linux-kernel - Re: [patch] ext2: xip check fix

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Date:	Thu, 6 Dec 2007 00:33:45 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	carsteno@...ibm.com
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-fsdevel@...r.kernel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>, rob@...dley.net,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [patch] ext2: xip check fix

On Wed, Dec 05, 2007 at 04:43:16PM +0100, Carsten Otte wrote:
> Nick Piggin wrote:
> >Am I missing something here? I wonder how s390 works without this change?
> >
> >--
> >ext2 should not worry about checking sb->s_blocksize for XIP before the
> >sb's blocksize actually gets set.
> >
> >Signed-off-by: Nick Piggin <npiggin@...e.de>
> >---
> >Index: linux-2.6/fs/ext2/super.c
> >===================================================================
> >--- linux-2.6.orig/fs/ext2/super.c
> >+++ linux-2.6/fs/ext2/super.c
> >@@ -844,8 +844,7 @@ static int ext2_fill_super(struct super_
> >
> > 	blocksize = BLOCK_SIZE << le32_to_cpu(sbi->s_es->s_log_block_size);
> >
> >-	if ((ext2_use_xip(sb)) && ((blocksize != PAGE_SIZE) ||
> >-				  (sb->s_blocksize != blocksize))) {
> >+	if (ext2_use_xip(sb) && blocksize != PAGE_SIZE) {
> > 		if (!silent)
> > 			printk("XIP: Unsupported blocksize\n");
> > 		goto failed_mount;
> "blocksize" contains the blocksize of the device here, and 
> sb->s_blocksize does contain the filesystem block size as saved in the 
> super block.

You mean blocksize is the size of the ext2 block, and s_blocksize is the
default size of the block device.


> Xip does only work, if both do match PAGE_SIZE because it 
> does'nt support multiple calls to direct_access in the get_xip_page 
> address space operation. Thus we check both here, actually this was 
> changed from how it looks after your patch as a bugfix where our 
> tester tried a 4k filesystem on a 2k blockdev.
> Did I miss something?

However, the bdev block size may be changed with sb_set_blocksize. It
doesn't actually have to match the hardware sector size -- if this
does matter for XIP, then I think you need some other check here.
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