New APIs: findfs-label and findfs-uuid

These two calls wrap up the /sbin/findfs command, allowing you
to find a filesystem by only knowing its label or UUID.

This is especially useful when resolving LABEL=... or UUID=...
entries in /etc/fstab.

Sample guestfish session:

><fs> vfs-uuid /dev/vda1
277dd61c-bf34-4253-a8dc-df500a05e7df
><fs> findfs-uuid 277dd61c-bf34-4253-a8dc-df500a05e7df
/dev/vda1
><fs> vfs-label /dev/vda1
/boot
><fs> findfs-label /boot
/dev/vda1
><fs> vfs-uuid /dev/VolGroup00/LogVol00
40ce7c36-82ce-4a12-a99d-48f5e054162c
><fs> findfs-uuid 40ce7c36-82ce-4a12-a99d-48f5e054162c
/dev/mapper/VolGroup00-LogVol00
><fs> findfs-uuid 12345678
libguestfs: error: findfs_uuid: findfs: unable to resolve 'UUID=12345678'

2 files changed, 73 insertions, 0 deletions

diff --git a/daemon/Makefile.am b/daemon/Makefile.am
index 27fca2a2..0c8be08e 100644
--- a/daemon/Makefile.am
+++ b/daemon/Makefile.am
@@ -84,6 +84,7 @@ guestfsd_SOURCES = \
 	ext2.c \
 	fallocate.c \
 	file.c \
+	findfs.c \
 	fill.c \
 	find.c \
 	fsck.c \
diff --git a/daemon/findfs.c b/daemon/findfs.c
new file mode 100644
index 00000000..0520f181
--- /dev/null
+++ b/daemon/findfs.c
@@ -0,0 +1,72 @@
+/* libguestfs - the guestfsd daemon
+ * Copyright (C) 2010 Red Hat Inc.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include "daemon.h"
+#include "actions.h"
+
+static char *
+findfs (const char *tag, const char *label_or_uuid)
+{
+  /* Kill the cache file, forcing blkid to reread values from the
+   * original filesystems.  In blkid there is a '-p' option which is
+   * supposed to do this, but (a) it doesn't work and (b) that option
+   * is not supported in RHEL 5.
+   */
+  unlink ("/etc/blkid/blkid.tab");
+
+  size_t len = strlen (tag) + strlen (label_or_uuid) + 2;
+  char arg[len];
+  snprintf (arg, len, "%s=%s", tag, label_or_uuid);
+
+  char *out, *err;
+  int r = command (&out, &err, "findfs", arg, NULL);
+  if (r == -1) {
+    reply_with_error ("%s", err);
+    free (out);
+    free (err);
+    return NULL;
+  }
+
+  free (err);
+
+  /* Trim trailing \n if present. */
+  len = strlen (out);
+  if (len > 0 && out[len-1] == '\n')
+    out[len-1] = '\0';
+
+  return out;                   /* caller frees */
+}
+
+char *
+do_findfs_uuid (const char *uuid)
+{
+  return findfs ("UUID", uuid);
+}
+
+char *
+do_findfs_label (const char *label)
+{
+  return findfs ("LABEL", label);
+}