Re: [PATCH] xfsprogs: copy_range don't truncate dstfile if same with srcfile

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

On Wed, Sep 04, 2019 at 02:32:22PM +0800, Jianhong.Yin wrote:
> now if we do copy_range in same file without any extra option
> will truncate the file, and not any document indicate this default
> action. that's risky to users.
> 
> '''
> $ LANG=C ll testfile
> -rw-rw-r--. 1 yjh yjh 4054 Sep  4 14:22 testfile
> $ ./xfs_io -c 'copy_range testfile' testfile
> $ LANG=C ll testfile
> -rw-rw-r--. 1 yjh yjh 4054 Sep  4 14:23 testfile
> '''
> 
> Signed-off-by: Jianhong Yin <yin-jianhong@163.com>
> ---
>  io/copy_file_range.c | 23 +++++++++++++++++++----
>  1 file changed, 19 insertions(+), 4 deletions(-)
> 
> diff --git a/io/copy_file_range.c b/io/copy_file_range.c
> index b7b9fd88..487041c0 100644
> --- a/io/copy_file_range.c
> +++ b/io/copy_file_range.c
> @@ -75,6 +75,19 @@ copy_dst_truncate(void)
>  	return ret;
>  }
>  
> +int is_same_file(int fd1, int fd2) {
> +	struct stat stat1, stat2;
> +	if (fstat(fd1, &stat1) < 0) {
> +		perror("fstat");
> +		return -1;
> +	}
> +	if (fstat(fd2, &stat2) < 0) {
> +		perror("fstat");
> +		return -1;
> +	}
> +	return (stat1.st_dev == stat2.st_dev) && (stat1.st_ino == stat2.st_ino);
> +}
> +
>  static int
>  copy_range_f(int argc, char **argv)
>  {
> @@ -147,10 +160,12 @@ copy_range_f(int argc, char **argv)
>  		}
>  		len = sz;
>  
> -		ret = copy_dst_truncate();
> -		if (ret < 0) {
> -			ret = 1;
> -			goto out;
> +		if (!is_same_file(fd, file->fd)) {

Uggggh, why does xfs_io copy_range have this weird behavior?  It should
be a simple wrapper for copy_file_range (the syscall) and nothing else.

The code patch looks fine for solving this edge case, but we really
shouldn't have this "extra" functionality in a debugging tool that
should be athin wrapper around the syscall for xfstests purposes.

--D

> +			ret = copy_dst_truncate();
> +			if (ret < 0) {
> +				ret = 1;
> +				goto out;
> +			}
>  		}
>  	}
>  
> -- 
> 2.17.2
>