[PATCH] cdev documentation

[deliverable/linux.git] / fs / char_dev.c

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

#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/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>

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

/*
 * 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 = {
        .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),
};

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 file_operations *fops;
        struct cdev *cdev;              /* will die */
} *chrdevs[CHRDEV_MAJOR_HASH_SIZE];

/* index in the above */
static inline int major_to_index(int 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;
        strncpy(cd->name,name, 64);

        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;
}

/**
 * register_chrdev_region() - register a range of device numbers
 * @from: the first in the desired range of device numbers; must include
 *        the major number.
 * @count: the number of consecutive device numbers required
 * @name: the name of the device or driver.
 *
 * Return value is zero on success, a negative error code on failure.
 */
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);
}

/**
 * alloc_chrdev_region() - register a range of char device numbers
 * @dev: output parameter for first assigned number
 * @baseminor: first of the requested range of minor numbers
 * @count: the number of minor numbers required
 * @name: the name of the associated device or driver
 *
 * Allocates a range of char device numbers.  The major number will be
 * chosen dynamically, and returned (along with the first minor number)
 * in @dev.  Returns zero or a negative error code.
 */
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;
}

/**
 * register_chrdev() - Register a major number for character devices.
 * @major: major device number or 0 for dynamic allocation
 * @name: name of this range of devices
 * @fops: file operations associated with this devices
 *
 * If @major == 0 this functions will dynamically allocate a major and return
 * its number.
 *
 * If @major > 0 this function will attempt to reserve a device with the given
 * major number and will return zero on success.
 *
 * Returns a -ve errno on failure.
 *
 * The name of this device has nothing to do with the name of the device in
 * /dev. It only helps to keep track of the different owners of devices. If
 * your module name has only one type of devices it's ok to use e.g. the name
 * of the module here.
 *
 * This function registers a range of 256 minor numbers. The first minor number
 * is 0.
 */
int register_chrdev(unsigned int major, const char *name,
                    const 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;
        kobject_set_name(&cdev->kobj, "%s", name);
        for (s = strchr(kobject_name(&cdev->kobj),'/'); 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;
}

/**
 * unregister_chrdev_region() - return a range of device numbers
 * @from: the first in the range of numbers to unregister
 * @count: the number of device numbers to unregister
 *
 * This function will unregister a range of @count device numbers,
 * starting with @from.  The caller should normally be the one who
 * allocated those numbers in the first place...
 */
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 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
 */
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);
}

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,
};

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;
}

/**
 * cdev_add() - add a char device to the system
 * @p: the cdev structure for the device
 * @dev: the first device number for which this device is responsible
 * @count: the number of consecutive minor numbers corresponding to this
 *         device
 *
 * cdev_add() adds the device represented by @p to the system, making it
 * live immediately.  A negative error code is returned on failure.
 */
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);
}

/**
 * cdev_del() - remove a cdev from the system
 * @p: the cdev structure to be removed
 *
 * cdev_del() removes @p from the system, possibly freeing the structure
 * itself.
 */
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);
        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,
};

/**
 * cdev_alloc() - allocate a cdev structure
 *
 * Allocates and returns a cdev structure, or NULL on failure.
 */
struct cdev *cdev_alloc(void)
{
        struct cdev *p = kzalloc(sizeof(struct cdev), GFP_KERNEL);
        if (p) {
                p->kobj.ktype = &ktype_cdev_dynamic;
                INIT_LIST_HEAD(&p->list);
                kobject_init(&p->kobj);
        }
        return p;
}

/**
 * cdev_init() - initialize a cdev structure
 * @cdev: the structure to initialize
 * @fops: the file_operations for this device
 *
 * Initializes @cdev, remembering @fops, making it ready to add to the
 * system with cdev_add().
 */
void cdev_init(struct cdev *cdev, const struct file_operations *fops)
{
        memset(cdev, 0, sizeof *cdev);
        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)
{
        cdev_map = kobj_map_init(base_probe, &chrdevs_lock);
}


/* 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);