docs: update TODO (add item about mnt_context_get_excode() )

- add item about https://github.com/karelzak/util-linux/issues/1208
- remove old CAP_SYS_ADMIN note (in last versions mount(8) drops suid if
  necessary).

Addresses: https://github.com/karelzak/util-linux/issues/1208
Signed-off-by: Karel Zak <kzak@redhat.com>

Documentation/TODO

@@ -64,6 +64,13 @@ bash completion
 libmount (mount/umount)
 -----------------------
 
+ - mnt_context_get_excode() does not return error messages from /sbin/[u]mount.<type>
+   external helpers. It is disadvantages in same cases (non-terminal progarms).
+   The solution is to use pipe(), keep output from helper in memory and return it later
+   by mnt_context_get_excode() (or mnt_context_get_helper_output(), etc.). This feature
+   should be optional and disabled by default.
+   see: https://github.com/karelzak/util-linux/issues/1208
+
  - add --onlyonce to force mount(8) to check if mountpoint is already used. Now
    "already mounted" detection is used for --all only. The problem is if you
    call "mount <mountpoint>" more than once for in fstab defined tmpfs (or network
@@ -71,15 +78,6 @@ libmount (mount/umount)
    of the FS is created. https://github.com/karelzak/util-linux/issues/448
    (... just idea, maybe wrong idea)
 
- - support CAP_SYS_ADMIN; for mount(2) syscall the CAP_SYS_ADMIN is good
-   enough. Unfortunately, mount(8) does more things like check for filesystem
-   type (but it's usually done by udev, so root perms are unnecessary), create
-   loop devices, write to /run/mount/utab or /etc/mtab, etc.
-
-   It would be nice to improve libmount to check for CAP_SYS_ADMIN if suid not
-   set and allow using it for simple tasks where no another operation is
-   necessary.
-
 partx
 -----
 

libmount/src/context.c

@@ -2723,6 +2723,9 @@ int mnt_context_get_generic_excode(int rc, char *buf, size_t bufsz, char *fmt, .
  * and mnt_context_get_helper_status(). Note that mount(8) and umount(8) utils
  * always return code from helper without extra care about it.
  *
+ * The current implementation does not read error message from external
+ * helper into @buf.
+ *
  * If the argument @buf is not NULL then error message is generated (if
  * anything failed).
  *