linux-ext4 - Re: [PATCH 5 2/4] Return 32/64-bit dir name hash according to usage type

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Date:	Tue, 06 Mar 2012 01:40:05 +0100
From:	Bernd Schubert <bernd.schubert@...m.fraunhofer.de>
To:	Ted Ts'o <tytso@....edu>
CC:	linux-nfs@...r.kernel.org, linux-ext4@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, Fan Yong <yong.fan@...mcloud.com>,
	bfields@...hat.com, sandeen@...hat.com,
	Andreas Dilger <adilger@...mcloud.com>
Subject: Re: [PATCH 5 2/4] Return 32/64-bit dir name hash according to usage
 type

On 03/05/2012 04:59 PM, Ted Ts'o wrote:
> On Mon, Jan 09, 2012 at 02:21:48PM +0100, Bernd Schubert wrote:
>> diff --git a/fs/ext4/hash.c b/fs/ext4/hash.c
>> index ac8f168..fa8e491 100644
>> --- a/fs/ext4/hash.c
>> +++ b/fs/ext4/hash.c
>> @@ -200,8 +200,8 @@ int ext4fs_dirhash(const char *name, int len, struct dx_hash_info *hinfo)
>>   		return -1;
>>   	}
>>   	hash = hash&  ~1;
>> -	if (hash == (EXT4_HTREE_EOF<<  1))
>> -		hash = (EXT4_HTREE_EOF-1)<<  1;
>> +	if (hash == (EXT4_HTREE_EOF_32BIT<<  1))
>> +		hash = (EXT4_HTREE_EOF_32BIT - 1)<<  1;
>>   	hinfo->hash = hash;
>>   	hinfo->minor_hash = minor_hash;
>>   	return 0;
>
> Is there a reason why we don't need to avoid the collsion with the
> 64-bit EOF value as well?  i.e., I think we also need to add:
>
> 	if (hash == (EXT4_HTREE_EOF_64BIT<<  1))
> 		hash = (EXT4_HTREE_EOF_64BIT - 1)<<  1;
>
> 		       			       	  - Ted


Thanks for looking into it, really appreciated!

Yeah, you are right, we also should check for 64-bit EOF. But wouldn't 
be something like this be better?

	/* check for hash collision */
	if(is_32bit_api() ) {
		if (hash == (EXT4_HTREE_EOF_32BIT<<  1))
			hash = (EXT4_HTREE_EOF_32BIT - 1)<<  1;
	} else {
		if (hash == (EXT4_HTREE_EOF_64BIT<<  1))
			hash = (EXT4_HTREE_EOF_64BIT - 1)<<  1;
	}



Or am I over engineering?


Thanks,
Bernd


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