Hi Joel,
On Fri, 6 Jul 2007, Joel Becker wrote:
> On Wed, Jul 04, 2007 at 04:38:24PM +0530, Satyam Sharma wrote:
> > struct netconsole_target {
> > struct list_head list;
> > + struct config_item item;
> > + int id;
> > + int enabled;
> > int dev_status;
> > struct netpoll np;
> > };
>
> If you're trying to be good with your CONFIG_NETCONSOLE_DYNAMIC
> ifdefs, you probably want to ifdef the item. You'll save space when
> NETCONSOLE_DYNAMIC is off.
Hmm, I had thought about this, but thought people might not like
another #ifdef. But then this kind of thing is very idiomatic throughout
the kernel, so ok, I'll do this.
[ BTW that .id field also looks like it can be gotten rid of altogether.
I was using it to print informational / error messages in the store()
operations below, but I guess I'll just use config_item_name() there
as well. ]
> > +#ifdef CONFIG_NETCONSOLE_DYNAMIC
> > +
> > +/*
> > + * Targets that were created by parsing the boot/module option string
> > + * do not exist in the configfs hierarchy and will never go away (and
> > + * have zeroed-out config_item members). So make these a no-op for them.
> > + */
> > +static void netconsole_target_get(struct netconsole_target *nt)
> > +{
> > + static struct config_item empty_item; /* Zeroed-out config_item */
> > +
> > + if (memcmp(&nt->item, &empty_item, sizeof(struct config_item)))
> > + config_item_get(&nt->item);
> > +}
>
> I was going to point out that you could merely check
> config_item_name(&nt->item) != NULL, because a valid configfs object has
> a name and your zeroed object does not.
Ok.
[ BTW: not related to dynamic netconsole / issue at hand, but ... I
just noticed in fs/configfs/item.c that ci_name is set to point to
embedded ci_namebuf array in config_item_set_name (if name was small
enough to be set in ci_namebuf itself), which is called from
config_item_init_type_name(). So, this keeps ci_name and ci_namebuf
in sync for such items.
However, for items that are statically initialized (often the
group->cg_item members of subsystems or default groups) we often simply
set ci_namebuf and then call config_item_init() -- say via
config_group_init(), like I've done with the netconsole subsystem in this
patch -- but config_item_init() does not set ci_name for such items to
ci_namebuf. This means the ci_name member of _initialized_ config_items
with their names in ci_namebuf is left un-initialized (NULL, actually,
because the subsys / default group would likely be static).
This doesn't really affect dynamic netconsole, because all config_items
that will be checked in the get() / put() check above are targets that
were initialized with config_item_init_type_name(), but something to
think about for perhaps other users?
Perhaps users who want to statically initialize their config_items must
be asked to just use ci_name and avoid ci_namebuf altogether? ]
> I don't, off the top of my head, see a problem with removing the
> _get/_put cycle, because you do have them under the spinlock. Things
> should behave correctly. However, the _get/_put pair is "cleaner", in
> that it expresses the relationship and doesn't add a special case of "I
> happen to know this is safe".
Right. We shouldn't special case (at least not without adding a comment
why that would be right) and we never know what might happen to the code
at some later day. So let's keep the get() / put() pair.
> > + /*
> > + * Skip netpoll_parse_options() -- all the attributes are
> > + * already configured in nt->np through configfs. But at
> > + * least let's print the useful stuff it used to output :-)
> > + */
> > + printk(KERN_INFO "%s: local port %d\n",
> > + np->name, np->local_port);
> > + printk(KERN_INFO "%s: local IP %d.%d.%d.%d\n",
> > + np->name, HIPQUAD(np->local_ip));
> > + printk(KERN_INFO "%s: interface %s\n",
> > + np->name, np->dev_name);
> > + printk(KERN_INFO "%s: remote port %d\n",
> > + np->name, np->remote_port);
> > + printk(KERN_INFO "%s: remote IP %d.%d.%d.%d\n",
> > + np->name, HIPQUAD(np->remote_ip));
> > + printk(KERN_INFO "%s: remote ethernet address "
> > + "%02x:%02x:%02x:%02x:%02x:%02x\n",
> > + np->name,
> > + np->remote_mac[0], np->remote_mac[1],
> > + np->remote_mac[2], np->remote_mac[3],
> > + np->remote_mac[4], np->remote_mac[5]);
>
> Shouldn't you break this out into a function so that both places
> can use it?
Hmm, netpoll_parse_options() currently prints these separately as and
how it walks through the input string parsing it. But changing that to
just print all these out together at the end if / when the parse is
successful seems better than what it's doing right now. I'll do this too.
> > +#define NETCONSOLE_TARGET_ATTR_RO(_name) \
> > +static struct netconsole_target_attr netconsole_target_##_name = \
> > +__CONFIGFS_ATTR(_name, S_IRUGO, show_##_name, NULL)
> > +
> > +#define NETCONSOLE_TARGET_ATTR_RW(_name) \
> > +static struct netconsole_target_attr netconsole_target_##_name = \
> > +__CONFIGFS_ATTR(_name, S_IRUGO | S_IWUSR, show_##_name, store_##_name)
>
> Perhaps an indent would be clearer, but that's a tiny nitpick.
Yes, an indent would be good there.
> > /*
> > - * Neither the netdev notifier, nor the console have been
> > - * registered so far. Nobody's racing us, so skip the lock.
> > + * Neither the netdev notifier, not the configfs subsystem and
> > + * nor the console have been registered so far. Nobody's racing us,
> > + * so skip the lock.
>
> Once again, while you know you can skip the lock, it's unclear
> without the comment. Perhaps using the lock makes it explicitly
> "correct"? Food for thought.
Yes. That special-casing was really ugly and unnecessary -- we just need
to hold the lock around list_add(). I was going to set that right in the
next iteration myself.
> > @@ -251,6 +796,17 @@ static int __init init_netconsole(void)
> > if (err)
> > goto fail;
> >
> > +#ifdef CONFIG_NETCONSOLE_DYNAMIC
> > + config_group_init(&netconsole_subsys.su_group);
> > + mutex_init(&netconsole_subsys.su_mtx);
> > +
> > + err = configfs_register_subsystem(&netconsole_subsys);
> > + if (err) {
> > + unregister_netdevice_notifier(&netconsole_netdev_notifier);
> > + goto fail;
> > + }
> > +#endif /* CONFIG_NETCONSOLE_DYNAMIC */
>
> I'd abstract this to a dynamic_init() function.
>
> > +
> > +#ifdef CONFIG_NETCONSOLE_DYNAMIC
> > + configfs_unregister_subsystem(&netconsole_subsys);
> > +#endif /* CONFIG_NETCONSOLE_DYNAMIC */
> > +
>
> and this to an dynamic_fini() function. Basically, do what you
> did with _get()/_put(). This keeps the ifdef up above and out of the
> functions themselves.
>
> #ifdef CONFIG_NETCONSOLE_DYNAMIC
> static int __init dynamic_netconsole_init(void)
> {
> config_group_init(&netconsole_subsys.su_group);
> mutex_init(&netconsole_subsys.su_mtx);
> return configfs_register_subsystem(&netconsole_subsys);
> }
> #else
> static int __init dynamic_netconsole_init(void)
> {
> return 0;
> }
> #endif
Right, this looks neater and is again the idiom followed throughout the
kernel.
Thanks,
Satyam
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