linux-ext4 - Re: [RFC PATCH] ext4: Fix fallocate to update the file size in each transaction.

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Message-Id: <1204905803.7975.17.camel@norville.austin.ibm.com>
Date:	Fri, 07 Mar 2008 10:03:23 -0600
From:	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>
To:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
Cc:	Mingming Cao <cmm@...ibm.com>, tytso@....edu, sandeen@...hat.com,
	linux-ext4@...r.kernel.org
Subject: Re: [RFC PATCH] ext4: Fix fallocate to update the file size in
	each transaction.

On Fri, 2008-03-07 at 17:14 +0530, Aneesh Kumar K.V wrote:
> On Fri, Mar 07, 2008 at 03:30:57AM -0800, Mingming Cao wrote:
> > On Fri, 2008-03-07 at 16:23 +0530, Aneesh Kumar K.V wrote:

> > > @@ -2814,8 +2834,7 @@ long ext4_fallocate(struct inode *inode, int mode, loff_t offset, loff_t len)
> > >  		return -ENODEV;
> > > 
> > >  	block = offset >> blkbits;
> > > -	max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
> > > -			- block;
> > > +	max_blocks = EXT4_BLOCK_ALIGN(len, blkbits) >> blkbits;
> > > 
> > 
> > Not sure about this change... Other than this looks fine to me
> > 
> 
> max_blocks actually represented the number of blocks that we are
> requesting. The above change makes it simple.

I think it's too simple.  :-(

Take an example of an empty file (no allocated blocks), offset=0xC00,
length = 0x800, block_size = 0x1000.

The existing code will result in max_blocks = 2, accounting for both the
blocks that the allocation spans, but your new code will result in
max_blocks = 1.
-- 
David Kleikamp
IBM Linux Technology Center

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