Re: [PATCH 4/6] Ext4: fail if we try to use hole punch

[Josef Bacik <josef@redhat.com>]

On Tue, Nov 16, 2010 at 04:20:43PM +0000, P=E1draig Brady wrote:
> On 15/11/10 17:05, Josef Bacik wrote:
> > Ext4 doesn't have the ability to punch holes yet, so make sure we r=
eturn
> > EOPNOTSUPP if we try to use hole punching through fallocate.  This =
support can
> > be added later.  Thanks,
> >=20
> > Signed-off-by: Josef Bacik <josef@redhat.com>
> > ---
> >  fs/ext4/extents.c |    4 ++++
> >  1 files changed, 4 insertions(+), 0 deletions(-)
> >=20
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index 0554c48..35bca73 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -3622,6 +3622,10 @@ long ext4_fallocate(struct inode *inode, int=
 mode, loff_t offset, loff_t len)
> >  	struct ext4_map_blocks map;
> >  	unsigned int credits, blkbits =3D inode->i_blkbits;
> > =20
> > +	/* We only support the FALLOC_FL_KEEP_SIZE mode */
> > +	if (mode && (mode !=3D FALLOC_FL_KEEP_SIZE))
> > +		return -EOPNOTSUPP;
> > +
> >  	/*
> >  	 * currently supporting (pre)allocate mode for extent-based
> >  	 * files _only_
>=20
> So for older versions of ext4 or other filesystems, how do we know
> that fallocate(...,FALLOC_FL_PUNCH_HOLE) is not supported.
> I.E. how do we detect at runtime that the call succeeded
> and didn't just do a normal fallocate()?
>

Older kernels won't accept FALLOC_FL_PUNCH_HOLE, so you'll get an error=
=2E
Thanks,

Josef=20