Re: [PATCH] Rearrange i_flags to be consistent with FS_IOC_GETFLAGS

[Dave Chinner <david@fromorbit.com>]

On Mon, Jul 05, 2010 at 04:43:19PM +0100, David Howells wrote:
> Rearrange the constituent bits of i_flags to be consistent with the flag values
> returned by the FS_IOC_GETFLAGS ioctl where flags with common meanings occur.
> Otherwise pack the bits of i_flags as low as possible so that RISC CPUs can
> use small instructions.
> 
> This allows those filesystems that use i_flags (Ext2/3/4) to simplify their
> get/set flags routines.

This seems like a nasty landmine just waiting for someone to step
on.  The S_* flags are VFS level flags used by all filesytsems, not
just extN, and have a history of changing values and meaning as uses
come and go.  This code forces the VFS to use certain flag values
that *match on-disk values* of ext2/3/4.

Further, it opens up the possibility that further down the track
someone modifies S_* flag values (say when adding some XFS
functionality) and corrupts extN filesystems all over the place.
There isn't even compiler guards to catch someone modifying the S_*
flags in a way that makes it incompatible with the extN on-disk
definitions.


Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com