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kernfs: implement kernfs_ops->atomic_write_len

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A write to a kernfs_node is buffered through a kernel buffer.  Writes
<= PAGE_SIZE are performed atomically, while larger ones are executed
in PAGE_SIZE chunks.  While this is enough for sysfs, cgroup which is
scheduled to be converted to use kernfs needs a bit more control over
it.

This patch adds kernfs_ops->atomic_write_len.  If not set (zero), the
behavior stays the same.  If set, writes upto the size are executed
atomically and larger writes are rejected with -E2BIG.

A different implementation strategy would be allowing configuring
chunking size while making the original write size available to the
write method; however, such strategy, while being more complicated,
doesn't really buy anything.  If the write implementation has to
handle chunking, the specific chunk size shouldn't matter all that
much.

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo 2014-02-03 14:09:13 -05:00 committed by Greg Kroah-Hartman
parent d35258ef70
commit 4d3773c4bb
2 changed files with 37 additions and 20 deletions
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49
fs/kernfs/file.c
View file

@ -252,19 +252,9 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
{
struct kernfs_open_file *of = kernfs_of(file);
ssize_t len = min_t(size_t, count, PAGE_SIZE);
const struct kernfs_ops *ops;
char *buf;
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf)
return -ENOMEM;
if (copy_from_user(buf, user_buf, len)) {
len = -EFAULT;
goto out_free;
}
buf[len] = '\0'; /* guarantee string termination */
char *buf = NULL;
ssize_t len;
/*
* @of->mutex nests outside active ref and is just to ensure that
@ -273,22 +263,45 @@ static ssize_t kernfs_fop_write(struct file *file, const char __user *user_buf,
mutex_lock(&of->mutex);
if (!kernfs_get_active(of->kn)) {
mutex_unlock(&of->mutex);
len = -ENODEV;
goto out_free;
return -ENODEV;
}
ops = kernfs_ops(of->kn);
if (ops->write)
len = ops->write(of, buf, len, *ppos);
else
if (!ops->write) {
len = -EINVAL;
goto out_unlock;
}
if (ops->atomic_write_len) {
len = count;
if (len > ops->atomic_write_len) {
len = -E2BIG;
goto out_unlock;
}
} else {
len = min_t(size_t, count, PAGE_SIZE);
}
buf = kmalloc(len + 1, GFP_KERNEL);
if (!buf) {
len = -ENOMEM;
goto out_unlock;
}
if (copy_from_user(buf, user_buf, len)) {
len = -EFAULT;
goto out_unlock;
}
buf[len] = '\0'; /* guarantee string termination */
len = ops->write(of, buf, len, *ppos);
out_unlock:
kernfs_put_active(of->kn);
mutex_unlock(&of->mutex);
if (len > 0)
*ppos += len;
out_free:
kfree(buf);
return len;
}

8
include/linux/kernfs.h
View file

@ -178,9 +178,13 @@ struct kernfs_ops {
loff_t off);
/*
* write() is bounced through kernel buffer and a write larger than
* PAGE_SIZE results in partial operation of PAGE_SIZE.
* write() is bounced through kernel buffer. If atomic_write_len
* is not set, a write larger than PAGE_SIZE results in partial
* operations of PAGE_SIZE chunks. If atomic_write_len is set,
* writes upto the specified size are executed atomically but
* larger ones are rejected with -E2BIG.
*/
size_t atomic_write_len;
ssize_t (*write)(struct kernfs_open_file *of, char *buf, size_t bytes,
loff_t off);