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Commit c2b19daf authored by Tejun Heo's avatar Tejun Heo Committed by Greg Kroah-Hartman
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sysfs, kernfs: prepare read path for kernfs 



We're in the process of separating out core sysfs functionality into
kernfs which will deal with sysfs_dirents directly.  This patch
rearranges read path so that the kernfs and sysfs parts are separate.

* Regular file read path is refactored such that
  kernfs_seq_start/next/stop/show() handle all the boilerplate work
  including locking and updating event count for poll, while
  sysfs_kf_seq_show() deals with interaction with kobj show method.

* Bin file read path is refactored such that kernfs_file_direct_read()
  handles all the boilerplate work including buffer management and
  locking, while sysfs_kf_bin_read() deals with interaction with
  bin_attribute read method.

kernfs_file_read() is added.  It invokes either the seq_file or direct
read path depending on the file type.  This will eventually allow
using the same file_operations for both file types, which is necessary
to separate out kernfs.

While this patch changes the order of some operations, it shouldn't
change any visible behavior.

v2: Dropped unnecessary zeroing of @count from sysfs_kf_seq_show().
    Add comments explaining single_open() behavior.  Both suggested by
    Pavel.

v3: seq_stop() is called even after seq_start() failed.
    kernfs_seq_start() updated so that it doesn't unlock
    sysfs_open_file->mutex on failure so that kernfs_seq_stop()
    doesn't try to unlock an already unlocked mutex.  Reported by
    Fengguang.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 93b2b8e4

fs/sysfs/file.c

+126 −65
Original line number Diff line number Diff line
@@ -86,13 +86,13 @@ static const struct sysfs_ops *sysfs_file_ops(struct sysfs_dirent *sd) 
 * details like buffering and seeking.  The following function pipes

 * sysfs_ops->show() result through seq_file.

 */

static int sysfs_seq_show(struct seq_file *sf, void *v)

static int sysfs_kf_seq_show(struct seq_file *sf, void *v)

{

	struct sysfs_open_file *of = sf->private;

	struct kobject *kobj = of->sd->s_parent->priv;

	const struct sysfs_ops *ops;

	char *buf;

	const struct sysfs_ops *ops = sysfs_file_ops(of->sd);

	ssize_t count;

	char *buf;



	/* acquire buffer and ensure that it's >= PAGE_SIZE */

	count = seq_get_buf(sf, &buf);
@@ -102,33 +102,14 @@ static int sysfs_seq_show(struct seq_file *sf, void *v) 
	}



	/*

	 * Need @of->sd for attr and ops, its parent for kobj.  @of->mutex

	 * nests outside active ref and is just to ensure that the ops

	 * aren't called concurrently for the same open file.

	 */

	mutex_lock(&of->mutex);

	if (!sysfs_get_active(of->sd)) {

		mutex_unlock(&of->mutex);

		return -ENODEV;

	}



	of->event = atomic_read(&of->sd->s_attr.open->event);



	/*

	 * Lookup @ops and invoke show().  Control may reach here via seq

	 * file lseek even if @ops->show() isn't implemented.

	 * Invoke show().  Control may reach here via seq file lseek even

	 * if @ops->show() isn't implemented.

	 */

	ops = sysfs_file_ops(of->sd);

	if (ops->show)

	if (ops->show) {

		count = ops->show(kobj, of->sd->priv, buf);

	else

		count = 0;



	sysfs_put_active(of->sd);

	mutex_unlock(&of->mutex);



		if (count < 0)

			return count;

	}



	/*

	 * The code works fine with PAGE_SIZE return but it's likely to
@@ -144,68 +125,146 @@ static int sysfs_seq_show(struct seq_file *sf, void *v) 
	return 0;

}



/*

 * Read method for bin files.  As reading a bin file can have side-effects,

 * the exact offset and bytes specified in read(2) call should be passed to

 * the read callback making it difficult to use seq_file.  Implement

 * simplistic custom buffering for bin files.

 */

static ssize_t sysfs_bin_read(struct file *file, char __user *userbuf,

			      size_t bytes, loff_t *off)

static ssize_t sysfs_kf_bin_read(struct sysfs_open_file *of, char *buf,

				 size_t count, loff_t pos)

{

	struct sysfs_open_file *of = sysfs_of(file);

	struct bin_attribute *battr = of->sd->priv;

	struct kobject *kobj = of->sd->s_parent->priv;

	loff_t size = file_inode(file)->i_size;

	int count = min_t(size_t, bytes, PAGE_SIZE);

	loff_t offs = *off;

	char *buf;

	loff_t size = file_inode(of->file)->i_size;



	if (!bytes)

	if (!count)

		return 0;



	if (size) {

		if (offs > size)

		if (pos > size)

			return 0;

		if (offs + count > size)

			count = size - offs;

		if (pos + count > size)

			count = size - pos;

	}



	if (!battr->read)

		return -EIO;



	return battr->read(of->file, kobj, battr, buf, pos, count);

}



static void *kernfs_seq_start(struct seq_file *sf, loff_t *ppos)

{

	struct sysfs_open_file *of = sf->private;



	/*

	 * @of->mutex nests outside active ref and is just to ensure that

	 * the ops aren't called concurrently for the same open file.

	 */

	mutex_lock(&of->mutex);

	if (!sysfs_get_active(of->sd))

		return ERR_PTR(-ENODEV);



	/*

	 * The same behavior and code as single_open().  Returns !NULL if

	 * pos is at the beginning; otherwise, NULL.

	 */

	return NULL + !*ppos;

}



static void *kernfs_seq_next(struct seq_file *sf, void *v, loff_t *ppos)

{

	/*

	 * The same behavior and code as single_open(), always terminate

	 * after the initial read.

	 */

	++*ppos;

	return NULL;

}



	buf = kmalloc(count, GFP_KERNEL);

static void kernfs_seq_stop(struct seq_file *sf, void *v)

{

	struct sysfs_open_file *of = sf->private;



	sysfs_put_active(of->sd);

	mutex_unlock(&of->mutex);

}



static int kernfs_seq_show(struct seq_file *sf, void *v)

{

	struct sysfs_open_file *of = sf->private;



	of->event = atomic_read(&of->sd->s_attr.open->event);



	return sysfs_kf_seq_show(sf, v);

}



static const struct seq_operations kernfs_seq_ops = {

	.start = kernfs_seq_start,

	.next = kernfs_seq_next,

	.stop = kernfs_seq_stop,

	.show = kernfs_seq_show,

};



/*

 * As reading a bin file can have side-effects, the exact offset and bytes

 * specified in read(2) call should be passed to the read callback making

 * it difficult to use seq_file.  Implement simplistic custom buffering for

 * bin files.

 */

static ssize_t kernfs_file_direct_read(struct sysfs_open_file *of,

				       char __user *user_buf, size_t count,

				       loff_t *ppos)

{

	ssize_t len = min_t(size_t, count, PAGE_SIZE);

	char *buf;



	buf = kmalloc(len, GFP_KERNEL);

	if (!buf)

		return -ENOMEM;



	/* need of->sd for battr, its parent for kobj */

	/*

	 * @of->mutex nests outside active ref and is just to ensure that

	 * the ops aren't called concurrently for the same open file.

	 */

	mutex_lock(&of->mutex);

	if (!sysfs_get_active(of->sd)) {

		count = -ENODEV;

		len = -ENODEV;

		mutex_unlock(&of->mutex);

		goto out_free;

	}



	if (battr->read)

		count = battr->read(file, kobj, battr, buf, offs, count);

	else

		count = -EIO;

	len = sysfs_kf_bin_read(of, buf, len, *ppos);



	sysfs_put_active(of->sd);

	mutex_unlock(&of->mutex);



	if (count < 0)

	if (len < 0)

		goto out_free;



	if (copy_to_user(userbuf, buf, count)) {

		count = -EFAULT;

	if (copy_to_user(user_buf, buf, len)) {

		len = -EFAULT;

		goto out_free;

	}



	pr_debug("offs = %lld, *off = %lld, count = %d\n", offs, *off, count);



	*off = offs + count;

	*ppos += len;



 out_free:

	kfree(buf);

	return count;

	return len;

}



/**

 * kernfs_file_read - kernfs vfs read callback

 * @file: file pointer

 * @user_buf: data to write

 * @count: number of bytes

 * @ppos: starting offset

 */

static ssize_t kernfs_file_read(struct file *file, char __user *user_buf,

				size_t count, loff_t *ppos)

{

	struct sysfs_open_file *of = sysfs_of(file);



	if (sysfs_is_bin(of->sd))

		return kernfs_file_direct_read(of, user_buf, count, ppos);

	else

		return seq_read(file, user_buf, count, ppos);

}



/**
@@ -677,12 +736,14 @@ static int sysfs_open_file(struct inode *inode, struct file *file) 
	 * and readable regular files are the vast majority anyway.

	 */

	if (sysfs_is_bin(attr_sd))

		error = single_open(file, NULL, of);

		error = seq_open(file, NULL);

	else

		error = single_open(file, sysfs_seq_show, of);

		error = seq_open(file, &kernfs_seq_ops);

	if (error)

		goto err_free;



	((struct seq_file *)file->private_data)->private = of;



	/* seq_file clears PWRITE unconditionally, restore it if WRITE */

	if (file->f_mode & FMODE_WRITE)

		file->f_mode |= FMODE_PWRITE;
@@ -697,7 +758,7 @@ static int sysfs_open_file(struct inode *inode, struct file *file) 
	return 0;



err_close:

	single_release(inode, file);

	seq_release(inode, file);

err_free:

	kfree(of);

err_out:
@@ -711,7 +772,7 @@ static int sysfs_release(struct inode *inode, struct file *filp) 
	struct sysfs_open_file *of = sysfs_of(filp);



	sysfs_put_open_dirent(sd, of);

	single_release(inode, filp);

	seq_release(inode, filp);

	kfree(of);



	return 0;
@@ -816,7 +877,7 @@ void sysfs_notify(struct kobject *k, const char *dir, const char *attr) 
EXPORT_SYMBOL_GPL(sysfs_notify);



const struct file_operations sysfs_file_operations = {

	.read		= seq_read,

	.read		= kernfs_file_read,

	.write		= sysfs_write_file,

	.llseek		= generic_file_llseek,

	.open		= sysfs_open_file,
@@ -825,7 +886,7 @@ const struct file_operations sysfs_file_operations = { 
};



const struct file_operations sysfs_bin_operations = {

	.read		= sysfs_bin_read,

	.read		= kernfs_file_read,

	.write		= sysfs_write_file,

	.llseek		= generic_file_llseek,

	.mmap		= sysfs_bin_mmap,