New API: blkdiscard - discard all blocks on a block device.

daemon/Makefile.am

@@ -83,6 +83,7 @@ guestfsd_SOURCES = \
 	available.c \
 	augeas.c \
 	base64.c \
+	blkdiscard.c \
 	blkid.c \
 	blockdev.c \
 	btrfs.c \

daemon/blkdiscard.c

@@ -0,0 +1,90 @@
+/* libguestfs - the guestfsd daemon
+ * Copyright (C) 2014 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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <inttypes.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/ioctl.h>
+#include <linux/fs.h>
+
+#include "daemon.h"
+#include "actions.h"
+#include "optgroups.h"
+
+/* http://rwmj.wordpress.com/2014/03/11/blkdiscard-blkzeroout-blkdiscardzeroes-blksecdiscard/ */
+
+#ifdef BLKDISCARD
+
+int
+optgroup_blkdiscard_available (void)
+{
+  return 1;
+}
+
+int
+do_blkdiscard (const char *device)
+{
+  /* XXX We could read /sys/block/<device>/queue/discard_* in order to
+   * determine if discard is supported and the largest request size we
+   * are allowed to make.  However:
+   *
+   * (1) Mapping the device name to /sys/block/<device> is quite hard
+   * (cf. the lv_canonical function in daemon/lvm.c)
+   *
+   * (2) We don't really need to do this in modern libguestfs since
+   * we're very likely to be using virtio-scsi, which supports
+   * arbitrary block discards.
+   *
+   * Let's wait to see if it causes a problem in real world
+   * situations.
+   */
+  uint64_t range[2];
+  int64_t size;
+  int fd;
+
+  size = do_blockdev_getsize64 (device);
+  if (size == -1)
+    return -1;
+
+  range[0] = 0;
+  range[1] = (uint64_t) size;
+
+  fd = open (device, O_WRONLY|O_CLOEXEC);
+  if (fd == -1) {
+    reply_with_perror ("open: %s", device);
+    return -1;
+  }
+
+  if (ioctl (fd, BLKDISCARD, range) == -1) {
+    reply_with_perror ("ioctl: %s: BLKDISCARD", device);
+    close (fd);
+    return -1;
+  }
+
+  close (fd);
+  return 0;
+}
+
+#else /* !BLKDISCARD */
+OPTGROUP_BLKDISCARD_NOT_AVAILABLE
+#endif

generator/actions.ml

@@ -11818,6 +11818,22 @@ device C<device>.  Note that partitions are numbered from 1.
 The partition name can only be read on certain types of partition
 table.  This works on C<gpt> but not on C<mbr> partitions." };
 
+  { defaults with
+    name = "blkdiscard";
+    style = RErr, [Device "device"], [];
+    proc_nr = Some 417;
+    optional = Some "blkdiscard";
+    shortdesc = "discard all blocks on a device";
+    longdesc = "\
+This discards all blocks on the block device C<device>, giving
+the free space back to the host.
+
+This operation requires support in libguestfs, the host filesystem,
+qemu and the host kernel.  If this support isn't present it may give
+an error or even appear to run but do nothing.  You must also
+set the C<discard> attribute on the underlying drive (see
+C<guestfs_add_drive_opts>)." };
+
 ]
 
 (* Non-API meta-commands available only in guestfish.

po/POTFILES

@@ -16,6 +16,7 @@ daemon/acl.c
 daemon/augeas.c
 daemon/available.c
 daemon/base64.c
+daemon/blkdiscard.c
 daemon/blkid.c
 daemon/blockdev.c
 daemon/btrfs.c

src/MAX_PROC_NR

@@ -1 +1 @@
-416
+417