Re: simpler _xfs_dic2xflags() ?

Dave Chinner
2010-08-13T23:15:57Z

On Sat, Aug 14, 2010 at 12:29:51AM +0200, utz lehmann wrote:
> Hello
>
> I just found following function in xfs_inode.c:
>
> STATIC uint
> _xfs_dic2xflags(
> __uint16_t di_flags)
> {
> uint flags = 0;
>
> if (di_flags & XFS_DIFLAG_ANY) {
> if (di_flags & XFS_DIFLAG_REALTIME)
> flags |= XFS_XFLAG_REALTIME;
> if (di_flags & XFS_DIFLAG_PREALLOC)
> flags |= XFS_XFLAG_PREALLOC;
> if (di_flags & XFS_DIFLAG_IMMUTABLE)
> flags |= XFS_XFLAG_IMMUTABLE;
> if (di_flags & XFS_DIFLAG_APPEND)
> flags |= XFS_XFLAG_APPEND;
> if (di_flags & XFS_DIFLAG_SYNC)
> flags |= XFS_XFLAG_SYNC;
> if (di_flags & XFS_DIFLAG_NOATIME)
> flags |= XFS_XFLAG_NOATIME;
> if (di_flags & XFS_DIFLAG_NODUMP)
> flags |= XFS_XFLAG_NODUMP;
> if (di_flags & XFS_DIFLAG_RTINHERIT)
> flags |= XFS_XFLAG_RTINHERIT;
> if (di_flags & XFS_DIFLAG_PROJINHERIT)
> flags |= XFS_XFLAG_PROJINHERIT;
> if (di_flags & XFS_DIFLAG_NOSYMLINKS)
> flags |= XFS_XFLAG_NOSYMLINKS;
> if (di_flags & XFS_DIFLAG_EXTSIZE)
> flags |= XFS_XFLAG_EXTSIZE;
> if (di_flags & XFS_DIFLAG_EXTSZINHERIT)
> flags |= XFS_XFLAG_EXTSZINHERIT;
> if (di_flags & XFS_DIFLAG_NODEFRAG)
> flags |= XFS_XFLAG_NODEFRAG;
> if (di_flags & XFS_DIFLAG_FILESTREAM)
> flags |= XFS_XFLAG_FILESTREAM;
> }
>
> return flags;
> }
>
> Can't the whole function be replaced by something like this?
>
> flags = di_flags & MASK;
>
> The corresponding XFS_DIFLAGS and XFS_XFLAGS have the same values.

Sure they have the same value right now, but remember that
XFS_XFLAG_* values are part of userspace ABI and the XFS_DIFLAG_*
define to the on-disk format values.

We keep a logical separation of the two as there is no guarantee
they will remain the same over time. Indeed, there are XFS_XFLAGS_*
values that have no equivalent XFS_DIFLAG_ value. Further, we are
out of space for new flags in the inode flags field and hence any
new on-disk flags will be in a different format to the current on
disk values and hence we'd break any masking based optimisation if
we change them...

Cheers,

Dave.

--
Dave Chinner
david@fromorbit.com

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