Re: [RFC PATCH xfsprogs] xfs_io: add support for linkat() AT_LINK_REPLACE

[Zorro Lang <zlang@redhat.com>]

On Wed, Jan 29, 2020 at 12:58:29AM -0800, Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
> 
> Signed-off-by: Omar Sandoval <osandov@fb.com>
> ---

And this patch would be better to send to/cc linux-xfs@vger.kernel.org to get
xfsprogs maintainers/developers review.

>  io/link.c         | 24 ++++++++++++++++++++----
>  man/man8/xfs_io.8 |  9 ++++++++-
>  2 files changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/io/link.c b/io/link.c
> index f4f4b139..3fc3e24d 100644
> --- a/io/link.c
> +++ b/io/link.c
> @@ -12,6 +12,9 @@
>  #ifndef AT_EMPTY_PATH
>  #define AT_EMPTY_PATH	0x1000
>  #endif
> +#ifndef AT_LINK_REPLACE
> +#define AT_LINK_REPLACE	0x10000
> +#endif
>  
>  static cmdinfo_t flink_cmd;
>  
> @@ -22,6 +25,7 @@ flink_help(void)
>  "\n"
>  "link the open file descriptor to the supplied filename\n"
>  "\n"
> +" -f -- overwrite the target filename if it exists (AT_LINK_REPLACE)\n"
>  "\n"));
>  }
>  
> @@ -30,10 +34,22 @@ flink_f(
>  	int		argc,
>  	char		**argv)
>  {
> -	if (argc != 2)
> +	int		flags = AT_EMPTY_PATH;
> +	int		c;
> +
> +	while ((c = getopt(argc, argv, "f")) != EOF) {
> +		switch (c) {
> +		case 'f':
> +			flags |= AT_LINK_REPLACE;
> +			break;
> +		default:
> +			return command_usage(&flink_cmd);
> +		}
> +	}
> +	if (optind != argc - 1)
>  		return command_usage(&flink_cmd);
>  
> -	if (linkat(file->fd, "", AT_FDCWD, argv[1], AT_EMPTY_PATH) < 0) {
> +	if (linkat(file->fd, "", AT_FDCWD, argv[optind], flags) < 0) {
>  		perror("flink");
>  		return 0;
>  	}
> @@ -46,9 +62,9 @@ flink_init(void)
>  	flink_cmd.name = "flink";
>  	flink_cmd.cfunc = flink_f;
>  	flink_cmd.argmin = 1;
> -	flink_cmd.argmax = 1;
> +	flink_cmd.argmax = -1;
>  	flink_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK | CMD_FLAG_ONESHOT;
> -	flink_cmd.args = _("filename");
> +	flink_cmd.args = _("[-f] filename");
>  	flink_cmd.oneline =
>  		_("link the open file descriptor to the supplied filename");
>  	flink_cmd.help = flink_help;
> diff --git a/man/man8/xfs_io.8 b/man/man8/xfs_io.8
> index c69b295d..f79b3a59 100644
> --- a/man/man8/xfs_io.8
> +++ b/man/man8/xfs_io.8
> @@ -807,8 +807,15 @@ for the full list) is available via the
>  .B help
>  command.
>  .TP
> -.BI "flink " path
> +.BI "flink [ \-f ]" " path"
>  Link the currently open file descriptor into the filesystem namespace.
> +.RS 1.0i
> +.PD 0
> +.TP 0.4i
> +.B \-f
> +overwrite the target path if it exists (AT_LINK_REPLACE).
> +.PD
> +.RE
>  .TP
>  .BR stat " [ " \-v "|" \-r " ]"
>  Selected statistics from
> -- 
> 2.25.0
>