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

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Message-ID: <459D59D8.5040308@us.ibm.com>
Date:	Thu, 04 Jan 2007 11:47:36 -0800
From:	Mingming Cao <cmm@...ibm.com>
To:	Alex Tomas <alex@...sterfs.com>
CC:	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-ext4@...r.kernel.org, suparna@...ibm.com
Subject: Re: [PATCH 1/1 version2] Extent overlap bugfix in ext4

Alex Tomas 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;
> 
> I thought existing code already does this:
> 
> 	/* if found extent covers block, simply return it */
>         if (iblock >= ee_block && iblock < ee_block + ee_len) {
> 		newblock = iblock - ee_block + ee_start;
> 		/* number of remaining blocks in the extent */
> 		allocated = ee_len - (iblock - ee_block);
> 
> 
> thanks, Alex
That's different: the existing code address the case when the left part 
of the new extent  overlaps with an exisitng extent, in that case I 
understand it just returns the allocated part of extent, and continue 
the block allocation in the next call of get_blocks().

Well Amit's new code here trying to address the case when the right part 
of the new extent overlap with an exisitng extent. He was trying to 
update the new extent length to prevent that. As I mentioned ealier we 
could put this code into ext4_ext_check_overlap,let it judge whether 
there is overlap, and if so, what's the right start block number and length

Thanks,
Mingming

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