[PATCH] init: Support mounting devices from kernel command line

[Sasha Levin <levinsasha928@gmail.com>]

This patch adds support to mounting devices using a kernel parameter.

Such feature is usefull for virtual guests. It allows easily automating
mounts without having to change the base image (which can be read-only).

In /tools/kvm we are interested in such feature to allow us to automatically
mount user home directory using virtio-9p from the host to the guest
filesystem under '/hostfs'.

Cc: Avi Kivity <avi@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 Documentation/kernel-parameters.txt |    6 +++
 init/do_mounts.c                    |   61 +++++++++++++++++++++++++++++++++++
 2 files changed, 67 insertions(+), 0 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index aa47be7..e1955fb 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1476,6 +1476,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 			log everything. Information is printed at KERN_DEBUG
 			so loglevel=8 may also need to be specified.
 
+	mount=
+			[KNL] Mount a device to a mount point after loading
+			rootfs and setting up devices. Can be used to mount
+			up to 16 devices.
+			Format: <source>,<destination>,<fs>[,<params>]
+
 	mousedev.tap_time=
 			[MOUSE] Maximum time between finger touching and
 			leaving touchpad surface for touch to be considered
diff --git a/init/do_mounts.c b/init/do_mounts.c
index c0851a8..0948f1d 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -29,9 +29,24 @@ int root_mountflags = MS_RDONLY | MS_SILENT;
 static char * __initdata root_device_name;
 static char __initdata saved_root_name[64];
 static int __initdata root_wait;
+static char * __initdata user_mount[16];
+static int __initdata user_mount_count;
 
 dev_t ROOT_DEV;
 
+static int __init setup_user_mount(char *str)
+{
+	if (user_mount_count > 15) {
+		printk(KERN_ERR "More than 16 'mount=' options specified.")
+		return 1;
+	}
+	
+	user_mount[user_mount_count++] = str;
+
+	return 1;
+}
+__setup("mount=", setup_user_mount);
+
 static int __init load_ramdisk(char *str)
 {
 	rd_doload = simple_strtol(str,NULL,0) & 3;
@@ -431,6 +446,51 @@ void __init mount_root(void)
 #endif
 }
 
+int __init do_user_mounts(void)
+{
+	int i, res;
+	char *src, *dst, *fs, *params, *cur;
+
+	for (i = 0; i < user_mount_count; i++) {
+		src = user_mount[i];
+		cur = strstr(user_mount[i], ",");
+		if (!cur)
+			goto fail_str;
+
+		*cur = '\0';
+		dst = ++cur;
+
+		cur = strstr(cur, ",");
+		if (!cur)
+			goto fail_str;
+
+		*cur = '\0';
+		fs = ++cur;
+
+		cur = strstr(cur, ",");
+		if (cur) {
+			*cur = '\0';
+			params = ++cur;
+		} else {
+			params = NULL;
+		}
+
+		res = sys_mount(src, dst, fs, 0, params);
+		if (res == 0)
+			printk(KERN_INFO "Mounted (%s filesystem) %s to %s\n",
+				fs, src, dst);
+		else
+			printk(KERN_ERR "Failed mounting (%s filesystem) %s to"
+				" %s. Err: %d\n", fs, src, dst, res);
+	}
+
+	return 0;
+
+fail_str:
+	printk(KERN_ERR "Bad mount str: %s\n", user_mount[i]);
+	return -1;
+}
+
 /*
  * Prepare the namespace - decide what/where to mount, load ramdisks, etc.
  */
@@ -490,4 +550,5 @@ out:
 	devtmpfs_mount("dev");
 	sys_mount(".", "/", NULL, MS_MOVE, NULL);
 	sys_chroot((const char __user __force *)".");
+	do_user_mounts();
 }
-- 
1.7.6