Re: [PATCH 2/2] xfs_io: allow open file permissions to be changed

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

On Mon, Dec 03, 2018 at 07:53:43AM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
> 
> I need to be able to open a file read-write, then change the
> permissions on the file to read-only to check that copy_file_range
> returns EPERM correctly in that case. This can't be done as root,
> because root ignores file permissions, but as a normal user we can't
> open a 0444 file for writing and so can't actually test writing to
> a read-only file without some method of "open read-write, change
> permissions to read-only, try to write to file through open
> read-write file".
> 
> So, allow adding or removing write permissions on an open file.
> 
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
>  io/open.c | 54 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 54 insertions(+)
> 
> diff --git a/io/open.c b/io/open.c
> index b1d9a0fa317c..153d4a836d4c 100644
> --- a/io/open.c
> +++ b/io/open.c
> @@ -44,6 +44,7 @@ static cmdinfo_t chproj_cmd;
>  static cmdinfo_t lsproj_cmd;
>  static cmdinfo_t extsize_cmd;
>  static cmdinfo_t inode_cmd;
> +static cmdinfo_t chmod_cmd;
>  static prid_t prid;
>  static long extsize;
>  
> @@ -809,6 +810,48 @@ inode_f(
>  	return 0;
>  }
>  
> +static void
> +chmod_help(void)
> +{
> +	printf(_(
> +"\n"
> +" Change the read/write permissions on the current file\n"
> +"\n"
> +" Options:\n"
> +" -r -- make the file read only (0444 permissions)\n"
> +" -w -- make the file read/write (0664 permissions)\n"
> +"\n"));
> +}
> +
> +static int
> +chmod_f(
> +	int		argc,
> +	char		**argv)
> +{
> +	mode_t		mode = S_IRUSR | S_IRGRP | S_IROTH;
> +	int		c;
> +
> +	while ((c = getopt(argc, argv, "rw")) != EOF) {
> +		switch (c) {
> +		case 'r':
> +			break;
> +		case 'w':
> +			mode |= S_IWUSR | S_IWGRP;
> +			break;
> +		default:
> +			return command_usage(&chmod_cmd);
> +		}
> +	}
> +
> +	if (argc != optind)
> +		return command_usage(&chmod_cmd);
> +
> +	if (fchmod(file->fd, mode) < 0) {
> +		exitcode = 1;
> +		perror("fchmod");
> +	}
> +	return 0;
> +}
>  void
>  open_init(void)
>  {
> @@ -871,10 +914,21 @@ open_init(void)
>  		_("Query inode number usage in the filesystem");
>  	inode_cmd.help = inode_help;
>  
> +	chmod_cmd.name = "chmod";
> +	chmod_cmd.cfunc = chmod_f;
> +	chmod_cmd.args = _("-r | -w");
> +	chmod_cmd.argmin = 1;
> +	chmod_cmd.argmax = 1;
> +	chmod_cmd.flags = CMD_NOMAP_OK | CMD_FOREIGN_OK | CMD_FLAG_ONESHOT;
> +	chmod_cmd.oneline =
> +		_("change the read/write permissios on the currently open file");

"permissions"...

Also, there needs to be a manpage update for this, or else xfs/293 fails.

--D

> +	chmod_cmd.help = chmod_help;
> +
>  	add_command(&open_cmd);
>  	add_command(&close_cmd);
>  	add_command(&chproj_cmd);
>  	add_command(&lsproj_cmd);
>  	add_command(&extsize_cmd);
>  	add_command(&inode_cmd);
> +	add_command(&chmod_cmd);
>  }
> -- 
> 2.19.1
>