Re: [RFC PATCH] block: wire blkdev_fallocate() to block_device_operations' reserve_space

Mike Snitzer
2016-04-12T21:04:34Z

On Tue, Apr 12 2016 at 4:39pm -0400,
Darrick J. Wong <darrick.wong@oracle.com> wrote:

> On Tue, Apr 12, 2016 at 04:04:59PM -0400, Mike Snitzer wrote:
> > diff --git a/fs/block_dev.c b/fs/block_dev.c
> > index 5a2c3ab..b34c07b 100644
> > --- a/fs/block_dev.c
> > +++ b/fs/block_dev.c
> > @@ -1801,17 +1801,13 @@ long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> > struct request_queue *q = bdev_get_queue(bdev);
> > struct address_space *mapping;
> > loff_t end = start + len - 1;
> > - loff_t bs_mask, isize;
> > + loff_t isize;
> > int error;
> >
> > /* We only support zero range and punch hole. */
> > if (mode & ~BLKDEV_FALLOC_FL_SUPPORTED)
> > return -EOPNOTSUPP;
> >
> > - /* We haven't a primitive for "ensure space exists" right now. */
> > - if (!(mode & ~FALLOC_FL_KEEP_SIZE))
> > - return -EOPNOTSUPP;
> > -
> > /* Only punch if the device can do zeroing discard. */
> > if ((mode & FALLOC_FL_PUNCH_HOLE) &&
> > (!blk_queue_discard(q) || !q->limits.discard_zeroes_data))
> > @@ -1829,9 +1825,12 @@ long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> > return -EINVAL;
> > }
> >
> > - /* Don't allow IO that isn't aligned to logical block size */
> > - bs_mask = bdev_logical_block_size(bdev) - 1;
> > - if ((start | len) & bs_mask)
> > + /*
> > + * Don't allow IO that isn't aligned to minimum IO size (io_min)
> > + * - for normal device's io_min is usually logical block size
> > + * - but for more exotic devices (e.g. DM thinp) it may be larger
> > + */
> > + if ((start | len) % bdev_io_min(bdev))
> > return -EINVAL;
>
> Noted. Will update the original patch.

BTW, I just noticed your "block: require write_same and discard requests
align to logical block size" -- doesn't look right.

But maybe I'm just too hyper-focused on DM thinp's needs (which would
much prefer these checks be done in terms of minimum_io_size, rather
than logical_block_size, and _not_ assuming power-of-2 math will work).

But at least for discard: your lbs-based check is fine; since we have
discard_granularity to cover thinp's more specific requirements.