diff options
| author | Eric Blake <eblake@redhat.com> | 2016-10-14 13:33:17 -0500 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2016-11-02 09:28:56 +0100 |
| commit | 1f4d6d18edfeaea64ae74bf5254b8d0e923dc73f (patch) | |
| tree | a8cd9fbf92b2639ac0749a72a5702d0ecdb90d11 /include/block | |
| parent | b6f5d3b573fe43da1f9fa07b7454e4492f409411 (diff) | |
| download | qemu-1f4d6d18edfeaea64ae74bf5254b8d0e923dc73f.zip | |
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 <eblake@redhat.com>
Message-Id: <1476469998-28592-16-git-send-email-eblake@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'include/block')
| -rw-r--r-- | include/block/nbd.h | 8 |
1 files changed, 6 insertions, 2 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 |