diff options
| author | Eric Blake <eblake@redhat.com> | 2016-06-23 16:37:06 -0600 |
|---|---|---|
| committer | Kevin Wolf <kwolf@redhat.com> | 2016-07-05 16:46:24 +0200 |
| commit | a604fa2ba55f645abbb082469ed595f58f657ac8 (patch) | |
| tree | 78b51a354097ea4fe70f8af15e84b873ed5e09bb /block | |
| parent | cff86b38aca34c9cc5c6f8846cc1c5b3d181c376 (diff) | |
block: Document supported flags during bdrv_aligned_preadv()
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 <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Diffstat (limited to 'block')
| -rw-r--r-- | block/io.c | 10 |
1 files changed, 9 insertions, 1 deletions
diff --git a/block/io.c b/block/io.c index b95e856cf9..994d3fafbf 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) { |