nbd: invert client logic for negotiating protocol version

The nbd_receive_negotiate() method takes different code
paths based on whether 'name == NULL', and then checks
the expected protocol version in each branch.

This patch inverts the logic, so that it takes different
code paths based on what protocol version it receives and
then checks if name is NULL or not as needed.

This facilitates later code which allows the client to
be capable of using the new style protocol regardless
of whether an export name is listed or not.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Message-Id: <1455129674-17255-8-git-send-email-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 29 insertions, 31 deletions

diff --git a/nbd/client.c b/nbd/client.c
index f6dd0a3..5064788 100644
--- a/nbd/client.c
+++ b/nbd/client.c
@@ -116,20 +116,11 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags,
     magic = be64_to_cpu(magic);
     TRACE("Magic is 0x%" PRIx64, magic);
 
-    if (name) {
+    if (magic == NBD_OPTS_MAGIC) {
         uint32_t reserved = 0;
         uint32_t opt;
         uint32_t namesize;
 
-        TRACE("Checking magic (opts_magic)");
-        if (magic != NBD_OPTS_MAGIC) {
-            if (magic == NBD_CLIENT_MAGIC) {
-                error_setg(errp, "Server does not support export names");
-            } else {
-                error_setg(errp, "Bad magic received");
-            }
-            goto fail;
-        }
         if (read_sync(ioc, &tmp, sizeof(tmp)) != sizeof(tmp)) {
             error_setg(errp, "Failed to read server flags");
             goto fail;
@@ -142,6 +133,10 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags,
             goto fail;
         }
         /* write the export name */
+        if (!name) {
+            error_setg(errp, "Server requires an export name");
+            goto fail;
+        }
         magic = cpu_to_be64(magic);
         if (write_sync(ioc, &magic, sizeof(magic)) != sizeof(magic)) {
             error_setg(errp, "Failed to send export name magic");
@@ -162,39 +157,42 @@ int nbd_receive_negotiate(QIOChannel *ioc, const char *name, uint32_t *flags,
             error_setg(errp, "Failed to send export name");
             goto fail;
         }
-    } else {
-        TRACE("Checking magic (cli_magic)");
 
-        if (magic != NBD_CLIENT_MAGIC) {
-            if (magic == NBD_OPTS_MAGIC) {
-                error_setg(errp, "Server requires an export name");
-            } else {
-                error_setg(errp, "Bad magic received");
-            }
+        if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) {
+            error_setg(errp, "Failed to read export length");
             goto fail;
         }
-    }
+        *size = be64_to_cpu(s);
+        TRACE("Size is %" PRIu64, *size);
 
-    if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) {
-        error_setg(errp, "Failed to read export length");
-        goto fail;
-    }
-    *size = be64_to_cpu(s);
-    TRACE("Size is %" PRIu64, *size);
+        if (read_sync(ioc, &tmp, sizeof(tmp)) != sizeof(tmp)) {
+            error_setg(errp, "Failed to read export flags");
+            goto fail;
+        }
+        *flags |= be16_to_cpu(tmp);
+    } else if (magic == NBD_CLIENT_MAGIC) {
+        if (name) {
+            error_setg(errp, "Server does not support export names");
+            goto fail;
+        }
+
+        if (read_sync(ioc, &s, sizeof(s)) != sizeof(s)) {
+            error_setg(errp, "Failed to read export length");
+            goto fail;
+        }
+        *size = be64_to_cpu(s);
+        TRACE("Size is %" PRIu64, *size);
 
-    if (!name) {
         if (read_sync(ioc, flags, sizeof(*flags)) != sizeof(*flags)) {
             error_setg(errp, "Failed to read export flags");
             goto fail;
         }
         *flags = be32_to_cpup(flags);
     } else {
-        if (read_sync(ioc, &tmp, sizeof(tmp)) != sizeof(tmp)) {
-            error_setg(errp, "Failed to read export flags");
-            goto fail;
-        }
-        *flags |= be16_to_cpu(tmp);
+        error_setg(errp, "Bad magic received");
+        goto fail;
     }
+
     if (read_sync(ioc, &buf, 124) != 124) {
         error_setg(errp, "Failed to read reserved block");
         goto fail;