linux-kernel - Re: [PATCH] Rearrange i_flags to be consistent with FS_IOC

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Date:	Wed, 7 Jul 2010 11:55:30 +1000
From:	Dave Chinner <david@...morbit.com>
To:	David Howells <dhowells@...hat.com>
Cc:	viro@...IV.linux.org.uk, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: [PATCH] Rearrange i_flags to be consistent with FS_IOC_GETFLAGS

On Wed, Jul 07, 2010 at 12:45:25AM +0100, David Howells wrote:
> Dave Chinner <david@...morbit.com> wrote:
> 
> > I'd prefer generic flags are not dependent on fixed values from a
> > specific filesystem several layers down the storage stack.
> 
> They're not so dependent.

History says otherwise. :)

> They're based on the FS_IOC_[GS]ETFLAGS ioctl which
> even XFS translates its flags for.

Sure, because the ioctl flags values are derived
from the ext2 on-disk format flags and hence don't match anything
XFS related at all.

> These ioctl flags must now remain
> invariant.  Whilst they might have originated as Ext2/3/4 flags, they're now
> independent of that.

Yes, the ioctl flags must remain invariant. OTOH, the generic inode
flags (S_*) have no such invariant requirement and have a history of
frequent change. IMO, that means some flags should not be tied to
the value of a specific subsystem just so a subsystem specific
optimisation can be made. It just seems like a dangerous layering
violation to be making...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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