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[Qemu-devel] [PATCH v3 02/22] block: Document supported flags during bdr
From: |
Eric Blake |
Subject: |
[Qemu-devel] [PATCH v3 02/22] block: Document supported flags during bdrv_aligned_preadv() |
Date: |
Thu, 23 Jun 2016 16:37:06 -0600 |
We don't pass any flags on to drivers to handle. Tighten an
assert to explain why we pass 0 to bdrv_driver_preadv(), and add
some comments on things to be aware of if we want to turn on
per-BDS BDRV_REQ_FUA support during reads in the future. Also,
document that we may want to consider using unmap during
copy-on-read operations where the read is all zeroes.
Signed-off-by: Eric Blake <address@hidden>
Reviewed-by: Kevin Wolf <address@hidden>
Reviewed-by: Fam Zheng <address@hidden>
Reviewed-by: Stefan Hajnoczi <address@hidden>
---
v3: no change
v2: retitle from 'Honor flags during bdrv_aligned_preadv()', and
change scope of patch
---
block/io.c | 10 +++++++++-
1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/block/io.c b/block/io.c
index b95e856..994d3fa 100644
--- a/block/io.c
+++ b/block/io.c
@@ -945,6 +945,9 @@ static int coroutine_fn
bdrv_co_do_copy_on_readv(BlockDriverState *bs,
if (drv->bdrv_co_pwrite_zeroes &&
buffer_is_zero(bounce_buffer, iov.iov_len)) {
+ /* FIXME: Should we (perhaps conditionally) be setting
+ * BDRV_REQ_MAY_UNMAP, if it will allow for a sparser copy
+ * that still correctly reads as zero? */
ret = bdrv_co_do_pwrite_zeroes(bs, cluster_offset, cluster_bytes, 0);
} else {
/* This does not change the data on the disk, it is not necessary
@@ -987,7 +990,12 @@ static int coroutine_fn
bdrv_aligned_preadv(BlockDriverState *bs,
assert((bytes & (align - 1)) == 0);
assert(!qiov || bytes == qiov->size);
assert((bs->open_flags & BDRV_O_NO_IO) == 0);
- assert(!(flags & ~BDRV_REQ_MASK));
+
+ /* TODO: We would need a per-BDS .supported_read_flags and
+ * potential fallback support, if we ever implement any read flags
+ * to pass through to drivers. For now, there aren't any
+ * passthrough flags. */
+ assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ)));
/* Handle Copy on Read and associated serialisation */
if (flags & BDRV_REQ_COPY_ON_READ) {
--
2.5.5
- [Qemu-devel] [PATCH v3 00/22] Byte-based block limits, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 04/22] nbd: Allow larger requests, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 09/22] blkdebug: Set request_alignment during .bdrv_refresh_limits(), Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 08/22] block: Give nonzero result to blk_get_max_transfer_length(), Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 02/22] block: Document supported flags during bdrv_aligned_preadv(),
Eric Blake <=
- [Qemu-devel] [PATCH v3 06/22] iscsi: Advertise realistic limits to block layer, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 05/22] nbd: Advertise realistic limits to block layer, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 07/22] scsi: Advertise limits by blocksize, not 512, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 01/22] block: Tighter assertions on bdrv_aligned_pwritev(), Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 13/22] block: Set request_alignment during .bdrv_refresh_limits(), Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 10/22] iscsi: Set request_alignment during .bdrv_refresh_limits(), Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 15/22] block: Switch transfer length bounds to byte-based, Eric Blake, 2016/06/23
- [Qemu-devel] [PATCH v3 17/22] block: Switch discard length bounds to byte-based, Eric Blake, 2016/06/23