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

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Date:   Fri, 20 May 2022 15:50:30 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org
Cc:     "Jason A. Donenfeld" <Jason@...c4.com>,
        Al Viro <viro@...iv.linux.org.uk>, Jens Axboe <axboe@...nel.dk>
Subject: [PATCH] char/mem: only use {read,write}_iter, not the old {read,write} functions

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@...uxfoundation.org>
Cc: Al Viro <viro@...iv.linux.org.uk>
Cc: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Jason A. Donenfeld <Jason@...c4.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