linux-kernel - Re: [PATCH 3/3] block: implement (some of) fallocate for block devices

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Date:	Mon, 21 Mar 2016 10:52:35 -0700
From:	"Darrick J. Wong" <darrick.wong@...cle.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	axboe@...nel.dk, torvalds@...ux-foundation.org,
	bfields@...ldses.org, tytso@....edu, martin.petersen@...cle.com,
	linux-api@...r.kernel.org, david@...morbit.com,
	linux-kernel@...r.kernel.org, shane.seymour@....com,
	linux-fsdevel@...r.kernel.org, jlayton@...chiereds.net,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 3/3] block: implement (some of) fallocate for block
 devices

On Mon, Mar 21, 2016 at 08:38:27AM -0700, Christoph Hellwig wrote:
> On Tue, Mar 15, 2016 at 12:42:44PM -0700, Darrick J. Wong wrote:
> >  #include <linux/cleancache.h>
> >  #include <linux/dax.h>
> >  #include <asm/uaccess.h>
> > +#include <linux/falloc.h>
> 
> Maybe keep this before asm/uaccess.h
> 
> > +long blkdev_fallocate(struct file *file, int mode, loff_t start, loff_t len)
> 
> should be marked static.

Ok (to both).

> 
> > +	/* We haven't a primitive for "ensure space exists" right now. */
> > +	if (!(mode & ~FALLOC_FL_KEEP_SIZE))
> > +		return -EOPNOTSUPP;
> 
> I don't really understand the comment.  But I think you'd be much

I don't know of a block device primitive that corresponds to the "default"
mode of fallocate, as documented in the manpage (i.e. mode == 0).  I agree
that the whole thing could be simplified in the manner you point out below.

> better off with having blkdev_fallocate as just a tiny wrapper that has
> a switch for the supported modes, e.g.
> 
> 	switch (mode) {
> 	case FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE:
> 		return blkdev_punch_hole();
> 	case FALLOC_FL_ZERO_RANGE | FALLOC_FL_KEEP_SIZE::
> 		return blkdev_zero_range();
> 	default:
> 		return -EOPNOTSUPP;
> 	}
> 
> > +EXPORT_SYMBOL_GPL(blkdev_fallocate);
> 
> and no need to export it either..

Ok.

--D

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