Add the dump_one_dev callback to ethnl_request_ops, allowing commands
to provide custom per-device dump logic with sub-positioning. Extend
ethnl_dump_ctx with ifindex and pos_sub fields.

No functional change; no command uses dump_one_dev yet.

Signed-off-by: Björn Töpel <[email protected]>
---
 net/ethtool/netlink.c | 66 ++++++++++++++++++-------------------------
 net/ethtool/netlink.h | 31 ++++++++++++++++++++
 2 files changed, 58 insertions(+), 39 deletions(-)

diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index 5046023a30b1..8d161f0882d0 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -346,36 +346,6 @@ int ethnl_multicast(struct sk_buff *skb, struct net_device 
*dev)
 
 /* GET request helpers */
 
-/**
- * struct ethnl_dump_ctx - context structure for generic dumpit() callback
- * @ops:        request ops of currently processed message type
- * @req_info:   parsed request header of processed request
- * @reply_data: data needed to compose the reply
- * @pos_ifindex: saved iteration position - ifindex
- *
- * These parameters are kept in struct netlink_callback as context preserved
- * between iterations. They are initialized by ethnl_default_start() and used
- * in ethnl_default_dumpit() and ethnl_default_done().
- */
-struct ethnl_dump_ctx {
-       const struct ethnl_request_ops  *ops;
-       struct ethnl_req_info           *req_info;
-       struct ethnl_reply_data         *reply_data;
-       unsigned long                   pos_ifindex;
-};
-
-/**
- * struct ethnl_perphy_dump_ctx - context for dumpit() PHY-aware callbacks
- * @ethnl_ctx: generic ethnl context
- * @ifindex: For Filtered DUMP requests, the ifindex of the targeted netdev
- * @pos_phyindex: iterator position for multi-msg DUMP
- */
-struct ethnl_perphy_dump_ctx {
-       struct ethnl_dump_ctx   ethnl_ctx;
-       unsigned int            ifindex;
-       unsigned long           pos_phyindex;
-};
-
 static const struct ethnl_request_ops *
 ethnl_default_requests[__ETHTOOL_MSG_USER_CNT] = {
        [ETHTOOL_MSG_STRSET_GET]        = &ethnl_strset_request_ops,
@@ -618,6 +588,7 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
                                struct netlink_callback *cb)
 {
        struct ethnl_dump_ctx *ctx = ethnl_dump_context(cb);
+       const struct genl_info *info = genl_info_dump(cb);
        struct net *net = sock_net(skb->sk);
        netdevice_tracker dev_tracker;
        struct net_device *dev;
@@ -625,10 +596,20 @@ static int ethnl_default_dumpit(struct sk_buff *skb,
 
        rcu_read_lock();
        for_each_netdev_dump(net, dev, ctx->pos_ifindex) {
+               if (ctx->ifindex && ctx->ifindex != ctx->pos_ifindex)
+                       break;
+
                netdev_hold(dev, &dev_tracker, GFP_ATOMIC);
                rcu_read_unlock();
 
-               ret = ethnl_default_dump_one(skb, dev, ctx, genl_info_dump(cb));
+               if (ctx->ops->dump_one_dev) {
+                       ctx->req_info->dev = dev;
+                       ret = ctx->ops->dump_one_dev(skb, ctx, &ctx->pos_sub,
+                                                    info);
+                       ctx->req_info->dev = NULL;
+               } else {
+                       ret = ethnl_default_dump_one(skb, dev, ctx, info);
+               }
 
                rcu_read_lock();
                netdev_put(dev, &dev_tracker);
@@ -674,19 +655,26 @@ static int ethnl_default_start(struct netlink_callback 
*cb)
        ret = ethnl_default_parse(req_info, &info->info, ops, false);
        if (ret < 0)
                goto free_reply_data;
-       if (req_info->dev) {
-               /* We ignore device specification in dump requests but as the
-                * same parser as for non-dump (doit) requests is used, it
-                * would take reference to the device if it finds one
-                */
-               netdev_put(req_info->dev, &req_info->dev_tracker);
-               req_info->dev = NULL;
-       }
 
        ctx->ops = ops;
        ctx->req_info = req_info;
        ctx->reply_data = reply_data;
        ctx->pos_ifindex = 0;
+       ctx->ifindex = 0;
+       ctx->pos_sub = 0;
+
+       if (req_info->dev) {
+               if (ops->dump_one_dev) {
+                       /* Sub-iterator dumps keep track of the dev's ifindex
+                        * so the dumpit handler can grab/release the netdev
+                        * per iteration.
+                        */
+                       ctx->ifindex = req_info->dev->ifindex;
+                       ctx->pos_ifindex = ctx->ifindex;
+               }
+               netdev_put(req_info->dev, &req_info->dev_tracker);
+               req_info->dev = NULL;
+       }
 
        return 0;
 
diff --git a/net/ethtool/netlink.h b/net/ethtool/netlink.h
index aaf6f2468768..e01adc5db02f 100644
--- a/net/ethtool/netlink.h
+++ b/net/ethtool/netlink.h
@@ -10,6 +10,28 @@
 
 struct ethnl_req_info;
 
+/**
+ * struct ethnl_dump_ctx - context structure for generic dumpit() callback
+ * @ops:        request ops of currently processed message type
+ * @req_info:   parsed request header of processed request
+ * @reply_data: data needed to compose the reply
+ * @pos_ifindex: saved iteration position - ifindex
+ * @ifindex:    for filtered dump requests, the ifindex of the targeted netdev
+ * @pos_sub:    iterator position for per-device iteration
+ *
+ * These parameters are kept in struct netlink_callback as context preserved
+ * between iterations. They are initialized by ethnl_default_start() and used
+ * in ethnl_default_dumpit() and ethnl_default_done().
+ */
+struct ethnl_dump_ctx {
+       const struct ethnl_request_ops  *ops;
+       struct ethnl_req_info           *req_info;
+       struct ethnl_reply_data         *reply_data;
+       unsigned long                   pos_ifindex;
+       unsigned int                    ifindex;
+       unsigned long                   pos_sub;
+};
+
 u32 ethnl_bcast_seq_next(void);
 int ethnl_parse_header_dev_get(struct ethnl_req_info *req_info,
                               const struct nlattr *nest, struct net *net,
@@ -365,6 +387,10 @@ int ethnl_sock_priv_set(struct sk_buff *skb, struct 
net_device *dev, u32 portid,
  *     used e.g. to free any additional data structures outside the main
  *     structure which were allocated by ->prepare_data(). When processing
  *     dump requests, ->cleanup() is called for each message.
+ * @dump_one_dev:
+ *     Optional callback for dumping data for a single device. When set,
+ *     overrides the default dump behavior for GET requests, allowing
+ *     per-device iteration with sub-positioning via @pos_sub.
  * @set_validate:
  *     Check if set operation is supported for a given device, and perform
  *     extra input checks. Expected return values:
@@ -409,6 +435,11 @@ struct ethnl_request_ops {
                          const struct ethnl_reply_data *reply_data);
        void (*cleanup_data)(struct ethnl_reply_data *reply_data);
 
+       int (*dump_one_dev)(struct sk_buff *skb,
+                           struct ethnl_dump_ctx *ctx,
+                           unsigned long *pos_sub,
+                           const struct genl_info *info);
+
        int (*set_validate)(struct ethnl_req_info *req_info,
                            struct genl_info *info);
        int (*set)(struct ethnl_req_info *req_info,
-- 
2.53.0


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