lib: Turn qemu_escape_param into a shared function.

This function appeared twice (identically).  Turn it into a single
shared function.

This also adds some documentation for the two files affected.

src/create.c

@@ -16,6 +16,12 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+/**
+ * APIs for creating empty disks.
+ *
+ * Mostly this consists of wrappers around the L<qemu-img(1)> program.
+ */
+
 #include <config.h>
 
 #include <stdio.h>
@@ -42,7 +48,6 @@
 
 static int disk_create_raw (guestfs_h *g, const char *filename, int64_t size, const struct guestfs_disk_create_argv *optargs);
 static int disk_create_qcow2 (guestfs_h *g, const char *filename, int64_t size, const char *backingfile, const struct guestfs_disk_create_argv *optargs);
-static char *qemu_escape_param (guestfs_h *g, const char *param);
 
 int
 guestfs_impl_disk_create (guestfs_h *g, const char *filename,
@@ -313,7 +318,7 @@ disk_create_qcow2 (guestfs_h *g, const char *orig_filename, int64_t size,
 
   /* -o parameter. */
   if (backingfile) {
-    CLEANUP_FREE char *p = qemu_escape_param (g, backingfile);
+    CLEANUP_FREE char *p = guestfs_int_qemu_escape_param (g, backingfile);
     guestfs_int_add_sprintf (g, &optionsv, "backing_file=%s", p);
   }
   if (backingformat)
@@ -345,21 +350,3 @@ disk_create_qcow2 (guestfs_h *g, const char *orig_filename, int64_t size,
 
   return 0;
 }
-
-/* XXX Duplicated in launch-direct.c. */
-static char *
-qemu_escape_param (guestfs_h *g, const char *param)
-{
-  size_t i, len = strlen (param);
-  char *p, *ret;
-
-  ret = p = safe_malloc (g, len*2 + 1); /* max length of escaped name*/
-  for (i = 0; i < len; ++i) {
-    *p++ = param[i];
-    if (param[i] == ',')
-      *p++ = ',';
-  }
-  *p = '\0';
-
-  return ret;
-}

src/guestfs-internal.h

@@ -903,6 +903,7 @@ extern void guestfs_int_cleanup_cmd_close (struct command **);
 /* launch-direct.c */
 extern char *guestfs_int_drive_source_qemu_param (guestfs_h *g, const struct drive_source *src);
 extern bool guestfs_int_discard_possible (guestfs_h *g, struct drive *drv, unsigned long qemu_version);
+extern char *guestfs_int_qemu_escape_param (guestfs_h *g, const char *param);
 
 /* launch-*.c constructors */
 void guestfs_int_init_direct_backend (void) __attribute__((constructor));

src/launch-direct.c

@@ -16,6 +16,12 @@
  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  */
 
+/**
+ * Implementation of the C<direct> backend.
+ *
+ * For more details see L<guestfs(3)/BACKENDS>.
+ */
+
 #include <config.h>
 
 #include <stdio.h>
@@ -69,7 +75,6 @@ static void print_qemu_command_line (guestfs_h *g, char **argv);
 static int qemu_supports (guestfs_h *g, struct backend_direct_data *, const char *option);
 static int qemu_supports_device (guestfs_h *g, struct backend_direct_data *, const char *device_name);
 static int qemu_supports_virtio_scsi (guestfs_h *g, struct backend_direct_data *);
-static char *qemu_escape_param (guestfs_h *g, const char *param);
 
 static char *
 create_cow_overlay_direct (guestfs_h *g, void *datav, struct drive *drv)
@@ -501,7 +506,7 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
 
       /* Make the file= parameter. */
       file = guestfs_int_drive_source_qemu_param (g, &drv->src);
-      escaped_file = qemu_escape_param (g, file);
+      escaped_file = guestfs_int_qemu_escape_param (g, file);
 
       /* Make the first part of the -drive parameter, everything up to
        * the if=... at the end.
@@ -521,7 +526,7 @@ launch_direct (guestfs_h *g, void *datav, const char *arg)
     }
     else {
       /* Writable qcow2 overlay on top of read-only drive. */
-      escaped_file = qemu_escape_param (g, drv->overlay);
+      escaped_file = guestfs_int_qemu_escape_param (g, drv->overlay);
       param = safe_asprintf
         (g, "file=%s,cache=unsafe,format=qcow2%s%s,id=hd%zu",
          escaped_file,
@@ -1137,11 +1142,13 @@ qemu_supports_virtio_scsi (guestfs_h *g, struct backend_direct_data *data)
   return data->virtio_scsi == 1;
 }
 
-/* Escape a qemu parameter.  Every ',' becomes ',,'.  The caller must
- * free the returned string.
+/**
+ * Escape a qemu parameter.
+ *
+ * Every C<,> becomes C<,,>.  The caller must free the returned string.
  */
-static char *
-qemu_escape_param (guestfs_h *g, const char *param)
+char *
+guestfs_int_qemu_escape_param (guestfs_h *g, const char *param)
 {
   size_t i, len = strlen (param);
   char *p, *ret;