dm thin: fix stacking of geometry limits

Do not blindly override the queue limits (specifically io_min and
io_opt).  Allow traditional stacking of these limits if io_opt is a
factor of the thin-pool's data block size.

Without this patch mkfs.xfs does not recognize the thin device's
provided limits as a useful geometry (e.g. raid) so these hints are
ignored.  This was due to setting io_min to a useless value.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Acked-by: Joe Thornber <ejt@redhat.com>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 88f2f80..21328a3 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -2648,9 +2648,17 @@ static void pool_io_hints(struct dm_target *ti, struct queue_limits *limits)
 {
        struct pool_c *pt = ti->private;
        struct pool *pool = pt->pool;
+       uint64_t io_opt_sectors = limits->io_opt >> SECTOR_SHIFT;
 
-       blk_limits_io_min(limits, 0);
-       blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
+       /*
+        * If the system-determined stacked limits are compatible with the
+        * pool's blocksize (io_opt is a factor) do not override them.
+        */
+       if (io_opt_sectors < pool->sectors_per_block ||
+           do_div(io_opt_sectors, pool->sectors_per_block)) {
+               blk_limits_io_min(limits, 0);
+               blk_limits_io_opt(limits, pool->sectors_per_block << SECTOR_SHIFT);
+       }
 
        /*
         * pt->adjusted_pf is a staging area for the actual features to use.