Re: [dm-devel] [PATCH] dm: dm-cache fails to write the cachedevice in writethrough mode

From: Alasdair G Kergon
Date: Fri Mar 22 2013 - 23:01:05 EST

On Fri, Mar 22, 2013 at 01:11:51PM -0700, Darrick J. Wong wrote:
> The new writethrough strategy for dm-cache issues a bio to the origin device,
> remaps the bio to the cache device, and issues the bio to the cache device.
> However, the block layer modifies bi_sector and bi_size, so we need to preserve
> these or else nothing gets written to the cache (bi_size == 0). This fixes the
> problem where someone writes a block through the cache, but a subsequent reread
> (from the cache) returns old contents.

If this needs doing here, please use dm_bio_record() and dm_bio_restore().
E.g. Look at how dm-raid1.c does something similar.


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