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

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Date:	Mon, 21 Mar 2016 08:38:27 -0700
From:	Christoph Hellwig <hch@...radead.org>
To:	"Darrick J. Wong" <darrick.wong@...cle.com>
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,
	hch@...radead.org, 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 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.

> +	/* 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
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..