kernel-ark/include/linux/shmem_fs.h
Kay Sievers 2b2af54a5b 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 <kay.sievers@vrfy.org>
Signed-off-by: Jan Blunck <jblunck@suse.de>
Tested-By: Harald Hoyer <harald@redhat.com>
Tested-By: Scott James Remnant <scott@ubuntu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
2009-09-15 09:50:49 -07:00

61 lines
1.9 KiB
C

#ifndef __SHMEM_FS_H
#define __SHMEM_FS_H
#include <linux/swap.h>
#include <linux/mempolicy.h>
/* inode in-kernel data */
#define SHMEM_NR_DIRECT 16
struct shmem_inode_info {
spinlock_t lock;
unsigned long flags;
unsigned long alloced; /* data pages alloced to file */
unsigned long swapped; /* subtotal assigned to swap */
unsigned long next_index; /* highest alloced index + 1 */
struct shared_policy policy; /* NUMA memory alloc policy */
struct page *i_indirect; /* top indirect blocks page */
swp_entry_t i_direct[SHMEM_NR_DIRECT]; /* first blocks */
struct list_head swaplist; /* chain of maybes on swap */
struct inode vfs_inode;
};
struct shmem_sb_info {
unsigned long max_blocks; /* How many blocks are allowed */
unsigned long free_blocks; /* How many are left for allocation */
unsigned long max_inodes; /* How many inodes are allowed */
unsigned long free_inodes; /* How many are left for allocation */
spinlock_t stat_lock; /* Serialize shmem_sb_info changes */
uid_t uid; /* Mount uid for root directory */
gid_t gid; /* Mount gid for root directory */
mode_t mode; /* Mount mode for root directory */
struct mempolicy *mpol; /* default memory policy for mappings */
};
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 *);
extern struct xattr_handler shmem_xattr_acl_access_handler;
extern struct xattr_handler shmem_xattr_acl_default_handler;
extern struct generic_acl_operations shmem_acl_ops;
#else
static inline int shmem_acl_init(struct inode *inode, struct inode *dir)
{
return 0;
}
#endif /* CONFIG_TMPFS_POSIX_ACL */
#endif