linux-ext4 - Re: [PATCH 1/6] fs: add hole punching to fallocate

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Message-ID: <20101116131451.GH4757@quack.suse.cz>
Date:	Tue, 16 Nov 2010 14:14:51 +0100
From:	Jan Kara <jack@...e.cz>
To:	Josef Bacik <josef@...hat.com>
Cc:	Jan Kara <jack@...e.cz>, david@...morbit.com,
	linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
	linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	xfs@....sgi.com, cmm@...ibm.com, cluster-devel@...hat.com,
	ocfs2-devel@....oracle.com
Subject: Re: [PATCH 1/6] fs: add hole punching to fallocate

On Tue 16-11-10 07:52:50, Josef Bacik wrote:
> On Tue, Nov 16, 2010 at 12:43:46PM +0100, Jan Kara wrote:
> > On Tue 16-11-10 12:16:11, Jan Kara wrote:
> > > On Mon 15-11-10 12:05:18, Josef Bacik wrote:
> > > > diff --git a/fs/open.c b/fs/open.c
> > > > index 4197b9e..ab8dedf 100644
> > > > --- a/fs/open.c
> > > > +++ b/fs/open.c
> > > > @@ -223,7 +223,7 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
> > > >  		return -EINVAL;
> > > >  
> > > >  	/* Return error if mode is not supported */
> > > > -	if (mode && !(mode & FALLOC_FL_KEEP_SIZE))
> > > > +	if (mode && (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)))
> > >   Why not just:
> > > if (mode & ~(FALLOC_FL_KEEP_SIZE | FALLOC_FL_PUNCH_HOLE)) ?
> >   And BTW, since FALLOC_FL_PUNCH_HOLE does not change the file size, should
> > not we enforce that FALLOC_FL_KEEP_SIZE is / is not set? I don't mind too
> > much which way but keeping it ambiguous (ignored) in the interface usually
> > proves as a bad idea in future when we want to further extend the interface...
> >
> 
> Yeah I went back and forth on this.  KEEP_SIZE won't change the behavior of
> PUNCH_HOLE since PUNCH_HOLE implicitly means keep the size.  I figured since its
> "mode" and not "flags" it would be ok to make either way accepted, but if you
> prefer PUNCH_HOLE means you have to have KEEP_SIZE set then I'm cool with that,
> just let me know one way or the other.  Thanks,
  I was wondering about 'mode' vs 'flags' as well. The manpage says:
The mode argument determines the operation to be performed on the given
range.  Currently only one flag is supported for mode...
  So we call it "mode" but speak about "flags"? Seems a bit inconsistent.
I'd maybe lean a bit at the "flags" side and just make sure that
only one of FALLOC_FL_KEEP_SIZE, FALLOC_FL_PUNCH_HOLE is set (interpreting
FALLOC_FL_KEEP_SIZE as allocate blocks beyond i_size). But I'm not sure
what others think.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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