devtmpfs.c

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/*
 * devtmpfs - kernel-maintained tmpfs-based /dev
 *
 * Copyright (C) 2009, Kay Sievers <[email protected]>
 *
 * 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 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/sched.h>
#include <linux/slab.h>
#include <linux/kthread.h>

static struct task_struct *thread;

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

static DEFINE_SPINLOCK(req_lock);

static struct req {
    struct req *next;
    struct completion done;
    int err;
    const char *name;
    umode_t mode;   /* 0 => delete */
    struct device *dev;
} *requests;

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

static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
              const char *dev_name, void *data)
{
#ifdef CONFIG_TMPFS
    return mount_single(fs_type, flags, data, shmem_fill_super);
#else
    return mount_single(fs_type, flags, data, ramfs_fill_super);
#endif
}

static struct file_system_type dev_fs_type = {
    .name = "devtmpfs",
    .mount = dev_mount,
    .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

int devtmpfs_create_node(struct device *dev)
{
    const char *tmp = NULL;
    struct req req;

    if (!thread)
        return 0;

    req.mode = 0;
    req.name = device_get_devnode(dev, &req.mode, &tmp);
    if (!req.name)
        return -ENOMEM;

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

    req.dev = dev;

    init_completion(&req.done);

    spin_lock(&req_lock);
    req.next = requests;
    requests = &req;
    spin_unlock(&req_lock);

    wake_up_process(thread);
    wait_for_completion(&req.done);

    kfree(tmp);

    return req.err;
}

int devtmpfs_delete_node(struct device *dev)
{
    const char *tmp = NULL;
    struct req req;

    if (!thread)
        return 0;

    req.name = device_get_devnode(dev, NULL, &tmp);
    if (!req.name)
        return -ENOMEM;

    req.mode = 0;
    req.dev = dev;

    init_completion(&req.done);

    spin_lock(&req_lock);
    req.next = requests;
    requests = &req;
    spin_unlock(&req_lock);

    wake_up_process(thread);
    wait_for_completion(&req.done);

    kfree(tmp);
    return req.err;
}

static int dev_mkdir(const char *name, umode_t mode)
{
    struct dentry *dentry;
    struct path path;
    int err;

    dentry = kern_path_create(AT_FDCWD, name, &path, 1);
    if (IS_ERR(dentry))
        return PTR_ERR(dentry);

    err = vfs_mkdir(path.dentry->d_inode, dentry, mode);
    if (!err)
        /* mark as kernel-created inode */
        dentry->d_inode->i_private = &thread;
    done_path_create(&path, dentry);
    return err;
}

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

    /* parent directories do not exist, create them */
    path = kstrdup(nodepath, GFP_KERNEL);
    if (!path)
        return -ENOMEM;

    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);
    return err;
}

static int handle_create(const char *nodename, umode_t mode, struct device *dev)
{
    struct dentry *dentry;
    struct path path;
    int err;

    dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
    if (dentry == ERR_PTR(-ENOENT)) {
        create_path(nodename);
        dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
    }
    if (IS_ERR(dentry))
        return PTR_ERR(dentry);

    err = vfs_mknod(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 = &thread;
    }
    done_path_create(&path, dentry);
    return err;
}

static int dev_rmdir(const char *name)
{
    struct path parent;
    struct dentry *dentry;
    int err;

    dentry = kern_path_locked(name, &parent);
    if (IS_ERR(dentry))
        return PTR_ERR(dentry);
    if (dentry->d_inode) {
        if (dentry->d_inode->i_private == &thread)
            err = vfs_rmdir(parent.dentry->d_inode, dentry);
        else
            err = -EPERM;
    } else {
        err = -ENOENT;
    }
    dput(dentry);
    mutex_unlock(&parent.dentry->d_inode->i_mutex);
    path_put(&parent);
    return err;
}

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

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

    for (;;) {
        char *base;

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

    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 != &thread)
        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;
}

static int handle_remove(const char *nodename, struct device *dev)
{
    struct path parent;
    struct dentry *dentry;
    int deleted = 1;
    int err;

    dentry = kern_path_locked(nodename, &parent);
    if (IS_ERR(dentry))
        return PTR_ERR(dentry);

    if (dentry->d_inode) {
        struct kstat stat;
        err = vfs_getattr(parent.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 = GLOBAL_ROOT_UID;
            newattrs.ia_gid = GLOBAL_ROOT_GID;
            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(parent.dentry->d_inode, dentry);
            if (!err || err == -ENOENT)
                deleted = 1;
        }
    } else {
        err = -ENOENT;
    }
    dput(dentry);
    mutex_unlock(&parent.dentry->d_inode->i_mutex);

    path_put(&parent);
    if (deleted && strchr(nodename, '/'))
        delete_path(nodename);
    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 (!mount_dev)
        return 0;

    if (!thread)
        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;
}

static DECLARE_COMPLETION(setup_done);

static int handle(const char *name, umode_t mode, struct device *dev)
{
    if (mode)
        return handle_create(name, mode, dev);
    else
        return handle_remove(name, dev);
}

static int devtmpfsd(void *p)
{
    char options[] = "mode=0755";
    int *err = p;
    *err = sys_unshare(CLONE_NEWNS);
    if (*err)
        goto out;
    *err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
    if (*err)
        goto out;
    sys_chdir("/.."); /* will traverse into overmounted root */
    sys_chroot(".");
    complete(&setup_done);
    while (1) {
        spin_lock(&req_lock);
        while (requests) {
            struct req *req = requests;
            requests = NULL;
            spin_unlock(&req_lock);
            while (req) {
                struct req *next = req->next;
                req->err = handle(req->name, req->mode, req->dev);
                complete(&req->done);
                req = next;
            }
            spin_lock(&req_lock);
        }
        __set_current_state(TASK_INTERRUPTIBLE);
        spin_unlock(&req_lock);
        schedule();
    }
    return 0;
out:
    complete(&setup_done);
    return *err;
}

/*
 * Create devtmpfs instance, driver-core devices will add their device
 * nodes here.
 */
int __init devtmpfs_init(void)
{
    int err = register_filesystem(&dev_fs_type);
    if (err) {
        printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
               "type %i\n", err);
        return err;
    }

    thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
    if (!IS_ERR(thread)) {
        wait_for_completion(&setup_done);
    } else {
        err = PTR_ERR(thread);
        thread = NULL;
    }

    if (err) {
        printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
        unregister_filesystem(&dev_fs_type);
        return err;
    }

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