Subject: Re: [PATCH net-next 13/14] devlink: add by-instance dump infra

From: Jakub Kicinski <[email-masked]>
Date: Wed, 4 Jan 2023 19:46:04 -0800

On Wed, 4 Jan 2023 17:50:33 +0100 Jiri Pirko wrote:
> Wed, Jan 04, 2023 at 05:16:35AM CET, [email-masked] wrote:
> >Most dumpit implementations walk the devlink instances.
> >This requires careful lock taking and reference dropping.
> >Factor the loop out and provide just a callback to handle
> >a single instance dump.
> >
> >Convert one user as an example, other users converted
> >in the next change.
> >
> >Slightly inspired by ethtool netlink code.

> >diff --git a/net/devlink/devl_internal.h b/net/devlink/devl_internal.h
> >index 5adac38454fd..e49b82dd77cd 100644
> >--- a/net/devlink/devl_internal.h
> >+++ b/net/devlink/devl_internal.h
> >@@ -122,6 +122,11 @@ struct devlink_nl_dump_state {
> > 	};
> > };
> > 
> >+struct devlink_gen_cmd {  
> 
> What is "gen"? Generic netlink?

Generic devlink command. In other words the implementation 
is straightforward enough to factor out the common parts.

> Not sure why perhaps "nl" would be fine to be consistent with the
> rest of the code? Why "cmd"? That looks a bit odd to me.
> 
> >+	int (*dump_one)(struct sk_buff *msg, struct devlink
> >*devlink,
> >+			struct netlink_callback *cb);  
> 
> Do you plan to have more callbacks here? If no, wouldn't it be better
> to just have typedef and assign the pointer to the dump_one in
> devl_gen_cmds array?

If I find the time - yes, more refactoring is possible.

> >+};
> >+
> > /* Iterate over devlink pointers which were possible to get
> > reference to.
> >  * devlink_put() needs to be called for each iterated devlink
> > pointer
> >  * in loop body in order to release the reference.
> >@@ -138,6 +143,9 @@ struct devlink *devlink_get_from_attrs(struct
> >net *net, struct nlattr **attrs);
> > void devlink_notify_unregister(struct devlink *devlink);
> > void devlink_notify_register(struct devlink *devlink);
> > 
> >+int devlink_instance_iter_dump(struct sk_buff *msg,
> >+			       struct netlink_callback *cb);
> >+
> > static inline struct devlink_nl_dump_state *
> > devl_dump_state(struct netlink_callback *cb)
> > {
> >@@ -173,6 +181,8 @@ devlink_linecard_get_from_info(struct devlink
> >*devlink, struct genl_info *info);
> > void devlink_linecard_put(struct devlink_linecard *linecard);
> > 
> > /* Rates */
> >+extern const struct devlink_gen_cmd devl_gen_rate_get;  
> 
> The struct name is *_cmd, not sure why the variable name is *_get
> Shouldn't it be rather devl_gen_cmd_rate?

It is the implementation of get.. there's also a set command.. 
which would be under a different index...

> >+			dump->idx = idx;
> >+			break;
> >+		}
> >+		idx++;
> > 	}
> >-out:
> >-	if (err != -EMSGSIZE)
> >-		return err;
> > 
> >-	return msg->len;
> >+	return err;
> > }
> > 
> >+const struct devlink_gen_cmd devl_gen_rate_get = {
> >+	.dump_one		=
> >devlink_nl_cmd_rate_get_dumpinst,  
> 
> dump_one/dumpinst inconsistency in names

Sure...

> >+};
> >+
> > static int devlink_nl_cmd_rate_get_doit(struct sk_buff *skb,
> > 					struct genl_info *info)
> > {
> >@@ -9130,7 +9123,7 @@ const struct genl_small_ops devlink_nl_ops[56]
> >= {
> > 	{
> > 		.cmd = DEVLINK_CMD_RATE_GET,
> > 		.doit = devlink_nl_cmd_rate_get_doit,
> >-		.dumpit = devlink_nl_cmd_rate_get_dumpit,
> >+		.dumpit = devlink_instance_iter_dump,  
> 
> again, inconsistency:
> devlink_instance_iter_dumpit

You mean it doesn't have nl, cmd, dump_one in the name?
Could you *please* at least say what you want the names to be if you're
sending all those subjective nit picks? :/

I'll call it devlink_nl_instance_iter_dump

> > 		.internal_flags = DEVLINK_NL_FLAG_NEED_RATE,
> > 		/* can be retrieved by unprivileged users */  
> 
> Unrelated to this patch, I wonder, why you didn't move devlink_nl_ops
> along with the rest of the netlink code to netlink.c?

It's explained in the commit message for patch 3 :/

> > 	},
> >diff --git a/net/devlink/netlink.c b/net/devlink/netlink.c
> >index ce1a7d674d14..fcf10c288480 100644
> >--- a/net/devlink/netlink.c
> >+++ b/net/devlink/netlink.c
> >@@ -5,6 +5,7 @@
> >  */
> > 
> > #include <net/genetlink.h>
> >+#include <net/sock.h>
> > 
> > #include "devl_internal.h"
> > 
> >@@ -177,6 +178,38 @@ static void devlink_nl_post_doit(const struct
> >genl_split_ops *ops,
> > 	devlink_put(devlink);
> > }
> > 
> >+static const struct devlink_gen_cmd *devl_gen_cmds[] = {
> >+	[DEVLINK_CMD_RATE_GET]		= &devl_gen_rate_get,
> > 
> 
> static const devlink_nl_dump_one_t *devlink_nl_dump_one[] = {
> 	[DEVLINK_CMD_RATE_GET]	= &devl_nl_rate_dump_one,
> }
> Maybe? (not sure how the devlink/devl should be used here though)

Nope.