From 4f4e329628b6d530cf74d792f0297f651e18e6ba Mon Sep 17 00:00:00 2001
From: John Snow <jsnow@redhat.com>
Date: Wed, 27 Mar 2019 17:22:24 +0100
Subject: [PATCH 085/163] nbd/client: Drop pointless buf variable

RH-Author: John Snow <jsnow@redhat.com>
Message-id: <20190327172308.31077-12-jsnow@redhat.com>
Patchwork-id: 85182
O-Subject: [RHEL-7.7 qemu-kvm-rhev PATCH 11/55] nbd/client: Drop pointless buf variable
Bugzilla: 1691009
RH-Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
RH-Acked-by: Max Reitz <mreitz@redhat.com>
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>

From: Eric Blake <eblake@redhat.com>

There's no need to read into a temporary buffer (oversized
since commit 7d3123e1) followed by a byteswap into a uint64_t
to check for a magic number via memcmp(), when the code
immediately below demonstrates reading into the uint64_t then
byteswapping in place and checking for a magic number via
integer math.  What's more, having a different error message
when the server's first reply byte is 0 is unusual - it's no
different from any other wrong magic number, and we already
detected short reads. That whole strlen() issue has been
present and useless since commit 1d45f8b5 in 2010; perhaps it
was leftover debugging (since the correct magic number happens
to be ASCII)?  Make the error messages more consistent and
detailed while touching things.

Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Richard W.M. Jones <rjones@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20181215135324.152629-9-eblake@redhat.com>
(cherry picked from commit ef2e35fcc8e14bcc9366df5fdf53f65d679f8dca)
Signed-off-by: John Snow <jsnow@redhat.com>
Signed-off-by: Miroslav Rezanina <mrezanin@redhat.com>
---
 nbd/client.c       | 22 +++++++---------------
 nbd/nbd-internal.h |  3 ++-
 2 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/nbd/client.c b/nbd/client.c
index 5a03a84..f625c20 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -733,7 +733,6 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name,
                           QIOChannel **outioc, NBDExportInfo *info,
                           Error **errp)
 {
-    char buf[256];
     uint64_t magic;
     int rc;
     bool zeroes = true;
@@ -754,27 +753,20 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name,
         goto fail;
     }
 
-    if (nbd_read(ioc, buf, 8, errp) < 0) {
-        error_prepend(errp, "Failed to read data: ");
-        goto fail;
-    }
-
-    buf[8] = '\0';
-    if (strlen(buf) == 0) {
-        error_setg(errp, "Server connection closed unexpectedly");
+    if (nbd_read(ioc, &magic, sizeof(magic), errp) < 0) {
+        error_prepend(errp, "Failed to read initial magic: ");
         goto fail;
     }
-
-    magic = ldq_be_p(buf);
+    magic = be64_to_cpu(magic);
     trace_nbd_receive_negotiate_magic(magic);
 
-    if (memcmp(buf, "NBDMAGIC", 8) != 0) {
-        error_setg(errp, "Invalid magic received");
+    if (magic != NBD_INIT_MAGIC) {
+        error_setg(errp, "Bad initial magic received: 0x%" PRIx64, magic);
         goto fail;
     }
 
     if (nbd_read(ioc, &magic, sizeof(magic), errp) < 0) {
-        error_prepend(errp, "Failed to read magic: ");
+        error_prepend(errp, "Failed to read server magic: ");
         goto fail;
     }
     magic = be64_to_cpu(magic);
@@ -913,7 +905,7 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name,
         }
         info->flags = oldflags;
     } else {
-        error_setg(errp, "Bad magic received");
+        error_setg(errp, "Bad server magic received: 0x%" PRIx64, magic);
         goto fail;
     }
 
diff --git a/nbd/nbd-internal.h b/nbd/nbd-internal.h
index f38be9e..82aa221 100644
--- a/nbd/nbd-internal.h
+++ b/nbd/nbd-internal.h
@@ -46,8 +46,9 @@
 /* Size of oldstyle negotiation */
 #define NBD_OLDSTYLE_NEGOTIATE_SIZE (8 + 8 + 8 + 4 + 124)
 
+#define NBD_INIT_MAGIC              0x4e42444d41474943LL /* ASCII "NBDMAGIC" */
 #define NBD_REQUEST_MAGIC           0x25609513
-#define NBD_OPTS_MAGIC              0x49484156454F5054LL
+#define NBD_OPTS_MAGIC              0x49484156454F5054LL /* ASCII "IHAVEOPT" */
 #define NBD_CLIENT_MAGIC            0x0000420281861253LL
 #define NBD_REP_MAGIC               0x0003e889045565a9LL
 
-- 
1.8.3.1