Re: [Libguestfs] [Qemu-devel] [PATCH 2/5] nbd: Prepare for NBD_CMD_FLAG_FAST_ZERO

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 <eblake(a)redhat.com&gt; --- 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);