Re: [PATCH] duperemove: test presence of dedupe ioctl

[Christoph Hellwig <hch@infradead.org>]

On Fri, Dec 09, 2016 at 09:56:45AM -0800, Darrick J. Wong wrote:
> Since a zero-length dedupe operation is guaranteed to succeed, use that
> to test whether or not this filesystem supports dedupe.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  file_scan.c |   47 +++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 37 insertions(+), 10 deletions(-)
> 
> diff --git a/file_scan.c b/file_scan.c
> index 617f166..a34453e 100644
> --- a/file_scan.c
> +++ b/file_scan.c
> @@ -45,11 +45,7 @@
>  #include "file_scan.h"
>  #include "dbfile.h"
>  #include "util.h"
> -
> -/* This is not in linux/magic.h */
> -#ifndef	XFS_SB_MAGIC
> -#define	XFS_SB_MAGIC		0x58465342	/* 'XFSB' */
> -#endif
> +#include "btrfs-ioctl.h"
>  
>  static char path[PATH_MAX] = { 0, };
>  static char *pathp = path;
> @@ -189,6 +185,39 @@ static int walk_dir(const char *name)
>  	return ret;
>  }
>  
> +struct fake_btrfs_ioctl_same_args {
> +	struct btrfs_ioctl_same_args args;
> +	struct btrfs_ioctl_same_extent_info info;
> +};

Why does this need a fake structure here?