Driver core: fix race in sysfs between sysfs_remove_file() and read()/write()

[linux-2.6/mini2440.git] / fs / sysfs / file.c

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

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

#include "sysfs.h"

#define to_subsys(k) container_of(k,struct subsystem,kset.kobj)
#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 subsystem * s = to_subsys(kobj);
        struct subsys_attribute * sattr = to_sattr(attr);
        ssize_t ret = -EIO;

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

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

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

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

/**
 *      add_to_collection - add buffer to a collection
 *      @buffer:        buffer to be added
 *      @node           inode of set to add to
 */

static inline void
add_to_collection(struct sysfs_buffer *buffer, struct inode *node)
{
        struct sysfs_buffer_collection *set = node->i_private;

        mutex_lock(&node->i_mutex);
        list_add(&buffer->associates, &set->associates);
        mutex_unlock(&node->i_mutex);
}

static inline void
remove_from_collection(struct sysfs_buffer *buffer, struct inode *node)
{
        mutex_lock(&node->i_mutex);
        list_del(&buffer->associates);
        mutex_unlock(&node->i_mutex);
}

/**
 *      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. 
 */
static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
{
        struct sysfs_dirent * sd = dentry->d_fsdata;
        struct attribute * attr = to_attr(dentry);
        struct kobject * kobj = to_kobj(dentry->d_parent);
        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;

        buffer->event = atomic_read(&sd->s_event);
        count = ops->show(kobj,attr,buffer->page);
        buffer->needs_read_fill = 0;
        BUG_ON(count > (ssize_t)PAGE_SIZE);
        if (count >= 0)
                buffer->count = count;
        else
                ret = count;
        return ret;
}


/**
 *      flush_read_buffer - push buffer to userspace.
 *      @buffer:        data buffer for file.
 *      @buf:           user-passed buffer.
 *      @count:         number of bytes requested.
 *      @ppos:          file position.
 *
 *      Copy the buffer we filled in fill_read_buffer() to userspace.
 *      This is done at the reader's leisure, copying and advancing 
 *      the amount they specify each time.
 *      This may be called continuously until the buffer is empty.
 */
static int flush_read_buffer(struct sysfs_buffer * buffer, char __user * buf,
                             size_t count, loff_t * ppos)
{
        int error;

        if (*ppos > buffer->count)
                return 0;

        if (count > (buffer->count - *ppos))
                count = buffer->count - *ppos;

        error = copy_to_user(buf,buffer->page + *ppos,count);
        if (!error)
                *ppos += count;
        return error ? -EFAULT : count;
}

/**
 *      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;

        down(&buffer->sem);
        if (buffer->orphaned) {
                retval = -ENODEV;
                goto out;
        }
        if (buffer->needs_read_fill) {
                if ((retval = fill_read_buffer(file->f_path.dentry,buffer)))
                        goto out;
        }
        pr_debug("%s: count = %zd, ppos = %lld, buf = %s\n",
                 __FUNCTION__, count, *ppos, buffer->page);
        retval = flush_read_buffer(buffer,buf,count,ppos);
out:
        up(&buffer->sem);
        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 attribute * attr = to_attr(dentry);
        struct kobject * kobj = to_kobj(dentry->d_parent);
        struct sysfs_ops * ops = buffer->ops;

        return ops->store(kobj,attr,buffer->page,count);
}


/**
 *      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;

        down(&buffer->sem);
        if (buffer->orphaned) {
                len = -ENODEV;
                goto out;
        }
        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;
out:
        up(&buffer->sem);
        return len;
}

static int sysfs_open_file(struct inode *inode, struct file *file)
{
        struct kobject *kobj = sysfs_get_kobject(file->f_path.dentry->d_parent);
        struct attribute * attr = to_attr(file->f_path.dentry);
        struct sysfs_buffer_collection *set;
        struct sysfs_buffer * buffer;
        struct sysfs_ops * ops = NULL;
        int error = 0;

        if (!kobj || !attr)
                goto Einval;

        /* Grab the module reference for this attribute if we have one */
        if (!try_module_get(attr->owner)) {
                error = -ENODEV;
                goto Done;
        }

        /* 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;

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

        /* make sure we have a collection to add our buffers to */
        mutex_lock(&inode->i_mutex);
        if (!(set = inode->i_private)) {
                if (!(set = inode->i_private = kmalloc(sizeof(struct sysfs_buffer_collection), GFP_KERNEL))) {
                        error = -ENOMEM;
                        goto Done;
                } else {
                        INIT_LIST_HEAD(&set->associates);
                }
        }
        mutex_unlock(&inode->i_mutex);

        /* 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 Eaccess;

        }

        /* 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 Eaccess;
        }

        /* No error? Great, allocate a buffer for the file, and store it
         * it in file->private_data for easy access.
         */
        buffer = kzalloc(sizeof(struct sysfs_buffer), GFP_KERNEL);
        if (buffer) {
                INIT_LIST_HEAD(&buffer->associates);
                init_MUTEX(&buffer->sem);
                buffer->needs_read_fill = 1;
                buffer->ops = ops;
                add_to_collection(buffer, inode);
                file->private_data = buffer;
        } else
                error = -ENOMEM;
        goto Done;

 Einval:
        error = -EINVAL;
        goto Done;
 Eaccess:
        error = -EACCES;
        module_put(attr->owner);
 Done:
        if (error && kobj)
                kobject_put(kobj);
        return error;
}

static int sysfs_release(struct inode * inode, struct file * filp)
{
        struct kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
        struct attribute * attr = to_attr(filp->f_path.dentry);
        struct module * owner = attr->owner;
        struct sysfs_buffer * buffer = filp->private_data;

        if (buffer)
                remove_from_collection(buffer, inode);
        if (kobj) 
                kobject_put(kobj);
        /* After this point, attr should not be accessed. */
        module_put(owner);

        if (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 (Nether 'poll' or '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 kobject * kobj = to_kobj(filp->f_path.dentry->d_parent);
        struct sysfs_dirent * sd = filp->f_path.dentry->d_fsdata;
        int res = 0;

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

        if (buffer->event != atomic_read(&sd->s_event)) {
                res = POLLERR|POLLPRI;
                buffer->needs_read_fill = 1;
        }

        return res;
}


static struct dentry *step_down(struct dentry *dir, const char * name)
{
        struct dentry * de;

        if (dir == NULL || dir->d_inode == NULL)
                return NULL;

        mutex_lock(&dir->d_inode->i_mutex);
        de = lookup_one_len(name, dir, strlen(name));
        mutex_unlock(&dir->d_inode->i_mutex);
        dput(dir);
        if (IS_ERR(de))
                return NULL;
        if (de->d_inode == NULL) {
                dput(de);
                return NULL;
        }
        return de;
}

void sysfs_notify(struct kobject * k, char *dir, char *attr)
{
        struct dentry *de = k->dentry;
        if (de)
                dget(de);
        if (de && dir)
                de = step_down(de, dir);
        if (de && attr)
                de = step_down(de, attr);
        if (de) {
                struct sysfs_dirent * sd = de->d_fsdata;
                if (sd)
                        atomic_inc(&sd->s_event);
                wake_up_interruptible(&k->poll);
                dput(de);
        }
}
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 dentry * dir, const struct attribute * attr, int type)
{
        struct sysfs_dirent * parent_sd = dir->d_fsdata;
        umode_t mode = (attr->mode & S_IALLUGO) | S_IFREG;
        int error = -EEXIST;

        mutex_lock(&dir->d_inode->i_mutex);
        if (!sysfs_dirent_exist(parent_sd, attr->name))
                error = sysfs_make_dirent(parent_sd, NULL, (void *)attr,
                                          mode, type);
        mutex_unlock(&dir->d_inode->i_mutex);

        return error;
}


/**
 *      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->dentry || !attr);

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

}


/**
 * sysfs_update_file - update the modified timestamp on an object attribute.
 * @kobj: object we're acting for.
 * @attr: attribute descriptor.
 */
int sysfs_update_file(struct kobject * kobj, const struct attribute * attr)
{
        struct dentry * dir = kobj->dentry;
        struct dentry * victim;
        int res = -ENOENT;

        mutex_lock(&dir->d_inode->i_mutex);
        victim = lookup_one_len(attr->name, dir, strlen(attr->name));
        if (!IS_ERR(victim)) {
                /* make sure dentry is really there */
                if (victim->d_inode && 
                    (victim->d_parent->d_inode == dir->d_inode)) {
                        victim->d_inode->i_mtime = CURRENT_TIME;
                        fsnotify_modify(victim);
                        res = 0;
                } else
                        d_drop(victim);
                
                /**
                 * Drop the reference acquired from lookup_one_len() above.
                 */
                dput(victim);
        }
        mutex_unlock(&dir->d_inode->i_mutex);

        return res;
}


/**
 * 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 dentry *dir = kobj->dentry;
        struct dentry *victim;
        struct inode * inode;
        struct iattr newattrs;
        int res = -ENOENT;

        mutex_lock(&dir->d_inode->i_mutex);
        victim = lookup_one_len(attr->name, dir, strlen(attr->name));
        if (!IS_ERR(victim)) {
                if (victim->d_inode &&
                    (victim->d_parent->d_inode == dir->d_inode)) {
                        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;
                        res = notify_change(victim, &newattrs);
                        mutex_unlock(&inode->i_mutex);
                }
                dput(victim);
        }
        mutex_unlock(&dir->d_inode->i_mutex);

        return res;
}
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->dentry, attr->name);
}


EXPORT_SYMBOL_GPL(sysfs_create_file);
EXPORT_SYMBOL_GPL(sysfs_remove_file);
EXPORT_SYMBOL_GPL(sysfs_update_file);