Added drop-caches command.

daemon/Makefile.am

@@ -29,6 +29,7 @@ guestfsd_SOURCES = \
 	debug.c \
 	devsparts.c \
 	dir.c \
+	dropcaches.c \
 	ext2.c \
 	file.c \
 	fsck.c \

daemon/dropcaches.c

@@ -0,0 +1,52 @@
+/* libguestfs - the guestfsd daemon
+ * Copyright (C) 2009 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 <fcntl.h>
+
+#include "daemon.h"
+#include "actions.h"
+
+#define PROCFILE "/proc/sys/vm/drop_caches"
+
+int
+do_drop_caches (int what)
+{
+  FILE *fp;
+
+  sync ();
+
+  fp = fopen (PROCFILE, "w");
+  if (fp == NULL) {
+    reply_with_perror (PROCFILE);
+    return -1;
+  }
+
+  fprintf (fp, "%d", what);
+  if (fclose (fp) == EOF) {
+    reply_with_perror (PROCFILE);
+    return -1;
+  }
+
+  return 0;
+}

src/generator.ml

@@ -1737,6 +1737,20 @@ recursively using the C<cp -a> command.");
 This moves a file from C<src> to C<dest> where C<dest> is
 either a destination filename or destination directory.");
 
+  ("drop_caches", (RErr, [Int "whattodrop"]), 90, [],
+   [InitEmpty, TestRun (
+      [["drop_caches"; "3"]])],
+   "drop kernel page cache, dentries and inodes",
+   "\
+This instructs the guest kernel to drop its page cache,
+and/or dentries and inode caches.  The parameter C<whattodrop>
+tells the kernel what precisely to drop, see
+L<http://linux-mm.org/Drop_Caches>
+
+Setting C<whattodrop> to 3 should drop everything.
+
+This automatically calls L<sync(2)> before the operation,
+so that the maximum guest memory is freed.");
 
 ]