Re: [Libguestfs] [Qemu-devel] [PATCH 3/5] nbd: Implement client use of NBD FAST_ZERO

The client side is fairly straightforward: if the server advertised fast zero support, then we can map that to BDRV_REQ_NO_FALLBACK support. A server that advertises FAST_ZERO but not WRITE_ZEROES is technically broken, but we can ignore that situation as it does not change our behavior. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt;

--- Perhaps this is worth merging with the previous patch. --- block/nbd.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/block/nbd.c b/block/nbd.c index beed46fb3414..8339d7106366 100644 --- a/block/nbd.c +++ b/block/nbd.c @@ -1044,6 +1044,10 @@ static int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, if (!(flags & BDRV_REQ_MAY_UNMAP)) { request.flags |= NBD_CMD_FLAG_NO_HOLE; } + if (flags & BDRV_REQ_NO_FALLBACK) { + assert(s->info.flags & NBD_FLAG_SEND_FAST_ZERO); + request.flags |= NBD_CMD_FLAG_FAST_ZERO; + } if (!bytes) { return 0; @@ -1239,6 +1243,9 @@ static int nbd_client_connect(BlockDriverState *bs, Error **errp) } if (s->info.flags & NBD_FLAG_SEND_WRITE_ZEROES) { bs->supported_zero_flags |= BDRV_REQ_MAY_UNMAP; + if (s->info.flags & NBD_FLAG_SEND_FAST_ZERO) { + bs->supported_zero_flags |= BDRV_REQ_NO_FALLBACK; + } } s->sioc = sioc;