[PATCH] char/mem: only use {read,write}_iter, not the old {read,write} functions

Jason A. Donenfeld
2022-05-20T13:50:51Z

Currently mem.c implements both the {read,write}_iter functions and the
{read,write} functions. But with {read,write} going away at some point
in the future, and most kernel code made to prefer {read,write}_iter,
there's no point in keeping around the old code. Actually, this comment
in __kernel_read() indicates that having both might be plain wrong:

/*
* Also fail if ->read_iter and ->read are both wired up as that
* implies very convoluted semantics.
*/
if (unlikely(!file->f_op->read_iter || file->f_op->read))
return warn_unsupported(file, "read");

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
---
drivers/char/mem.c | 44 --------------------------------------------
1 file changed, 44 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index cc296f0823bd..0eb36b784b29 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -444,18 +444,6 @@ static ssize_t write_port(struct file *file, const char __user *buf,
return tmp-buf;
}

-static ssize_t read_null(struct file *file, char __user *buf,
- size_t count, loff_t *ppos)
-{
- return 0;
-}
-
-static ssize_t write_null(struct file *file, const char __user *buf,
- size_t count, loff_t *ppos)
-{
- return count;
-}
-
static ssize_t read_iter_null(struct kiocb *iocb, struct iov_iter *to)
{
return 0;
@@ -504,33 +492,6 @@ static ssize_t read_iter_zero(struct kiocb *iocb, struct iov_iter *iter)
return written;
}

-static ssize_t read_zero(struct file *file, char __user *buf,
- size_t count, loff_t *ppos)
-{
- size_t cleared = 0;
-
- while (count) {
- size_t chunk = min_t(size_t, count, PAGE_SIZE);
- size_t left;
-
- left = clear_user(buf + cleared, chunk);
- if (unlikely(left)) {
- cleared += (chunk - left);
- if (!cleared)
- return -EFAULT;
- break;
- }
- cleared += chunk;
- count -= chunk;
-
- if (signal_pending(current))
- break;
- cond_resched();
- }
-
- return cleared;
-}
-
static int mmap_zero(struct file *file, struct vm_area_struct *vma)
{
#ifndef CONFIG_MMU
@@ -640,7 +601,6 @@ static int open_port(struct inode *inode, struct file *filp)

#define zero_lseek null_lseek
#define full_lseek null_lseek
-#define write_zero write_null
#define write_iter_zero write_iter_null
#define open_mem open_port

@@ -658,8 +618,6 @@ static const struct file_operations __maybe_unused mem_fops = {

static const struct file_operations null_fops = {
.llseek = null_lseek,
- .read = read_null,
- .write = write_null,
.read_iter = read_iter_null,
.write_iter = write_iter_null,
.splice_write = splice_write_null,
@@ -674,9 +632,7 @@ static const struct file_operations __maybe_unused port_fops = {

static const struct file_operations zero_fops = {
.llseek = zero_lseek,
- .write = write_zero,
.read_iter = read_iter_zero,
- .read = read_zero,
.write_iter = write_iter_zero,
.mmap = mmap_zero,
.get_unmapped_area = get_unmapped_area_zero,
--
2.35.1