This will be useful for the next patch.

Based on a patch by Vladimir Sementsov-Ogievskiy

Signed-off-by: Eric Blake <eblake@redhat.com>
---
 nbd/server.c | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index 9943a911c3..d23bc2918a 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -186,18 +186,15 @@ static int nbd_negotiate_send_rep(NBDClient *client, uint32_t type,

 /* Send an error reply.
  * Return -errno on error, 0 on success. */
-static int GCC_FMT_ATTR(4, 5)
-nbd_negotiate_send_rep_err(NBDClient *client, uint32_t type,
-                           Error **errp, const char *fmt, ...)
+static int GCC_FMT_ATTR(4, 0)
+nbd_negotiate_send_rep_verr(NBDClient *client, uint32_t type,
+                            Error **errp, const char *fmt, va_list va)
 {
-    va_list va;
     char *msg;
     int ret;
     size_t len;

-    va_start(va, fmt);
     msg = g_strdup_vprintf(fmt, va);
-    va_end(va);
     len = strlen(msg);
     assert(len < 4096);
     trace_nbd_negotiate_send_rep_err(msg);
@@ -217,6 +214,21 @@ out:
     return ret;
 }

+/* Send an error reply.
+ * Return -errno on error, 0 on success. */
+static int GCC_FMT_ATTR(4, 5)
+nbd_negotiate_send_rep_err(NBDClient *client, uint32_t type,
+                           Error **errp, const char *fmt, ...)
+{
+    va_list va;
+    int ret;
+
+    va_start(va, fmt);
+    ret = nbd_negotiate_send_rep_verr(client, type, errp, fmt, va);
+    va_end(va);
+    return ret;
+}
+
 /* 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,
-- 
2.14.3

11.01.2018 02:08, Eric Blake wrote:
> This will be useful for the next patch.
>
> Based on a patch by Vladimir Sementsov-Ogievskiy
>
> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>   nbd/server.c | 24 ++++++++++++++++++------
>   1 file changed, 18 insertions(+), 6 deletions(-)
>
> diff --git a/nbd/server.c b/nbd/server.c
> index 9943a911c3..d23bc2918a 100644
> --- a/nbd/server.c
> +++ b/nbd/server.c
> @@ -186,18 +186,15 @@ static int nbd_negotiate_send_rep(NBDClient *client, uint32_t type,
>
>   /* Send an error reply.
>    * Return -errno on error, 0 on success. */
> -static int GCC_FMT_ATTR(4, 5)
> -nbd_negotiate_send_rep_err(NBDClient *client, uint32_t type,
> -                           Error **errp, const char *fmt, ...)
> +static int GCC_FMT_ATTR(4, 0)
> +nbd_negotiate_send_rep_verr(NBDClient *client, uint32_t type,
> +                            Error **errp, const char *fmt, va_list va)

Hmm you placed fmt and va after errp. Previously we discussed one 
exclusion from "errp should be last" -
"...", variable number of arguments. So, it is new exclusion (or I 
missed something?).. Looks good for me,
anyway, as it corresponds to "errp, fmt, ..." notation.

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

>   {
> -    va_list va;
>       char *msg;
>       int ret;
>       size_t len;
>
> -    va_start(va, fmt);
>       msg = g_strdup_vprintf(fmt, va);
> -    va_end(va);
>       len = strlen(msg);
>       assert(len < 4096);
>       trace_nbd_negotiate_send_rep_err(msg);
> @@ -217,6 +214,21 @@ out:
>       return ret;
>   }
>
> +/* Send an error reply.
> + * Return -errno on error, 0 on success. */
> +static int GCC_FMT_ATTR(4, 5)
> +nbd_negotiate_send_rep_err(NBDClient *client, uint32_t type,
> +                           Error **errp, const char *fmt, ...)
> +{
> +    va_list va;
> +    int ret;
> +
> +    va_start(va, fmt);
> +    ret = nbd_negotiate_send_rep_verr(client, type, errp, fmt, va);
> +    va_end(va);
> +    return ret;
> +}
> +
>   /* 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,


-- 
Best regards,
Vladimir

On 01/11/2018 12:05 PM, Vladimir Sementsov-Ogievskiy wrote:
> 11.01.2018 02:08, Eric Blake wrote:
>> This will be useful for the next patch.
>>
>> Based on a patch by Vladimir Sementsov-Ogievskiy
>>
>> Signed-off-by: Eric Blake <eblake@redhat.com>
>> ---
>>   nbd/server.c | 24 ++++++++++++++++++------
>>   1 file changed, 18 insertions(+), 6 deletions(-)
>>

>> -static int GCC_FMT_ATTR(4, 5)
>> -nbd_negotiate_send_rep_err(NBDClient *client, uint32_t type,
>> -                           Error **errp, const char *fmt, ...)
>> +static int GCC_FMT_ATTR(4, 0)
>> +nbd_negotiate_send_rep_verr(NBDClient *client, uint32_t type,
>> +                            Error **errp, const char *fmt, va_list va)
> 
> Hmm you placed fmt and va after errp. Previously we discussed one
> exclusion from "errp should be last" -
> "...", variable number of arguments. So, it is new exclusion (or I
> missed something?).. Looks good for me,
> anyway, as it corresponds to "errp, fmt, ..." notation.

Indeed, it is precisely because I value consistency between 'fmt, ...'
and 'fmt, va_list' higher than 'errp last' that I rearranged things from
your patch into the form I used.  Or worded another way, even though
va_list is only one argument in name, I treat it the same as the
variable number of arguments that warrants the exception to the errp
last rule of thumb.

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

Thanks; I think this series is now ready for staging on my NBD queue;
although my next pull request won't be until after the weekend.

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