tty: implement read_iter

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>

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index a34f8bc..8846d3b 100644 (file)
--- 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;
 }