linux-kernel - Re: [PATCH] squashfs broken when pageszie

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Message-ID: <alpine.LRH.2.00.0904171518040.28718@vixen.sonytel.be>
Date:	Fri, 17 Apr 2009 15:20:10 +0200 (CEST)
From:	Geert Uytterhoeven <Geert.Uytterhoeven@...ycom.com>
To:	Phillip Lougher <phillip@...gher.demon.co.uk>
cc:	Doug Chapman <doug.chapman@...com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	squashfs-devel@...ts.sourceforge.net
Subject: Re: [PATCH] squashfs broken when pageszie > blocksize

On Mon, 13 Apr 2009, Phillip Lougher wrote:
> Doug Chapman wrote:
> > Squashfs is broken on any system where the pageszie is larger than either
> > the block size of the squashfs image or larger than the metadata size
> > (8192).
> > This is easily fixed by ensuring cache->pages is always > 0.
> > 
> > Signed-off-by: Doug Chapman <doug.chapman@...com>
> > Cc: Phillip Lougher <phillip@...gher.demon.co.uk>
> 
> Good catch.  BTW what is the page size on ia64?

A quick grep on PAGE_{SIZE,SHIFT} in asm/page.h shows:

ia64, mips, sh: 4/8/16/64 KiB
parisc: 4/16/64 KiB
alpha, cris: 8 KiB
powerpc: 4/16/64/256 KiB

> For completeness there should also be a mount time check that
> the block size used in the Squashfs filesystem is at least as
> large as the pagesize.  This doesn't matter for metadata
> (size 8192), but does matter for data blocks, because Squashfs
> read_page doesn't handle block_size < pagesize.
> 
> Squashfs read_page used to handle block_size < pagesize but I
> removed that code when I removed filesystem support for block_sizes
> < 4K.  If ia64 users (or any other architecture with larger than
> 4K pagesizes) want to use Squashfs filesystems with blocksizes less
> than their pagesize, then I can put that code back in.

So I think it's a good idea to resurrect that code...

With kind regards,

Geert Uytterhoeven
Software Architect

Sony Techsoft Centre Europe
The Corporate Village · Da Vincilaan 7-D1 · B-1935 Zaventem · Belgium

Phone:    +32 (0)2 700 8453
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E-mail:   Geert.Uytterhoeven@...ycom.com
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