lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Date:	Fri, 20 Jul 2012 14:39:23 +0800
From:	Wang Sheng-Hui <shhuiw@...il.com>
To:	Andreas Dilger <aedilger@...il.com>
CC:	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: One question about ext4_fallocate

On 2012年07月19日 23:42, Andreas Dilger wrote:
> 
> On 2012-07-19, at 7:51 AM, Wang Sheng-Hui wrote:
>> I have one question about ext4_fallocate:
>> 	For its parameters, offset & len, it will preallocate
>> 	one space with length >= len, right?
>>
>> From the code:
>> 	map.m_lblk = offset >> blkbits;
>> 	/*
>> 	 * We can't just convert len to max_blocks because
>> 	 * If blocksize = 4096 offset = 3072 and len = 2048
>> 	 */
>> 	max_blocks = (EXT4_BLOCK_ALIGN(len + offset, blkbits) >> blkbits)
>> 		- map.m_lblk;
>>
>> We can see that the target space is enlarged to the (floor, ceiling) of 
>> (offset, offset+len). Right?
>>
>> If I'm wrong, please correct me.
> 
> A whole block has to be allocated for fallocate, but if KEEP_SIZE is not used, the i_size should be changed to match the actual requested size.
> 

Got it.

>From the code:
	/* Return error if mode is not supported */
	if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE))
		return -EOPNOTSUPP;

	if (mode & FALLOC_FL_PUNCH_HOLE)
		return ext4_punch_hole(file, offset, len);

ext4 only supports FALLOC_FL_KEEP_SIZE & FALLOC_FL_PUNCH_HOLE currently.
For FALLOC_FL_PUNCH_HOLE, it will turn to ext4_punch_hole, so the rest
path deals with only FALLOC_FL_KEEP_SIZE and thus it will use whole blocks.

Thanks, Andreas.
> Cheers, Andreas
> 
> 
> 
> 
> 

--
To unsubscribe from this list: send the line "unsubscribe linux-ext4" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists