Commit fe0480d6 and friends added BDRV_REQ_NO_FALLBACK as a way to
avoid wasting time on a preliminary write-zero request that will later
be rewritten by actual data, if it is known that the write-zero
request will use a slow fallback; but in doing so, could not optimize
for NBD. The NBD specification is now considering an extension that
will allow passing on those semantics; this patch updates the new
protocol bits and 'qemu-nbd --list' output to recognize the bit, as
well as the new errno value possible when using the new flag; while
upcoming patches will improve the client to use the feature when
present, and the server to advertise support for it.
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
docs/interop/nbd.txt | 3 ++-
include/block/nbd.h | 4 ++++
nbd/common.c | 5 +++++
nbd/server.c | 2 ++
qemu-nbd.c | 1 +
5 files changed, 14 insertions(+), 1 deletion(-)
diff --git a/docs/interop/nbd.txt b/docs/interop/nbd.txt
index 6dfec7f47647..45118809618e 100644
--- a/docs/interop/nbd.txt
+++ b/docs/interop/nbd.txt
@@ -53,4 +53,5 @@ the operation of that feature.
* 2.12: NBD_CMD_BLOCK_STATUS for "base:allocation"
* 3.0: NBD_OPT_STARTTLS with TLS Pre-Shared Keys (PSK),
NBD_CMD_BLOCK_STATUS for "qemu:dirty-bitmap:", NBD_CMD_CACHE
-* 4.2: NBD_FLAG_CAN_MULTI_CONN for sharable read-only exports
+* 4.2: NBD_FLAG_CAN_MULTI_CONN for sharable read-only exports,
+NBD_CMD_FLAG_FAST_ZERO
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 2c87b42dfd48..21550747cf35 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -140,6 +140,7 @@ enum {
NBD_FLAG_CAN_MULTI_CONN_BIT = 8, /* Multi-client cache consistent */
NBD_FLAG_SEND_RESIZE_BIT = 9, /* Send resize */
NBD_FLAG_SEND_CACHE_BIT = 10, /* Send CACHE (prefetch) */
+ NBD_FLAG_SEND_FAST_ZERO_BIT = 11, /* FAST_ZERO flag for WRITE_ZEROES */
};
#define NBD_FLAG_HAS_FLAGS (1 << NBD_FLAG_HAS_FLAGS_BIT)
@@ -153,6 +154,7 @@ enum {
#define NBD_FLAG_CAN_MULTI_CONN (1 << NBD_FLAG_CAN_MULTI_CONN_BIT)
#define NBD_FLAG_SEND_RESIZE (1 << NBD_FLAG_SEND_RESIZE_BIT)
#define NBD_FLAG_SEND_CACHE (1 << NBD_FLAG_SEND_CACHE_BIT)
+#define NBD_FLAG_SEND_FAST_ZERO (1 << NBD_FLAG_SEND_FAST_ZERO_BIT)
/* New-style handshake (global) flags, sent from server to client, and
control what will happen during handshake phase. */
@@ -205,6 +207,7 @@ enum {
#define NBD_CMD_FLAG_DF (1 << 2) /* don't fragment structured read */
#define NBD_CMD_FLAG_REQ_ONE (1 << 3) /* only one extent in BLOCK_STATUS
* reply chunk */
+#define NBD_CMD_FLAG_FAST_ZERO (1 << 4) /* fail if WRITE_ZEROES is not fast */
/* Supported request types */
enum {
@@ -270,6 +273,7 @@ static inline bool nbd_reply_type_is_error(int type)
#define NBD_EINVAL 22
#define NBD_ENOSPC 28
#define NBD_EOVERFLOW 75
+#define NBD_ENOTSUP 95
#define NBD_ESHUTDOWN 108
/* Details collected by NBD_OPT_EXPORT_NAME and NBD_OPT_GO */
diff --git a/nbd/common.c b/nbd/common.c
index cc8b278e541d..ddfe7d118371 100644
--- a/nbd/common.c
+++ b/nbd/common.c
@@ -201,6 +201,8 @@ const char *nbd_err_lookup(int err)
return "ENOSPC";
case NBD_EOVERFLOW:
return "EOVERFLOW";
+ case NBD_ENOTSUP:
+ return "ENOTSUP";
case NBD_ESHUTDOWN:
return "ESHUTDOWN";
default:
@@ -231,6 +233,9 @@ int nbd_errno_to_system_errno(int err)
case NBD_EOVERFLOW:
ret = EOVERFLOW;
break;
+ case NBD_ENOTSUP:
+ ret = ENOTSUP;
+ break;
case NBD_ESHUTDOWN:
ret = ESHUTDOWN;
break;
diff --git a/nbd/server.c b/nbd/server.c
index b5577828aa44..981bc3cb1151 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -55,6 +55,8 @@ static int system_errno_to_nbd_errno(int err)
return NBD_ENOSPC;
case EOVERFLOW:
return NBD_EOVERFLOW;
+ case ENOTSUP:
+ return NBD_ENOTSUP;
case ESHUTDOWN:
return NBD_ESHUTDOWN;
case EINVAL:
diff --git a/qemu-nbd.c b/qemu-nbd.c
index 079702bb837f..dce52f564b5a 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -294,6 +294,7 @@ static int qemu_nbd_client_list(SocketAddress *saddr,
QCryptoTLSCreds *tls,
[NBD_FLAG_CAN_MULTI_CONN_BIT] = "multi",
[NBD_FLAG_SEND_RESIZE_BIT] = "resize",
[NBD_FLAG_SEND_CACHE_BIT] = "cache",
+ [NBD_FLAG_SEND_FAST_ZERO_BIT] = "fast-zero",
};
printf(" size: %" PRIu64 "\n", list[i].size);
--
2.21.0
