[PATCH ethtool v2] netlink: Print and return an error when features weren't changed

[Maxim Mikityanskiy]

The legacy ethtool prints an error message and returns 1 if no features
were changed as requested. Port this behavior to ethtool-netlink.
req_mask is compared to wanted_mask to detect if any feature was
changed. If these masks are equal, it means that the kernel hasn't
changed anything, and all bits got to wanted.

Signed-off-by: Maxim Mikityanskiy <maxi...@mellanox.com>
---
 netlink/features.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/netlink/features.c b/netlink/features.c
index 133529d..7622594 100644
--- a/netlink/features.c
+++ b/netlink/features.c
@@ -243,6 +243,7 @@ int nl_gfeatures(struct cmd_context *ctx)
 /* FEATURES_SET */
 
 struct sfeatures_context {
+       bool                    nothing_changed;
        uint32_t                req_mask[0];
 };
 
@@ -411,10 +412,14 @@ static void show_feature_changes(struct nl_context *nlctx,
        if (!wanted_val || !wanted_mask || !active_val || !active_mask)
                goto err;
 
+       sfctx->nothing_changed = true;
        diff = false;
-       for (i = 0; i < words; i++)
+       for (i = 0; i < words; i++) {
+               if (wanted_mask[i] != sfctx->req_mask[i])
+                       sfctx->nothing_changed = false;
                if (wanted_mask[i] || (active_mask[i] & ~sfctx->req_mask[i]))
                        diff = true;
+       }
        if (!diff)
                return;
 
@@ -520,6 +525,10 @@ int nl_sfeatures(struct cmd_context *ctx)
        if (ret < 0)
                return 92;
        ret = nlsock_process_reply(nlsk, sfeatures_reply_cb, nlctx);
+       if (sfctx->nothing_changed) {
+               fprintf(stderr, "Could not change any device features\n");
+               return nlctx->exit_code ?: 1;
+       }
        if (ret == 0)
                return 0;
        return nlctx->exit_code ?: 92;
-- 
2.20.1