From: Rob Landley <rob@xxxxxxxxxxx> Make initramfs honor CONFIG_DEVTMPFS_MOUNT, and move /dev/console open after devtmpfs mount. Add workaround for Debian bug that was copied by Ubuntu. Signed-off-by: Rob Landley <rob@xxxxxxxxxxx> --- v2 discussion: http://lkml.iu.edu/hypermail/linux/kernel/1705.2/05611.html drivers/base/Kconfig | 14 ++++---------- fs/namespace.c | 14 ++++++++++++++ init/main.c | 15 +++++++++------ 3 files changed, 27 insertions(+), 16 deletions(-) diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig index f046d21..97352d4 100644 --- a/drivers/base/Kconfig +++ b/drivers/base/Kconfig @@ -48,16 +48,10 @@ config DEVTMPFS_MOUNT bool "Automount devtmpfs at /dev, after the kernel mounted the rootfs" 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. - 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. + Automatically mount devtmpfs at /dev on the root filesystem, which + lets the system to come up in rescue mode with [rd]init=/bin/sh. + Override with devtmpfs.mount=0 on the commandline. Initramfs can + create a /dev dir as needed, other rootfs needs the mount point. config STANDALONE bool "Select only drivers that don't need compile-time external firmware" diff --git a/fs/namespace.c b/fs/namespace.c index f8893dc..06057d7 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -2417,7 +2417,21 @@ static int do_add_mount(struct mount *newmnt, struct path *path, int mnt_flags) err = -EBUSY; if (path->mnt->mnt_sb == newmnt->mnt.mnt_sb && path->mnt->mnt_root == path->dentry) + { + if (IS_ENABLED(CONFIG_DEVTMPFS_MOUNT) && + !strcmp(path->mnt->mnt_sb->s_type->name, "devtmpfs")) + { + /* Debian's kernel config enables DEVTMPFS_MOUNT, then + its initramfs setup script tries to mount devtmpfs + again, and if the second mount-over-itself fails + the script overmounts a tmpfs on /dev to hide the + existing contents, then boot fails with empty /dev. */ + printk(KERN_WARNING "Debian bug workaround for devtmpfs overmount."); + + err = 0; + } goto unlock; + } err = -EINVAL; if (d_is_symlink(newmnt->mnt.mnt_root)) diff --git a/init/main.c b/init/main.c index 0ee9c686..0d8e5ec 100644 --- a/init/main.c +++ b/init/main.c @@ -1065,12 +1065,6 @@ 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 @@ -1082,8 +1076,17 @@ 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 (IS_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 * we're essentially up and running. Get rid of the
