xen: add xenfs to allow usermode <-> Xen interaction

The xenfs filesystem exports various interfaces to usermode.  Initially
this exports a file to allow usermode to interact with xenbus/xenstore.

Traditionally this appeared in /proc/xen.  Rather than extending procfs,
this patch adds a backward-compat mountpoint on /proc/xen, and provides
a xenfs filesystem which can be mounted there.

Signed-off-by: Alex Zeffertt <alex.zeffertt@eu.citrix.com>
Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 64 insertions, 0 deletions

diff --git a/drivers/xen/xenfs/super.c b/drivers/xen/xenfs/super.c
new file mode 100644
index 000000000000..515741a8e6b8
--- /dev/null
+++ b/drivers/xen/xenfs/super.c
@@ -0,0 +1,64 @@
+/*
+ *  xenfs.c - a filesystem for passing info between the a domain and
+ *  the hypervisor.
+ *
+ * 2008-10-07  Alex Zeffertt    Replaced /proc/xen/xenbus with xenfs filesystem
+ *                              and /proc/xen compatibility mount point.
+ *                              Turned xenfs into a loadable module.
+ */
+
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/fs.h>
+#include <linux/magic.h>
+
+#include "xenfs.h"
+
+#include <asm/xen/hypervisor.h>
+
+MODULE_DESCRIPTION("Xen filesystem");
+MODULE_LICENSE("GPL");
+
+static int xenfs_fill_super(struct super_block *sb, void *data, int silent)
+{
+	static struct tree_descr xenfs_files[] = {
+		[2] = {"xenbus", &xenbus_file_ops, S_IRUSR|S_IWUSR},
+		{""},
+	};
+
+	return simple_fill_super(sb, XENFS_SUPER_MAGIC, xenfs_files);
+}
+
+static int xenfs_get_sb(struct file_system_type *fs_type,
+			int flags, const char *dev_name,
+			void *data, struct vfsmount *mnt)
+{
+	return get_sb_single(fs_type, flags, data, xenfs_fill_super, mnt);
+}
+
+static struct file_system_type xenfs_type = {
+	.owner =	THIS_MODULE,
+	.name =		"xenfs",
+	.get_sb =	xenfs_get_sb,
+	.kill_sb =	kill_litter_super,
+};
+
+static int __init xenfs_init(void)
+{
+	if (xen_pv_domain())
+		return register_filesystem(&xenfs_type);
+
+	printk(KERN_INFO "XENFS: not registering filesystem on non-xen platform\n");
+	return 0;
+}
+
+static void __exit xenfs_exit(void)
+{
+	if (xen_pv_domain())
+		unregister_filesystem(&xenfs_type);
+}
+
+module_init(xenfs_init);
+module_exit(xenfs_exit);
+