From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42029) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bKSd6-0000kE-S9 for qemu-devel@nongnu.org; Tue, 05 Jul 2016 11:51:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bKSd1-0006Sq-WF for qemu-devel@nongnu.org; Tue, 05 Jul 2016 11:51:20 -0400 From: Kevin Wolf Date: Tue, 5 Jul 2016 17:50:12 +0200 Message-Id: <1467733852-27097-4-git-send-email-kwolf@redhat.com> In-Reply-To: <1467733852-27097-1-git-send-email-kwolf@redhat.com> References: <1467733852-27097-1-git-send-email-kwolf@redhat.com> Subject: [Qemu-devel] [PULL 03/43] block: Document supported flags during bdrv_aligned_preadv() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-block@nongnu.org Cc: kwolf@redhat.com, qemu-devel@nongnu.org From: Eric Blake 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 Reviewed-by: Kevin Wolf Reviewed-by: Fam Zheng Reviewed-by: Stefan Hajnoczi Signed-off-by: Kevin Wolf --- 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) { -- 1.8.3.1