From mboxrd@z Thu Jan  1 00:00:00 1970
From: erik quanstrom <quanstro@quanstro.net>
Date: Tue,  3 Jun 2014 11:47:07 -0400
To: 9fans@9fans.net
Message-ID: <d3a17694dd714f53054031e9ac67dd35@mikro.quanstro.net>
In-Reply-To: <C29EB1DC-4A22-4149-9510-3054933D77C5@fb.com>
References: <C29EB1DC-4A22-4149-9510-3054933D77C5@fb.com>
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Subject: Re: [9fans] kernel bug
Topicbox-Message-UUID: f4d62dd0-ead8-11e9-9d60-3106f5b1d025

> I think it should be
> if(mapsize > (SEGMAPSIZE))
>             mapsize = SEGMAPSIZE;

hmm.  i think this code is correct.  ssegmap is a static map
to handle small segments.  small segments fit in ssegmap.
the point must have been to avoid malloc.

this test is a little more questionable

>	if(mapsize > (SEGMAPSIZE*PTEPERTAB))
>		mapsize = (SEGMAPSIZE*PTEPERTAB);

cf. the check in ibrk

	if(newsize > (SEGMAPSIZE*PTEPERTAB)) {
		qunlock(&s->lk);
		error(Enovmem);
	}

i think this check is either not wrong, or more extensive rework
is necessary.

@anthony, do you know if this code or similar occurred in even older kernels?
if there was a cap also in ibrk() then i would suspect this code was originally
correct.

i don't know where a history of stuff older than sources (2002) is.

> Also why in the kernel they use 'struct Pte' instead of the better name Pagetable.
> In many places this is very confusing because when I see Pte I think of a Pagetable Entry
> where really they are speaking about a Pagetable.

i would naturally think a Pte* would be an array of Pte's, i.e. a Pte table,
just like an array of uchar* could be used as a table.

- erik