Re: [Qemu-devel] [PATCH] nbd/server: introduce NBD_CMD_CACHE

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

13.04.2018 17:31, Vladimir Sementsov-Ogievskiy wrote:
> Handle nbd CACHE command. Just do read, without sending read data back.
> Cache mechanism should be done by exported node driver chain.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
>   include/block/nbd.h |  3 ++-
>   nbd/server.c        | 10 ++++++----
>   2 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/include/block/nbd.h b/include/block/nbd.h
> index fcdcd54502..b4793d0a29 100644
> --- a/include/block/nbd.h
> +++ b/include/block/nbd.h
> @@ -135,6 +135,7 @@ typedef struct NBDExtent {
>   #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_DF           (1 << 7) /* Send DF (Do not Fragment) */
> +#define NBD_FLAG_SEND_CACHE        (1 << 8) /* Send CACHE (prefetch) */
>   
>   /* New-style handshake (global) flags, sent from server to client, and
>      control what will happen during handshake phase. */
> @@ -195,7 +196,7 @@ enum {
>       NBD_CMD_DISC = 2,
>       NBD_CMD_FLUSH = 3,
>       NBD_CMD_TRIM = 4,
> -    /* 5 reserved for failed experiment NBD_CMD_CACHE */
> +    NBD_CMD_CACHE = 5,
>       NBD_CMD_WRITE_ZEROES = 6,
>       NBD_CMD_BLOCK_STATUS = 7,
>   };
> diff --git a/nbd/server.c b/nbd/server.c
> index 9e1f227178..30d7d3f444 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -1134,7 +1134,7 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
>       int ret;
>       const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
>                                 NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA |
> -                              NBD_FLAG_SEND_WRITE_ZEROES);
> +                              NBD_FLAG_SEND_WRITE_ZEROES | NBD_FLAG_SEND_CACHE);
>       bool oldStyle;
>   
>       /* Old style negotiation header, no room for options
> @@ -1826,7 +1826,9 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request,
>           return -EIO;
>       }
>   
> -    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE) {
> +    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE ||
> +        request->type == NBD_CMD_CACHE)
> +    {
>           if (request->len > NBD_MAX_BUFFER_SIZE) {
>               error_setg(errp, "len (%" PRIu32" ) is larger than max len (%u)",
>                          request->len, NBD_MAX_BUFFER_SIZE);
> @@ -1911,7 +1913,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
>       int ret;
>       NBDExport *exp = client->exp;
>   
> -    assert(request->type == NBD_CMD_READ);
> +    assert(request->type == NBD_CMD_READ || request->type == NBD_CMD_CACHE);
>   
>       /* XXX: NBD Protocol only documents use of FUA with WRITE */
>       if (request->flags & NBD_CMD_FLAG_FUA) {
> @@ -1930,7 +1932,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
>   
>       ret = blk_pread(exp->blk, request->from + exp->dev_offset, data,
>                       request->len);
> -    if (ret < 0) {
> +    if (ret < 0 || request->type == NBD_CMD_CACHE) {
>           return nbd_send_generic_reply(client, request->handle, ret,
>                                         "reading from file failed", errp);
>       }

ohh, forget the main thing:

diff --git a/nbd/server.c b/nbd/server.c
index 30d7d3f444..d6a161c8d5 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1965,6 +1965,7 @@ static coroutine_fn int 
nbd_handle_request(NBDClient *client,

      switch (request->type) {
      case NBD_CMD_READ:
+    case NBD_CMD_CACHE:
          return nbd_do_cmd_read(client, request, data, errp);

      case NBD_CMD_WRITE:



-- 
Best regards,
Vladimir