Commit 476b923c authored Jun 23, 2016 by Eric Blake Committed by Kevin Wolf Jul 05, 2016

nbd: Allow larger requests



The NBD layer was breaking up request at a limit of 2040 sectors
(just under 1M) to cater to old qemu-nbd. But the server limit
was raised to 32M in commit 2d821488 to match the kernel, more
than three years ago; and the upstream NBD Protocol is proposing
documentation that without any explicit communication to state
otherwise, a client should be able to safely assume that a 32M
transaction will work.  It is time to rely on the larger sizing,
and any downstream distro that cares about maximum
interoperability to older qemu-nbd servers can just tweak the
value of #define NBD_MAX_SECTORS.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Cc: qemu-stable@nongnu.org
Reviewed-by: Fam Zheng <famz@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

parent 82524274

block/nbd-client.c

+0 −4

Original line number	Diff line number	Diff line
		@@ -269,10 +269,6 @@ static int nbd_co_writev_1(BlockDriverState *bs, int64_t sector_num,
		return -reply.error;
		}

		/* qemu-nbd has a limit of slightly less than 1M per request. Try to
		* remain aligned to 4K. */
		#define NBD_MAX_SECTORS 2040

		int nbd_client_co_readv(BlockDriverState *bs, int64_t sector_num,
		int nb_sectors, QEMUIOVector *qiov)
		{

include/block/nbd.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -77,6 +77,8 @@ enum {

		/* Maximum size of a single READ/WRITE data buffer */
		#define NBD_MAX_BUFFER_SIZE (32 * 1024 * 1024)
		#define NBD_MAX_SECTORS (NBD_MAX_BUFFER_SIZE / BDRV_SECTOR_SIZE)

		/* Maximum size of an export name. The NBD spec requires 256 and
		* suggests that servers support up to 4096, but we stick to only the
		* required size so that we can stack-allocate the names, and because