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Re: simpler _xfs_dic2xflags() ?

To: utz lehmann <xfs2@xxxxxxxxxx>
Subject: Re: simpler _xfs_dic2xflags() ?
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Sat, 14 Aug 2010 09:16:19 +1000
Cc: linux-xfs <linux-xfs@xxxxxxxxxxx>
In-reply-to: <1281738591.5897.17.camel@xxxxxxxxxxxxxxxxxxxx>
References: <1281738591.5897.17.camel@xxxxxxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.20 (2009-06-14)
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@xxxxxxxxxxxxx

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