[PATCH net] ethtool: fix ethtool msg len calculation for pause stats

ETHTOOL_A_PAUSE_STAT_MAX is the MAX attribute id,
so we need to subtract non-stats and add one to
get a count (IOW -2+1 == -1).

Otherwise we'll see:

  ethnl cmd 21: calculated reply length 40, but consumed 52

Fixes: 9a27a33027f2 ("ethtool: add standard pause stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
---
 net/ethtool/pause.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ethtool/pause.c b/net/ethtool/pause.c
index 9009f412151e..c9171234130b 100644
--- a/net/ethtool/pause.c
+++ b/net/ethtool/pause.c

@@ -57,7 +57,7 @@ static int pause_reply_size(const struct ethnl_req_info *req_base,
 	if (req_base->flags & ETHTOOL_FLAG_STATS)
 		n += nla_total_size(0) +	/* _PAUSE_STATS */
 			nla_total_size_64bit(sizeof(u64)) *
-				(ETHTOOL_A_PAUSE_STAT_MAX - 2);
+				(ETHTOOL_A_PAUSE_STAT_MAX - 1);
 	return n;
 }
 

-- 
2.31.1

On Mon, 2021-11-01 at 21:21 -0700, Jakub Kicinski wrote:

ETHTOOL_A_PAUSE_STAT_MAX is the MAX attribute id,
so we need to subtract non-stats and add one to
get a count (IOW -2+1 == -1).

Otherwise we'll see:

  ethnl cmd 21: calculated reply length 40, but consumed 52

Fixes: 9a27a33027f2 ("ethtool: add standard pause stats")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Reviewed-by: Saeed Mahameed <saeedm@nvidia.com>

Maybe for net-next we can improve readability here.
Just by staring at these lines, you'd think that this should've been
(ETHTOOL_A_PAUSE_STAT_MAX + 1), or even better, just
(ETHTOOL_A_PAUSE_STAT_CNT) /* Count of only stats */

maybe we need to separate stats from non-stats, or define
ETHTOOL_A_PAUSE_STAT_CNT where it needs to be defined.

On Tue, 2 Nov 2021 16:08:52 +0000 Saeed Mahameed wrote:

quoted

diff --git a/net/ethtool/pause.c b/net/ethtool/pause.c
index 9009f412151e..c9171234130b 100644
--- a/net/ethtool/pause.c
+++ b/net/ethtool/pause.c

@@ -57,7 +57,7 @@ static int pause_reply_size(const struct

ethnl_req_info *req_base,
        if (req_base->flags & ETHTOOL_FLAG_STATS)
                n += nla_total_size(0) +        /* _PAUSE_STATS */
                        nla_total_size_64bit(sizeof(u64)) *
-                               (ETHTOOL_A_PAUSE_STAT_MAX - 2);
+                               (ETHTOOL_A_PAUSE_STAT_MAX - 1);  

Maybe for net-next we can improve readability here.
Just by staring at these lines, you'd think that this should've been
(ETHTOOL_A_PAUSE_STAT_MAX + 1), or even better, just
(ETHTOOL_A_PAUSE_STAT_CNT) /* Count of only stats */

maybe we need to separate stats from non-stats, or define
ETHTOOL_A_PAUSE_STAT_CNT where it needs to be defined.

Fair point, something like this?

+++ b/include/uapi/linux/ethtool_netlink.h

@@ -411,10 +411,14 @@ enum {
        ETHTOOL_A_PAUSE_STAT_TX_FRAMES,
        ETHTOOL_A_PAUSE_STAT_RX_FRAMES,
 
-       /* add new constants above here */
+       /* add new constants above here
+        * adjust ETHTOOL_PAUSE_STAT_CNT if adding non-stats!
+        */
        __ETHTOOL_A_PAUSE_STAT_CNT,
        ETHTOOL_A_PAUSE_STAT_MAX = (__ETHTOOL_A_PAUSE_STAT_CNT - 1)
 };
+#define ETHTOOL_PAUSE_STAT_CNT (__ETHTOOL_A_PAUSE_STAT_CNT -           \
+                                ETHTOOL_A_PAUSE_STAT_TX_FRAMES)
 
 /* EEE */
 

On Tue, 2021-11-02 at 11:10 -0700, Jakub Kicinski wrote:

On Tue, 2 Nov 2021 16:08:52 +0000 Saeed Mahameed wrote:

quoted

quoted

...

quoted

maybe we need to separate stats from non-stats, or define
ETHTOOL_A_PAUSE_STAT_CNT where it needs to be defined.

Fair point, something like this?

LGTM