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path: root/block/qed-l2-cache.c
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2012-03-12qed: do not evict in-use L2 table cache entriesStefan Hajnoczi1-4/+18
The L2 table cache reduces QED metadata reads that would be required when translating LBAs to offsets into the image file. Since requests execute in parallel it is possible to share an L2 table between multiple requests. There is a potential data corruption issue when an in-use L2 table is evicted from the cache because the following situation occurs: 1. An allocating write performs an update to L2 table "A". 2. Another request needs L2 table "B" and causes table "A" to be evicted. 3. A new read request needs L2 table "A" but it is not cached. As a result the L2 update from #1 can overlap with the L2 fetch from #3. We must avoid doing overlapping I/O requests here since the worst case outcome is that the L2 fetch completes before the L2 update and yields stale data. In that case we would effectively discard the L2 update and lose data clusters! Thanks to Benoît Canet <benoit.canet@gmail.com> for extensive testing and debugging which lead to discovery of this bug. Reported-by: Benoît Canet <benoit.canet@gmail.com> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Tested-by: Benoît Canet <benoit.canet@gmail.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
2011-08-20Use glib memory allocation and free functionsAnthony Liguori1-3/+3
qemu_malloc/qemu_free no longer exist after this commit. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2010-12-17qed: Table, L2 cache, and cluster functionsStefan Hajnoczi1-0/+173
This patch adds code to look up data cluster offsets in the image via the L1/L2 tables. The L2 tables are writethrough cached in memory for performance (each read/write requires a lookup so it is essential to cache the tables). With cluster lookup code in place it is possible to implement bdrv_is_allocated() to query the number of contiguous allocated/unallocated clusters. Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>