Use common functions to handle file locking

 * lib/common.sh: implement
   - lock_open_write()
   - lock_open_read()
   - lock_close()
 * archbuild.in, makechrootpkg.in, mkarchroot.in: use said functions

This has two benefits:
 1. All programs using these methods gain the ability to inherit locks,
    something that only mkarchroot could do before.  This allows the
    commands to be more compos-able.
 2. It is more readable. File locking isn't obvious.

4 files changed, 55 insertions, 32 deletions

diff --git a/archbuild.in b/archbuild.in
index 7220391..9476415 100644
--- a/archbuild.in
+++ b/archbuild.in
@@ -43,17 +43,12 @@ if ${clean_first} || [[ ! -d "${chroots}/${repo}-${arch}" ]]; then
 		[[ -d $copy ]] || continue
 		msg2 "Deleting chroot copy '$(basename "${copy}")'..."
 
-		exec 9>"$copy.lock"
-		if ! flock -n 9; then
-			stat_busy "Locking chroot copy '$copy'"
-			flock 9
-			stat_done
-		fi
+		lock_open_write 9 "$copy.lock" "Locking chroot copy '$copy'"
 
 		{ type -P btrfs && btrfs subvolume delete "${copy}"; } &>/dev/null
 		rm -rf --one-file-system "${copy}"
 	done
-	exec 9>&-
+	lock_close 9
 
 	rm -rf --one-file-system "${chroots}/${repo}-${arch}"
 	mkdir -p "${chroots}/${repo}-${arch}"
diff --git a/lib/common.sh b/lib/common.sh
index b39bbbc..5204091 100644
--- a/lib/common.sh
+++ b/lib/common.sh
@@ -104,6 +104,55 @@ in_array() {
 }
 
 ##
+#  usage : lock_open_write( $fd, $path, $wait_message )
+##
+lock_open_write() {
+	local fd=$1
+	local path=$2
+	local msg=$3
+
+	# Only reopen the FD if it wasn't handed to us
+	if [[ $(readlink -f /dev/fd/$fd) != "${path}.lock" ]]; then
+		eval "exec $fd>${path}.lock"
+	fi
+
+	if ! flock -n $fd; then
+		stat_busy "$msg"
+		flock $fd
+		stat_done
+	fi
+}
+
+##
+#  usage : lock_open_read( $fd, $path, $wait_message )
+##
+lock_open_read() {
+	local fd=$1
+	local path=$2
+	local msg=$3
+
+	# Only reopen the FD if it wasn't handed to us
+	if [[ $(readlink -f /dev/fd/$fd) != "${path}.lock" ]]; then
+		eval "exec $fd>${path}.lock"
+	fi
+
+	if ! flock -sn $fd; then
+		stat_busy "$msg"
+		flock -s $fd
+		stat_done
+	fi
+}
+
+
+##
+#  usage : lock_close( $fd )
+##
+lock_close() {
+	local fd=$1
+	eval "exec $fd>&-"
+}
+
+##
 #  usage : get_full_version( [$pkgname] )
 # return : full version spec, including epoch (if necessary), pkgver, pkgrel
 ##
diff --git a/makechrootpkg.in b/makechrootpkg.in
index 6c0b013..f3333ca 100644
--- a/makechrootpkg.in
+++ b/makechrootpkg.in
@@ -114,23 +114,12 @@ umask 0022
 
 # Lock the chroot we want to use. We'll keep this lock until we exit.
 # Note this is the same FD number as in mkarchroot
-exec 9>"$copydir.lock"
-if ! flock -n 9; then
-	stat_busy "Locking chroot copy '$copy'"
-	flock 9
-	stat_done
-fi
+lock_open_write 9 "$copydir.lock" "Locking chroot copy '$copy'"
 
 if [[ ! -d $copydir ]] || $clean_first; then
 	# Get a read lock on the root chroot to make
 	# sure we don't clone a half-updated chroot
-	exec 8>"$chrootdir/root.lock"
-
-	if ! flock -sn 8; then
-		stat_busy "Locking clean chroot"
-		flock -s 8
-		stat_done
-	fi
+	lock_open_read 8 "$chrootdir/root.lock" "Locking clean chroot"
 
 	stat_busy 'Creating clean working copy'
 	use_rsync=false
@@ -149,7 +138,7 @@ if [[ ! -d $copydir ]] || $clean_first; then
 	stat_done
 
 	# Drop the read lock again
-	exec 8>&-
+	lock_close 8
 fi
 
 if [[ -n $install_pkg ]]; then
diff --git a/mkarchroot.in b/mkarchroot.in
index 76ad840..022943e 100644
--- a/mkarchroot.in
+++ b/mkarchroot.in
@@ -183,17 +183,7 @@ trap_chroot_umount () {
 }
 
 chroot_lock () {
-	# Only reopen the FD if it wasn't handed to us
-	if [[ $(readlink -f /dev/fd/9) != "${working_dir}.lock" ]]; then
-	  exec 9>"${working_dir}.lock"
-	fi
-
-	# Lock the chroot. Take note of the FD number.
-	if ! flock -n 9; then
-		stat_busy "Locking chroot"
-		flock 9
-		stat_done
-	fi
+	lock_open_write 9 "${working_dir}.lock" "Locking chroot"u
 }
 
 chroot_run() {