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

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Dec 14, 2016 at 02:44:36AM -0800, Christoph Hellwig wrote:
> 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?

In order to test the ioctl we have to fill out at least one
btrfs_ioctl_same_extent_info so that we get far enough into the fs-specific
dedupe_range handler that we've verified that the fs is capable of dedupe and
that the fs is willing to try to satisfy the request.

We could just malloc sizeof(_same_args) + sizeof(_same_extent_info)...

--D

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