launch: Make get-pid and max-disks APIs into virtual methods of the current attach-method.

src/guestfs-internal.h

@@ -165,6 +165,9 @@ struct qemu_param {
 struct attach_ops {
   int (*launch) (guestfs_h *g, const char *arg); /* Initialize and launch. */
   int (*shutdown) (guestfs_h *g); /* Shutdown and cleanup. */
+
+  int (*get_pid) (guestfs_h *g);         /* get-pid API. */
+  int (*max_disks) (guestfs_h *g);       /* max-disks API. */
 };
 extern struct attach_ops attach_ops_appliance;
 extern struct attach_ops attach_ops_libvirt;

src/launch-appliance.c

@@ -1011,16 +1011,8 @@ shutdown_appliance (guestfs_h *g)
   return ret;
 }
 
-struct attach_ops attach_ops_appliance = {
-  .launch = launch_appliance,
-  .shutdown = shutdown_appliance,
-};
-
-/* The APIs below this line depend in some way on this specific attach
- * method, and need some rethinking.
- */
-int
-guestfs__get_pid (guestfs_h *g)
+static int
+get_pid_appliance (guestfs_h *g)
 {
   if (g->app.pid > 0)
     return g->app.pid;
@@ -1031,11 +1023,18 @@ guestfs__get_pid (guestfs_h *g)
 }
 
 /* Maximum number of disks. */
-int
-guestfs__max_disks (guestfs_h *g)
+static int
+max_disks_appliance (guestfs_h *g)
 {
   if (qemu_supports_virtio_scsi (g))
     return 255;
   else
     return 27;                  /* conservative estimate */
 }
+
+struct attach_ops attach_ops_appliance = {
+  .launch = launch_appliance,
+  .shutdown = shutdown_appliance,
+  .get_pid = get_pid_appliance,
+  .max_disks = max_disks_appliance,
+};

src/launch-libvirt.c

@@ -1193,6 +1193,13 @@ libvirt_error (guestfs_h *g, const char *fs, ...)
   free (msg);
 }
 
+/* This backend assumes virtio-scsi is available. */
+static int
+max_disks_libvirt (guestfs_h *g)
+{
+  return 255;
+}
+
 #else /* no libvirt or libxml2 at compile time */
 
 #define NOT_IMPL(r)                                                     \
@@ -1211,9 +1218,16 @@ shutdown_libvirt (guestfs_h *g)
   NOT_IMPL (-1);
 }
 
+static int
+max_disks_libvirt (guestfs_h *g)
+{
+  NOT_IMPL (-1);
+}
+
 #endif /* no libvirt or libxml2 at compile time */
 
 struct attach_ops attach_ops_libvirt = {
   .launch = launch_libvirt,
   .shutdown = shutdown_libvirt,
+  .max_disks = max_disks_libvirt,
 };

src/launch.c

@@ -28,6 +28,7 @@
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <errno.h>
 
 #include "c-ctype.h"
 
@@ -320,6 +321,17 @@ guestfs__debug_drives (guestfs_h *g)
   return ret;                   /* caller frees */
 }
 
+static const struct attach_ops *
+get_attach_ops (guestfs_h *g)
+{
+  switch (g->attach_method) {
+  case ATTACH_METHOD_APPLIANCE: return &attach_ops_appliance;
+  case ATTACH_METHOD_LIBVIRT:   return &attach_ops_libvirt;
+  case ATTACH_METHOD_UNIX:      return &attach_ops_unix;
+  default: abort ();
+  }
+}
+
 int
 guestfs__launch (guestfs_h *g)
 {
@@ -351,23 +363,7 @@ guestfs__launch (guestfs_h *g)
     warning (g, "chmod: %s: %m (ignored)", g->tmpdir);
 
   /* Launch the appliance. */
-  switch (g->attach_method) {
-  case ATTACH_METHOD_APPLIANCE:
-    g->attach_ops = &attach_ops_appliance;
-    break;
-
-  case ATTACH_METHOD_LIBVIRT:
-    g->attach_ops = &attach_ops_libvirt;
-    break;
-
-  case ATTACH_METHOD_UNIX:
-    g->attach_ops = &attach_ops_unix;
-    break;
-
-  default:
-    abort ();
-  }
-
+  g->attach_ops = get_attach_ops (g);
   return g->attach_ops->launch (g, g->attach_method_arg);
 }
 
@@ -506,6 +502,38 @@ guestfs___remove_tmpdir (const char *dir)
   }
 }
 
+int
+guestfs__get_pid (guestfs_h *g)
+{
+  if (g->state != READY || g->attach_ops == NULL) {
+    error (g, _("get-pid can only be called after launch"));
+    return -1;
+  }
+
+  if (g->attach_ops->get_pid == NULL) {
+    guestfs_error_errno (g, ENOTSUP,
+                         _("the current attach-method does not support 'get-pid'"));
+    return -1;
+  }
+
+  return g->attach_ops->get_pid (g);
+}
+
+/* Maximum number of disks. */
+int
+guestfs__max_disks (guestfs_h *g)
+{
+  const struct attach_ops *attach_ops = get_attach_ops (g);
+
+  if (attach_ops->max_disks == NULL) {
+    guestfs_error_errno (g, ENOTSUP,
+                         _("the current attach-method does not allow max disks to be queried"));
+    return -1;
+  }
+
+  return attach_ops->max_disks (g);
+}
+
 /* You had to call this function after launch in versions <= 1.0.70,
  * but it is now a no-op.
  */