linux-kernel - Re: [patch 1/4] Linux Kernel Markers

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Date:	Sun, 26 Aug 2007 06:49:30 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [patch 1/4] Linux Kernel Markers - Architecture Independent
	Code

On Fri, 2007-08-24 at 12:26 -0400, Mathieu Desnoyers wrote:
> * Rusty Russell (rusty@...tcorp.com.au) wrote:
> > On Mon, 2007-08-20 at 16:27 -0400, Mathieu Desnoyers wrote:
> > > +{
> > > +	struct hlist_head *head;
> > > +	struct hlist_node *node;
> > > +	struct marker_entry *e;
> > > +	size_t len = strlen(name) + 1;
> > > +	u32 hash = jhash(name, len-1, 0);
> > > +
> > > +	head = &marker_table[hash & ((1 << MARKER_HASH_BITS)-1)];
> > > +	hlist_for_each_entry(e, node, head, hlist) {
> > > +		if (!strcmp(name, e->name))
> > > +			return e;
> > > +	}
> > > +	return NULL;
> > > +}
> > 
> > OK, don't understand the strlen, len, len-1 dance here?
> > 
> 
> Let's say we have abc\0 for marker name as name input.
> 
> len = 3 + 1 = 4 (including \0)
> hash is done only on the 3 first chars, excluding the \0 (therefore the
>                                                           len-1 there)
> 
> Actually, it's like this only for a matter of consistency between
> add_marker and remove_marker, which are quite similar, but add_marker
> needs name_len to include the \0 value. It would be odd to change the
> logic between the two functions to one including the \0 and the other
> excluding it.

Sure, but that doesn't really explain why the code does:

	size_t len = strlen(name) + 1;
	u32 hash = jhash(name, len-1, 0);

Rather than:

	u32 hash = jhash(name, strlen(name), 0);

> Thanks for the review,

That's fine, just some light reading...

Cheers,
Rusty.
> 

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