[PATCH 2/3] buffer writes to sysfs

[Mitch Williams]

This patch buffers writes to sysfs files and flushes them to the kobject
owner when the file is closed.

Generated from 2.6.11-rc1.

Signed-off-by:  Mitch Williams <mitch.a.williams@xxxxxxxxx>

diff -uprN -X dontdiff linux-2.6.11-clean/fs/sysfs/file.c linux-2.6.11/fs/sysfs/file.c
--- linux-2.6.11-clean/fs/sysfs/file.c	2004-12-24 13:33:50.000000000 -0800
+++ linux-2.6.11/fs/sysfs/file.c	2005-01-21 13:09:21.000000000 -0800
@@ -62,6 +62,7 @@ struct sysfs_buffer {
 	struct sysfs_ops	* ops;
 	struct semaphore	sem;
 	int			read_filled;
+	int			needs_write_flush;
 };


@@ -178,7 +178,8 @@ out:
  */

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

@@ -187,10 +189,11 @@ fill_write_buffer(struct sysfs_buffer *
 	if (!buffer->page)
 		return -ENOMEM;

-	if (count >= PAGE_SIZE)
-		count = PAGE_SIZE - 1;
+	if (count + pos > PAGE_SIZE)
+		count = (PAGE_SIZE - 1) - pos;
 	error = copy_from_user(buffer->page,buf,count);
-	buffer->needs_read_fill = 1;
+	buffer->needs_write_flush = 1;
+        buffer->count = pos + count;
 	return error ? -EFAULT : count;
 }

@@ -206,13 +209,13 @@ fill_write_buffer(struct sysfs_buffer *
  */

 static int
-flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer, size_t count)
+flush_write_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
 {
 	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);
+	return ops->store(kobj,attr, buffer->page, buffer->count);
 }


@@ -225,12 +228,9 @@ flush_write_buffer(struct dentry * dentr
  *
  *	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.
+ *	but don't push it to the kobject until the file is closed.
+ *      This allows for buffered writes, but unfortunately also hides error
+ *      codes returned individual store functions until close time.
  */

 static ssize_t
@@ -238,10 +238,10 @@ sysfs_write_file(struct file *file, cons
 {
 	struct sysfs_buffer * buffer = file->private_data;

+	if (*ppos >= PAGE_SIZE)
+		return -ENOSPC;
 	down(&buffer->sem);
-	count = fill_write_buffer(buffer,buf,count);
-	if (count > 0)
-		count = flush_write_buffer(file->f_dentry,buffer,count);
+	count = fill_write_buffer(buffer, buf, count, *ppos);
 	if (count > 0)
 		*ppos += count;
 	up(&buffer->sem);
@@ -337,6 +337,17 @@ static int sysfs_release(struct inode *
 	struct attribute * attr = to_attr(filp->f_dentry);
 	struct module * owner = attr->owner;
 	struct sysfs_buffer * buffer = filp->private_data;
+        int ret;
+
+	/* If data has been written to the file, then flush it
+	 * back to the kobject's store function here.
+	 */
+	if (buffer && kobj) {
+		down(&buffer->sem);
+		if (buffer->needs_write_flush)
+			ret = flush_write_buffer(filp->f_dentry, buffer);
+		up(&buffer->sem);
+	}

 	if (kobj)
 		kobject_put(kobj);
@@ -348,7 +352,10 @@ static int sysfs_release(struct inode *
 			free_page((unsigned long)buffer->page);
 		kfree(buffer);
 	}
-	return 0;
+	/* If flush_write_buffer returned an error, pass it up.
+	 * Otherwise, return success.
+	 */
+	return (ret < 0 ? ret : 0);
 }

 struct file_operations sysfs_file_operations = {
-
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