dm thin: fix non power of two discard granularity calc
Fix a discard granularity calculation to work for non power of 2 block sizes.
In order for thinp to passdown discard bios to the underlying data
device, the data device must have a discard granularity that is a
factor of the thinp block size. Originally this check was done by
using bitops since the block_size was known to be a power of two.
Introduced by commit f13945d75730081830b6f3360266950e2b7c9067
("dm thin: support a non power of 2 discard_granularity").
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index ab95e5f..004ad165 100644
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1577,6 +1577,11 @@
return q && blk_queue_discard(q);
}
+static bool is_factor(sector_t block_size, uint32_t n)
+{
+ return !sector_div(block_size, n);
+}
+
/*
* If discard_passdown was enabled verify that the data device
* supports discards. Disable discard_passdown if not.
@@ -1602,7 +1607,7 @@
else if (data_limits->discard_granularity > block_size)
reason = "discard granularity larger than a block";
- else if (block_size & (data_limits->discard_granularity - 1))
+ else if (!is_factor(block_size, data_limits->discard_granularity))
reason = "discard granularity not a factor of block size";
if (reason) {