk-lib.c
> > index 3cff5fb654f5..bea6f5a700b3 100644
> > --- a/block/blk-lib.c
> > +++ b/block/blk-lib.c
> > @@ -350,6 +350,7 @@ EXPORT_SYMBOL(blkdev_issue_secure_erase);
> >   * @sector:  start sector
> >   * @nr_sects:        number of sectors to provision
> >   * @gfp_mask:        memory allocation flags (for bio_alloc)
> > + * @flags:   controls detailed behavior
> >   *
> >   * Description:
> >   *  Issues a provision request to the block device for the range of sectors.
> > @@ -357,7 +358,7 @@ EXPORT_SYMBOL(blkdev_issue_secure_erase);
> >   *  underlying storage pool to allocate space for this block range.
> >   */
> >  int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> > -             sector_t nr_sects, gfp_t gfp)
> > +             sector_t nr_sects, gfp_t gfp, unsigned flags)
> >  {
> >       sector_t bs_mask = (bdev_logical_block_size(bdev) >> 9) - 1;
> >       unsigned int max_sectors = bdev_max_provision_sectors(bdev);
> > @@ -380,6 +381,9 @@ int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> >               bio->bi_iter.bi_sector = sector;
> >               bio->bi_iter.bi_size = req_sects << SECTOR_SHIFT;
> >
> > +             if (flags & BLKDEV_UNSHARE_RANGE)
>
> This is a provisioning flag, shouldn't this be ...
> BLKDEV_PROVISION_UNSHARE or something?
>
Done in v8, thanks!

> > +                     bio->bi_opf |= REQ_UNSHARE;
> > +
> >               sector += req_sects;
> >               nr_sects -= req_sects;
> >               if (!nr_sects) {
> > diff --git a/block/fops.c b/block/fops.c
> > index be2e41f160bf..6848756f0557 100644
> > --- a/block/fops.c
> > +++ b/block/fops.c
> > @@ -659,7 +659,11 @@ static long blkdev_fallocate(struct file *file, int mode, loff_t start,
> >       case FALLOC_FL_KEEP_SIZE:
> >       case FALLOC_FL_UNSHARE_RANGE | FALLOC_FL_KEEP_SIZE:
> >               error = blkdev_issue_provision(bdev, start >> SECTOR_SHIFT,
> > -                                            len >> SECTOR_SHIFT, GFP_KERNEL);
> > +                                            len >> SECTOR_SHIFT, GFP_KERNEL,
> > +                                            (mode &
> > +                                             FALLOC_FL_UNSHARE_RANGE) ?
> > +                                                    BLKDEV_UNSHARE_RANGE :
> > +                                                    0);
>
> You might want to do something about the six level indent here;
> Linus hates that.
>
Thanks for pointing it out, I switched it up a bit in v8 but it still
looks a bit weird to me.

Best
Sarthak

> --D
>
> >               break;
> >       case FALLOC_FL_ZERO_RANGE:
> >       case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE:
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index 7fe1a6629754..c844b145d666 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -306,6 +306,30 @@ static int lo_read_simple(struct loop_device *lo, struct request *rq,
> >       return 0;
> >  }
> >
> > +static bool validate_fallocate_mode(struct loop_device *lo, int mode)
> > +{
> > +     bool ret = true;
> > +
> > +     switch (mode) {
> > +     case FALLOC_FL_PUNCH_HOLE:
> > +     case FALLOC_FL_ZERO_RANGE:
> > +             if (!bdev_max_discard_sectors(lo->lo_device))
> > +                     ret = false;
> > +             break;
> > +     case 0:
> > +     case FALLOC_FL_UNSHARE_RANGE:
> > +             if (!bdev_max_provision_sectors(lo->lo_device))
> > +                     ret = false;
> > +             break;
> > +
> > +     default:
> > +             ret = false;
> > +     }
> > +
> > +     return ret;
> > +}
> > +
> > +
> >  static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
> >                       int mode)
> >  {
> > @@ -316,11 +340,7 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
> >       struct file *file = lo->lo_backing_file;
> >       int ret;
> >
> > -     if (mode & (FALLOC_FL_PUNCH_HOLE | FALLOC_FL_ZERO_RANGE) &&
> > -         !bdev_max_discard_sectors(lo->lo_device))
> > -             return -EOPNOTSUPP;
> > -
> > -     if (mode == 0 && !bdev_max_provision_sectors(lo->lo_device))
> > +     if (!validate_fallocate_mode(lo, mode))
> >               return -EOPNOTSUPP;
> >
> >       mode |= FALLOC_FL_KEEP_SIZE;
> > @@ -493,7 +513,10 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
> >       case REQ_OP_DISCARD:
> >               return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
> >       case REQ_OP_PROVISION:
> > -             return lo_fallocate(lo, rq, pos, 0);
> > +             return lo_fallocate(lo, rq, pos,
> > +                                 (rq->cmd_flags & REQ_UNSHARE) ?
> > +                                         FALLOC_FL_UNSHARE_RANGE :
> > +                                         0);
> >       case REQ_OP_WRITE:
> >               if (cmd->use_aio)
> >                       return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
> > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> > index b7bb0226fdee..1a536fd897cb 100644
> > --- a/include/linux/blk_types.h
> > +++ b/include/linux/blk_types.h
> > @@ -423,6 +423,8 @@ enum req_flag_bits {
> >        */
> >       /* for REQ_OP_WRITE_ZEROES: */
> >       __REQ_NOUNMAP,          /* do not free blocks when zeroing */
> > +     /* for REQ_OP_PROVISION: */
> > +     __REQ_UNSHARE,          /* unshare blocks */
> >
> >       __REQ_NR_BITS,          /* stops here */
> >  };
> > @@ -451,6 +453,7 @@ enum req_flag_bits {
> >  #define REQ_FS_PRIVATE       (__force blk_opf_t)(1ULL << __REQ_FS_PRIVATE)
> >
> >  #define REQ_NOUNMAP  (__force blk_opf_t)(1ULL << __REQ_NOUNMAP)
> > +#define REQ_UNSHARE  (__force blk_opf_t)(1ULL << __REQ_UNSHARE)
> >
> >  #define REQ_FAILFAST_MASK \
> >       (REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT | REQ_FAILFAST_DRIVER)
> > diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> > index 462ce586d46f..60c09b0d3fc9 100644
> > --- a/include/linux/blkdev.h
> > +++ b/include/linux/blkdev.h
> > @@ -1049,10 +1049,11 @@ int blkdev_issue_secure_erase(struct block_device *bdev, sector_t sector,
> >               sector_t nr_sects, gfp_t gfp);
> >
> >  extern int blkdev_issue_provision(struct block_device *bdev, sector_t sector,
> > -             sector_t nr_sects, gfp_t gfp_mask);
> > +             sector_t nr_sects, gfp_t gfp_mask, unsigned int flags);
> >
> >  #define BLKDEV_ZERO_NOUNMAP  (1 << 0)  /* do not free blocks */
> >  #define BLKDEV_ZERO_NOFALLBACK       (1 << 1)  /* don't write explicit zeroes */
> > +#define BLKDEV_UNSHARE_RANGE (1 << 2)  /* unshare range on provision */
> >
> >  extern int __blkdev_issue_zeroout(struct block_device *bdev, sector_t sector,
> >               sector_t nr_sects, gfp_t gfp_mask, struct bio **biop,
> > --
> > 2.39.2
> >

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