[Libguestfs] [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>
---
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;
--
2.21.0