Re: [PATCH 1/6] xfs: use XFS_IFORK_BOFF xchk_bmap_check_rmaps

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, May 12, 2020 at 11:31:32AM -0400, Brian Foster wrote:
> On Mon, May 11, 2020 at 05:10:04PM +0530, Chandan Babu R wrote:
> > On Sunday 10 May 2020 12:53:59 PM IST Christoph Hellwig wrote:
> > > XFS_IFORK_Q is to be used in boolean context, not for a size.  This
> > > doesn't make a difference in practice as size is only checked for
> > > 0, but this keeps the logic sane.
> > >
> > 
> > Wouldn't XFS_IFORK_ASIZE() be a better fit since it gives the space used by the
> > attr fork inside an inode's literal area?
> > 
> 
> I had the same thought. It's not clear to me what size is really
> supposed to be between the file size for a data fork and fork offset for
> the attr fork. I was also wondering if this should use
> XFS_IFORK_DSIZE(), but that won't be conditional based on population of
> the fork. At the same time, I don't think i_size != 0 necessarily
> correlates with the existence of blocks. The file could be completely
> sparse or could have any number of post-eof preallocated extents.

TBH I should have made that variable "bool empty" or something.

case XFS_DATA_FORK:
	empty = i_size_read() == 0;

case XFS_ATTR_FORK:
	empty = !XFS_IFORK_Q();

default:
	empty = true;

if ((is not btree) && (empty || nextents > 0))
	return 0;

--D

> Brian
> 
> > > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > > ---
> > >  fs/xfs/scrub/bmap.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/fs/xfs/scrub/bmap.c b/fs/xfs/scrub/bmap.c
> > > index add8598eacd5d..283424d6d2bb6 100644
> > > --- a/fs/xfs/scrub/bmap.c
> > > +++ b/fs/xfs/scrub/bmap.c
> > > @@ -591,7 +591,7 @@ xchk_bmap_check_rmaps(
> > >  		size = i_size_read(VFS_I(sc->ip));
> > >  		break;
> > >  	case XFS_ATTR_FORK:
> > > -		size = XFS_IFORK_Q(sc->ip);
> > > +		size = XFS_IFORK_BOFF(sc->ip);
> > >  		break;
> > >  	default:
> > >  		size = 0;
> > > 
> > 
> > 
> > -- 
> > chandan
> > 
> > 
> > 
>