[PATCH 3/6] tty: implement read_iter

Greg Kroah-Hartman
2021-01-21T09:05:01Z

From: Linus Torvalds <torvalds@linux-foundation.org>

Now that the ldisc read() function takes kernel pointers, it's fairly
straightforward to make the tty file operations use .read_iter() instead
of .read().

That automatically gives us vread() and friends, and also makes it
possible to do .splice_read() on ttys again.

Fixes: 36e2c7421f02 ("fs: don't allow splice read/write without explicit ops")
Reported-by: Oliver Giles <ohw.giles@gmail.com>
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>
---
drivers/tty/tty_io.c | 36 ++++++++++++++++++------------------
1 file changed, 18 insertions(+), 18 deletions(-)

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a34f8bcf875e..8846d3b99845 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -142,7 +142,7 @@ LIST_HEAD(tty_drivers); /* linked list of tty drivers */
/* Mutex to protect creating and releasing a tty */
DEFINE_MUTEX(tty_mutex);

-static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *);
+static ssize_t tty_read(struct kiocb *, struct iov_iter *);
static ssize_t tty_write(struct kiocb *, struct iov_iter *);
ssize_t redirected_tty_write(struct kiocb *, struct iov_iter *);
static __poll_t tty_poll(struct file *, poll_table *);
@@ -476,8 +476,9 @@ static void tty_show_fdinfo(struct seq_file *m, struct file *file)

static const struct file_operations tty_fops = {
.llseek = no_llseek,
- .read = tty_read,
+ .read_iter = tty_read,
.write_iter = tty_write,
+ .splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
.poll = tty_poll,
.unlocked_ioctl = tty_ioctl,
@@ -490,8 +491,9 @@ static const struct file_operations tty_fops = {

static const struct file_operations console_fops = {
.llseek = no_llseek,
- .read = tty_read,
+ .read_iter = tty_read,
.write_iter = redirected_tty_write,
+ .splice_read = generic_file_splice_read,
.splice_write = iter_file_splice_write,
.poll = tty_poll,
.unlocked_ioctl = tty_ioctl,
@@ -844,16 +846,17 @@ static void tty_update_time(struct timespec64 *time)
* data or clears the cookie. The cookie may be something that the
* ldisc maintains state for and needs to free.
*/
-static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct file *file,
- char __user *buf, size_t count)
+static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty,
+ struct file *file, struct iov_iter *to)
{
int retval = 0;
void *cookie = NULL;
unsigned long offset = 0;
char kernel_buf[64];
+ size_t count = iov_iter_count(to);

do {
- int size, uncopied;
+ int size, copied;

size = count > sizeof(kernel_buf) ? sizeof(kernel_buf) : count;
size = ld->ops->read(tty, file, kernel_buf, size, &cookie, offset);
@@ -869,10 +872,9 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
return size;
}

- uncopied = copy_to_user(buf+offset, kernel_buf, size);
- size -= uncopied;
- offset += size;
- count -= size;
+ copied = copy_to_iter(kernel_buf, size, to);
+ offset += copied;
+ count -= copied;

/*
* If the user copy failed, we still need to do another ->read()
@@ -880,7 +882,7 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
*
* But make sure size is zeroed.
*/
- if (unlikely(uncopied)) {
+ if (unlikely(copied != size)) {
count = 0;
retval = -EFAULT;
}
@@ -907,10 +909,10 @@ static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct
* read calls may be outstanding in parallel.
*/

-static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
- loff_t *ppos)
+static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to)
{
int i;
+ struct file *file = iocb->ki_filp;
struct inode *inode = file_inode(file);
struct tty_struct *tty = file_tty(file);
struct tty_ldisc *ld;
@@ -923,11 +925,9 @@ static ssize_t tty_read(struct file *file, char __user *buf, size_t count,
/* We want to wait for the line discipline to sort out in this
situation */
ld = tty_ldisc_ref_wait(tty);
- if (!ld)
- return hung_up_tty_read(file, buf, count, ppos);
i = -EIO;
- if (ld->ops->read)
- i = iterate_tty_read(ld, tty, file, buf, count);
+ if (ld && ld->ops->read)
+ i = iterate_tty_read(ld, tty, file, to);
tty_ldisc_deref(ld);

if (i > 0)
@@ -2927,7 +2927,7 @@ static long tty_compat_ioctl(struct file *file, unsigned int cmd,

static int this_tty(const void *t, struct file *file, unsigned fd)
{
- if (likely(file->f_op->read != tty_read))
+ if (likely(file->f_op->read_iter != tty_read))
return 0;
return file_tty(file) != t ? 0 : fd + 1;
}
--
2.30.0