From 2b2af54a5bb6f7e80ccf78f20084b93c398c3a8b Mon Sep 17 00:00:00 2001 From: Kay Sievers Date: Thu, 30 Apr 2009 15:23:42 +0200 Subject: Driver Core: devtmpfs - kernel-maintained tmpfs-based /dev Devtmpfs lets the kernel create a tmpfs instance called devtmpfs very early at kernel initialization, before any driver-core device is registered. Every device with a major/minor will provide a device node in devtmpfs. Devtmpfs can be changed and altered by userspace at any time, and in any way needed - just like today's udev-mounted tmpfs. Unmodified udev versions will run just fine on top of it, and will recognize an already existing kernel-created device node and use it. The default node permissions are root:root 0600. Proper permissions and user/group ownership, meaningful symlinks, all other policy still needs to be applied by userspace. If a node is created by devtmps, devtmpfs will remove the device node when the device goes away. If the device node was created by userspace, or the devtmpfs created node was replaced by userspace, it will no longer be removed by devtmpfs. If it is requested to auto-mount it, it makes init=/bin/sh work without any further userspace support. /dev will be fully populated and dynamic, and always reflect the current device state of the kernel. With the commonly used dynamic device numbers, it solves the problem where static devices nodes may point to the wrong devices. It is intended to make the initial bootup logic simpler and more robust, by de-coupling the creation of the inital environment, to reliably run userspace processes, from a complex userspace bootstrap logic to provide a working /dev. Signed-off-by: Kay Sievers Signed-off-by: Jan Blunck Tested-By: Harald Hoyer Tested-By: Scott James Remnant Signed-off-by: Greg Kroah-Hartman --- include/linux/device.h | 10 ++++++++++ include/linux/shmem_fs.h | 3 +++ 2 files changed, 13 insertions(+) (limited to 'include') diff --git a/include/linux/device.h b/include/linux/device.h index 62ff53a6793..847b763e40e 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -552,6 +552,16 @@ extern void put_device(struct device *dev); extern void wait_for_device_probe(void); +#ifdef CONFIG_DEVTMPFS +extern int devtmpfs_create_node(struct device *dev); +extern int devtmpfs_delete_node(struct device *dev); +extern int devtmpfs_mount(const char *mountpoint); +#else +static inline int devtmpfs_create_node(struct device *dev) { return 0; } +static inline int devtmpfs_delete_node(struct device *dev) { return 0; } +static inline int devtmpfs_mount(const char *mountpoint) { return 0; } +#endif + /* drivers/base/power/shutdown.c */ extern void device_shutdown(void); diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h index 6d3f2f449ea..deee7afd8d6 100644 --- a/include/linux/shmem_fs.h +++ b/include/linux/shmem_fs.h @@ -38,6 +38,9 @@ static inline struct shmem_inode_info *SHMEM_I(struct inode *inode) return container_of(inode, struct shmem_inode_info, vfs_inode); } +extern int init_tmpfs(void); +extern int shmem_fill_super(struct super_block *sb, void *data, int silent); + #ifdef CONFIG_TMPFS_POSIX_ACL int shmem_check_acl(struct inode *, int); int shmem_acl_init(struct inode *, struct inode *); -- cgit v1.2.3-70-g09d2