New kernel option alt_root for trying harder to find a valid root device

New kernel option alt_root for trying harder to find a valid root device

[Martin Bammer]

[-- Attachment #1: Type: text/plain, Size: 598 bytes --]

Hi,

the attached patch (created against 2.6.30) makes the kernel harder
finding a valid root device.
Changes are:
- New kernel option alt_root=<alternative root device>
- If an alternative root device is defined with alt_root, e.g.
alt_root=/dev/sda1, and the primary root device could not be found
because a) root device is defined by it's UUID and b) initrd is missing
or damaged, then the kernel will try to use /dev/sda1 as it's root
device.
- If an alternative root device is defined with alt_root and initrd is
damaged then the kernel will try to use /dev/sda1 as it's root device.

Martin


[-- Attachment #2: init_mounts_alt_root.diff --]
[-- Type: text/x-patch, Size: 2819 bytes --]

Signed-off-by: Martin Bammer <mrbm74@gmail.com>
diff --git a/linux-2.6.30-ep0/init/do_mounts.c b/linux-2.6.30-ep1/init/do_mounts.c
index dd7ee5f..b12e739 100644
--- a/linux-2.6.30-ep0/init/do_mounts.c
+++ b/linux-2.6.30-ep1/init/do_mounts.c
@@ -27,6 +27,7 @@ int __initdata rd_doload;	/* 1 = load RAM disk, 0 = don't load */
 int root_mountflags = MS_RDONLY | MS_SILENT;
 static char * __initdata root_device_name;
 static char __initdata saved_root_name[64];
+static char __initdata alt_saved_root_name[64];
 static int __initdata root_wait;
 
 dev_t ROOT_DEV;
@@ -152,6 +153,14 @@ static int __init root_dev_setup(char *line)
 
 __setup("root=", root_dev_setup);
 
+static int __init alt_root_dev_setup(char *line)
+{
+	strlcpy(alt_saved_root_name, line, sizeof(alt_saved_root_name));
+	return 1;
+}
+
+__setup("alt_root=", alt_root_dev_setup);
+
 static int __init rootwait_setup(char *str)
 {
 	if (*str)
@@ -412,6 +421,20 @@ void __init prepare_namespace(void)
 	if (is_floppy && rd_doload && rd_load_disk(0))
 		ROOT_DEV = Root_RAM0;
 
+	if ((ROOT_DEV == 0) && alt_saved_root_name[0]) {
+		printk(KERN_WARNING "VFS: Unable to find root device %s. Trying alternative device %s.\n",
+			root_device_name, alt_saved_root_name);
+		root_device_name = alt_saved_root_name;
+		if (!strncmp(root_device_name, "mtd", 3) ||
+		    !strncmp(root_device_name, "ubi", 3)) {
+			mount_block_root(root_device_name, root_mountflags);
+			goto out;
+		}
+		ROOT_DEV = name_to_dev_t(root_device_name);
+		if (strncmp(root_device_name, "/dev/", 5) == 0)
+			root_device_name += 5;
+	}
+
 	mount_root();
 out:
 	sys_mount(".", "/", NULL, MS_MOVE, NULL);
diff --git a/linux-2.6.30-ep0/init/do_mounts_initrd.c b/linux-2.6.30-ep1/init/do_mounts_initrd.c
index 614241b..d1d6e1c 100644
--- a/linux-2.6.30-ep0/init/do_mounts_initrd.c
+++ b/linux-2.6.30-ep1/init/do_mounts_initrd.c
@@ -38,7 +38,7 @@ static int __init do_linuxrc(void * shell)
 	return kernel_execve(shell, argv, envp_init);
 }
 
-static void __init handle_initrd(void)
+static int __init handle_initrd(void)
 {
 	int error;
 	int pid;
@@ -79,7 +79,7 @@ static void __init handle_initrd(void)
 
 	if (new_decode_dev(real_root_dev) == Root_RAM0) {
 		sys_chdir("/old");
-		return;
+		return 1;
 	}
 
 	ROOT_DEV = new_decode_dev(real_root_dev);
@@ -105,7 +105,12 @@ static void __init handle_initrd(void)
 			sys_close(fd);
 		}
 		printk(!error ? "okay\n" : "failed\n");
+		if (error) {
+			printk(KERN_ERR "Error %d handling initrd.\n", error);
+			return 0;
+		}
 	}
+	return 1;
 }
 
 int __init initrd_load(void)
@@ -120,8 +125,7 @@ int __init initrd_load(void)
 		 */
 		if (rd_load_image("/initrd.image") && ROOT_DEV != Root_RAM0) {
 			sys_unlink("/initrd.image");
-			handle_initrd();
-			return 1;
+			return handle_initrd();
 		}
 	}
 	sys_unlink("/initrd.image");