From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3A2E1C47082 for ; Sat, 5 Jun 2021 11:50:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 193296120F for ; Sat, 5 Jun 2021 11:50:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230110AbhFELwT (ORCPT ); Sat, 5 Jun 2021 07:52:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:52500 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229902AbhFELwS (ORCPT ); Sat, 5 Jun 2021 07:52:18 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id C4EA361380; Sat, 5 Jun 2021 11:50:21 +0000 (UTC) Date: Sat, 5 Jun 2021 13:50:19 +0200 From: Christian Brauner To: menglong8.dong@gmail.com Cc: viro@zeniv.linux.org.uk, keescook@chromium.org, samitolvanen@google.com, johan@kernel.org, ojeda@kernel.org, jeyu@kernel.org, masahiroy@kernel.org, joe@perches.com, dong.menglong@zte.com.cn, jack@suse.cz, hare@suse.de, axboe@kernel.dk, tj@kernel.org, gregkh@linuxfoundation.org, song@kernel.org, neilb@suse.de, akpm@linux-foundation.org, linux@rasmusvillemoes.dk, brho@google.com, f.fainelli@gmail.com, palmerdabbelt@google.com, wangkefeng.wang@huawei.com, mhiramat@kernel.org, rostedt@goodmis.org, vbabka@suse.cz, glider@google.com, pmladek@suse.com, johannes.berg@intel.com, ebiederm@xmission.com, jojing64@gmail.com, terrelln@fb.com, geert@linux-m68k.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, mcgrof@kernel.org, arnd@arndb.de, chris@chrisdown.name, mingo@kernel.org, bhelgaas@google.com, josh@joshtriplett.org Subject: Re: [PATCH v6 2/2] init/do_mounts.c: create second mount for initramfs Message-ID: <20210605115019.umjumoasiwrclcks@wittgenstein> References: <20210605034447.92917-1-dong.menglong@zte.com.cn> <20210605034447.92917-3-dong.menglong@zte.com.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20210605034447.92917-3-dong.menglong@zte.com.cn> Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat, Jun 05, 2021 at 11:44:47AM +0800, menglong8.dong@gmail.com wrote: > From: Menglong Dong > > If using container platforms such as Docker, upon initialization it > wants to use pivot_root() so that currently mounted devices do not > propagate to containers. An example of value in this is that > a USB device connected prior to the creation of a containers on the > host gets disconnected after a container is created; if the > USB device was mounted on containers, but already removed and > umounted on the host, the mount point will not go away until all > containers unmount the USB device. > > Another reason for container platforms such as Docker to use pivot_root > is that upon initialization the net-namspace is mounted under > /var/run/docker/netns/ on the host by dockerd. Without pivot_root > Docker must either wait to create the network namespace prior to > the creation of containers or simply deal with leaking this to each > container. > > pivot_root is supported if the rootfs is a initrd or block device, but > it's not supported if the rootfs uses an initramfs (tmpfs). This means > container platforms today must resort to using block devices if > they want to pivot_root from the rootfs. A workaround to use chroot() > is not a clean viable option given every container will have a > duplicate of every mount point on the host. > > In order to support using container platforms such as Docker on > all the supported rootfs types we must extend Linux to support > pivot_root on initramfs as well. This patch does the work to do > just that. > > pivot_root will unmount the mount of the rootfs from its parent mount > and mount the new root to it. However, when it comes to initramfs, it > donesn't work, because the root filesystem has not parent mount, which > makes initramfs not supported by pivot_root. > > In order to make pivot_root supported on initramfs, we create a second > mount with type of rootfs before unpacking cpio, and change root to > this mount after unpacking. > > While mounting the second rootfs, 'rootflags' is passed, and it means > that we can set options for the mount of rootfs in boot cmd now. > For example, the size of tmpfs can be set with 'rootflags=size=1024M'. > > Signed-off-by: Menglong Dong > --- > init/do_mounts.c | 44 ++++++++++++++++++++++++++++++++++++++++++++ > init/do_mounts.h | 17 ++++++++++++++++- > init/initramfs.c | 8 ++++++++ > usr/Kconfig | 10 ++++++++++ > 4 files changed, 78 insertions(+), 1 deletion(-) > > diff --git a/init/do_mounts.c b/init/do_mounts.c > index a78e44ee6adb..715bdaa89b81 100644 > --- a/init/do_mounts.c > +++ b/init/do_mounts.c > @@ -618,6 +618,49 @@ void __init prepare_namespace(void) > } > > static bool is_tmpfs; > +#ifdef CONFIG_INITRAMFS_MOUNT > + > +/* > + * Give systems running from the initramfs and making use of pivot_root a > + * proper mount so it can be umounted during pivot_root. > + */ > +int __init prepare_mount_rootfs(void) > +{ > + char *rootfs = "ramfs"; > + > + if (is_tmpfs) > + rootfs = "tmpfs"; > + > + return do_mount_root(rootfs, rootfs, > + root_mountflags & ~MS_RDONLY, > + root_mount_data); > +} > + > +/* > + * Revert to previous mount by chdir to '/' and unmounting the second > + * mount. > + */ > +void __init revert_mount_rootfs(void) > +{ > + init_chdir("/"); > + init_umount(".", MNT_DETACH); > +} > + > +/* > + * Change root to the new rootfs that mounted in prepare_mount_rootfs() > + * if cpio is unpacked successfully and 'ramdisk_execute_command' exist. > + */ > +void __init finish_mount_rootfs(void) > +{ > + init_mount(".", "/", NULL, MS_MOVE, NULL); > + if (likely(ramdisk_exec_exist())) > + init_chroot("."); > + else > + revert_mount_rootfs(); > +} > + > +#define rootfs_init_fs_context ramfs_init_fs_context Sorry, I think we're nearly there. What's the rationale for using ramfs when unconditionally when a separate mount for initramfs is requested? Meaning, why do we need this define at all? > +#else > static int rootfs_init_fs_context(struct fs_context *fc) > { > if (IS_ENABLED(CONFIG_TMPFS) && is_tmpfs) > @@ -625,6 +668,7 @@ static int rootfs_init_fs_context(struct fs_context *fc) > > return ramfs_init_fs_context(fc); > } > +#endif > > struct file_system_type rootfs_fs_type = { > .name = "rootfs", > diff --git a/init/do_mounts.h b/init/do_mounts.h > index 7a29ac3e427b..ae4ab306caa9 100644 > --- a/init/do_mounts.h > +++ b/init/do_mounts.h > @@ -10,9 +10,24 @@ > #include > #include > > +extern int root_mountflags; > + > void mount_block_root(char *name, int flags); > void mount_root(void); > -extern int root_mountflags; > + > +#ifdef CONFIG_INITRAMFS_MOUNT > + > +int prepare_mount_rootfs(void); > +void finish_mount_rootfs(void); > +void revert_mount_rootfs(void); > + > +#else > + > +static inline int prepare_mount_rootfs(void) { return 0; } > +static inline void finish_mount_rootfs(void) { } > +static inline void revert_mount_rootfs(void) { } > + > +#endif > > static inline __init int create_dev(char *name, dev_t dev) > { > diff --git a/init/initramfs.c b/init/initramfs.c > index af27abc59643..1833de3cf04e 100644 > --- a/init/initramfs.c > +++ b/init/initramfs.c > @@ -16,6 +16,8 @@ > #include > #include > > +#include "do_mounts.h" > + > static ssize_t __init xwrite(struct file *file, const char *p, size_t count, > loff_t *pos) > { > @@ -682,13 +684,19 @@ static void __init do_populate_rootfs(void *unused, async_cookie_t cookie) > else > printk(KERN_INFO "Unpacking initramfs...\n"); > > + if (prepare_mount_rootfs()) > + panic("Failed to mount rootfs"); > + > err = unpack_to_rootfs((char *)initrd_start, initrd_end - initrd_start); > if (err) { > + revert_mount_rootfs(); > #ifdef CONFIG_BLK_DEV_RAM > populate_initrd_image(err); > #else > printk(KERN_EMERG "Initramfs unpacking failed: %s\n", err); > #endif > + } else { > + finish_mount_rootfs(); > } > > done: > diff --git a/usr/Kconfig b/usr/Kconfig > index 8bbcf699fe3b..4f6ac12eafe9 100644 > --- a/usr/Kconfig > +++ b/usr/Kconfig > @@ -52,6 +52,16 @@ config INITRAMFS_ROOT_GID > > If you are not sure, leave it set to "0". > > +config INITRAMFS_MOUNT > + bool "Create second mount to make pivot_root() supported" > + default y > + help > + Before unpacking cpio, create a second mount and make it become > + the root filesystem. Therefore, initramfs will be supported by > + pivot_root(). > + > + If container platforms is used with initramfs, say Y. > + > config RD_GZIP > bool "Support initial ramdisk/ramfs compressed using gzip" > default y > -- > 2.32.0.rc0 >