launch: libvirt: Use <driver name="qemu" type=[format] />.

We were using format= which was bogus and libvirt was ignoring it and
forcing raw format instead.

Also in its default configuration libvirt won't do disk format
autodetection at all, so we must do it instead.

1 files changed, 99 insertions, 3 deletions

diff --git a/src/launch-libvirt.c b/src/launch-libvirt.c
index 788ca17c..bebdcfb1 100644
--- a/src/launch-libvirt.c
+++ b/src/launch-libvirt.c
@@ -28,6 +28,7 @@
 #include <assert.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/wait.h>
 
 #ifdef HAVE_LIBVIRT
 #include <libvirt/libvirt.h>
@@ -76,7 +77,7 @@ xmlBufferDetach (xmlBufferPtr buf)
 #endif
 
 static xmlChar *construct_libvirt_xml (guestfs_h *g, const char *capabilities_xml, const char *kernel, const char *initrd, const char *appliance, const char *guestfsd_sock, const char *console_sock);
-
+static char *autodetect_format (guestfs_h *g, const char *path);
 static void libvirt_error (guestfs_h *g, const char *fs, ...);
 
 static int
@@ -751,6 +752,7 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
   char drive_name[64] = "sd";
   char scsi_target[64];
   char *path = NULL;
+  char *format = NULL;
   struct stat statbuf;
   int is_host_device;
 
@@ -819,9 +821,18 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
                                          BAD_CAST "qemu"));
   if (drv->format) {
     XMLERROR (-1,
-              xmlTextWriterWriteAttribute (xo, BAD_CAST "format",
+              xmlTextWriterWriteAttribute (xo, BAD_CAST "type",
                                            BAD_CAST drv->format));
   }
+  else {
+    format = autodetect_format (g, path);
+    if (!format)
+      goto err;
+
+    XMLERROR (-1,
+              xmlTextWriterWriteAttribute (xo, BAD_CAST "type",
+                                           BAD_CAST format));
+  }
   if (drv->use_cache_none) {
     XMLERROR (-1,
               xmlTextWriterWriteAttribute (xo, BAD_CAST "cache",
@@ -859,10 +870,12 @@ construct_libvirt_xml_disk (guestfs_h *g, xmlTextWriterPtr xo,
   XMLERROR (-1, xmlTextWriterEndElement (xo));
 
   free (path);
+  free (format);
   return 0;
 
  err:
   free (path);
+  free (format);
   return -1;
 }
 
@@ -904,7 +917,7 @@ construct_libvirt_xml_appliance (guestfs_h *g, xmlTextWriterPtr xo,
             xmlTextWriterWriteAttribute (xo, BAD_CAST "name",
                                          BAD_CAST "qemu"));
   XMLERROR (-1,
-            xmlTextWriterWriteAttribute (xo, BAD_CAST "format",
+            xmlTextWriterWriteAttribute (xo, BAD_CAST "type",
                                          BAD_CAST "raw"));
   XMLERROR (-1,
             xmlTextWriterWriteAttribute (xo, BAD_CAST "cache",
@@ -1044,6 +1057,89 @@ construct_libvirt_xml_qemu_cmdline (guestfs_h *g, xmlTextWriterPtr xo)
   return -1;
 }
 
+/* libvirt has disabled the feature of detecting the disk format,
+ * unless the administrator sets allow_disk_format_probing=1 in
+ * qemu.conf.  There is no way to detect if this option is set, so we
+ * have to do format detection here using qemu-img and pass that to
+ * libvirt.
+ *
+ * This is still a security issue, so in most cases it is recommended
+ * the users pass the format to libguestfs which will faithfully pass
+ * that to libvirt and this function won't be used.
+ */
+static char *
+autodetect_format (guestfs_h *g, const char *path)
+{
+  pid_t pid;
+  int fd[2];
+  FILE *fp;
+  char *line = NULL;
+  size_t len;
+  char *p;
+  size_t n;
+  char *ret = NULL;
+
+  if (pipe2 (fd, O_CLOEXEC) == -1) {
+    perrorf (g, "pipe2");
+    return NULL;
+  }
+
+  pid = fork ();
+  if (pid == -1) {
+    perrorf (g, "fork");
+    close (fd[0]);
+    close (fd[1]);
+    return NULL;
+  }
+
+  if (pid == 0) {               /* child */
+    close (fd[0]);
+    dup2 (fd[1], 1);
+    close (fd[1]);
+
+    execlp ("qemu-img", "qemu-img", "info", path, NULL);
+    perror ("could not execute 'qemu-img info'");
+    _exit (EXIT_FAILURE);
+  }
+
+  close (fd[1]);
+
+  fp = fdopen (fd[0], "r");
+  if (fp == NULL) {
+    perrorf (g, "fdopen: qemu-img info");
+    close (fd[0]);
+    waitpid (pid, NULL, 0);
+    return NULL;
+  }
+
+  while (getline (&line, &len, fp) != -1) {
+    if (STRPREFIX (line, "file format: ")) {
+      p = &line[13];
+      n = strlen (p);
+      if (n > 0 && p[n-1] == '\n')
+        n--;
+      memmove (line, p, n);
+      line[n] = '\0';
+      ret = line;
+      break;
+    }
+  }
+
+  fclose (fp); /* also closes fd[0] */
+  waitpid (pid, NULL, 0);
+
+  if (ret == NULL) {
+    error (g, _("could not auto-detect the format of '%s'\n"
+                "If the format is known, pass the format to libguestfs, eg. using the\n"
+                "'--format=...' option, or via the optional 'format' argument to 'add-drive'."),
+           path);
+    free (line);
+    return NULL;
+  }
+
+  return ret;                   /* caller frees */
+}
+
 static int
 shutdown_libvirt (guestfs_h *g)
 {