linux-kernel - [PATCHv2] Make initramfs honor CONFIG_DEVTMPFS

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Message-ID: <ccf0bb10-2563-3d53-6bf0-58643451211e@landley.net>
Date:   Thu, 11 May 2017 12:05:03 -0500
From:   Rob Landley <rob@...dley.net>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Prarit Bhargava <prarit@...hat.com>,
        Yang Shi <yang.shi@...aro.org>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Kees Cook <keescook@...omium.org>,
        Emese Revfy <re.emese@...il.com>,
        Petr Mladek <pmladek@...e.com>,
        Fabian Frederick <fabf@...net.be>
Subject: [PATCHv2] Make initramfs honor CONFIG_DEVTMPFS_MOUNT

From: Rob Landley <rob@...dley.net>

Make initramfs honor CONFIG_DEVTMPFS_MOUNT, move /dev/console
open after devtmpfs mount, and update help text.

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

 drivers/base/Kconfig |   14 ++++----------
 init/main.c          |   15 +++++++++------
 2 files changed, 13 insertions(+), 16 deletions(-)

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index d718ae4..74779ee 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 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/init/main.c b/init/main.c
index f866510..9ec09ff 100644
--- a/init/main.c
+++ b/init/main.c
@@ -1038,12 +1038,6 @@ 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
@@ -1055,8 +1049,17 @@ 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