Improved handling of file descriptors, other minor changes

qq2clone

@@ -15,7 +15,7 @@ E_template=13   # Problem with a template
 E_extcom=14     # An external command failed
 E_xml=15        # Malformed XML or issue processing XML
 E_libvirt=16    # Invokation of a libvirt tool was unsuccesful
-E_timeout=17    # Timeout was exceeded before spice connection to clone
+E_timeout=17    # Timeout was exceeded before spice connection to VM
                 # was established
 E_file=18       # Expected file does not exist or is of wrong type/format
 E_unexpected=19 # Probably a bug in qq2clone
@@ -89,6 +89,7 @@ while IFS= read -r line <&3; do
     echo "$match"
     (($#)) && (($1 == 1)) && write_pipe 0 "$match"
   else
+    [[ "$line" == "EOF" ]] || unexpected_error "read_pipe"
     break
   fi
 done
@@ -107,9 +108,10 @@ write_pipe ()
 #   $2 and on: If $1 is 0, write_pipe will write the remaining parameters
 #=========================================================================#
 {
-# We put a + at the beginning of every line to let read_pipe work in a
-# non-blocking manner
+# + is put at the beginning of every line echoed to the pipe, so that
+# read_pipe can operate in a non-blocking manner
 local line
+{ [[ "$1" == "0" ]] || [[ "$1" == "1" ]]; } || unexpected_error write_pipe
 if (($1)); then
   while IFS= read -r line; do 
     echo "+$line" >&3
@@ -129,6 +131,12 @@ return 0
                           #@@@@@@@@@@@@@@@@@@@#
                           #-------------------#
 
+# lv_api_do is accessed in the background because it allows for only one
+#   subshell to be invoked when using lv_api_do repeatedly. Makes qq2clone
+#   more efficient (significantly, in some cases) but makes opening and
+#   closing lv_api_do into something that must be managed manually by the
+#   coder
+
 #=========================================================================#
 lv_api_do_close ()
 # DESCRIPTION: Tell lv_api_do to exit and close the extra pipe
@@ -138,8 +146,7 @@ lv_api_do_close ()
 #=========================================================================#
 {
   echo "exit" >&4
-  exec 4>&-
-  exec 4<&-
+  exec 4>&- 4<&-
   rm -rf "${lv_api_temp:?}"
   return 0
 }
@@ -147,12 +154,15 @@ lv_api_do_close ()
 lv_api_do_comm ()
 # DESCRIPTION: Issue a command to lv_api_do
 # INPUT: The command
-# OUTPUT: Return 0 on success, lv_api_do output can be accessed with 
-#   read_pipe. Return 1 on failure. Exit and error message if lv_api_do
-#   encounters a fatal error
+# OUTPUT: Return 0/1 on success/failure. lv_api_do output can be accessed
+#   with read_pipe.  Exit and error message if lv_api_do encounters
+#   a fatal error
 # PARAMETERS: $@: command string to lv_api_do
 #=========================================================================#
 {
+# Ensure lv_api_do is open
+( : >&4 ; ) &>/dev/null || unexpected_error lv_api_do_comm
+
 echo "$*" >&4
 local check
 read -r check <&3
@@ -3118,6 +3128,10 @@ return 0
                             #-----------------#
 
 if ! ((QQ2_NOEXECUTE)); then
+
+  #Ensure needed fds are not in use
+  exec 3>&- 3<&- 4>&- 4<&-;
+
   open_pipe
   if [[ -n "$QQ2_DIR" ]]; then
     : # If already set, use existing value