char_dev.c

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/*
 *  linux/fs/char_dev.c
 *
 *  Copyright (C) 1991, 1992  Linus Torvalds
 */

#include <linux/init.h>
#include <linux/fs.h>
#include <linux/kdev_t.h>
#include <linux/slab.h>
#include <linux/string.h>

#include <linux/major.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/seq_file.h>

#include <linux/kobject.h>
#include <linux/kobj_map.h>
#include <linux/cdev.h>
#include <linux/mutex.h>
#include <linux/backing-dev.h>
#include <linux/tty.h>

#include "internal.h"

/*
 * capabilities for /dev/mem, /dev/kmem and similar directly mappable character
 * devices
 * - permits shared-mmap for read, write and/or exec
 * - does not permit private mmap in NOMMU mode (can't do COW)
 * - no readahead or I/O queue unplugging required
 */
struct backing_dev_info directly_mappable_cdev_bdi = {
    .name = "char",
    .capabilities   = (
#ifdef CONFIG_MMU
        /* permit private copies of the data to be taken */
        BDI_CAP_MAP_COPY |
#endif
        /* permit direct mmap, for read, write or exec */
        BDI_CAP_MAP_DIRECT |
        BDI_CAP_READ_MAP | BDI_CAP_WRITE_MAP | BDI_CAP_EXEC_MAP |
        /* no writeback happens */
        BDI_CAP_NO_ACCT_AND_WRITEBACK),
};

static struct kobj_map *cdev_map;

static DEFINE_MUTEX(chrdevs_lock);

static struct char_device_struct {
    struct char_device_struct *next;
    unsigned int major;
    unsigned int baseminor;
    int minorct;
    char name[64];
    struct cdev *cdev;      /* will die */
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];

/* index in the above */
static inline int major_to_index(unsigned major)
{
    return major % CHRDEV_MAJOR_HASH_SIZE;
}

#ifdef CONFIG_PROC_FS

void chrdev_show(struct seq_file *f, off_t offset)
{
    struct char_device_struct *cd;

    if (offset < CHRDEV_MAJOR_HASH_SIZE) {
        mutex_lock(&chrdevs_lock);
        for (cd = chrdevs[offset]; cd; cd = cd->next)
            seq_printf(f, "%3d %s\n", cd->major, cd->name);
        mutex_unlock(&chrdevs_lock);
    }
}

#endif /* CONFIG_PROC_FS */

/*
 * Register a single major with a specified minor range.
 *
 * If major == 0 this functions will dynamically allocate a major and return
 * its number.
 *
 * If major > 0 this function will attempt to reserve the passed range of
 * minors and will return zero on success.
 *
 * Returns a -ve errno on failure.
 */
static struct char_device_struct *
__register_chrdev_region(unsigned int major, unsigned int baseminor,
               int minorct, const char *name)
{
    struct char_device_struct *cd, **cp;
    int ret = 0;
    int i;

    cd = kzalloc(sizeof(struct char_device_struct), GFP_KERNEL);
    if (cd == NULL)
        return ERR_PTR(-ENOMEM);

    mutex_lock(&chrdevs_lock);

    /* temporary */
    if (major == 0) {
        for (i = ARRAY_SIZE(chrdevs)-1; i > 0; i--) {
            if (chrdevs[i] == NULL)
                break;
        }

        if (i == 0) {
            ret = -EBUSY;
            goto out;
        }
        major = i;
        ret = major;
    }

    cd->major = major;
    cd->baseminor = baseminor;
    cd->minorct = minorct;
    strlcpy(cd->name, name, sizeof(cd->name));

    i = major_to_index(major);

    for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
        if ((*cp)->major > major ||
            ((*cp)->major == major &&
             (((*cp)->baseminor >= baseminor) ||
              ((*cp)->baseminor + (*cp)->minorct > baseminor))))
            break;

    /* Check for overlapping minor ranges.  */
    if (*cp && (*cp)->major == major) {
        int old_min = (*cp)->baseminor;
        int old_max = (*cp)->baseminor + (*cp)->minorct - 1;
        int new_min = baseminor;
        int new_max = baseminor + minorct - 1;

        /* New driver overlaps from the left.  */
        if (new_max >= old_min && new_max <= old_max) {
            ret = -EBUSY;
            goto out;
        }

        /* New driver overlaps from the right.  */
        if (new_min <= old_max && new_min >= old_min) {
            ret = -EBUSY;
            goto out;
        }
    }

    cd->next = *cp;
    *cp = cd;
    mutex_unlock(&chrdevs_lock);
    return cd;
out:
    mutex_unlock(&chrdevs_lock);
    kfree(cd);
    return ERR_PTR(ret);
}

static struct char_device_struct *
__unregister_chrdev_region(unsigned major, unsigned baseminor, int minorct)
{
    struct char_device_struct *cd = NULL, **cp;
    int i = major_to_index(major);

    mutex_lock(&chrdevs_lock);
    for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
        if ((*cp)->major == major &&
            (*cp)->baseminor == baseminor &&
            (*cp)->minorct == minorct)
            break;
    if (*cp) {
        cd = *cp;
        *cp = cd->next;
    }
    mutex_unlock(&chrdevs_lock);
    return cd;
}

int register_chrdev_region(dev_t from, unsigned count, const char *name)
{
    struct char_device_struct *cd;
    dev_t to = from + count;
    dev_t n, next;

    for (n = from; n < to; n = next) {
        next = MKDEV(MAJOR(n)+1, 0);
        if (next > to)
            next = to;
        cd = __register_chrdev_region(MAJOR(n), MINOR(n),
                   next - n, name);
        if (IS_ERR(cd))
            goto fail;
    }
    return 0;
fail:
    to = n;
    for (n = from; n < to; n = next) {
        next = MKDEV(MAJOR(n)+1, 0);
        kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
    }
    return PTR_ERR(cd);
}

int alloc_chrdev_region(dev_t *dev, unsigned baseminor, unsigned count,
            const char *name)
{
    struct char_device_struct *cd;
    cd = __register_chrdev_region(0, baseminor, count, name);
    if (IS_ERR(cd))
        return PTR_ERR(cd);
    *dev = MKDEV(cd->major, cd->baseminor);
    return 0;
}

int __register_chrdev(unsigned int major, unsigned int baseminor,
              unsigned int count, const char *name,
              const struct file_operations *fops)
{
    struct char_device_struct *cd;
    struct cdev *cdev;
    int err = -ENOMEM;

    cd = __register_chrdev_region(major, baseminor, count, name);
    if (IS_ERR(cd))
        return PTR_ERR(cd);

    cdev = cdev_alloc();
    if (!cdev)
        goto out2;

    cdev->owner = fops->owner;
    cdev->ops = fops;
    kobject_set_name(&cdev->kobj, "%s", name);

    err = cdev_add(cdev, MKDEV(cd->major, baseminor), count);
    if (err)
        goto out;

    cd->cdev = cdev;

    return major ? 0 : cd->major;
out:
    kobject_put(&cdev->kobj);
out2:
    kfree(__unregister_chrdev_region(cd->major, baseminor, count));
    return err;
}

void unregister_chrdev_region(dev_t from, unsigned count)
{
    dev_t to = from + count;
    dev_t n, next;

    for (n = from; n < to; n = next) {
        next = MKDEV(MAJOR(n)+1, 0);
        if (next > to)
            next = to;
        kfree(__unregister_chrdev_region(MAJOR(n), MINOR(n), next - n));
    }
}

void __unregister_chrdev(unsigned int major, unsigned int baseminor,
             unsigned int count, const char *name)
{
    struct char_device_struct *cd;

    cd = __unregister_chrdev_region(major, baseminor, count);
    if (cd && cd->cdev)
        cdev_del(cd->cdev);
    kfree(cd);
}

static DEFINE_SPINLOCK(cdev_lock);

static struct kobject *cdev_get(struct cdev *p)
{
    struct module *owner = p->owner;
    struct kobject *kobj;

    if (owner && !try_module_get(owner))
        return NULL;
    kobj = kobject_get(&p->kobj);
    if (!kobj)
        module_put(owner);
    return kobj;
}

void cdev_put(struct cdev *p)
{
    if (p) {
        struct module *owner = p->owner;
        kobject_put(&p->kobj);
        module_put(owner);
    }
}

/*
 * Called every time a character special file is opened
 */
static int chrdev_open(struct inode *inode, struct file *filp)
{
    struct cdev *p;
    struct cdev *new = NULL;
    int ret = 0;

    spin_lock(&cdev_lock);
    p = inode->i_cdev;
    if (!p) {
        struct kobject *kobj;
        int idx;
        spin_unlock(&cdev_lock);
        kobj = kobj_lookup(cdev_map, inode->i_rdev, &idx);
        if (!kobj)
            return -ENXIO;
        new = container_of(kobj, struct cdev, kobj);
        spin_lock(&cdev_lock);
        /* Check i_cdev again in case somebody beat us to it while
           we dropped the lock. */
        p = inode->i_cdev;
        if (!p) {
            inode->i_cdev = p = new;
            list_add(&inode->i_devices, &p->list);
            new = NULL;
        } else if (!cdev_get(p))
            ret = -ENXIO;
    } else if (!cdev_get(p))
        ret = -ENXIO;
    spin_unlock(&cdev_lock);
    cdev_put(new);
    if (ret)
        return ret;

    ret = -ENXIO;
    filp->f_op = fops_get(p->ops);
    if (!filp->f_op)
        goto out_cdev_put;

    if (filp->f_op->open) {
        ret = filp->f_op->open(inode, filp);
        if (ret)
            goto out_cdev_put;
    }

    return 0;

 out_cdev_put:
    cdev_put(p);
    return ret;
}

void cd_forget(struct inode *inode)
{
    spin_lock(&cdev_lock);
    list_del_init(&inode->i_devices);
    inode->i_cdev = NULL;
    spin_unlock(&cdev_lock);
}

static void cdev_purge(struct cdev *cdev)
{
    spin_lock(&cdev_lock);
    while (!list_empty(&cdev->list)) {
        struct inode *inode;
        inode = container_of(cdev->list.next, struct inode, i_devices);
        list_del_init(&inode->i_devices);
        inode->i_cdev = NULL;
    }
    spin_unlock(&cdev_lock);
}

/*
 * Dummy default file-operations: the only thing this does
 * is contain the open that then fills in the correct operations
 * depending on the special file...
 */
const struct file_operations def_chr_fops = {
    .open = chrdev_open,
    .llseek = noop_llseek,
};

static struct kobject *exact_match(dev_t dev, int *part, void *data)
{
    struct cdev *p = data;
    return &p->kobj;
}

static int exact_lock(dev_t dev, void *data)
{
    struct cdev *p = data;
    return cdev_get(p) ? 0 : -1;
}

int cdev_add(struct cdev *p, dev_t dev, unsigned count)
{
    int error;

    p->dev = dev;
    p->count = count;

    error = kobj_map(cdev_map, dev, count, NULL,
             exact_match, exact_lock, p);
    if (error)
        return error;

    kobject_get(p->kobj.parent);

    return 0;
}

static void cdev_unmap(dev_t dev, unsigned count)
{
    kobj_unmap(cdev_map, dev, count);
}

void cdev_del(struct cdev *p)
{
    cdev_unmap(p->dev, p->count);
    kobject_put(&p->kobj);
}


static void cdev_default_release(struct kobject *kobj)
{
    struct cdev *p = container_of(kobj, struct cdev, kobj);
    struct kobject *parent = kobj->parent;

    cdev_purge(p);
    kobject_put(parent);
}

static void cdev_dynamic_release(struct kobject *kobj)
{
    struct cdev *p = container_of(kobj, struct cdev, kobj);
    struct kobject *parent = kobj->parent;

    cdev_purge(p);
    kfree(p);
    kobject_put(parent);
}

static struct kobj_type ktype_cdev_default = {
    .release    = cdev_default_release,
};

static struct kobj_type ktype_cdev_dynamic = {
    .release    = cdev_dynamic_release,
};

struct cdev *cdev_alloc(void)
{
    struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
    if (p) {
        INIT_LIST_HEAD(&p->list);
        kobject_init(&p->kobj, &ktype_cdev_dynamic);
    }
    return p;
}

void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
    memset(cdev, 0, sizeof *cdev);
    INIT_LIST_HEAD(&cdev->list);
    kobject_init(&cdev->kobj, &ktype_cdev_default);
    cdev->ops = fops;
}

static struct kobject *base_probe(dev_t dev, int *part, void *data)
{
    if (request_module("char-major-%d-%d", MAJOR(dev), MINOR(dev)) > 0)
        /* Make old-style 2.4 aliases work */
        request_module("char-major-%d", MAJOR(dev));
    return NULL;
}

void __init chrdev_init(void)
{
    cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
    bdi_init(&directly_mappable_cdev_bdi);
}


/* Let modules do char dev stuff */
EXPORT_SYMBOL(register_chrdev_region);
EXPORT_SYMBOL(unregister_chrdev_region);
EXPORT_SYMBOL(alloc_chrdev_region);
EXPORT_SYMBOL(cdev_init);
EXPORT_SYMBOL(cdev_alloc);
EXPORT_SYMBOL(cdev_del);
EXPORT_SYMBOL(cdev_add);
EXPORT_SYMBOL(__register_chrdev);
EXPORT_SYMBOL(__unregister_chrdev);
EXPORT_SYMBOL(directly_mappable_cdev_bdi);