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


From: Vladimir Sementsov-Ogievskiy
Subject: Re: [Qemu-devel] [PATCH] nbd/server: introduce NBD_CMD_CACHE
Date: Thu, 17 May 2018 12:52:20 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0

Finally, what about this?

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 <address@hidden>
---
  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);
      }


--
Best regards,
Vladimir




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