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
---
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 056a101..9191772 100644
--- a/block/io.c
+++ b/block/io.c
@@ -933,6 +933,9 @@ 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
@@ -975,7 +978,12 @@ 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
