Re: [PATCH v6 5/5] loop: Add support for provision requests

Sarthak Kukreti
2023-05-15T21:32:01Z

On Mon, May 15, 2023 at 5:37 AM Brian Foster <bfoster@redhat.com> wrote:
>
> On Fri, May 05, 2023 at 11:29:09PM -0700, Sarthak Kukreti wrote:
> > Add support for provision requests to loopback devices.
> > Loop devices will configure provision support based on
> > whether the underlying block device/file can support
> > the provision request and upon receiving a provision bio,
> > will map it to the backing device/storage. For loop devices
> > over files, a REQ_OP_PROVISION request will translate to
> > an fallocate mode 0 call on the backing file.
> >
> > Signed-off-by: Sarthak Kukreti <sarthakkukreti@chromium.org>
> > ---
> > drivers/block/loop.c | 42 ++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 42 insertions(+)
> >
> > diff --git a/drivers/block/loop.c b/drivers/block/loop.c
> > index bc31bb7072a2..13c4b4f8b9c1 100644
> > --- a/drivers/block/loop.c
> > +++ b/drivers/block/loop.c
> > @@ -327,6 +327,24 @@ static int lo_fallocate(struct loop_device *lo, struct request *rq, loff_t pos,
> > return ret;
> > }
> >
> > +static int lo_req_provision(struct loop_device *lo, struct request *rq, loff_t pos)
> > +{
> > + struct file *file = lo->lo_backing_file;
> > + struct request_queue *q = lo->lo_queue;
> > + int ret;
> > +
> > + if (!q->limits.max_provision_sectors) {
> > + ret = -EOPNOTSUPP;
> > + goto out;
> > + }
> > +
> > + ret = file->f_op->fallocate(file, 0, pos, blk_rq_bytes(rq));
> > + if (unlikely(ret && ret != -EINVAL && ret != -EOPNOTSUPP))
> > + ret = -EIO;
> > + out:
> > + return ret;
> > +}
> > +
> > static int lo_req_flush(struct loop_device *lo, struct request *rq)
> > {
> > int ret = vfs_fsync(lo->lo_backing_file, 0);
> > @@ -488,6 +506,8 @@ static int do_req_filebacked(struct loop_device *lo, struct request *rq)
> > FALLOC_FL_PUNCH_HOLE);
> > case REQ_OP_DISCARD:
> > return lo_fallocate(lo, rq, pos, FALLOC_FL_PUNCH_HOLE);
> > + case REQ_OP_PROVISION:
> > + return lo_req_provision(lo, rq, pos);
>
> Hi Sarthak,
>
> The only thing that stands out to me is the separate lo_req_provision()
> helper here. It seems it might be a little cleaner to extend and reuse
> lo_req_fallocate()..? But that's not something I feel strongly about, so
> this all looks pretty good to me either way, FWIW.
>
Fair point, I think that should shorten the patch (and for
correctness, we'd want to add FALLOC_FL_KEEP_SIZE for REQ_OP_PROVISION
too). I'll fix this up in v7.

Best
Sarthak

> Brian
>
> > case REQ_OP_WRITE:
> > if (cmd->use_aio)
> > return lo_rw_aio(lo, cmd, pos, ITER_SOURCE);
> > @@ -754,6 +774,25 @@ static void loop_sysfs_exit(struct loop_device *lo)
> > &loop_attribute_group);
> > }
> >
> > +static void loop_config_provision(struct loop_device *lo)
> > +{
> > + struct file *file = lo->lo_backing_file;
> > + struct inode *inode = file->f_mapping->host;
> > +
> > + /*
> > + * If the backing device is a block device, mirror its provisioning
> > + * capability.
> > + */
> > + if (S_ISBLK(inode->i_mode)) {
> > + blk_queue_max_provision_sectors(lo->lo_queue,
> > + bdev_max_provision_sectors(I_BDEV(inode)));
> > + } else if (file->f_op->fallocate) {
> > + blk_queue_max_provision_sectors(lo->lo_queue, UINT_MAX >> 9);
> > + } else {
> > + blk_queue_max_provision_sectors(lo->lo_queue, 0);
> > + }
> > +}
> > +
> > static void loop_config_discard(struct loop_device *lo)
> > {
> > struct file *file = lo->lo_backing_file;
> > @@ -1092,6 +1131,7 @@ static int loop_configure(struct loop_device *lo, fmode_t mode,
> > blk_queue_io_min(lo->lo_queue, bsize);
> >
> > loop_config_discard(lo);
> > + loop_config_provision(lo);
> > loop_update_rotational(lo);
> > loop_update_dio(lo);
> > loop_sysfs_init(lo);
> > @@ -1304,6 +1344,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
> > }
> >
> > loop_config_discard(lo);
> > + loop_config_provision(lo);
> >
> > /* update dio if lo_offset or transfer is changed */
> > __loop_update_dio(lo, lo->use_dio);
> > @@ -1830,6 +1871,7 @@ static blk_status_t loop_queue_rq(struct blk_mq_hw_ctx *hctx,
> > case REQ_OP_FLUSH:
> > case REQ_OP_DISCARD:
> > case REQ_OP_WRITE_ZEROES:
> > + case REQ_OP_PROVISION:
> > cmd->use_aio = false;
> > break;
> > default:
> > --
> > 2.40.1.521.gf1e218fcd8-goog
> >
>