[PATCH] Make CONFIG_DEVTMPFS_MOUNT apply to initramfs/initmpfs.

From: Rob Landley
Date: Wed Jun 22 2016 - 15:06:53 EST


From: Rob Landley <rob@xxxxxxxxxxx>

Make CONFIG_DEVTMPFS_MOUNT apply to initramfs/initmpfs.

Update help text, slightly improve error reporting, move /dev/console open
down after devtmpfs mount, don't check IS_ENABLED(CONFIG_TMPFS) before
mounting devtmpfs (it's always there, even if just a ramfs alias), and
report whether we think we're using tmpfs or ramfs for rootfs.

Signed-off-by: Rob Landley <rob@xxxxxxxxxxx>
---

drivers/base/Kconfig | 10 ++++++----
drivers/base/devtmpfs.c | 3 ++-
init/do_mounts.c | 7 +++----
init/main.c | 17 ++++++++++-------
4 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index 98504ec..3fb07c1 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -45,16 +45,18 @@ config DEVTMPFS
file system will be used instead.

config DEVTMPFS_MOUNT
- bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs"
+ bool "Automount devtmpfs at /dev"
depends on DEVTMPFS
help
This will instruct the kernel to automatically mount the
devtmpfs filesystem at /dev, directly after the kernel has
mounted the root filesystem. The behavior can be overridden
with the commandline parameter: devtmpfs.mount=0|1.
- This option does not affect initramfs based booting, here
- the devtmpfs filesystem always needs to be mounted manually
- after the rootfs is mounted.
+
+ In an initramfs based system, this can create the /dev directory
+ as well. Other root filesystems require a /dev directory to exist
+ to act as a mount point.
+
With this option enabled, it allows to bring up a system in
rescue mode with init=/bin/sh, even when the /dev directory
on the rootfs is completely empty.
diff --git a/drivers/base/devtmpfs.c b/drivers/base/devtmpfs.c
index 44a74cf..eaf8532 100644
--- a/drivers/base/devtmpfs.c
+++ b/drivers/base/devtmpfs.c
@@ -356,7 +356,8 @@ int devtmpfs_mount(const char *mntdir)

err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
if (err)
- printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
+ printk(KERN_ERR "devtmpfs: error %i mounting on %s\n",
+ err, mntdir);
else
printk(KERN_INFO "devtmpfs: mounted\n");
return err;
diff --git a/init/do_mounts.c b/init/do_mounts.c
index dea5de9..6daf63e 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -599,7 +599,6 @@ void __init prepare_namespace(void)

mount_root();
out:
- devtmpfs_mount("dev");
sys_mount(".", "/", NULL, MS_MOVE, NULL);
sys_chroot(".");
}
@@ -614,8 +613,9 @@ static struct dentry *rootfs_mount(struct file_system_type *fs_type,
if (test_and_set_bit(0, &once))
return ERR_PTR(-ENODEV);

- if (IS_ENABLED(CONFIG_TMPFS) && is_tmpfs)
+ if (is_tmpfs)
fill = shmem_fill_super;
+ printk(KERN_INFO "rootfs is %s\n", is_tmpfs ? "tmpfs" : "ramfs");

return mount_nodev(fs_type, flags, data, fill);
}
@@ -637,9 +637,8 @@ int __init init_rootfs(void)
(!root_fs_names || strstr(root_fs_names, "tmpfs"))) {
err = shmem_init();
is_tmpfs = true;
- } else {
+ } else
err = init_ramfs_fs();
- }

if (err)
unregister_filesystem(&rootfs_fs_type);
diff --git a/init/main.c b/init/main.c
index b3c6e36..e6bf551 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1007,12 +1007,6 @@ static noinline void __init kernel_init_freeable(void)

do_basic_setup();

- /* Open the /dev/console on the rootfs, this should never fail */
- if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
- pr_err("Warning: unable to open an initial console.\n");
-
- (void) sys_dup(0);
- (void) sys_dup(0);
/*
* check if there is an early userspace init. If yes, let it do all
* the work
@@ -1024,7 +1018,16 @@ static noinline void __init kernel_init_freeable(void)
if (sys_access((const char __user *) ramdisk_execute_command, 0) != 0) {
ramdisk_execute_command = NULL;
prepare_namespace();
- }
+ } else if (config_enabled(CONFIG_DEVTMPFS_MOUNT))
+ sys_mkdir("/dev", 0755);
+ devtmpfs_mount("dev");
+
+ /* Open the /dev/console on the rootfs, this should never fail */
+ if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0)
+ pr_err("Warning: unable to open an initial console.\n");
+
+ (void) sys_dup(0);
+ (void) sys_dup(0);

/*
* Ok, we have completed the initial bootup, and