linux-ext4 - Re: [PATCH 1/1 version2] Extent overlap bugfix in ext4

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Message-ID: <20070105061802.GA25583@amitarora.in.ibm.com>
Date:	Fri, 5 Jan 2007 11:48:02 +0530
From:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>
To:	Mingming Cao <cmm@...ibm.com>
Cc:	Alex Tomas <alex@...sterfs.com>, linux-ext4@...r.kernel.org,
	suparna@...ibm.com
Subject: Re: [PATCH 1/1 version2] Extent overlap bugfix in ext4

On Thu, Jan 04, 2007 at 11:47:36AM -0800, Mingming Cao (MC) wrote:
> Alex Tomas (AT) wrote:
> 
> >>>>>>Amit K Arora (AKA) writes:
> >
> >
> > > AKA> @@ -1984,6 +2034,10 @@ int ext4_ext_get_blocks(handle_t *handle
> > > AKA>  		 */
> > > AKA>  		if (ee_len > EXT_MAX_LEN)
> > > AKA>  			goto out2;
> > > AKA> +
> > > AKA> +		if (iblock < ee_block && iblock + max_blocks >= 
> > > ee_block)
> > > AKA> +			allocated = ee_block - iblock;
> > > AKA> +
> > > AKA>  		/* if found extent covers block, simply return it */
> > > AKA>  	        if (iblock >= ee_block && iblock < ee_block + 
> > > ee_len) {
> > > AKA>  			newblock = iblock - ee_block + ee_start;
> > >
> > AT> I thought existing code already does this:
> >
> > AT>   /* if found extent covers block, simply return it */
> > AT>   if (iblock >= ee_block && iblock < ee_block + ee_len) {
> > AT>	      newblock = iblock - ee_block + ee_start;
> > AT>	      /* number of remaining blocks in the extent */
> > AT>	      allocated = ee_len - (iblock - ee_block);
> MC> That's different: the existing code address the case when the left part
> MC> of the new extent  overlaps with an exisitng extent, in that case I
> MC> understand it just returns the allocated part of extent, and continue
> MC> the block allocation in the next call of get_blocks().
Right.
 
> MC> Well Amit's new code here trying to address the case when the right part
> MC> of the new extent overlap with an exisitng extent. He was trying to
> MC> update the new extent length to prevent that. As I mentioned ealier we
> MC> could put this code into ext4_ext_check_overlap,let it judge whether
> MC> there is overlap, and if so, what's the right start block number and length
Yes, this check will no longer be required with the modified
ext4_ext_check_overlap, which will check for this condition as well.

--
Regards,
Amit Arora
> 
> Thanks,
> Mingming
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