Re: [PATCH-RFC-RESEND 1/9] vfs: pull btrfs clone API to vfs layer

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

On Wed, Aug 26, 2015 at 03:37:23PM +0200, David Sterba wrote:
> On Wed, Aug 26, 2015 at 04:16:42PM +0800, Peng Tao wrote:
> > +struct file_clone_range {
> > +	__s64 src_fd;
> > +	__u64 src_offset;
> > +	__u64 src_length;
> > +	__u64 dest_offset;
> > +};
> 
> Might be a good idea to add some spare bytes to the structure.

But... structure size is encoded in the ioctl definition, so adding bytes
to struct file_clone_range now will change the ioctl number and break
userland.

--D

> 
> >  struct fstrim_range {
> >  	__u64 start;
> >  	__u64 len;
> > @@ -159,6 +166,8 @@ struct inodes_stat_t {
> >  #define FIFREEZE	_IOWR('X', 119, int)	/* Freeze */
> >  #define FITHAW		_IOWR('X', 120, int)	/* Thaw */
> >  #define FITRIM		_IOWR('X', 121, struct fstrim_range)	/* Trim */
> > +#define FICLONE		_IOW(0x94, 9, int)	/* Clone */
> > +#define FICLONERANGE	_IOW(0x94, 13, struct file_clone_range)	/* Clone range */
> 
> FICLONE is a special case of FICLONERANGE. The whole file clone had come
> historically first and then was refined, I don't think this needs to be
> copied to the generic API. A zeroed file_clone_range is simple to use
> for that purpose.
> --
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