linux-ext4 - Re: [RFC] Heads up on sys

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Message-Id: <13E89496-3752-42ED-AE23-F1EF6DE23029@cam.ac.uk>
Date:	Mon, 5 Mar 2007 15:07:26 +0000
From:	Anton Altaparmakov <aia21@....ac.uk>
To:	Theodore Tso <tytso@....edu>
Cc:	Ulrich Drepper <drepper@...hat.com>, Arnd Bergmann <arnd@...db.de>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Kleikamp <shaggy@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Amit K. Arora" <aarora@...ux.vnet.ibm.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org, suparna@...ibm.com, cmm@...ibm.com,
	alex@...sterfs.com, suzuki@...ibm.com
Subject: Re: [RFC] Heads up on sys_fallocate()

On 5 Mar 2007, at 14:37, Theodore Tso wrote:
> On Sun, Mar 04, 2007 at 11:22:06PM +0000, Anton Altaparmakov wrote:
>> And I specifically did NOT update the initialized size in the inode
>> thus it will remain at its old value thus all new allocated blocks
>> will be considered as present but not initialized thus a read will
>> always return zero whilst a write will do the right thing and pad
>> with zeroes as necessary (if the write is smaller than the block
>> size, etc).
>
> 	You're describing a method of doing in-advance preallocation
> where the filesystem format explicitly has support for this kind of
> feature in a way that doesn't require pre-zeroing the data blocks in
> question.

Indeed.

> 	The question which this subthread was concerned about was
> whether the kernel should get involved in initializing datablocks in
> the case where the filesystem format does not have this support, or
> whether this functionality should continue to be done in userspace.
> Given that glibc already has to support this for older kernels, I
> would argue that there's no point putting in generic support for
> filesystem that can't support a more advanced way of doing things.

Yes, I understood that after I had sent my post...  And yes, I would  
agree.  If glibc already does this there does not appear to be any  
value in just moving existing functionality into the kernel.  Simply  
let "dumb" file systems return ENOSYS and let glibc do it...  And any  
FS which can do it better can implement the function and then glibc  
should not go anywhere near it.

Best regards,

	Anton
-- 
Anton Altaparmakov <aia21 at cam.ac.uk> (replace at with @)
Unix Support, Computing Service, University of Cambridge, CB2 3QH, UK
Linux NTFS maintainer, http://www.linux-ntfs.org/


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