do_unmount: add parallel unmounting

this turns mouninfo into a multicall binary which can also do
parallel unmounting. most mountinfo code is unchanged; only
notable change is find_mounts() now returns the number of mounts
found and also takes the "process" function as an argument; so
that is_mounted() can be implemented on top of it.

do_unmount mostly follows the logic of previous code. some
notable changes:

- do_unmount is now "lazy" when it comes to retrying failed
  unmounts. it will greedily keep running unmount as long as it
  can before it looks at the "waiting" queue.
- it will check if the mountpoint is still mounted or not when
  umount returns non-zero exit code. this is due to the fact that
  multiple umount calls might race to unmount a shared mount. so
  if umount fails _but_ the mountpoint is no longer mounted, we
  assume success.
- do_unmount used to fail if fuser did not find any pids using
  the mount. the new code tries one more time; the rationale being
  that there's a gap between the umount call and the fuser call,
  and so whatever was using the mount before might have stopped
  using it now and so it's worth another attempt.

Fixes: #662
Closes: #698

Author: N-R-K

init.d/localmount.in

@@ -112,7 +112,7 @@ stop()
 	# Umount loop devices
 	einfo "Unmounting loop devices"
 	eindent
-	do_unmount "umount -d" --skip-point-regex "$no_umounts_r" \
+	do_unmount -d -- --skip-point-regex "$no_umounts_r" \
 		--node-regex "^/dev/loop"
 	eoutdent
 
@@ -125,7 +125,7 @@ stop()
 		fs="$fs${fs:+|}$x"
 	done
 	[ -n "$fs" ] && fs="^($fs)$"
-	do_unmount umount --skip-point-regex "$no_umounts_r" \
+	do_unmount -- --skip-point-regex "$no_umounts_r" \
 		"${fs:+--skip-fstype-regex}" $fs --nonetdev
 	eoutdent
 

init.d/mount-ro.in

@@ -25,8 +25,6 @@ start()
 	sync
 
 	ebegin "Remounting remaining filesystems read-only"
-	# We need the do_unmount function
-	. "$RC_LIBEXECDIR"/sh/rc-mount.sh
 	eindent
 
 	# Bug 381783
@@ -48,7 +46,7 @@ start()
 		fs="$fs${fs:+|}$x"
 	done
 	[ -n "$fs" ] && fs="^($fs)$"
-	do_unmount "umount -r" \
+	do_unmount -r -- \
 		--skip-point-regex "$m" \
 		"${fs:+--skip-fstype-regex}" $fs --nonetdev
 	ret=$?

init.d/netmount.in

@@ -64,7 +64,6 @@ stop()
 	local x= fs=
 
 	ebegin "Unmounting network filesystems"
-	. "$RC_LIBEXECDIR"/sh/rc-mount.sh
 
 	for x in $net_fs_list $extra_net_fs_list; do
 		fs="$fs${fs:+,}$x"
@@ -79,7 +78,7 @@ stop()
 		fs="$fs${fs:+|}$x"
 	done
 	[ -n "$fs" ] && fs="^($fs)$"
-	do_unmount umount ${fs:+--fstype-regex} $fs --netdev
+	do_unmount -- ${fs:+--fstype-regex} $fs --netdev
 	retval=$?
 
 	eoutdent

sh/meson.build

@@ -9,7 +9,6 @@ sh_conf_data.set('SYSCONFDIR', get_option('sysconfdir'))
 
 sh = [
   'rc-functions.sh',
-  'rc-mount.sh',
   'runit.sh',
   's6.sh',
   'start-stop-daemon.sh',

sh/rc-mount.sh

@@ -1,5 +1,7 @@
-executable('mountinfo', 'mountinfo.c',
-  include_directories: incdir,
-  dependencies: [rc, einfo, shared],
-  install: true,
-  install_dir: rc_bindir)
+foreach exec : ['mountinfo', 'do_unmount']
+  executable(exec, 'mountinfo.c',
+    include_directories: incdir,
+    dependencies: [rc, einfo, shared],
+    install: true,
+    install_dir: rc_bindir)
+endforeach