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From e0d145328022f5c0897a6d157400a9d071acc767 Mon Sep 17 00:00:00 2001
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From: John Snow <jsnow@redhat.com>
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Date: Wed, 18 Jul 2018 22:55:06 +0200
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Subject: [PATCH 248/268] nbd/server: introduce NBD_CMD_CACHE
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RH-Author: John Snow <jsnow@redhat.com>
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Message-id: <20180718225511.14878-31-jsnow@redhat.com>
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Patchwork-id: 81419
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O-Subject: [RHEL-7.6 qemu-kvm-rhev PATCH 30/35] nbd/server: introduce NBD_CMD_CACHE
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Bugzilla: 1207657
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RH-Acked-by: Eric Blake <eblake@redhat.com>
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RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
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RH-Acked-by: Fam Zheng <famz@redhat.com>
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From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Handle nbd CACHE command. Just do read, without sending read data back.
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Cache mechanism should be done by exported node driver chain.
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Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
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Message-Id: <20180413143156.11409-1-vsementsov@virtuozzo.com>
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Reviewed-by: Eric Blake <eblake@redhat.com>
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[eblake: fix two missing case labels in switch statements]
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Signed-off-by: Eric Blake <eblake@redhat.com>
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(cherry picked from commit bc37b06a5cde24fb24c2a2cc44dd86756034ba9d)
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Signed-off-by: John Snow <jsnow@redhat.com>
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Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
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---
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 include/block/nbd.h |  3 ++-
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 nbd/common.c        |  2 ++
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 nbd/server.c        | 11 +++++++----
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 3 files changed, 11 insertions(+), 5 deletions(-)
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diff --git a/include/block/nbd.h b/include/block/nbd.h
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index 8bb9606..daaeae6 100644
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--- a/include/block/nbd.h
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+++ b/include/block/nbd.h
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@@ -135,6 +135,7 @@ typedef struct NBDExtent {
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 #define NBD_FLAG_SEND_TRIM         (1 << 5) /* Send TRIM (discard) */
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 #define NBD_FLAG_SEND_WRITE_ZEROES (1 << 6) /* Send WRITE_ZEROES */
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 #define NBD_FLAG_SEND_DF           (1 << 7) /* Send DF (Do not Fragment) */
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+#define NBD_FLAG_SEND_CACHE        (1 << 8) /* Send CACHE (prefetch) */
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 /* New-style handshake (global) flags, sent from server to client, and
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    control what will happen during handshake phase. */
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@@ -195,7 +196,7 @@ enum {
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     NBD_CMD_DISC = 2,
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     NBD_CMD_FLUSH = 3,
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     NBD_CMD_TRIM = 4,
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-    /* 5 reserved for failed experiment NBD_CMD_CACHE */
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+    NBD_CMD_CACHE = 5,
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     NBD_CMD_WRITE_ZEROES = 6,
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     NBD_CMD_BLOCK_STATUS = 7,
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 };
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diff --git a/nbd/common.c b/nbd/common.c
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index 8c95c1d..41f5ed8 100644
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--- a/nbd/common.c
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+++ b/nbd/common.c
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@@ -148,6 +148,8 @@ const char *nbd_cmd_lookup(uint16_t cmd)
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         return "flush";
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     case NBD_CMD_TRIM:
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         return "trim";
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+    case NBD_CMD_CACHE:
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+        return "cache";
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     case NBD_CMD_WRITE_ZEROES:
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         return "write zeroes";
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     case NBD_CMD_BLOCK_STATUS:
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diff --git a/nbd/server.c b/nbd/server.c
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index 2c2d62c..2746046 100644
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--- a/nbd/server.c
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+++ b/nbd/server.c
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@@ -1252,7 +1252,7 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
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     int ret;
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     const uint16_t myflags = (NBD_FLAG_HAS_FLAGS | NBD_FLAG_SEND_TRIM |
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                               NBD_FLAG_SEND_FLUSH | NBD_FLAG_SEND_FUA |
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-                              NBD_FLAG_SEND_WRITE_ZEROES);
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+                              NBD_FLAG_SEND_WRITE_ZEROES | NBD_FLAG_SEND_CACHE);
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     bool oldStyle;
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     /* Old style negotiation header, no room for options
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@@ -2034,7 +2034,9 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request,
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         return -EIO;
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     }
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-    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE) {
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+    if (request->type == NBD_CMD_READ || request->type == NBD_CMD_WRITE ||
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+        request->type == NBD_CMD_CACHE)
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+    {
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         if (request->len > NBD_MAX_BUFFER_SIZE) {
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             error_setg(errp, "len (%" PRIu32" ) is larger than max len (%u)",
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                        request->len, NBD_MAX_BUFFER_SIZE);
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@@ -2119,7 +2121,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
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     int ret;
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     NBDExport *exp = client->exp;
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-    assert(request->type == NBD_CMD_READ);
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+    assert(request->type == NBD_CMD_READ || request->type == NBD_CMD_CACHE);
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     /* XXX: NBD Protocol only documents use of FUA with WRITE */
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     if (request->flags & NBD_CMD_FLAG_FUA) {
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@@ -2138,7 +2140,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request,
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     ret = blk_pread(exp->blk, request->from + exp->dev_offset, data,
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                     request->len);
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-    if (ret < 0) {
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+    if (ret < 0 || request->type == NBD_CMD_CACHE) {
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         return nbd_send_generic_reply(client, request->handle, ret,
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                                       "reading from file failed", errp);
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     }
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@@ -2171,6 +2173,7 @@ static coroutine_fn int nbd_handle_request(NBDClient *client,
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     switch (request->type) {
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     case NBD_CMD_READ:
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+    case NBD_CMD_CACHE:
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         return nbd_do_cmd_read(client, request, data, errp);
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     case NBD_CMD_WRITE:
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-- 
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1.8.3.1
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