| Message ID | 1465939839-30097-5-git-send-email-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 14/06/2016 23:30, Eric Blake wrote: > 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 2d8214885 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> > > --- > v2: new patch > --- > include/block/nbd.h | 1 + > block/nbd-client.c | 4 ---- > 2 files changed, 1 insertion(+), 4 deletions(-) > > diff --git a/include/block/nbd.h b/include/block/nbd.h > index b86a976..36dde24 100644 > --- a/include/block/nbd.h > +++ b/include/block/nbd.h > @@ -76,6 +76,7 @@ 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) > > ssize_t nbd_wr_syncv(QIOChannel *ioc, > struct iovec *iov, > diff --git a/block/nbd-client.c b/block/nbd-client.c > index 4d13444..420bce8 100644 > --- a/block/nbd-client.c > +++ b/block/nbd-client.c > @@ -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) > { > Acked-by: Paolo Bonzini <pbonzini@redhat.com>
On Tue, 06/14 15:30, Eric Blake wrote: > 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 2d8214885 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: Fam Zheng <famz@redhat.com>
On Tue, Jun 14, 2016 at 03:30:26PM -0600, Eric Blake wrote: > 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 2d8214885 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> > > --- > v2: new patch > --- > include/block/nbd.h | 1 + > block/nbd-client.c | 4 ---- > 2 files changed, 1 insertion(+), 4 deletions(-) Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/include/block/nbd.h b/include/block/nbd.h index b86a976..36dde24 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -76,6 +76,7 @@ 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) ssize_t nbd_wr_syncv(QIOChannel *ioc, struct iovec *iov, diff --git a/block/nbd-client.c b/block/nbd-client.c index 4d13444..420bce8 100644 --- a/block/nbd-client.c +++ b/block/nbd-client.c @@ -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) {
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 2d8214885 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> --- v2: new patch --- include/block/nbd.h | 1 + block/nbd-client.c | 4 ---- 2 files changed, 1 insertion(+), 4 deletions(-)