sysfs: implement sysfs_open_dirent

[linux-2.6] / fs / sysfs / file.c

/*
 * file.c - operations for regular (text) files.
 */

#include <linux/module.h>
#include <linux/kobject.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/list.h>
#include <linux/mutex.h>
#include <asm/uaccess.h>

#include "sysfs.h"

#define to_sattr(a) container_of(a,struct subsys_attribute, attr)

/*
 * Subsystem file operations.
 * These operations allow subsystems to have files that can be 
 * read/written. 
 */
static ssize_t 
subsys_attr_show(struct kobject * kobj, struct attribute * attr, char * page)
{
        struct kset *kset = to_kset(kobj);
        struct subsys_attribute * sattr = to_sattr(attr);
        ssize_t ret = -EIO;

        if (sattr->show)
                ret = sattr->show(kset, page);
        return ret;
}

static ssize_t 
subsys_attr_store(struct kobject * kobj, struct attribute * attr, 
                  const char * page, size_t count)
{
        struct kset *kset = to_kset(kobj);
        struct subsys_attribute * sattr = to_sattr(attr);
        ssize_t ret = -EIO;

        if (sattr->store)
                ret = sattr->store(kset, page, count);
        return ret;
}

static struct sysfs_ops subsys_sysfs_ops = {
        .show   = subsys_attr_show,
        .store  = subsys_attr_store,
};

/*
 * There's one sysfs_buffer for each open file and one
 * sysfs_open_dirent for each sysfs_dirent with one or more open
 * files.
 *
 * filp->private_data points to sysfs_buffer and
 * sysfs_dirent->s_attr.open points to sysfs_open_dirent.  s_attr.open
 * is protected by sysfs_open_dirent_lock.
 */
static spinlock_t sysfs_open_dirent_lock = SPIN_LOCK_UNLOCKED;

struct sysfs_open_dirent {
        atomic_t                refcnt;
        struct list_head        buffers; /* goes through sysfs_buffer.list */
};

struct sysfs_buffer {
        size_t                  count;
        loff_t                  pos;
        char                    * page;
        struct sysfs_ops        * ops;
        struct mutex            mutex;
        int                     needs_read_fill;
        int                     event;
        struct list_head        list;
};

/**
 *      fill_read_buffer - allocate and fill buffer from object.
 *      @dentry:        dentry pointer.
 *      @buffer:        data buffer for file.
 *
 *      Allocate @buffer->page, if it hasn't been already, then call the
 *      kobject's show() method to fill the buffer with this attribute's 
 *      data. 
 *      This is called only once, on the file's first read unless an error
 *      is returned.
 */
static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
{
        struct sysfs_dirent *attr_sd = dentry->d_fsdata;
        struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
        struct sysfs_ops * ops = buffer->ops;
        int ret = 0;
        ssize_t count;

        if (!buffer->page)
                buffer->page = (char *) get_zeroed_page(GFP_KERNEL);
        if (!buffer->page)
                return -ENOMEM;

        /* need attr_sd for attr and ops, its parent for kobj */
        if (!sysfs_get_active_two(attr_sd))
                return -ENODEV;

        buffer->event = atomic_read(&attr_sd->s_event);
        count = ops->show(kobj, attr_sd->s_attr.attr, buffer->page);

        sysfs_put_active_two(attr_sd);

        BUG_ON(count > (ssize_t)PAGE_SIZE);
        if (count >= 0) {
                buffer->needs_read_fill = 0;
                buffer->count = count;
        } else {
                ret = count;
        }
        return ret;
}

/**
 *      sysfs_read_file - read an attribute. 
 *      @file:  file pointer.
 *      @buf:   buffer to fill.
 *      @count: number of bytes to read.
 *      @ppos:  starting offset in file.
 *
 *      Userspace wants to read an attribute file. The attribute descriptor
 *      is in the file's ->d_fsdata. The target object is in the directory's
 *      ->d_fsdata.
 *
 *      We call fill_read_buffer() to allocate and fill the buffer from the
 *      object's show() method exactly once (if the read is happening from
 *      the beginning of the file). That should fill the entire buffer with
 *      all the data the object has to offer for that attribute.
 *      We then call flush_read_buffer() to copy the buffer to userspace
 *      in the increments specified.
 */

static ssize_t
sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
{
        struct sysfs_buffer * buffer = file->private_data;
        ssize_t retval = 0;

        mutex_lock(&buffer->mutex);
        if (buffer->needs_read_fill) {
                retval = fill_read_buffer(file->f_path.dentry,buffer);
                if (retval)
                        goto out;
        }
        pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
                 __FUNCTION__, count, *ppos, buffer->page);
        retval = simple_read_from_buffer(buf, count, ppos, buffer->page,
                                         buffer->count);
out:
        mutex_unlock(&buffer->mutex);
        return retval;
}

/**
 *      fill_write_buffer - copy buffer from userspace.
 *      @buffer:        data buffer for file.
 *      @buf:           data from user.
 *      @count:         number of bytes in @userbuf.
 *
 *      Allocate @buffer->page if it hasn't been already, then
 *      copy the user-supplied buffer into it.
 */

static int 
fill_write_buffer(struct sysfs_buffer * buffer, const char __user * buf, size_t count)
{
        int error;

        if (!buffer->page)
                buffer->page = (char *)get_zeroed_page(GFP_KERNEL);
        if (!buffer->page)
                return -ENOMEM;

        if (count >= PAGE_SIZE)
                count = PAGE_SIZE - 1;
        error = copy_from_user(buffer->page,buf,count);
        buffer->needs_read_fill = 1;
        /* if buf is assumed to contain a string, terminate it by \0,
           so e.g. sscanf() can scan the string easily */
        buffer->page[count] = 0;
        return error ? -EFAULT : count;
}


/**
 *      flush_write_buffer - push buffer to kobject.
 *      @dentry:        dentry to the attribute
 *      @buffer:        data buffer for file.
 *      @count:         number of bytes
 *
 *      Get the correct pointers for the kobject and the attribute we're
 *      dealing with, then call the store() method for the attribute, 
 *      passing the buffer that we acquired in fill_write_buffer().
 */

static int
flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
{
        struct sysfs_dirent *attr_sd = dentry->d_fsdata;
        struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
        struct sysfs_ops * ops = buffer->ops;
        int rc;

        /* need attr_sd for attr and ops, its parent for kobj */
        if (!sysfs_get_active_two(attr_sd))
                return -ENODEV;

        rc = ops->store(kobj, attr_sd->s_attr.attr, buffer->page, count);

        sysfs_put_active_two(attr_sd);

        return rc;
}


/**
 *      sysfs_write_file - write an attribute.
 *      @file:  file pointer
 *      @buf:   data to write
 *      @count: number of bytes
 *      @ppos:  starting offset
 *
 *      Similar to sysfs_read_file(), though working in the opposite direction.
 *      We allocate and fill the data from the user in fill_write_buffer(),
 *      then push it to the kobject in flush_write_buffer().
 *      There is no easy way for us to know if userspace is only doing a partial
 *      write, so we don't support them. We expect the entire buffer to come
 *      on the first write. 
 *      Hint: if you're writing a value, first read the file, modify only the
 *      the value you're changing, then write entire buffer back. 
 */

static ssize_t
sysfs_write_file(struct file *file, const char __user *buf, size_t count, loff_t *ppos)
{
        struct sysfs_buffer * buffer = file->private_data;
        ssize_t len;

        mutex_lock(&buffer->mutex);
        len = fill_write_buffer(buffer, buf, count);
        if (len > 0)
                len = flush_write_buffer(file->f_path.dentry, buffer, len);
        if (len > 0)
                *ppos += len;
        mutex_unlock(&buffer->mutex);
        return len;
}

/**
 *      sysfs_get_open_dirent - get or create sysfs_open_dirent
 *      @sd: target sysfs_dirent
 *      @buffer: sysfs_buffer for this instance of open
 *
 *      If @sd->s_attr.open exists, increment its reference count;
 *      otherwise, create one.  @buffer is chained to the buffers
 *      list.
 *
 *      LOCKING:
 *      Kernel thread context (may sleep).
 *
 *      RETURNS:
 *      0 on success, -errno on failure.
 */
static int sysfs_get_open_dirent(struct sysfs_dirent *sd,
                                 struct sysfs_buffer *buffer)
{
        struct sysfs_open_dirent *od, *new_od = NULL;

 retry:
        spin_lock(&sysfs_open_dirent_lock);

        if (!sd->s_attr.open && new_od) {
                sd->s_attr.open = new_od;
                new_od = NULL;
        }

        od = sd->s_attr.open;
        if (od) {
                atomic_inc(&od->refcnt);
                list_add_tail(&buffer->list, &od->buffers);
        }

        spin_unlock(&sysfs_open_dirent_lock);

        if (od) {
                kfree(new_od);
                return 0;
        }

        /* not there, initialize a new one and retry */
        new_od = kmalloc(sizeof(*new_od), GFP_KERNEL);
        if (!new_od)
                return -ENOMEM;

        atomic_set(&new_od->refcnt, 0);
        INIT_LIST_HEAD(&new_od->buffers);
        goto retry;
}

/**
 *      sysfs_put_open_dirent - put sysfs_open_dirent
 *      @sd: target sysfs_dirent
 *      @buffer: associated sysfs_buffer
 *
 *      Put @sd->s_attr.open and unlink @buffer from the buffers list.
 *      If reference count reaches zero, disassociate and free it.
 *
 *      LOCKING:
 *      None.
 */
static void sysfs_put_open_dirent(struct sysfs_dirent *sd,
                                  struct sysfs_buffer *buffer)
{
        struct sysfs_open_dirent *od = sd->s_attr.open;

        spin_lock(&sysfs_open_dirent_lock);

        list_del(&buffer->list);
        if (atomic_dec_and_test(&od->refcnt))
                sd->s_attr.open = NULL;
        else
                od = NULL;

        spin_unlock(&sysfs_open_dirent_lock);

        kfree(od);
}

static int sysfs_open_file(struct inode *inode, struct file *file)
{
        struct sysfs_dirent *attr_sd = file->f_path.dentry->d_fsdata;
        struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;
        struct sysfs_buffer * buffer;
        struct sysfs_ops * ops = NULL;
        int error;

        /* need attr_sd for attr and ops, its parent for kobj */
        if (!sysfs_get_active_two(attr_sd))
                return -ENODEV;

        /* if the kobject has no ktype, then we assume that it is a subsystem
         * itself, and use ops for it.
         */
        if (kobj->kset && kobj->kset->ktype)
                ops = kobj->kset->ktype->sysfs_ops;
        else if (kobj->ktype)
                ops = kobj->ktype->sysfs_ops;
        else
                ops = &subsys_sysfs_ops;

        error = -EACCES;

        /* No sysfs operations, either from having no subsystem,
         * or the subsystem have no operations.
         */
        if (!ops)
                goto err_out;

        /* File needs write support.
         * The inode's perms must say it's ok, 
         * and we must have a store method.
         */
        if (file->f_mode & FMODE_WRITE) {
                if (!(inode->i_mode & S_IWUGO) || !ops->store)
                        goto err_out;
        }

        /* File needs read support.
         * The inode's perms must say it's ok, and we there
         * must be a show method for it.
         */
        if (file->f_mode & FMODE_READ) {
                if (!(inode->i_mode & S_IRUGO) || !ops->show)
                        goto err_out;
        }

        /* No error? Great, allocate a buffer for the file, and store it
         * it in file->private_data for easy access.
         */
        error = -ENOMEM;
        buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
        if (!buffer)
                goto err_out;

        mutex_init(&buffer->mutex);
        buffer->needs_read_fill = 1;
        buffer->ops = ops;
        file->private_data = buffer;

        /* make sure we have open dirent struct */
        error = sysfs_get_open_dirent(attr_sd, buffer);
        if (error)
                goto err_free;

        /* open succeeded, put active references */
        sysfs_put_active_two(attr_sd);
        return 0;

 err_free:
        kfree(buffer);
 err_out:
        sysfs_put_active_two(attr_sd);
        return error;
}

static int sysfs_release(struct inode *inode, struct file *filp)
{
        struct sysfs_dirent *sd = filp->f_path.dentry->d_fsdata;
        struct sysfs_buffer *buffer = filp->private_data;

        sysfs_put_open_dirent(sd, buffer);

        if (buffer->page)
                free_page((unsigned long)buffer->page);
        kfree(buffer);

        return 0;
}

/* Sysfs attribute files are pollable.  The idea is that you read
 * the content and then you use 'poll' or 'select' to wait for
 * the content to change.  When the content changes (assuming the
 * manager for the kobject supports notification), poll will
 * return POLLERR|POLLPRI, and select will return the fd whether
 * it is waiting for read, write, or exceptions.
 * Once poll/select indicates that the value has changed, you
 * need to close and re-open the file, as simply seeking and reading
 * again will not get new data, or reset the state of 'poll'.
 * Reminder: this only works for attributes which actively support
 * it, and it is not possible to test an attribute from userspace
 * to see if it supports poll (Neither 'poll' nor 'select' return
 * an appropriate error code).  When in doubt, set a suitable timeout value.
 */
static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
{
        struct sysfs_buffer * buffer = filp->private_data;
        struct sysfs_dirent *attr_sd = filp->f_path.dentry->d_fsdata;
        struct kobject *kobj = attr_sd->s_parent->s_dir.kobj;

        /* need parent for the kobj, grab both */
        if (!sysfs_get_active_two(attr_sd))
                goto trigger;

        poll_wait(filp, &kobj->poll, wait);

        sysfs_put_active_two(attr_sd);

        if (buffer->event != atomic_read(&attr_sd->s_event))
                goto trigger;

        return 0;

 trigger:
        buffer->needs_read_fill = 1;
        return POLLERR|POLLPRI;
}

void sysfs_notify(struct kobject *k, char *dir, char *attr)
{
        struct sysfs_dirent *sd = k->sd;

        mutex_lock(&sysfs_mutex);

        if (sd && dir)
                sd = sysfs_find_dirent(sd, dir);
        if (sd && attr)
                sd = sysfs_find_dirent(sd, attr);
        if (sd) {
                atomic_inc(&sd->s_event);
                wake_up_interruptible(&k->poll);
        }

        mutex_unlock(&sysfs_mutex);
}
EXPORT_SYMBOL_GPL(sysfs_notify);

const struct file_operations sysfs_file_operations = {
        .read           = sysfs_read_file,
        .write          = sysfs_write_file,
        .llseek         = generic_file_llseek,
        .open           = sysfs_open_file,
        .release        = sysfs_release,
        .poll           = sysfs_poll,
};


int sysfs_add_file(struct sysfs_dirent *dir_sd, const struct attribute *attr,
                   int type)
{
        umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
        struct sysfs_addrm_cxt acxt;
        struct sysfs_dirent *sd;
        int rc;

        sd = sysfs_new_dirent(attr->name, mode, type);
        if (!sd)
                return -ENOMEM;
        sd->s_attr.attr = (void *)attr;

        sysfs_addrm_start(&acxt, dir_sd);
        rc = sysfs_add_one(&acxt, sd);
        sysfs_addrm_finish(&acxt);

        if (rc)
                sysfs_put(sd);

        return rc;
}


/**
 *      sysfs_create_file - create an attribute file for an object.
 *      @kobj:  object we're creating for. 
 *      @attr:  atrribute descriptor.
 */

int sysfs_create_file(struct kobject * kobj, const struct attribute * attr)
{
        BUG_ON(!kobj || !kobj->sd || !attr);

        return sysfs_add_file(kobj->sd, attr, SYSFS_KOBJ_ATTR);

}


/**
 * sysfs_add_file_to_group - add an attribute file to a pre-existing group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
int sysfs_add_file_to_group(struct kobject *kobj,
                const struct attribute *attr, const char *group)
{
        struct sysfs_dirent *dir_sd;
        int error;

        dir_sd = sysfs_get_dirent(kobj->sd, group);
        if (!dir_sd)
                return -ENOENT;

        error = sysfs_add_file(dir_sd, attr, SYSFS_KOBJ_ATTR);
        sysfs_put(dir_sd);

        return error;
}
EXPORT_SYMBOL_GPL(sysfs_add_file_to_group);

/**
 * sysfs_chmod_file - update the modified mode value on an object attribute.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @mode: file permissions.
 *
 */
int sysfs_chmod_file(struct kobject *kobj, struct attribute *attr, mode_t mode)
{
        struct sysfs_dirent *victim_sd = NULL;
        struct dentry *victim = NULL;
        struct inode * inode;
        struct iattr newattrs;
        int rc;

        rc = -ENOENT;
        victim_sd = sysfs_get_dirent(kobj->sd, attr->name);
        if (!victim_sd)
                goto out;

        mutex_lock(&sysfs_rename_mutex);
        victim = sysfs_get_dentry(victim_sd);
        mutex_unlock(&sysfs_rename_mutex);
        if (IS_ERR(victim)) {
                rc = PTR_ERR(victim);
                victim = NULL;
                goto out;
        }

        inode = victim->d_inode;

        mutex_lock(&inode->i_mutex);

        newattrs.ia_mode = (mode & S_IALLUGO) | (inode->i_mode & ~S_IALLUGO);
        newattrs.ia_valid = ATTR_MODE | ATTR_CTIME;
        rc = notify_change(victim, &newattrs);

        if (rc == 0) {
                mutex_lock(&sysfs_mutex);
                victim_sd->s_mode = newattrs.ia_mode;
                mutex_unlock(&sysfs_mutex);
        }

        mutex_unlock(&inode->i_mutex);
 out:
        dput(victim);
        sysfs_put(victim_sd);
        return rc;
}
EXPORT_SYMBOL_GPL(sysfs_chmod_file);


/**
 *      sysfs_remove_file - remove an object attribute.
 *      @kobj:  object we're acting for.
 *      @attr:  attribute descriptor.
 *
 *      Hash the attribute name and kill the victim.
 */

void sysfs_remove_file(struct kobject * kobj, const struct attribute * attr)
{
        sysfs_hash_and_remove(kobj->sd, attr->name);
}


/**
 * sysfs_remove_file_from_group - remove an attribute file from a group.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 * @group: group name.
 */
void sysfs_remove_file_from_group(struct kobject *kobj,
                const struct attribute *attr, const char *group)
{
        struct sysfs_dirent *dir_sd;

        dir_sd = sysfs_get_dirent(kobj->sd, group);
        if (dir_sd) {
                sysfs_hash_and_remove(dir_sd, attr->name);
                sysfs_put(dir_sd);
        }
}
EXPORT_SYMBOL_GPL(sysfs_remove_file_from_group);

struct sysfs_schedule_callback_struct {
        struct kobject          *kobj;
        void                    (*func)(void *);
        void                    *data;
        struct module           *owner;
        struct work_struct      work;
};

static void sysfs_schedule_callback_work(struct work_struct *work)
{
        struct sysfs_schedule_callback_struct *ss = container_of(work,
                        struct sysfs_schedule_callback_struct, work);

        (ss->func)(ss->data);
        kobject_put(ss->kobj);
        module_put(ss->owner);
        kfree(ss);
}

/**
 * sysfs_schedule_callback - helper to schedule a callback for a kobject
 * @kobj: object we're acting for.
 * @func: callback function to invoke later.
 * @data: argument to pass to @func.
 * @owner: module owning the callback code
 *
 * sysfs attribute methods must not unregister themselves or their parent
 * kobject (which would amount to the same thing).  Attempts to do so will
 * deadlock, since unregistration is mutually exclusive with driver
 * callbacks.
 *
 * Instead methods can call this routine, which will attempt to allocate
 * and schedule a workqueue request to call back @func with @data as its
 * argument in the workqueue's process context.  @kobj will be pinned
 * until @func returns.
 *
 * Returns 0 if the request was submitted, -ENOMEM if storage could not
 * be allocated, -ENODEV if a reference to @owner isn't available.
 */
int sysfs_schedule_callback(struct kobject *kobj, void (*func)(void *),
                void *data, struct module *owner)
{
        struct sysfs_schedule_callback_struct *ss;

        if (!try_module_get(owner))
                return -ENODEV;
        ss = kmalloc(sizeof(*ss), GFP_KERNEL);
        if (!ss) {
                module_put(owner);
                return -ENOMEM;
        }
        kobject_get(kobj);
        ss->kobj = kobj;
        ss->func = func;
        ss->data = data;
        ss->owner = owner;
        INIT_WORK(&ss->work, sysfs_schedule_callback_work);
        schedule_work(&ss->work);
        return 0;
}
EXPORT_SYMBOL_GPL(sysfs_schedule_callback);


EXPORT_SYMBOL_GPL(sysfs_create_file);
EXPORT_SYMBOL_GPL(sysfs_remove_file);