| Message ID | 1465939839-30097-3-git-send-email-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 06/14 15:30, Eric Blake wrote: > 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: Fam Zheng <famz@redhat.com>
On Tue, Jun 14, 2016 at 03:30:24PM -0600, Eric Blake wrote: > 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> > > --- > 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(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
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) {
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> --- 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(-)