Re: [PATCH 1/2] Btrfs: factor out extent dropping code from hole punch handler

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On Fri, Jun 28, 2019 at 08:32:15AM +0300, Nikolay Borisov wrote:
> 
> 
> On 27.06.19 г. 20:00 ч., fdmanana@xxxxxxxxxx wrote:
> > From: Filipe Manana <fdmanana@xxxxxxxx>
> > 
> > Move the code that is responsible for dropping extents in a range out of
> > btrfs_punch_hole() into a new helper function, btrfs_punch_hole_range(),
> > so that later it can be used by the reflinking (extent cloning and dedup)
> > code to fix a ENOSPC bug.
> > 
> > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
> > ---
> >  fs/btrfs/file.c | 308 ++++++++++++++++++++++++++++++--------------------------
> >  1 file changed, 166 insertions(+), 142 deletions(-)
> > 
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 1c7533db16b0..393a6d23b6b0 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -2448,27 +2448,171 @@ static int btrfs_punch_hole_lock_range(struct inode *inode,
> >  	return 0;
> >  }
> >  
> > +/*
> > + * The respective range must have been previously locked, as well as the inode.
> > + * The end offset is inclusive (last byte of the range).
> > + */
> > +static int btrfs_punch_hole_range(struct inode *inode, struct btrfs_path *path,
> > +				  const u64 start, const u64 end,
> > +				  struct btrfs_trans_handle **trans_out)
> 
> I'm not a big fan of the way a lower function starts a transaction which
> is then passed to the caller. So while it fixes a real bug in the next
> patch it isn't really pushing the code in the right direction. I see
> that this transaction is bound to whether no_hole is enabled or not so
> it's not just a matter of lifting it up to the caller. And there's also
> the while loop which commits it and starts a new one. So yeah, it
> doesn't seem like there's a significantly better way of doing that now
> but IMO we need to think of cleaning that up later.

I agree with the point about starting the transaction from the lower
function, and also don't see a better way to do it right now. Oh well.



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