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Subject[RFC PATCH] Introduce a 'recovery' command line option
Date
Recovery option can be used to define a secondary rootfs
in case mounting of the primary root fails. This allows
the kernel to automatically switch to a recovery
filesystem without the initrd or the bootloader support
for the switch.

Signed-off-by: Janne Karhunen <Janne.Karhunen@gmail.com>
---
Documentation/kernel-parameters.txt | 4 ++++
init/do_mounts.c | 47 +++++++++++++++++++++++++++++++++----
2 files changed, 46 insertions(+), 5 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 46c030a..febbd3e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3587,6 +3587,10 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
reboot_cpu is s[mp]#### with #### being the processor
to be used for rebooting.

+ recovery= [KNL]
+ Recovery root filesystem. This partition is attempted as
+ root in case default root filesystem does not mount.
+
relax_domain_level=
[KNL, SMP] Set scheduler's default relax_domain_level.
See Documentation/cgroup-v1/cpusets.txt.
diff --git a/init/do_mounts.c b/init/do_mounts.c
index dea5de9..c746dce 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -39,8 +39,11 @@ 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 recovery_device_name;
static char __initdata saved_root_name[64];
+static char __initdata saved_recovery_name[64];
static int root_wait;
+static int recovery_attempt;

dev_t ROOT_DEV;

@@ -298,6 +301,15 @@ static int __init root_dev_setup(char *line)

__setup("root=", root_dev_setup);

+static int __init recovery_setup(char *line)
+{
+ strlcpy(saved_recovery_name, line, sizeof(saved_recovery_name));
+ recovery_attempt = 1;
+ return 1;
+}
+
+__setup("recovery=", recovery_setup);
+
static int __init rootwait_setup(char *str)
{
if (*str)
@@ -384,6 +396,7 @@ void __init mount_block_root(char *name, int flags)
__GFP_NOTRACK_FALSE_POSITIVE);
char *fs_names = page_address(page);
char *p;
+ int err;
#ifdef CONFIG_BLOCK
char b[BDEVNAME_SIZE];
#else
@@ -393,7 +406,7 @@ void __init mount_block_root(char *name, int flags)
get_fs_names(fs_names);
retry:
for (p = fs_names; *p; p += strlen(p)+1) {
- int err = do_mount_root(name, p, flags, root_mount_data);
+ err = do_mount_root(name, p, flags, root_mount_data);
switch (err) {
case 0:
goto out;
@@ -401,6 +414,31 @@ retry:
case -EINVAL:
continue;
}
+ if (!(flags & MS_RDONLY)) {
+ pr_warn("Retrying rootfs mount as read-only.\n");
+ flags |= MS_RDONLY;
+ goto retry;
+ }
+ if (recovery_device_name && recovery_attempt) {
+ recovery_attempt = 0;
+
+ ROOT_DEV = name_to_dev_t(recovery_device_name);
+ if (strncmp(recovery_device_name, "/dev/", 5) == 0)
+ recovery_device_name += 5;
+
+ pr_warn("Unable to mount rootfs at %s, error %d\n",
+ root_device_name, err);
+ pr_warn("Attempting %s for recovery as requested.\n",
+ recovery_device_name);
+
+ err = create_dev("/dev/root", ROOT_DEV);
+ if (err < 0)
+ pr_emerg("Failed to create /dev/root: %d\n", err);
+
+ root_device_name = recovery_device_name;
+ goto retry;
+ }
+
/*
* Allow the user to distinguish between failed sys_open
* and bad superblock on root device.
@@ -420,10 +458,6 @@ retry:
#endif
panic("VFS: Unable to mount root fs on %s", b);
}
- if (!(flags & MS_RDONLY)) {
- flags |= MS_RDONLY;
- goto retry;
- }

printk("List of all partitions:\n");
printk_all_partitions();
@@ -567,6 +601,9 @@ void __init prepare_namespace(void)

md_run_setup();

+ if (saved_recovery_name[0])
+ recovery_device_name = saved_recovery_name;
+
if (saved_root_name[0]) {
root_device_name = saved_root_name;
if (!strncmp(root_device_name, "mtd", 3) ||
--
1.9.1
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