New APIs: is-zero and is-zero-device, to test if file or device is all zeroes.

daemon/zero.c

@@ -1,5 +1,5 @@
 /* libguestfs - the guestfsd daemon
- * Copyright (C) 2009 Red Hat Inc.
+ * Copyright (C) 2009-2011 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
@@ -105,3 +105,76 @@ do_zero_device (const char *device)
 
   return 0;
 }
+
+static char zero[BUFSIZ];
+
+int
+do_is_zero (const char *path)
+{
+  int fd;
+  char buf[BUFSIZ];
+  ssize_t r;
+
+  CHROOT_IN;
+  fd = open (path, O_RDONLY);
+  CHROOT_OUT;
+
+  if (fd == -1) {
+    reply_with_perror ("open: %s", path);
+    return -1;
+  }
+
+  while ((r = read (fd, buf, sizeof buf)) > 0) {
+    if (memcmp (buf, zero, r) != 0) {
+      close (fd);
+      return 0;
+    }
+  }
+
+  if (r == -1) {
+    reply_with_perror ("read: %s", path);
+    close (fd);
+    return -1;
+  }
+
+  if (close (fd) == -1) {
+    reply_with_perror ("close: %s", path);
+    return -1;
+  }
+
+  return 1;
+}
+
+int
+do_is_zero_device (const char *device)
+{
+  int fd;
+  char buf[BUFSIZ];
+  ssize_t r;
+
+  fd = open (device, O_RDONLY);
+  if (fd == -1) {
+    reply_with_perror ("open: %s", device);
+    return -1;
+  }
+
+  while ((r = read (fd, buf, sizeof buf)) > 0) {
+    if (memcmp (buf, zero, r) != 0) {
+      close (fd);
+      return 0;
+    }
+  }
+
+  if (r == -1) {
+    reply_with_perror ("read: %s", device);
+    close (fd);
+    return -1;
+  }
+
+  if (close (fd) == -1) {
+    reply_with_perror ("close: %s", device);
+    return -1;
+  }
+
+  return 1;
+}

generator/generator_actions.ml

@@ -2273,7 +2273,7 @@ command and it can change in future in ways beyond our control.
 In other words, the output is not guaranteed by the ABI.
 
 See also: L<file(1)>, C<guestfs_vfs_type>, C<guestfs_lstat>,
-C<guestfs_is_file>, C<guestfs_is_blockdev> (etc).");
+C<guestfs_is_file>, C<guestfs_is_blockdev> (etc), C<guestfs_is_zero>.");
 
   ("command", (RString "output", [StringList "arguments"], []), 50, [ProtocolLimitWarning],
    [InitScratchFS, Always, TestOutput (
@@ -2979,7 +2979,8 @@ How many blocks are zeroed isn't specified (but it's I<not> enough
 to securely wipe the device).  It should be sufficient to remove
 any partition tables, filesystem superblocks and so on.
 
-See also: C<guestfs_zero_device>, C<guestfs_scrub_device>.");
+See also: C<guestfs_zero_device>, C<guestfs_scrub_device>,
+C<guestfs_is_zero_device>");
 
   ("grub_install", (RErr, [Pathname "root"; Device "device"], []), 86, [],
    (* See:
@@ -5937,6 +5938,29 @@ Instead, use the autosync flag (C<guestfs_set_autosync>) to
 control whether or not this operation is performed when the
 handle is closed.");
 
+  ("is_zero", (RBool "zeroflag", [Pathname "path"], []), 283, [],
+   [InitISOFS, Always, TestOutputTrue (
+      [["is_zero"; "/100kallzeroes"]]);
+    InitISOFS, Always, TestOutputFalse (
+      [["is_zero"; "/100kallspaces"]])],
+   "test if a file contains all zero bytes",
+   "\
+This returns true iff the file exists and the file is empty or
+it contains all zero bytes.");
+
+  ("is_zero_device", (RBool "zeroflag", [Device "device"], []), 284, [],
+   [InitBasicFS, Always, TestOutputTrue (
+      [["umount"; "/dev/sda1"];
+       ["zero_device"; "/dev/sda1"];
+       ["is_zero_device"; "/dev/sda1"]]);
+    InitBasicFS, Always, TestOutputFalse (
+      [["is_zero_device"; "/dev/sda1"]])],
+   "test if a device contains all zero bytes",
+   "\
+This returns true iff the device exists and contains all zero bytes.
+
+Note that for large devices this can take a long time to run.");
+
 ]
 
 let all_functions = non_daemon_functions @ daemon_functions

src/MAX_PROC_NR

@@ -1 +1 @@
-282
+284