root/fs/char_dev.c

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

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

#include <linux/major.h>
#include <linux/errno.h>
#include <linux/module.h>
#include <linux/smp_lock.h>
#include <linux/devfs_fs_kernel.h>

#include <linux/kobject.h>
#include <linux/kobj_map.h>
#include <linux/cdev.h>

#ifdef CONFIG_KMOD
#include <linux/kmod.h>
#endif

static struct kobj_map *cdev_map;

#define MAX_PROBE_HASH 255      /* random */

static rwlock_t chrdevs_lock = RW_LOCK_UNLOCKED;

static struct char_device_struct {
        struct char_device_struct *next;
        unsigned int major;
        unsigned int baseminor;
        int minorct;
        const char *name;
        struct file_operations *fops;
        struct cdev *cdev;              /* will die */
} *chrdevs[MAX_PROBE_HASH];

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

/* get char device names in somewhat random order */
int get_chrdev_list(char *page)
{
        struct char_device_struct *cd;
        int i, len;

        len = sprintf(page, "Character devices:\n");

        read_lock(&chrdevs_lock);
        for (i = 0; i < ARRAY_SIZE(chrdevs) ; i++) {
                for (cd = chrdevs[i]; cd; cd = cd->next)
                        len += sprintf(page+len, "%3d %s\n",
                                       cd->major, cd->name);
        }
        read_unlock(&chrdevs_lock);

        return len;
}

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

        memset(cd, 0, sizeof(struct char_device_struct));

        write_lock_irq(&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;
        cd->name = name;

        i = major_to_index(major);

        for (cp = &chrdevs[i]; *cp; cp = &(*cp)->next)
                if ((*cp)->major > major ||
                    ((*cp)->major == major && (*cp)->baseminor >= baseminor))
                        break;
        if (*cp && (*cp)->major == major &&
            (*cp)->baseminor < baseminor + minorct) {
                ret = -EBUSY;
                goto out;
        }
        cd->next = *cp;
        *cp = cd;
        write_unlock_irq(&chrdevs_lock);
        return cd;
out:
        write_unlock_irq(&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);

        write_lock_irq(&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;
        }
        write_unlock_irq(&chrdevs_lock);
        return cd;
}

int register_chrdev_region(dev_t from, unsigned count, 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, 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, const char *name,
                    struct file_operations *fops)
{
        struct char_device_struct *cd;
        struct cdev *cdev;
        char *s;
        int err = -ENOMEM;

        cd = __register_chrdev_region(major, 0, 256, name);
        if (IS_ERR(cd))
                return PTR_ERR(cd);
        
        cdev = cdev_alloc();
        if (!cdev)
                goto out2;

        cdev->owner = fops->owner;
        cdev->ops = fops;
        strcpy(cdev->kobj.name, name);
        for (s = strchr(cdev->kobj.name, '/'); s; s = strchr(s, '/'))
                *s = '!';
                
        err = cdev_add(cdev, MKDEV(cd->major, 0), 256);
        if (err)
                goto out;

        cd->cdev = cdev;

        return major ? 0 : cd->major;
out:
        kobject_put(&cdev->kobj);
out2:
        kfree(__unregister_chrdev_region(cd->major, 0, 256));
        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));
        }
}

int unregister_chrdev(unsigned int major, const char *name)
{
        struct char_device_struct *cd;
        cd = __unregister_chrdev_region(major, 0, 256);
        if (cd && cd->cdev)
                cdev_del(cd->cdev);
        kfree(cd);
        return 0;
}

static spinlock_t cdev_lock = SPIN_LOCK_UNLOCKED;
/*
 * Called every time a character special file is opened
 */
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);
                p = inode->i_cdev;
                if (!p) {
                        inode->i_cdev = p = new;
                        inode->i_cindex = idx;
                        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;
        filp->f_op = fops_get(p->ops);
        if (!filp->f_op) {
                cdev_put(p);
                return -ENXIO;
        }
        if (filp->f_op->open) {
                lock_kernel();
                ret = filp->f_op->open(inode,filp);
                unlock_kernel();
        }
        if (ret)
                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);
}

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...
 */
struct file_operations def_chr_fops = {
        .open = chrdev_open,
};

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)
{
        p->dev = dev;
        p->count = count;
        return kobj_map(cdev_map, dev, count, NULL, exact_match, exact_lock, p);
}

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);
}

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) {
                kobject_put(&p->kobj);
                module_put(p->owner);
        }
}

static decl_subsys(cdev, NULL, NULL);

static void cdev_default_release(struct kobject *kobj)
{
        struct cdev *p = container_of(kobj, struct cdev, kobj);
        cdev_purge(p);
}

static void cdev_dynamic_release(struct kobject *kobj)
{
        struct cdev *p = container_of(kobj, struct cdev, kobj);
        cdev_purge(p);
        kfree(p);
}

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 = kmalloc(sizeof(struct cdev), GFP_KERNEL);
        if (p) {
                memset(p, 0, sizeof(struct cdev));
                p->kobj.ktype = &ktype_cdev_dynamic;
                INIT_LIST_HEAD(&p->list);
                kobject_init(&p->kobj);
        }
        return p;
}

void cdev_init(struct cdev *cdev, struct file_operations *fops)
{
        INIT_LIST_HEAD(&cdev->list);
        cdev->kobj.ktype = &ktype_cdev_default;
        kobject_init(&cdev->kobj);
        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)
{
/*
 * Keep cdev_subsys around because (and only because) the kobj_map code
 * depends on the rwsem it contains.  We don't make it public in sysfs,
 * however.
 */
        subsystem_init(&cdev_subsys);
        cdev_map = kobj_map_init(base_probe, &cdev_subsys);
}


/* 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_get);
EXPORT_SYMBOL(cdev_put);
EXPORT_SYMBOL(cdev_del);
EXPORT_SYMBOL(cdev_add);
EXPORT_SYMBOL(register_chrdev);
EXPORT_SYMBOL(unregister_chrdev);