tmpfs: expand "help" to explain value of TMPFS_POSIX_ACL

Expand the fs/Kconfig "help" info to clarify why it's a bad idea to
deselect the TMPFS_POSIX_ACL config variable.

Signed-off-by: Robert P. J. Day <[email protected]>
Acked-by: Randy Dunlap <[email protected]>
Acked-by: Hugh Dickins <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/Kconfig

@@ -127,14 +127,21 @@ config TMPFS_POSIX_ACL
 	select TMPFS_XATTR
 	select GENERIC_ACL
 	help
-	  POSIX Access Control Lists (ACLs) support permissions for users and
-	  groups beyond the owner/group/world scheme.
+	  POSIX Access Control Lists (ACLs) support additional access rights
+	  for users and groups beyond the standard owner/group/world scheme,
+	  and this option selects support for ACLs specifically for tmpfs
+	  filesystems.
+
+	  If you've selected TMPFS, it's possible that you'll also need
+	  this option as there are a number of Linux distros that require
+	  POSIX ACL support under /dev for certain features to work properly.
+	  For example, some distros need this feature for ALSA-related /dev
+	  files for sound to work properly.  In short, if you're not sure,
+	  say Y.
 
 	  To learn more about Access Control Lists, visit the POSIX ACLs for
 	  Linux website <http://acl.bestbits.at/>.
 
-	  If you don't know what Access Control Lists are, say N.
-
 config TMPFS_XATTR
 	bool "Tmpfs extended attributes"
 	depends on TMPFS