linux-kernel - Re: [PATCH 6/7 v3] overlay: hybrid overlay filesystem prototype

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Date:	Fri, 24 Sep 2010 13:16:24 -0400
From:	Valerie Aurora <vaurora@...hat.com>
To:	Jens Axboe <axboe@...nel.dk>
Cc:	Miklos Szeredi <miklos@...redi.hu>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, neilb@...e.de,
	viro@...iv.linux.org.uk
Subject: Re: [PATCH 6/7 v3] overlay: hybrid overlay filesystem prototype

On Fri, Sep 24, 2010 at 04:33:05PM +0200, Jens Axboe wrote:
> On 2010-09-23 01:21, Valerie Aurora wrote:
> > On Mon, Sep 20, 2010 at 08:04:10PM +0200, Miklos Szeredi wrote:
> >> From: Miklos Szeredi <mszeredi@...e.cz>
> >>
> >> This overlay filesystem is a hybrid of entirely filesystem based
> >> (unionfs, aufs) and entierly VFS based (union mounts) solutions.
> > 
> > [...]
> > 
> >> +static int ovl_copy_up_data(struct path *old, struct path *new, loff_t len)
> >> +{
> >> +	struct file *old_file;
> >> +	struct file *new_file;
> >> +	int error = 0;
> >> +
> >> +	if (len == 0)
> >> +		return 0;
> >> +
> >> +	old_file = path_open(old, O_RDONLY);
> >> +	if (IS_ERR(old_file))
> >> +		return PTR_ERR(old_file);
> >> +
> >> +	new_file = path_open(new, O_WRONLY);
> >> +	if (IS_ERR(new_file)) {
> >> +		error = PTR_ERR(new_file);
> >> +		goto out_fput;
> >> +	}
> >> +
> >> +	/* FIXME: copy up sparse files efficiently */
> >> +	while (len) {
> >> +		loff_t offset = new_file->f_pos;
> >> +		size_t this_len = OVL_COPY_UP_CHUNK_SIZE;
> >> +		long bytes;
> >> +
> >> +		if (len < this_len)
> >> +			this_len = len;
> >> +
> >> +		if (signal_pending_state(TASK_KILLABLE, current))
> >> +			return -EINTR;
> >> +
> >> +		bytes = do_splice_direct(old_file, &offset, new_file, this_len,
> >> +				 SPLICE_F_MOVE);
> > 
> > Interruptible copyup is good.  But it looks like splice setup is kind
> > of heavyweight and we should do it as seldom as possible.
> > 
> > What about implementing splice flag SPLICE_F_INTERRUPTIBLE instead?
> 
> The pipe alloc and such? That is lazily done and sticks around.

Thanks!  So this looks like a good way to implement interruptible
in-kernel file copyup?

-VAL
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