[Toybox] [PATCH 3/3] Add support for -o x-mount.mkdir[=0755]

[Isaac Dunham]

On Sat, Mar 28, 2015 at 08:38:14PM +0000, Isaac Dunham wrote:
> Add support for -o x-mount.mkdir[=0755]
> 
> This is a feature of recent versions of util-linux, which allows
> creating a missing directory on mount.
> Probably it should actually be integrated into mount_filesystem()
> and made to check the existence/type of the source and mountpoint.
> 
> Creating a chmod 0000 directory and using it as a mountpoint actually
> works, so we need something other than 0 for a magic "don't create a
> directory" value.
> So we use S_IFLNK as a magic flag, since we don't want to create a link.

Consider this patch an initial version.
I'm not sure what the ideal approach is, but this illustrates the concept.

> ---
>  toys/lsb/mount.c | 27 ++++++++++++++++++++++-----
>  1 file changed, 22 insertions(+), 5 deletions(-)
> 
> diff --git a/toys/lsb/mount.c b/toys/lsb/mount.c
> index 913a434..1711123 100644
> --- a/toys/lsb/mount.c
> +++ b/toys/lsb/mount.c
> @@ -77,7 +77,7 @@ GLOBALS(
>  // TODO mount image.img sub (auto-loopback) then umount image.img
>  
>  // Strip flags out of comma separated list of options, return flags,.
> -static long flag_opts(char *new, long flags, char **more)
> +static long flag_opts(char *new, long flags, char **more, mode_t *mode)
>  {
>    struct {
>      char *name;
> @@ -126,7 +126,11 @@ static long flag_opts(char *new, long flags, char **more)
>          *more = xrealloc(*more, i + strlen(new) + 2);
>          if (i) (*more)[i++] = ',';
>          strcpy(i+*more, new);
> -      } //TODO: handle x-mount.mkdir[=mode] option
> +      } else if (!strncmp(new, "x-mount.mkdir", 13)) {
> +        // handle x-mount.mkdir[=mode] option
> +        if (new[13] == '=') *mode = (mode_t)strtol(new + 14, NULL, 8);
> +        else *mode = 0755;
> +      }
>      }
>  
>      if (!comma) break;
> @@ -251,6 +255,7 @@ void mount_main(void)
>  {
>    char *opts = 0, *dev = 0, *dir = 0, **ss;
>    long flags = MS_SILENT;
> +  mode_t dirmode = S_IFLNK;
>    struct arg_list *o;
>    struct mtab_list *mtl, *mtl2 = 0, *mm, *remount;
>  
> @@ -332,9 +337,15 @@ void mount_main(void)
>   
>        // user only counts from fstab, not opts.
>        if (!mmm) {
> +        dirmode = S_IFLNK;
>          TT.okuser = comma_scan(mm->opts, "user", 1);
> -        aflags = flag_opts(mm->opts, flags, &aopts);
> -        aflags = flag_opts(opts, aflags, &aopts);
> +        aflags = flag_opts(mm->opts, flags, &aopts, &dirmode);
> +        aflags = flag_opts(opts, aflags, &aopts, &dirmode);
> +
> +        if (!getuid() && !(dirmode & S_IFLNK)) {
> +          mkpathat(AT_FDCWD, mm->dir, dirmode, 2);
> +          mkdir(dir, dirmode);
> +        }
>  
>          mount_filesystem(mm->device, mm->dir, mm->type, aflags, aopts);
>        } // TODO else if (getuid()) error_msg("already there") ?
> @@ -365,8 +376,14 @@ void mount_main(void)
>    // two arguments
>    } else {
>      char *more = 0;
> +    long aflags = flag_opts(opts, flags, &more, &dirmode);
> +
> +    if (!getuid() && !(dirmode & S_IFLNK)) { 
> +      mkpathat(AT_FDCWD, dir, dirmode, 2);
> +      mkdir(dir, dirmode);
> +    }
>  
> -    mount_filesystem(dev, dir, TT.type, flag_opts(opts, flags, &more), more);
> +    mount_filesystem(dev, dir, TT.type, aflags, more);
>      if (CFG_TOYBOX_FREE) free(more);
>    }
>  }
> -- 
> 2.1.4
> 

 1427577114.0