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SubjectRe: [PATCH v3] Make initramfs honor CONFIG_DEVTMPFS_MOUNT
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Le 14/09/2017 à 01:51, Rob Landley a écrit :
> From: Rob Landley <rob@landley.net>
>
> Make initramfs honor CONFIG_DEVTMPFS_MOUNT, and move
> /dev/console open after devtmpfs mount.
>
> Add workaround for Debian bug that was copied by Ubuntu.

Is that a bug only for Debian ? Why ?
Why should a Debian bug be fixed by a workaround in the mainline kernel ?

>
> Signed-off-by: Rob Landley <rob@landley.net>
> ---
>
> 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.

Why modifying the initial text ?
Why talking about rescue mode only, whereas this feature mainly concerns
the standard mode.

>
> 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. */

Does it matter for the kernel code what Debian's kernel config does ?

> + printk(KERN_WARNING "Debian bug workaround for devtmpfs overmount.");

Is this log message worth it when this modification goes in mainline
kernel ?

If so, pr_err() should be used instead.

> +
> + 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);

Why not, but couldn't we also expect the initramfs to already contains
that mountpoint ?

> + 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
>


Christophe

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