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dm thin: fix non power of two discard granularity calc

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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 f13945d757
("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>
This commit is contained in:
Joe Thornber 2013-03-20 17:21:25 +00:00 committed by Alasdair G Kergon
parent f046f89a99
commit 58051b94e0
1 changed files with 6 additions and 1 deletions
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7
drivers/md/dm-thin.c
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@ -1577,6 +1577,11 @@ static bool data_dev_supports_discard(struct pool_c *pt)
return q && blk_queue_discard(q); 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 * If discard_passdown was enabled verify that the data device
* supports discards. Disable discard_passdown if not. * supports discards. Disable discard_passdown if not.
@ -1602,7 +1607,7 @@ static void disable_passdown_if_not_supported(struct pool_c *pt)
else if (data_limits->discard_granularity > block_size) else if (data_limits->discard_granularity > block_size)
reason = "discard granularity larger than a block"; 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"; reason = "discard granularity not a factor of block size";
if (reason) { if (reason) {