RFC because there is still discussion on the NBD list about
adding an NBD_OPT_ to let the client suggest server defaults
related to scanning for zeroes during NBD_CMD_WRITE, which may
tweak this patch.
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 a hole.
Signed-off-by: Eric Blake <ebl...@redhat.com>
---
include/block/nbd.h | 5 ++++-
nbd/server.c | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++---
2 files changed, 64 insertions(+), 4 deletions(-)
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 4c57754..a1d955c 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -70,6 +70,7 @@ typedef struct nbd_reply nbd_reply;
#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 */
#define NBD_FLAG_SEND_CLOSE (1 << 8) /* Send CLOSE */
/* New-style handshake (global) flags, sent from server to client, and
@@ -92,7 +93,8 @@ typedef struct nbd_reply nbd_reply;
#define NBD_REP_ERR_UNKNOWN ((UINT32_C(1) << 31) | 6) /* Export unknown */
/* 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 {
@@ -101,6 +103,7 @@ enum {
NBD_CMD_DISC = 2,
NBD_CMD_FLUSH = 3,
NBD_CMD_TRIM = 4,
+ NBD_CMD_WRITE_ZEROES = 5,
NBD_CMD_CLOSE = 7,
};
diff --git a/nbd/server.c b/nbd/server.c
index 2a6eaf2..09af915 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -625,7 +625,8 @@ static coroutine_fn int nbd_negotiate(NBDClientNewData
*data)
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_CLOSE);
+ NBD_FLAG_SEND_CLOSE |
+ NBD_FLAG_SEND_WRITE_ZEROES);
bool oldStyle;
size_t len;
@@ -1088,7 +1089,7 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
struct nbd_request *reque
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);
return -EINVAL;
}
@@ -1102,7 +1103,13 @@ static ssize_t nbd_co_receive_request(NBDRequest *req,
struct nbd_request *reque
TRACE("Decoding type");
command = request->type;
- if (command == NBD_CMD_READ || command == NBD_CMD_WRITE) {
+ if (request->flags & NBD_CMD_FLAG_NO_HOLE &&
+ !(command == NBD_CMD_WRITE || command == NBD_CMD_WRITE_ZEROES)) {
+ LOG("NO_HOLE flag valid only with write operation");
+ return -EINVAL;
+ }
+ if (command == NBD_CMD_READ || command == NBD_CMD_WRITE ||
+ command == NBD_CMD_WRITE_ZEROES) {
if (request->len > NBD_MAX_BUFFER_SIZE) {
LOG("len (%" PRIu32" ) is larger than max len (%u)",
request->len, NBD_MAX_BUFFER_SIZE);
@@ -1143,6 +1150,7 @@ static void nbd_trip(void *opaque)
struct nbd_reply reply;
ssize_t ret;
uint32_t command;
+ int flags;
TRACE("Reading request.");
if (client->closing) {
@@ -1221,6 +1229,9 @@ static void nbd_trip(void *opaque)
TRACE("Writing to device");
+ /* FIXME: if the client passes NBD_CMD_FLAG_NO_HOLE, can we
+ * make that override a server that is set to look for
+ * holes? */
ret = blk_write(exp->blk,
(request.from + exp->dev_offset) / BDRV_SECTOR_SIZE,
req->data, request.len / BDRV_SECTOR_SIZE);
@@ -1243,6 +1254,52 @@ static void nbd_trip(void *opaque)
goto out;
}
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)) {
+ /* FIXME: should this depend on whether the server is set to
+ look for holes? */
+ flags |= BDRV_REQ_MAY_UNMAP;
+ }
+ ret = blk_write_zeroes(exp->blk,
+ ((request.from + exp->dev_offset) /
+ BDRV_SECTOR_SIZE),
+ request.len / BDRV_SECTOR_SIZE,
+ flags);
+ if (ret < 0) {
+ LOG("writing to file failed");
+ reply.error = -ret;
+ goto error_reply;
+ }
+
+ /* FIXME: do we need FUA flush here, if we also passed it to
+ * blk_write_zeroes? */
+ if (request.flags & NBD_CMD_FLAG_FUA) {
+ ret = blk_co_flush(exp->blk);
+ if (ret < 0) {
+ LOG("flush failed");
+ reply.error = -ret;
+ goto error_reply;
+ }
+ }
+
+ if (nbd_co_send_reply(req, &reply, 0) < 0) {
+ goto out;
+ }
+ break;
case NBD_CMD_DISC:
TRACE("Request type is DISCONNECT");
goto out;
--
2.5.5
