linux-kernel - [PATCH 1/2] random: convert to using fops->read

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Date:   Thu, 19 May 2022 13:31:32 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     tytso@....edu, Jason@...c4.com
Cc:     hch@....de, linux-kernel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>
Subject: [PATCH 1/2] random: convert to using fops->read_iter()

This is a pre-requisite to writing up splice() again for the random
and urandom drivers.

Signed-off-by: Jens Axboe <axboe@...nel.dk>
---
 drivers/char/random.c | 37 +++++++++++++++++++------------------
 1 file changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index 4c9adb4f3d5d..529afd31d549 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -528,11 +528,12 @@ void get_random_bytes(void *buf, size_t nbytes)
 }
 EXPORT_SYMBOL(get_random_bytes);
 
-static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
+static ssize_t get_random_bytes_user(struct iov_iter *to)
 {
-	size_t len, left, ret = 0;
+	size_t len, ret = 0;
 	u32 chacha_state[CHACHA_STATE_WORDS];
 	u8 output[CHACHA_BLOCK_SIZE];
+	size_t nbytes = iov_iter_count(to);
 
 	if (!nbytes)
 		return 0;
@@ -549,7 +550,7 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
 	 * the user directly.
 	 */
 	if (nbytes <= CHACHA_KEY_SIZE) {
-		ret = nbytes - copy_to_user(buf, &chacha_state[4], nbytes);
+		ret = copy_to_iter(&chacha_state[4], nbytes, to);
 		goto out_zero_chacha;
 	}
 
@@ -559,13 +560,10 @@ static ssize_t get_random_bytes_user(void __user *buf, size_t nbytes)
 			++chacha_state[13];
 
 		len = min_t(size_t, nbytes, CHACHA_BLOCK_SIZE);
-		left = copy_to_user(buf, output, len);
-		if (left) {
-			ret += len - left;
+		len = copy_to_iter(output, len, to);
+		if (!len)
 			break;
-		}
 
-		buf += len;
 		ret += len;
 		nbytes -= len;
 		if (!nbytes)
@@ -1466,6 +1464,9 @@ static void try_to_generate_entropy(void)
 SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
 		flags)
 {
+	struct iovec iov = { .iov_base = buf };
+	struct iov_iter iter;
+
 	if (flags & ~(GRND_NONBLOCK | GRND_RANDOM | GRND_INSECURE))
 		return -EINVAL;
 
@@ -1488,7 +1489,9 @@ SYSCALL_DEFINE3(getrandom, char __user *, buf, size_t, count, unsigned int,
 		if (unlikely(ret))
 			return ret;
 	}
-	return get_random_bytes_user(buf, count);
+	iov.iov_len = count;
+	iov_iter_init(&iter, READ, &iov, 1, count);
+	return get_random_bytes_user(&iter);
 }
 
 static __poll_t random_poll(struct file *file, poll_table *wait)
@@ -1540,8 +1543,7 @@ static ssize_t random_write(struct file *file, const char __user *buffer,
 	return (ssize_t)count;
 }
 
-static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
-			    loff_t *ppos)
+static ssize_t urandom_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 {
 	static int maxwarn = 10;
 
@@ -1556,21 +1558,20 @@ static ssize_t urandom_read(struct file *file, char __user *buf, size_t nbytes,
 		maxwarn--;
 		if (__ratelimit(&urandom_warning))
 			pr_notice("%s: uninitialized urandom read (%zd bytes read)\n",
-				  current->comm, nbytes);
+				  current->comm, iov_iter_count(to));
 	}
 
-	return get_random_bytes_user(buf, nbytes);
+	return get_random_bytes_user(to);
 }
 
-static ssize_t random_read(struct file *file, char __user *buf, size_t nbytes,
-			   loff_t *ppos)
+static ssize_t random_read_iter(struct kiocb *kiocb, struct iov_iter *to)
 {
 	int ret;
 
 	ret = wait_for_random_bytes();
 	if (ret != 0)
 		return ret;
-	return get_random_bytes_user(buf, nbytes);
+	return get_random_bytes_user(to);
 }
 
 static long random_ioctl(struct file *f, unsigned int cmd, unsigned long arg)
@@ -1639,7 +1640,7 @@ static int random_fasync(int fd, struct file *filp, int on)
 }
 
 const struct file_operations random_fops = {
-	.read = random_read,
+	.read_iter = random_read_iter,
 	.write = random_write,
 	.poll = random_poll,
 	.unlocked_ioctl = random_ioctl,
@@ -1649,7 +1650,7 @@ const struct file_operations random_fops = {
 };
 
 const struct file_operations urandom_fops = {
-	.read = urandom_read,
+	.read_iter = urandom_read_iter,
 	.write = random_write,
 	.unlocked_ioctl = random_ioctl,
 	.compat_ioctl = compat_ptr_ioctl,
-- 
2.35.1