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[Qemu-devel] [PATCH v2 14/18] block: protect against "torn reads" for gu
From: |
Paolo Bonzini |
Subject: |
[Qemu-devel] [PATCH v2 14/18] block: protect against "torn reads" for guest_block_size > host_block_size |
Date: |
Thu, 26 Jan 2012 18:22:45 +0100 |
When the guest sees a higher alignment than the host, writes may be
done in multiple steps. So, reads have to be serialized against
overlapping writes, so that the writes look atomic to the guest.
This is true even when O_DIRECT is not in use.
Signed-off-by: Paolo Bonzini <address@hidden>
---
block.c | 22 ++++++++++++++++++++++
1 files changed, 22 insertions(+), 0 deletions(-)
diff --git a/block.c b/block.c
index c78ca47..683d4a3 100644
--- a/block.c
+++ b/block.c
@@ -1613,6 +1613,16 @@ static int coroutine_fn
bdrv_co_do_readv(BlockDriverState *bs,
get_cluster_size(bs), false);
}
+ /* When the guest sees a higher alignment than the host, writes may be
+ * done in multiple steps. So, reads have to be serialized against
+ * overlapping writes, so that the writes look atomic to the guest,
+ * even when O_DIRECT is not in use.
+ */
+ if (bs->guest_block_size > bs->host_block_size) {
+ wait_for_overlapping_requests(bs, sector_num, nb_sectors,
+ bs->guest_block_size, true);
+ }
+
tracked_request_begin(&req, bs, sector_num, nb_sectors, false);
if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -3629,6 +3639,18 @@ BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
void bdrv_set_guest_block_size(BlockDriverState *bs, int align)
{
bs->guest_block_size = align;
+ if ((bs->open_flags & BDRV_O_RDWR) &&
+ bs->host_block_size < bs->guest_block_size) {
+ error_report("Host block size is %d, guest block size is %d. Due to
partially\n"
+ "written sectors, power failures may cause data
corruption.%s",
+ bs->host_block_size, bs->guest_block_size,
+
+ /* The host block size might not be detected correctly if
+ * the guest is not using O_DIRECT. */
+ (bs->open_flags & BDRV_O_NOCACHE) ? "" : "\n"
+ "If you think this message is wrong, start the guest with
cache=none\n"
+ "and see if it disappears.");
+ }
}
void *qemu_blockalign(BlockDriverState *bs, size_t size)
--
1.7.7.6
- [Qemu-devel] [PATCH v2 02/18] block: store actual flags in bs->open_flags, (continued)
- [Qemu-devel] [PATCH v2 02/18] block: store actual flags in bs->open_flags, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 04/18] block: non-raw protocols never cache, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 05/18] block: remove enable_write_cache, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 06/18] block: move flag bits together, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 07/18] raw: remove the aligned_buf, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 09/18] block: add host_block_size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 11/18] iscsi: save host block size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 08/18] block: rename buffer_alignment to guest_block_size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 10/18] raw: probe host_block_size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 12/18] block: allow waiting only for overlapping writes, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 14/18] block: protect against "torn reads" for guest_block_size > host_block_size,
Paolo Bonzini <=
- [Qemu-devel] [PATCH v2 17/18] block: default min_io_size to host block size when doing rmw, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 16/18] block: default physical block size to host block size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 18/18] qemu-io: add blocksize argument to open, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 15/18] block: align and serialize I/O when guest_block_size < host_block_size, Paolo Bonzini, 2012/01/26
- [Qemu-devel] [PATCH v2 13/18] block: allow waiting at arbitrary granularity, Paolo Bonzini, 2012/01/26