linux-kernel - Re: [PATCH 4/8 ver5] exofs: address_space

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Date:	Tue, 31 Mar 2009 03:15:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Avishay Traeger <avishay@...il.com>, Jeff Garzik <jeff@...zik.org>,
	Evgeniy Polyakov <zbr@...emap.net>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	open-osd <osd-dev@...n-osd.org>,
	Marcin Slusarz <marcin.slusarz@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Subject: Re: [PATCH 4/8 ver5] exofs: address_space_operations

On Tue, 31 Mar 2009 12:04:36 +0300 Boaz Harrosh <bharrosh@...asas.com> wrote:

> >> +static int write_exec(struct page_collect *pcol)
> >> +{
> >> +	struct exofs_i_info *oi = exofs_i(pcol->inode);
> >> +	struct osd_obj_id obj = {pcol->sbi->s_pid,
> >> +					pcol->inode->i_ino + EXOFS_OBJ_OFF};
> >> +	struct osd_request *or = NULL;
> >> +	struct page_collect *pcol_copy = NULL;
> >> +	loff_t i_start = pcol->pg_first << PAGE_CACHE_SHIFT;
> > 
> > bug.  On 32-bit this shift will overflow prior to getting promoted to
> > 64-bit.  Do:
> > 
> > 	loff_t i_start = (loff_t)pcol->pg_first << PAGE_CACHE_SHIFT;
> > 
> 
> In that case I might make pcol->pg_first loff_t.

That would work.

> Why is inode->i_index not an loff_t then?

hm, what's i_index?

> Page-index <=> byte-offset, is done all the time 12 bits does not
> make a difference.

Page indices are 32-bit on 32-bit CPUs.  File offsets are 64-bit.  We
are careful to avoid the above overflow bug whenever the conversion
from page index to file size is made.  Try

	fgrep '(loff_t)' mm/*.c


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