drivers/base/devtmpfs.c - kernel/skids - Git at Google

 /*
  * devtmpfs - kernel-maintained tmpfs-based /dev
  *
  * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
  *
  * During bootup, before any driver core device is registered,
  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
  * device which requests a device node, will add a node in this
  * filesystem.
  * By default, all devices are named after the the name of the
  * device, owned by root and have a default mode of 0600. Subsystems
  * can overwrite the default setting if needed.
  */

 #include <linux/kernel.h>
 #include <linux/syscalls.h>
 #include <linux/mount.h>
 #include <linux/device.h>
 #include <linux/genhd.h>
 #include <linux/namei.h>
 #include <linux/fs.h>
 #include <linux/shmem_fs.h>
 #include <linux/ramfs.h>
 #include <linux/cred.h>
 #include <linux/sched.h>
 #include <linux/init_task.h>
 #include <linux/slab.h>

 static struct vfsmount *dev_mnt;

 #if defined CONFIG_DEVTMPFS_MOUNT
 static int dev_mount = 1;
 #else
 static int dev_mount;
 #endif

 static DEFINE_MUTEX(dirlock);

 static int __init mount_param(char *str)
 {
 	dev_mount = simple_strtoul(str, NULL, 0);
 	return 1;
 }
 __setup("devtmpfs.mount=", mount_param);

 static int dev_get_sb(struct file_system_type *fs_type, int flags,
 		      const char *dev_name, void *data, struct vfsmount *mnt)
 {
 #ifdef CONFIG_TMPFS
 	return get_sb_single(fs_type, flags, data, shmem_fill_super, mnt);
 #else
 	return get_sb_single(fs_type, flags, data, ramfs_fill_super, mnt);
 #endif
 }

 static struct file_system_type dev_fs_type = {
 	.name = "devtmpfs",
 	.get_sb = dev_get_sb,
 	.kill_sb = kill_litter_super,
 };

 #ifdef CONFIG_BLOCK
 static inline int is_blockdev(struct device *dev)
 {
 	return dev->class == &block_class;
 }
 #else
 static inline int is_blockdev(struct device *dev) { return 0; }
 #endif

 static int dev_mkdir(const char *name, mode_t mode)
 {
 	struct nameidata nd;
 	struct dentry *dentry;
 	int err;

 	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 			      name, LOOKUP_PARENT, &nd);
 	if (err)
 		return err;

 	dentry = lookup_create(&nd, 1);
 	if (!IS_ERR(dentry)) {
 		err = vfs_mkdir(nd.path.dentry->d_inode, dentry, mode);
 		if (!err)
 			/* mark as kernel-created inode */
 			dentry->d_inode->i_private = &dev_mnt;
 		dput(dentry);
 	} else {
 		err = PTR_ERR(dentry);
 	}

 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 	path_put(&nd.path);
 	return err;
 }

 static int create_path(const char *nodepath)
 {
 	int err;

 	mutex_lock(&dirlock);
 	err = dev_mkdir(nodepath, 0755);
 	if (err == -ENOENT) {
 		char *path;
 		char *s;

 		/* parent directories do not exist, create them */
 		path = kstrdup(nodepath, GFP_KERNEL);
 		if (!path) {
 			err = -ENOMEM;
 			goto out;
 		}
 		s = path;
 		for (;;) {
 			s = strchr(s, '/');
 			if (!s)
 				break;
 			s[0] = '\0';
 			err = dev_mkdir(path, 0755);
 			if (err && err != -EEXIST)
 				break;
 			s[0] = '/';
 			s++;
 		}
 		kfree(path);
 	}
 out:
 	mutex_unlock(&dirlock);
 	return err;
 }

 int devtmpfs_create_node(struct device *dev)
 {
 	const char *tmp = NULL;
 	const char *nodename;
 	const struct cred *curr_cred;
 	mode_t mode = 0;
 	struct nameidata nd;
 	struct dentry *dentry;
 	int err;

 	if (!dev_mnt)
 		return 0;

 	nodename = device_get_devnode(dev, &mode, &tmp);
 	if (!nodename)
 		return -ENOMEM;

 	if (mode == 0)
 		mode = 0600;
 	if (is_blockdev(dev))
 		mode |= S_IFBLK;
 	else
 		mode |= S_IFCHR;

 	curr_cred = override_creds(&init_cred);

 	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 			      nodename, LOOKUP_PARENT, &nd);
 	if (err == -ENOENT) {
 		create_path(nodename);
 		err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 				      nodename, LOOKUP_PARENT, &nd);
 	}
 	if (err)
 		goto out;

 	dentry = lookup_create(&nd, 0);
 	if (!IS_ERR(dentry)) {
 		err = vfs_mknod(nd.path.dentry->d_inode,
 				dentry, mode, dev->devt);
 		if (!err) {
 			struct iattr newattrs;

 			/* fixup possibly umasked mode */
 			newattrs.ia_mode = mode;
 			newattrs.ia_valid = ATTR_MODE;
 			mutex_lock(&dentry->d_inode->i_mutex);
 			notify_change(dentry, &newattrs);
 			mutex_unlock(&dentry->d_inode->i_mutex);

 			/* mark as kernel-created inode */
 			dentry->d_inode->i_private = &dev_mnt;
 		}
 		dput(dentry);
 	} else {
 		err = PTR_ERR(dentry);
 	}

 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 	path_put(&nd.path);
 out:
 	kfree(tmp);
 	revert_creds(curr_cred);
 	return err;
 }

 static int dev_rmdir(const char *name)
 {
 	struct nameidata nd;
 	struct dentry *dentry;
 	int err;

 	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 			      name, LOOKUP_PARENT, &nd);
 	if (err)
 		return err;

 	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 	if (!IS_ERR(dentry)) {
 		if (dentry->d_inode) {
 			if (dentry->d_inode->i_private == &dev_mnt)
 				err = vfs_rmdir(nd.path.dentry->d_inode,
 						dentry);
 			else
 				err = -EPERM;
 		} else {
 			err = -ENOENT;
 		}
 		dput(dentry);
 	} else {
 		err = PTR_ERR(dentry);
 	}

 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 	path_put(&nd.path);
 	return err;
 }

 static int delete_path(const char *nodepath)
 {
 	const char *path;
 	int err = 0;

 	path = kstrdup(nodepath, GFP_KERNEL);
 	if (!path)
 		return -ENOMEM;

 	mutex_lock(&dirlock);
 	for (;;) {
 		char *base;

 		base = strrchr(path, '/');
 		if (!base)
 			break;
 		base[0] = '\0';
 		err = dev_rmdir(path);
 		if (err)
 			break;
 	}
 	mutex_unlock(&dirlock);

 	kfree(path);
 	return err;
 }

 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
 {
 	/* did we create it */
 	if (inode->i_private != &dev_mnt)
 		return 0;

 	/* does the dev_t match */
 	if (is_blockdev(dev)) {
 		if (!S_ISBLK(stat->mode))
 			return 0;
 	} else {
 		if (!S_ISCHR(stat->mode))
 			return 0;
 	}
 	if (stat->rdev != dev->devt)
 		return 0;

 	/* ours */
 	return 1;
 }

 int devtmpfs_delete_node(struct device *dev)
 {
 	const char *tmp = NULL;
 	const char *nodename;
 	const struct cred *curr_cred;
 	struct nameidata nd;
 	struct dentry *dentry;
 	struct kstat stat;
 	int deleted = 1;
 	int err;

 	if (!dev_mnt)
 		return 0;

 	nodename = device_get_devnode(dev, NULL, &tmp);
 	if (!nodename)
 		return -ENOMEM;

 	curr_cred = override_creds(&init_cred);
 	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
 			      nodename, LOOKUP_PARENT, &nd);
 	if (err)
 		goto out;

 	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
 	if (!IS_ERR(dentry)) {
 		if (dentry->d_inode) {
 			err = vfs_getattr(nd.path.mnt, dentry, &stat);
 			if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
 				struct iattr newattrs;
 				/*
 				 * before unlinking this node, reset permissions
 				 * of possible references like hardlinks
 				 */
 				newattrs.ia_uid = 0;
 				newattrs.ia_gid = 0;
 				newattrs.ia_mode = stat.mode & ~0777;
 				newattrs.ia_valid =
 					ATTR_UID|ATTR_GID|ATTR_MODE;
 				mutex_lock(&dentry->d_inode->i_mutex);
 				notify_change(dentry, &newattrs);
 				mutex_unlock(&dentry->d_inode->i_mutex);
 				err = vfs_unlink(nd.path.dentry->d_inode,
 						 dentry);
 				if (!err || err == -ENOENT)
 					deleted = 1;
 			}
 		} else {
 			err = -ENOENT;
 		}
 		dput(dentry);
 	} else {
 		err = PTR_ERR(dentry);
 	}
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);

 	path_put(&nd.path);
 	if (deleted && strchr(nodename, '/'))
 		delete_path(nodename);
 out:
 	kfree(tmp);
 	revert_creds(curr_cred);
 	return err;
 }

 /*
  * If configured, or requested by the commandline, devtmpfs will be
  * auto-mounted after the kernel mounted the root filesystem.
  */
 int devtmpfs_mount(const char *mntdir)
 {
 	int err;

 	if (!dev_mount)
 		return 0;

 	if (!dev_mnt)
 		return 0;

 	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
 	if (err)
 		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
 	else
 		printk(KERN_INFO "devtmpfs: mounted\n");
 	return err;
 }

 /*
  * Create devtmpfs instance, driver-core devices will add their device
  * nodes here.
  */
 int __init devtmpfs_init(void)
 {
 	int err;
 	struct vfsmount *mnt;
 	char options[] = "mode=0755";

 	err = register_filesystem(&dev_fs_type);
 	if (err) {
 		printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
 		       "type %i\n", err);
 		return err;
 	}

 	mnt = kern_mount_data(&dev_fs_type, options);
 	if (IS_ERR(mnt)) {
 		err = PTR_ERR(mnt);
 		printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
 		unregister_filesystem(&dev_fs_type);
 		return err;
 	}
 	dev_mnt = mnt;

 	printk(KERN_INFO "devtmpfs: initialized\n");
 	return 0;
 }
	/*
	* devtmpfs - kernel-maintained tmpfs-based /dev
	*
	* Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
	*
	* During bootup, before any driver core device is registered,
	* devtmpfs, a tmpfs-based filesystem is created. Every driver-core
	* device which requests a device node, will add a node in this
	* filesystem.
	* By default, all devices are named after the the name of the
	* device, owned by root and have a default mode of 0600. Subsystems
	* can overwrite the default setting if needed.
	*/

	#include <linux/kernel.h>
	#include <linux/syscalls.h>
	#include <linux/mount.h>
	#include <linux/device.h>
	#include <linux/genhd.h>
	#include <linux/namei.h>
	#include <linux/fs.h>
	#include <linux/shmem_fs.h>
	#include <linux/ramfs.h>
	#include <linux/cred.h>
	#include <linux/sched.h>
	#include <linux/init_task.h>
	#include <linux/slab.h>

	static struct vfsmount *dev_mnt;

	#if defined CONFIG_DEVTMPFS_MOUNT
	static int dev_mount = 1;
	#else
	static int dev_mount;
	#endif

	static DEFINE_MUTEX(dirlock);

	static int __init mount_param(char *str)
	{
	dev_mount = simple_strtoul(str, NULL, 0);
	return 1;
	}
	__setup("devtmpfs.mount=", mount_param);

	static int dev_get_sb(struct file_system_type *fs_type, int flags,
	const char dev_name, void data, struct vfsmount *mnt)
	{
	#ifdef CONFIG_TMPFS
	return get_sb_single(fs_type, flags, data, shmem_fill_super, mnt);
	#else
	return get_sb_single(fs_type, flags, data, ramfs_fill_super, mnt);
	#endif
	}

	static struct file_system_type dev_fs_type = {
	.name = "devtmpfs",
	.get_sb = dev_get_sb,
	.kill_sb = kill_litter_super,
	};

	#ifdef CONFIG_BLOCK
	static inline int is_blockdev(struct device *dev)
	{
	return dev->class == &block_class;
	}
	#else
	static inline int is_blockdev(struct device *dev) { return 0; }
	#endif

	static int dev_mkdir(const char *name, mode_t mode)
	{
	struct nameidata nd;
	struct dentry *dentry;
	int err;

	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
	name, LOOKUP_PARENT, &nd);
	if (err)
	return err;

	dentry = lookup_create(&nd, 1);
	if (!IS_ERR(dentry)) {
	err = vfs_mkdir(nd.path.dentry->d_inode, dentry, mode);
	if (!err)
	/* mark as kernel-created inode */
	dentry->d_inode->i_private = &dev_mnt;
	dput(dentry);
	} else {
	err = PTR_ERR(dentry);
	}

	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
	path_put(&nd.path);
	return err;
	}

	static int create_path(const char *nodepath)
	{
	int err;

	mutex_lock(&dirlock);
	err = dev_mkdir(nodepath, 0755);
	if (err == -ENOENT) {
	char *path;
	char *s;

	/* parent directories do not exist, create them */
	path = kstrdup(nodepath, GFP_KERNEL);
	if (!path) {
	err = -ENOMEM;
	goto out;
	}
	s = path;
	for (;;) {
	s = strchr(s, '/');
	if (!s)
	break;
	s[0] = '\0';
	err = dev_mkdir(path, 0755);
	if (err && err != -EEXIST)
	break;
	s[0] = '/';
	s++;
	}
	kfree(path);
	}
	out:
	mutex_unlock(&dirlock);
	return err;
	}

	int devtmpfs_create_node(struct device *dev)
	{
	const char *tmp = NULL;
	const char *nodename;
	const struct cred *curr_cred;
	mode_t mode = 0;
	struct nameidata nd;
	struct dentry *dentry;
	int err;

	if (!dev_mnt)
	return 0;

	nodename = device_get_devnode(dev, &mode, &tmp);
	if (!nodename)
	return -ENOMEM;

	if (mode == 0)
	mode = 0600;
	if (is_blockdev(dev))
	mode \|= S_IFBLK;
	else
	mode \|= S_IFCHR;

	curr_cred = override_creds(&init_cred);

	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
	nodename, LOOKUP_PARENT, &nd);
	if (err == -ENOENT) {
	create_path(nodename);
	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
	nodename, LOOKUP_PARENT, &nd);
	}
	if (err)
	goto out;

	dentry = lookup_create(&nd, 0);
	if (!IS_ERR(dentry)) {
	err = vfs_mknod(nd.path.dentry->d_inode,
	dentry, mode, dev->devt);
	if (!err) {
	struct iattr newattrs;

	/* fixup possibly umasked mode */
	newattrs.ia_mode = mode;
	newattrs.ia_valid = ATTR_MODE;
	mutex_lock(&dentry->d_inode->i_mutex);
	notify_change(dentry, &newattrs);
	mutex_unlock(&dentry->d_inode->i_mutex);

	/* mark as kernel-created inode */
	dentry->d_inode->i_private = &dev_mnt;
	}
	dput(dentry);
	} else {
	err = PTR_ERR(dentry);
	}

	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
	path_put(&nd.path);
	out:
	kfree(tmp);
	revert_creds(curr_cred);
	return err;
	}

	static int dev_rmdir(const char *name)
	{
	struct nameidata nd;
	struct dentry *dentry;
	int err;

	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
	name, LOOKUP_PARENT, &nd);
	if (err)
	return err;

	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
	if (!IS_ERR(dentry)) {
	if (dentry->d_inode) {
	if (dentry->d_inode->i_private == &dev_mnt)
	err = vfs_rmdir(nd.path.dentry->d_inode,
	dentry);
	else
	err = -EPERM;
	} else {
	err = -ENOENT;
	}
	dput(dentry);
	} else {
	err = PTR_ERR(dentry);
	}

	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
	path_put(&nd.path);
	return err;
	}

	static int delete_path(const char *nodepath)
	{
	const char *path;
	int err = 0;

	path = kstrdup(nodepath, GFP_KERNEL);
	if (!path)
	return -ENOMEM;

	mutex_lock(&dirlock);
	for (;;) {
	char *base;

	base = strrchr(path, '/');
	if (!base)
	break;
	base[0] = '\0';
	err = dev_rmdir(path);
	if (err)
	break;
	}
	mutex_unlock(&dirlock);

	kfree(path);
	return err;
	}

	static int dev_mynode(struct device dev, struct inode inode, struct kstat *stat)
	{
	/* did we create it */
	if (inode->i_private != &dev_mnt)
	return 0;

	/* does the dev_t match */
	if (is_blockdev(dev)) {
	if (!S_ISBLK(stat->mode))
	return 0;
	} else {
	if (!S_ISCHR(stat->mode))
	return 0;
	}
	if (stat->rdev != dev->devt)
	return 0;

	/* ours */
	return 1;
	}

	int devtmpfs_delete_node(struct device *dev)
	{
	const char *tmp = NULL;
	const char *nodename;
	const struct cred *curr_cred;
	struct nameidata nd;
	struct dentry *dentry;
	struct kstat stat;
	int deleted = 1;
	int err;

	if (!dev_mnt)
	return 0;

	nodename = device_get_devnode(dev, NULL, &tmp);
	if (!nodename)
	return -ENOMEM;

	curr_cred = override_creds(&init_cred);
	err = vfs_path_lookup(dev_mnt->mnt_root, dev_mnt,
	nodename, LOOKUP_PARENT, &nd);
	if (err)
	goto out;

	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
	dentry = lookup_one_len(nd.last.name, nd.path.dentry, nd.last.len);
	if (!IS_ERR(dentry)) {
	if (dentry->d_inode) {
	err = vfs_getattr(nd.path.mnt, dentry, &stat);
	if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
	struct iattr newattrs;
	/*
	* before unlinking this node, reset permissions
	* of possible references like hardlinks
	*/
	newattrs.ia_uid = 0;
	newattrs.ia_gid = 0;
	newattrs.ia_mode = stat.mode & ~0777;
	newattrs.ia_valid =
	ATTR_UID\|ATTR_GID\|ATTR_MODE;
	mutex_lock(&dentry->d_inode->i_mutex);
	notify_change(dentry, &newattrs);
	mutex_unlock(&dentry->d_inode->i_mutex);
	err = vfs_unlink(nd.path.dentry->d_inode,
	dentry);
	if (!err \|\| err == -ENOENT)
	deleted = 1;
	}
	} else {
	err = -ENOENT;
	}
	dput(dentry);
	} else {
	err = PTR_ERR(dentry);
	}
	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);

	path_put(&nd.path);
	if (deleted && strchr(nodename, '/'))
	delete_path(nodename);
	out:
	kfree(tmp);
	revert_creds(curr_cred);
	return err;
	}

	/*
	* If configured, or requested by the commandline, devtmpfs will be
	* auto-mounted after the kernel mounted the root filesystem.
	*/
	int devtmpfs_mount(const char *mntdir)
	{
	int err;

	if (!dev_mount)
	return 0;

	if (!dev_mnt)
	return 0;

	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
	if (err)
	printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
	else
	printk(KERN_INFO "devtmpfs: mounted\n");
	return err;
	}

	/*
	* Create devtmpfs instance, driver-core devices will add their device
	* nodes here.
	*/
	int __init devtmpfs_init(void)
	{
	int err;
	struct vfsmount *mnt;
	char options[] = "mode=0755";

	err = register_filesystem(&dev_fs_type);
	if (err) {
	printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
	"type %i\n", err);
	return err;
	}

	mnt = kern_mount_data(&dev_fs_type, options);
	if (IS_ERR(mnt)) {
	err = PTR_ERR(mnt);
	printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
	unregister_filesystem(&dev_fs_type);
	return err;
	}
	dev_mnt = mnt;

	printk(KERN_INFO "devtmpfs: initialized\n");
	return 0;
	}