lib: Fix memory leak and simplify command code.

Fix the following memory leak found by valgrind:

==13629== 498 (112 direct, 386 indirect) bytes in 1 blocks are definitely lost in loss record 99 of 110
==13629==    at 0x4A06B2F: calloc (vg_replace_malloc.c:593)
==13629==    by 0x4CA564E: guestfs_safe_calloc (alloc.c:71)
==13629==    by 0x4CA9B02: guestfs___new_command (command.c:143)
==13629==    by 0x4CA66E9: guestfs___build_appliance (appliance.c:690)
==13629==    by 0x4CBD1B9: launch_libvirt (launch-libvirt.c:188)
==13629==    by 0x402E7E: main (virt-filesystems.c:349)

Also adjust the command code in several places to make it simpler.  We
can almost always call guestfs___cmd_close right after
guestfs___cmd_run, avoiding any need to close the handle along error
paths.

Tested by running the test suite under valgrind.

1 files changed, 2 insertions, 5 deletions

diff --git a/src/info.c b/src/info.c
index 156c11fe..6df3aafa 100644
--- a/src/info.c
+++ b/src/info.c
@@ -168,7 +168,7 @@ run_qemu_img_info (guestfs_h *g, const char *filename,
 {
   char *abs_filename = NULL;
   char *safe_filename = NULL;
-  struct command *cmd = NULL;
+  struct command *cmd;
   int r;
 
   if (guestfs___lazy_make_tmpdir (g) == -1)
@@ -194,6 +194,7 @@ run_qemu_img_info (guestfs_h *g, const char *filename,
   guestfs___cmd_add_arg (cmd, safe_filename);
   guestfs___cmd_set_stdout_callback (cmd, fn, data, 0);
   r = guestfs___cmd_run (cmd);
+  guestfs___cmd_close (cmd);
   if (r == -1)
     goto error;
   if (!WIFEXITED (r) || WEXITSTATUS (r) != 0) {
@@ -201,15 +202,11 @@ run_qemu_img_info (guestfs_h *g, const char *filename,
     goto error;
   }
 
-  guestfs___cmd_close (cmd);
   free (safe_filename);
   free (abs_filename);
   return 0;
 
  error:
-  if (cmd)
-    guestfs___cmd_close (cmd);
-
   free (safe_filename);
   free (abs_filename);