Message-ID: <41F8530C.6010305@comcast.net>
Date: Wed, 26 Jan 2005 21:33:48 -0500
From: John Richard Moser <nigelenki@comcast.net>
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To: "Randy.Dunlap" <rddunlap@osdl.org>
CC: linux-kernel@vger.kernel.org
Subject: Re: /proc parent &proc_root == NULL?
References: <41F82218.1080705@comcast.net> <41F84313.4030509@osdl.org>
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Randy.Dunlap wrote:
> John Richard Moser wrote:
> 
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>>
>> proc_misc_init() has both these lines in it:
>>
>> entry = create_proc_entry("kmsg", S_IRUSR, &proc_root);
>> proc_root_kcore = create_proc_entry("kcore", S_IRUSR, NULL);
>>
>> Both entries show up in /proc, as /proc/kmsg and /proc/kcore.  So I ask,
>> as I can't see after several minutes of examination, what's the
>> difference?  Why is NULL used for some and &proc_root used for others?
>>
>> I'm looking at 2.6.10
> 
> 
> create_proc_entry() passes &parent to proc_create().
> See proc_create():
> ...
> This is an error path:
>     if (!(*parent) && xlate_proc_name(name, parent, &fn) != 0)
>         goto out;
> but xlate_proc_name() searches for a /proc/.... and returns the
> all-but-final-part-of-name *parent (hope that makes some sense,
> see the comments above the function), so it returns &proc_root.
> 
> HTH.  If not, fire back.

create_proc_entry("kmsg", S_IRUSR, &proc_root);

So this is asking for proc_root to be filled?

create_proc_entry("kcore", S_IRUSR, NULL);

And this is just saying to shove it in proc's root?


I'm trying to locate a specific proc entry, using this lovely piece of
code I ripped off:

/*
 * Find a proc entry
 * Duplicated from remove_proc_entry()
 */
struct proc_dir_entry **get_proc_entry(const char *name, struct
proc_dir_entry *parent) {
        struct proc_dir_entry **p;
        const char *fn = name;
        int len;
        if (!parent && xlate_proc_name(name, &parent, &fn) != 0)
                goto out;
        len = strlen(fn);
        for (p = &parent->subdir; *p; p=&(*p)->next ) {
                if (!proc_match(len, fn, *p))
                        continue;
                return p;
        }
out:
        return NULL;
}


And I'm trying to figure out if, say, /proc/devices would be found by...

get_proc_entry("devices",NULL);
- -OR-
get_proc_entry("devices",&proc_root);

Oh well.  I'll figure it out eventually.  :)  I've already caused my
kernel to not boot :) figured it out too, it was that very function
above; I replaced a chunk of remove_proc_entry() with a modified version
of that and I'd busted it horribly so it didn't work.  Just more things
to remind me that I know not what it is I do.

- --
All content of all messages exchanged herein are left in the
Public Domain, unless otherwise explicitly stated.

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