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

[Zorro Lang <zlang@xxxxxxxxxx>]

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

Finally we turn to talk about this part now:) The patch itself looks fine to me.

I just have one question to other xfsprogs developers, why the copy_range would
like to truncate(0) the target file by default (len=0 by default)? I think this's
not a same or not same files problem, this's why we truncate the target file?

Why not set the 'len' to the size of srcfile(copy_src_filesize) by default if
there's not a '-l N' specified? And never truncate the target file (if someone need
to truncate target file, do it by -c 'truncate N' or '-t').

Anyway, talk is cheap, show my demo code to explain what I mean:

diff --git a/io/copy_file_range.c b/io/copy_file_range.c
index b7b9fd88..51c3dc55 100644
--- a/io/copy_file_range.c
+++ b/io/copy_file_range.c
@@ -66,15 +66,6 @@ copy_src_filesize(int fd)
        return st.st_size;
 }
 
-static int
-copy_dst_truncate(void)
-{
-       int ret = ftruncate(file->fd, 0);
-       if (ret < 0)
-               perror("ftruncate");
-       return ret;
-}
-
 static int
 copy_range_f(int argc, char **argv)
 {
@@ -87,6 +78,7 @@ copy_range_f(int argc, char **argv)
        int src_path_arg = 1;
        int src_file_nr = 0;
        size_t fsblocksize, fssectsize;
+       int lflag=0;
 
        init_cvtnum(&fsblocksize, &fssectsize);
 
@@ -112,6 +104,7 @@ copy_range_f(int argc, char **argv)
                                printf(_("invalid length -- %s\n"), optarg);
                                return 0;
                        }
+                       lflag = 1;
                        break;
                case 'f':
                        src_file_nr = atoi(argv[1]);
@@ -137,23 +130,15 @@ copy_range_f(int argc, char **argv)
                fd = filetable[src_file_nr].fd;
        }
 
-       if (src == 0 && dst == 0 && len == 0) {
+       if (!lflag) {
                off64_t sz;
-
                sz = copy_src_filesize(fd);
-               if (sz < 0 || (unsigned long long)sz > SIZE_MAX) {
-                       ret = 1;
-                       goto out;
-               }
-               len = sz;
-
-               ret = copy_dst_truncate();
-               if (ret < 0) {
+               if (sz < 0 || (unsigned long long)sz > SIZE_MAX || sz < src) {
                        ret = 1;
                        goto out;
                }
+               len = sz - src;
        }
-
        ret = copy_file_range_cmd(fd, &src, &dst, len);
 out:
        close(fd);

Thanks,
Zorro

>  		}
>  	}
>  
> -- 
> 2.17.2
>