Revert the following upstream patch, which dramatically decreased the performance of shell buffers in Emacs. From 41c6f6b926d0e712d0321f8a8f6511fea748e814 Mon Sep 17 00:00:00 2001 From: Linus Torvalds Date: Tue, 19 Jan 2021 10:49:19 -0800 Subject: tty: implement read_iter [ Upstream commit dd78b0c483e33225e0e0782b0ed887129b00f956 ] 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 Cc: Christoph Hellwig Cc: Greg Kroah-Hartman Cc: Al Viro Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- 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 a50c8a4318228..3f55fe7293f31 100644 --- b/drivers/tty/tty_io.c +++ a/drivers/tty/tty_io.c @@ -142,7 +142,7 @@ /* Mutex to protect creating and releasing a tty */ DEFINE_MUTEX(tty_mutex); -static ssize_t tty_read(struct kiocb *, struct iov_iter *); +static ssize_t tty_read(struct file *, char __user *, size_t, loff_t *); static ssize_t tty_write(struct kiocb *, struct iov_iter *); static __poll_t tty_poll(struct file *, poll_table *); static int tty_open(struct inode *, struct file *); @@ -473,9 +473,8 @@ static const struct file_operations tty_fops = { .llseek = no_llseek, - .read_iter = tty_read, + .read = 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, @@ -488,9 +487,8 @@ static const struct file_operations console_fops = { .llseek = no_llseek, - .read_iter = tty_read, + .read = 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, @@ -843,17 +841,16 @@ * 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, struct iov_iter *to) +static int iterate_tty_read(struct tty_ldisc *ld, struct tty_struct *tty, struct file *file, + char __user *buf, size_t count) { int retval = 0; void *cookie = NULL; unsigned long offset = 0; char kernel_buf[64]; - size_t count = iov_iter_count(to); do { - int size, copied; + int size, uncopied; size = count > sizeof(kernel_buf) ? sizeof(kernel_buf) : count; size = ld->ops->read(tty, file, kernel_buf, size, &cookie, offset); @@ -869,9 +866,10 @@ return size; } - copied = copy_to_iter(kernel_buf, size, to); - offset += copied; - count -= copied; + uncopied = copy_to_user(buf+offset, kernel_buf, size); + size -= uncopied; + offset += size; + count -= size; /* * If the user copy failed, we still need to do another ->read() @@ -879,7 +877,7 @@ * * But make sure size is zeroed. */ - if (unlikely(copied != size)) { + if (unlikely(uncopied)) { count = 0; retval = -EFAULT; } @@ -906,10 +904,10 @@ * read calls may be outstanding in parallel. */ -static ssize_t tty_read(struct kiocb *iocb, struct iov_iter *to) +static ssize_t tty_read(struct file *file, char __user *buf, size_t count, + loff_t *ppos) { 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; @@ -922,9 +920,11 @@ /* 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 && ld->ops->read) - i = iterate_tty_read(ld, tty, file, to); + if (ld->ops->read) + i = iterate_tty_read(ld, tty, file, buf, count); tty_ldisc_deref(ld); if (i > 0) @@ -2943,7 +2943,7 @@ static int this_tty(const void *t, struct file *file, unsigned fd) { - if (likely(file->f_op->read_iter != tty_read)) + if (likely(file->f_op->read != tty_read)) return 0; return file_tty(file) != t ? 0 : fd + 1; }