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sysfs: use transient write buffer

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There isn't much to be gained by keeping around kernel buffer while a
file is open especially as the read path planned to be converted to
use seq_file and won't use the buffer.  This patch makes
sysfs_write_file() use per-write transient buffer instead of
sysfs_open_file->page.

This simplifies the write path, enables removing sysfs_open_file->page
once read path is updated and will help merging bin file write path
which already requires the use of a transient buffer due to a locking
order issue.

As the function comments of flush_write_buffer() and
sysfs_write_buffer() are being updated anyway, reformat them so that
they're more conventional.

v2: Use min_t() instead of min() in sysfs_write_file() to avoid build
    warning on arm.  Reported by build test robot.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Tejun Heo 2013-10-01 17:42:01 -04:00 committed by Greg Kroah-Hartman
parent bcafe4eea3
commit 8ef445f080
1 changed files with 52 additions and 62 deletions
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114
fs/sysfs/file.c
View file

@ -162,92 +162,82 @@ out:
}
/**
* fill_write_buffer - copy buffer from userspace.
* @of: open file struct.
* @buf: data from user.
* @count: number of bytes in @userbuf.
* flush_write_buffer - push buffer to kobject
* @of: open file
* @buf: data buffer for file
* @count: number of bytes
*
* Allocate @of->page if it hasn't been already, then copy the
* user-supplied buffer into it.
* Get the correct pointers for the kobject and the attribute we're dealing
* with, then call the store() method for it with @buf.
*/
static int fill_write_buffer(struct sysfs_open_file *of,
const char __user *buf, size_t count)
{
int error;
if (!of->page)
of->page = (char *)get_zeroed_page(GFP_KERNEL);
if (!of->page)
return -ENOMEM;
if (count >= PAGE_SIZE)
count = PAGE_SIZE - 1;
error = copy_from_user(of->page, buf, count);
/*
* If buf is assumed to contain a string, terminate it by \0, so
* e.g. sscanf() can scan the string easily.
*/
of->page[count] = 0;
return error ? -EFAULT : count;
}
/**
* flush_write_buffer - push buffer to kobject.
* @of: open 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 sysfs_open_file *of, size_t count)
static int flush_write_buffer(struct sysfs_open_file *of, char *buf,
size_t count)
{
struct kobject *kobj = of->sd->s_parent->s_dir.kobj;
const struct sysfs_ops *ops;
int rc;
int rc = 0;
/* need @of->sd for attr and ops, its parent for kobj */
if (!sysfs_get_active(of->sd))
/*
* 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;
}
ops = sysfs_file_ops(of->sd);
rc = ops->store(kobj, of->sd->s_attr.attr, of->page, count);
rc = ops->store(kobj, of->sd->s_attr.attr, buf, count);
sysfs_put_active(of->sd);
mutex_unlock(&of->mutex);
return rc;
}
/**
* sysfs_write_file - write an attribute.
* @file: file pointer
* @buf: data to write
* @count: number of bytes
* @ppos: starting offset
* sysfs_write_file - write an attribute
* @file: file pointer
* @user_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.
* Copy data in from userland and pass it to the matching
* sysfs_ops->store() by invoking 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,
static ssize_t sysfs_write_file(struct file *file, const char __user *user_buf,
size_t count, loff_t *ppos)
{
struct sysfs_open_file *of = file->private_data;
ssize_t len;
ssize_t len = min_t(size_t, count, PAGE_SIZE - 1);
char *buf;
mutex_lock(&of->mutex);
len = fill_write_buffer(of, buf, count);
if (len > 0)
len = flush_write_buffer(of, len);
if (!len)
return 0;
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 */
len = flush_write_buffer(of, buf, len);
if (len > 0)
*ppos += len;
mutex_unlock(&of->mutex);
out_free:
kfree(buf);
return len;
}