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tty: convert tty_ldisc_ops 'read()' function to take a kernel pointer

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[ Upstream commit 3b830a9c34d5897be07176ce4e6f2d75e2c8cfd7 ]

The tty line discipline .read() function was passed the final user
pointer destination as an argument, which doesn't match the 'write()'
function, and makes it very inconvenient to do a splice method for
ttys.

This is a conversion to use a kernel buffer instead.

NOTE! It does this by passing the tty line discipline ->read() function
an additional "cookie" to fill in, and an offset into the cookie data.

The line discipline can fill in the cookie data with its own private
information, and then the reader will repeat the read until either the
cookie is cleared or it runs out of data.

The only real user of this is N_HDLC, which can use this to handle big
packets, even if the kernel buffer is smaller than the whole packet.

Cc: Christoph Hellwig <hch@lst.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Linus Torvalds
2021-01-18 13:31:30 -08:00
committed by Greg Kroah-Hartman
parent 65a10cb163
commit 279e54536d
14 changed files with 178 additions and 102 deletions
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60
drivers/tty/n_hdlc.c
View File

@@ -416,13 +416,19 @@ static void n_hdlc_tty_receive(struct tty_struct *tty, const __u8 *data,
* Returns the number of bytes returned or error code.
*/
static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
__u8 __user *buf, size_t nr)
__u8 *kbuf, size_t nr,
void **cookie, unsigned long offset)
{
struct n_hdlc *n_hdlc = tty->disc_data;
int ret = 0;
struct n_hdlc_buf *rbuf;
DECLARE_WAITQUEUE(wait, current);
/* Is this a repeated call for an rbuf we already found earlier? */
rbuf = *cookie;
if (rbuf)
goto have_rbuf;
add_wait_queue(&tty->read_wait, &wait);
for (;;) {
@@ -436,25 +442,8 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
set_current_state(TASK_INTERRUPTIBLE);
rbuf = n_hdlc_buf_get(&n_hdlc->rx_buf_list);
if (rbuf) {
if (rbuf->count > nr) {
/* too large for caller's buffer */
ret = -EOVERFLOW;
} else {
__set_current_state(TASK_RUNNING);
if (copy_to_user(buf, rbuf->buf, rbuf->count))
ret = -EFAULT;
else
ret = rbuf->count;
}
if (n_hdlc->rx_free_buf_list.count >
DEFAULT_RX_BUF_COUNT)
kfree(rbuf);
else
n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
if (rbuf)
break;
}
/* no data */
if (tty_io_nonblock(tty, file)) {
@@ -473,6 +462,39 @@ static ssize_t n_hdlc_tty_read(struct tty_struct *tty, struct file *file,
remove_wait_queue(&tty->read_wait, &wait);
__set_current_state(TASK_RUNNING);
if (!rbuf)
return ret;
*cookie = rbuf;
have_rbuf:
/* Have we used it up entirely? */
if (offset >= rbuf->count)
goto done_with_rbuf;
/* More data to go, but can't copy any more? EOVERFLOW */
ret = -EOVERFLOW;
if (!nr)
goto done_with_rbuf;
/* Copy as much data as possible */
ret = rbuf->count - offset;
if (ret > nr)
ret = nr;
memcpy(kbuf, rbuf->buf+offset, ret);
offset += ret;
/* If we still have data left, we leave the rbuf in the cookie */
if (offset < rbuf->count)
return ret;
done_with_rbuf:
*cookie = NULL;
if (n_hdlc->rx_free_buf_list.count > DEFAULT_RX_BUF_COUNT)
kfree(rbuf);
else
n_hdlc_buf_put(&n_hdlc->rx_free_buf_list, rbuf);
return ret;
} /* end of n_hdlc_tty_read() */