linux-ext4 - Re: Question on fallocate/ftruncate sequence (and flags)

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Date:	Thu, 23 Jul 2009 12:48:37 -0700
From:	Frank Mayhar <fmayhar@...gle.com>
To:	Andreas Dilger <adilger@....com>
Cc:	Eric Sandeen <sandeen@...hat.com>,
	Curt Wohlgemuth <curtw@...gle.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question on fallocate/ftruncate sequence (and flags)

On Tue, 2009-07-21 at 15:54 -0600, Andreas Dilger wrote:
> That said, we might need to have some kind of flag in the on-disk
> inode to indicate that it was preallocated beyond EOF.  Otherwise,
> e2fsck will try and extend the file size to match the block count,
> which isn't correct.  We could also use this flag to determine if
> truncate needs to be run on the inode even if the new size is the
> same.

As it happens there's already a flag, FS_FALLOC_FL, set by ext2 in
fallocate().  Unfortunately ext4 is using that bit (0x00040000) for
EXT4_HUGE_FILE_FL.  (Ext4 is using another bit as well, 0x00100000, for
EXT4_EXT_MIGRATE_FL when fs.h defines it as FS_DIRECTIO_FL.)  I really
want to use the FS_FALLOC_FL bit for this purpose but that means
reallocating HUGE_FILE_FL to some other big.  Objections?
-- 
Frank Mayhar <fmayhar@...gle.com>
Google, Inc.

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