From 1f4d6d18edfeaea64ae74bf5254b8d0e923dc73f Mon Sep 17 00:00:00 2001 From: Eric Blake Date: Fri, 14 Oct 2016 13:33:17 -0500 Subject: [PATCH] nbd: Implement NBD_CMD_WRITE_ZEROES on server Upstream NBD protocol recently added the ability to efficiently write zeroes without having to send the zeroes over the wire, along with a flag to control whether the client wants to allow a hole. Note that when it comes to requiring full allocation, vs. permitting optimizations, the NBD spec intentionally picked a different sense for the flag; the rules in qemu are: MAY_UNMAP == 0: must write zeroes MAY_UNMAP == 1: may use holes if reads will see zeroes while in NBD, the rules are: FLAG_NO_HOLE == 1: must write zeroes FLAG_NO_HOLE == 0: may use holes if reads will see zeroes In all cases, the 'may use holes' scenario is optional (the server need not use a hole, and must not use a hole if subsequent reads would not see zeroes). Signed-off-by: Eric Blake Message-Id: <1476469998-28592-16-git-send-email-eblake@redhat.com> Signed-off-by: Paolo Bonzini --- include/block/nbd.h | 8 ++++++-- nbd/server.c | 42 ++++++++++++++++++++++++++++++++++++++++-- 2 files changed, 46 insertions(+), 4 deletions(-) diff --git a/include/block/nbd.h b/include/block/nbd.h index eea7ef0536..3e373f0498 100644 --- a/include/block/nbd.h +++ b/include/block/nbd.h @@ -71,6 +71,7 @@ typedef struct NBDReply NBDReply; #define NBD_FLAG_SEND_FUA (1 << 3) /* Send FUA (Force Unit Access) */ #define NBD_FLAG_ROTATIONAL (1 << 4) /* Use elevator algorithm - rotational media */ #define NBD_FLAG_SEND_TRIM (1 << 5) /* Send TRIM (discard) */ +#define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) /* Send WRITE_ZEROES */ /* New-style handshake (global) flags, sent from server to client, and control what will happen during handshake phase. */ @@ -96,7 +97,8 @@ typedef struct NBDReply NBDReply; #define NBD_REP_ERR_SHUTDOWN NBD_REP_ERR(7) /* Server shutting down */ /* Request flags, sent from client to server during transmission phase */ -#define NBD_CMD_FLAG_FUA (1 << 0) +#define NBD_CMD_FLAG_FUA (1 << 0) /* 'force unit access' during write */ +#define NBD_CMD_FLAG_NO_HOLE (1 << 1) /* don't punch hole on zero run */ /* Supported request types */ enum { @@ -104,7 +106,9 @@ enum { NBD_CMD_WRITE = 1, NBD_CMD_DISC = 2, NBD_CMD_FLUSH = 3, - NBD_CMD_TRIM = 4 + NBD_CMD_TRIM = 4, + /* 5 reserved for failed experiment NBD_CMD_CACHE */ + NBD_CMD_WRITE_ZEROES = 6, }; #define NBD_DEFAULT_PORT 10809 diff --git a/nbd/server.c b/nbd/server.c index 0b50caad9e..5b76261666 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -616,7 +616,8 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData *data) char buf[8 + 8 + 8 + 128]; int rc; const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM | - NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA); + NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA | + NBD_FLAG_SEND_WRITE_ZEROES); bool oldStyle; size_t len; @@ -1146,11 +1147,17 @@ static ssize_t nbd_co_receive_request(NBDRequestData *req, rc = request->type == NBD_CMD_WRITE ? -ENOSPC : -EINVAL; goto out; } - if (request->flags & ~NBD_CMD_FLAG_FUA) { + if (request->flags & ~(NBD_CMD_FLAG_FUA | NBD_CMD_FLAG_NO_HOLE)) { LOG("unsupported flags (got 0x%x)", request->flags); rc = -EINVAL; goto out; } + if (request->type != NBD_CMD_WRITE_ZEROES && + (request->flags & NBD_CMD_FLAG_NO_HOLE)) { + LOG("unexpected flags (got 0x%x)", request->flags); + rc = -EINVAL; + goto out; + } rc = 0; @@ -1255,6 +1262,37 @@ static void nbd_trip(void *opaque) } break; + case NBD_CMD_WRITE_ZEROES: + TRACE("Request type is WRITE_ZEROES"); + + if (exp->nbdflags & NBD_FLAG_READ_ONLY) { + TRACE("Server is read-only, return error"); + reply.error = EROFS; + goto error_reply; + } + + TRACE("Writing to device"); + + flags = 0; + if (request.flags & NBD_CMD_FLAG_FUA) { + flags |= BDRV_REQ_FUA; + } + if (!(request.flags & NBD_CMD_FLAG_NO_HOLE)) { + flags |= BDRV_REQ_MAY_UNMAP; + } + ret = blk_pwrite_zeroes(exp->blk, request.from + exp->dev_offset, + request.len, flags); + if (ret < 0) { + LOG("writing to file failed"); + reply.error = -ret; + goto error_reply; + } + + if (nbd_co_send_reply(req, &reply, 0) < 0) { + goto out; + } + break; + case NBD_CMD_DISC: /* unreachable, thanks to special case in nbd_co_receive_request() */ abort();