linux-ext4 - Re: [PATCH] fiemap support for ext3

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Message-ID: <480FCAC9.8050105@redhat.com>
Date:	Wed, 23 Apr 2008 18:48:25 -0500
From:	Eric Sandeen <sandeen@...hat.com>
To:	Andreas Dilger <adilger@....com>
CC:	Josef Bacik <jbacik@...hat.com>, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] fiemap support for ext3

Andreas Dilger wrote:
> On Apr 23, 2008  15:39 -0400, Josef Bacik wrote:

>> +	/*
>> +	 * we want the comparisons to be unsigned, in case somebody passes -1,
>> +	 * meaning they want they want the entire file, but the result has to be
>> +	 * signed so we can handle the case where we get more blocks than the
>> +	 * size of the file
>> +	 */
>> +	length = (long)min((unsigned long)fiemap_s->fm_length,
>> +			   (unsigned long)i_size_read(inode));
> 
> This might be written as:
> 
> 	length = (long)min_t(unsigned long,fiemap_s->fm_len,i_size_read(inode));
> 
> Also, what about files that have blocks mapped after i_size?

That'll be tough for ext3, though I guess for a generic interface it
could happen, so I guess it needs to be handled.  Maybe check i_blocks
against i_size, see if i_blocks indicates blocks past EOF?  Hm, I guess
that's not going to work in general; you could be completely sparse up
to an EOF at 100G and have 100M of blocks past that...

I don't know how you'd handle this in the generic case...?

-Eric
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