Add helper to read name in format:

  uint32 len       (<= NBD_MAX_NAME_SIZE)
  len bytes string (not 0-terminated)

The helper would be reused in following patch.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

v2: splitted and changed a lot helper from larger patch of v1

 nbd/server.c | 55 ++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 42 insertions(+), 13 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index d163964cf9..085e14afbf 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -273,6 +273,47 @@ static int nbd_opt_read(NBDClient *client, void *buffer, size_t size,
     return qio_channel_read_all(client->ioc, buffer, size, errp) < 0 ? -EIO : 1;
 }
 
+/* nbd_opt_read_name
+ *
+ * Read string in format:
+ *   uint32_t len     (<= NBD_MAX_NAME_SIZE)
+ *   len bytes string (not 0-terminated)
+ *
+ * @name should be enough to store NBD_MAX_NAME_SIZE+1.
+ * if @length is non-zero, it would be set to read string length.
+ *
+ * Return -errno on I/O error, 0 if option was completely handled by
+ * sending a reply about inconsistent lengths, or 1 on success. */
+static int nbd_opt_read_name(NBDClient *client, char *name, uint32_t *length,
+                             Error **errp)
+{
+    int ret;
+    uint32_t len;
+
+    ret = nbd_opt_read(client, &len, sizeof(len), errp);
+    if (ret <= 0) {
+        return ret;
+    }
+    cpu_to_be32s(&len);
+
+    if (len > NBD_MAX_NAME_SIZE) {
+        return nbd_opt_invalid(client, errp,
+                               "Invalid name length: %" PRIu32, len);
+    }
+
+    ret = nbd_opt_read(client, name, len, errp);
+    if (ret <= 0) {
+        return ret;
+    }
+    name[len] = '\0';
+
+    if (length) {
+        *length = len;
+    }
+
+    return 1;
+}
+
 /* Send a single NBD_REP_SERVER reply to NBD_OPT_LIST, including payload.
  * Return -errno on error, 0 on success. */
 static int nbd_negotiate_send_rep_list(NBDClient *client, NBDExport *exp,
@@ -455,19 +496,7 @@ static int nbd_negotiate_handle_info(NBDClient *client, uint16_t myflags,
         2 bytes: N, number of requests (can be 0)
         N * 2 bytes: N requests
     */
-    rc = nbd_opt_read(client, &namelen, sizeof(namelen), errp);
-    if (rc <= 0) {
-        return rc;
-    }
-    be32_to_cpus(&namelen);
-    if (namelen >= sizeof(name)) {
-        return nbd_opt_invalid(client, errp, "name too long for qemu");
-    }
-    rc = nbd_opt_read(client, name, namelen, errp);
-    if (rc <= 0) {
-        return rc;
-    }
-    name[namelen] = '\0';
+    rc = nbd_opt_read_name(client, name, &namelen, errp);
     trace_nbd_negotiate_handle_export_name_request(name);
 
     rc = nbd_opt_read(client, &requests, sizeof(requests), errp);
-- 
2.11.1

On 03/12/2018 10:21 AM, Vladimir Sementsov-Ogievskiy wrote:
> Add helper to read name in format:
> 
>    uint32 len       (<= NBD_MAX_NAME_SIZE)
>    len bytes string (not 0-terminated)
> 
> The helper would be reused in following patch.

s/would/will/

> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> 
> v2: splitted and changed a lot helper from larger patch of v1

'split' (one of those weird English words whose past and present tense 
are spelled the same way; there is no 'splitted')

> 
>   nbd/server.c | 55 ++++++++++++++++++++++++++++++++++++++++++-------------
>   1 file changed, 42 insertions(+), 13 deletions(-)
> 
> diff --git a/nbd/server.c b/nbd/server.c
> index d163964cf9..085e14afbf 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -273,6 +273,47 @@ static int nbd_opt_read(NBDClient *client, void *buffer, size_t size,
>       return qio_channel_read_all(client->ioc, buffer, size, errp) < 0 ? -EIO : 1;
>   }
>   
> +/* nbd_opt_read_name
> + *
> + * Read string in format:

Read a string in the format:

> + *   uint32_t len     (<= NBD_MAX_NAME_SIZE)
> + *   len bytes string (not 0-terminated)
> + *
> + * @name should be enough to store NBD_MAX_NAME_SIZE+1.
> + * if @length is non-zero, it would be set to read string length.

s/if/If/
s/would/will/
s/read/the actual/

> + *
> + * Return -errno on I/O error, 0 if option was completely handled by
> + * sending a reply about inconsistent lengths, or 1 on success. */
> +static int nbd_opt_read_name(NBDClient *client, char *name, uint32_t *length,
> +                             Error **errp)
> +{

Function looks good.

> @@ -455,19 +496,7 @@ static int nbd_negotiate_handle_info(NBDClient *client, uint16_t myflags,
>           2 bytes: N, number of requests (can be 0)
>           N * 2 bytes: N requests
>       */
> -    rc = nbd_opt_read(client, &namelen, sizeof(namelen), errp);
> -    if (rc <= 0) {
> -        return rc;
> -    }
> -    be32_to_cpus(&namelen);
> -    if (namelen >= sizeof(name)) {
> -        return nbd_opt_invalid(client, errp, "name too long for qemu");
> -    }
> -    rc = nbd_opt_read(client, name, namelen, errp);
> -    if (rc <= 0) {
> -        return rc;
> -    }
> -    name[namelen] = '\0';
> +    rc = nbd_opt_read_name(client, name, &namelen, errp);
>       trace_nbd_negotiate_handle_export_name_request(name);
>   
>       rc = nbd_opt_read(client, &requests, sizeof(requests), errp);

Oh, so close. You overwrote rc instead of checking for errors.  I'm 
squashing in the obvious fix, plus the grammar changes, then adding:
Reviewed-by: Eric Blake <eblake@redhat.com>

diff --git i/nbd/server.c w/nbd/server.c
index 850c6cd2dad..e28526600c4 100644
--- i/nbd/server.c
+++ w/nbd/server.c
@@ -497,6 +497,9 @@ static int nbd_negotiate_handle_info(NBDClient 
*client, uint16_t myflags,
          N * 2 bytes: N requests
      */
      rc = nbd_opt_read_name(client, name, &namelen, errp);
+    if (rc <= 0) {
+        return rc;
+    }
      trace_nbd_negotiate_handle_export_name_request(name);

      rc = nbd_opt_read(client, &requests, sizeof(requests), errp);


-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org