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

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Message-Id: <1248382893.14764.8.camel@bobble.smo.corp.google.com>
Date:	Thu, 23 Jul 2009 14:01:33 -0700
From:	Frank Mayhar <fmayhar@...gle.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	Andreas Dilger <adilger@....com>,
	Curt Wohlgemuth <curtw@...gle.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: Question on fallocate/ftruncate sequence (and flags)

On Thu, 2009-07-23 at 15:37 -0500, Eric Sandeen wrote:
> I'm confused (again?) :).  I don't see FS_FALLOC_FL in the latest kernel
> source, and ext2 (well, my ext2 anyway) can't do fallocate().  Google
> (well, my google search) can't find it either.  Is this something in
> your tree?

No, I'm the one who got confused, yes, that's part of a hack in our
tree.

You did answer my question, though, at least partly:

> As for:
> 
> #define EXT4_EXT_MIGRATE                0x00100000 /* Inode is migrating */
> 
> this is not in the mask that FS_IOC_GETFLAGS can see ... and I don't
> think anyone else uses FS_DIRECTIO_FL.
> 
> I'm not sure if the flags not in FS_FL_USER_VISIBLE are supposed to be
> fs-unique.

The flag will need to be generic in any case, since inode_setattr() has
to look at it when it's deciding whether or not to call vmtruncate().
Other filesystems that properly implement fallocate() may want to use it
for this purpose as well.
-- 
Frank Mayhar <fmayhar@...gle.com>
Google, Inc.

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