Commit ea308da1 authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: use printk_buffers for devkmsg 



Replace the buffers in struct devkmsg_user with a struct
printk_buffers. This reduces the number of buffers to keep track of.

As a side-effect, @text_buf was 8kB large, even though it only
needed to be the max size of a ringbuffer record. By switching to
struct printk_buffers, ~7kB less memory is allocated when opening
/dev/kmsg.

And since struct printk_buffers will be used now, reduce duplicate
code by calling printk_get_next_message() to handle the record
reading and formatting.

Note that since /dev/kmsg never suppresses records based on
loglevel, printk_get_next_message() is extended with an extra
bool argument to specify if suppression is allowed.

Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20230109100800.1085541-8-john.ogness@linutronix.de
parent c4fcc617

kernel/printk/printk.c

+22 −27
Original line number Diff line number Diff line
@@ -695,16 +695,15 @@ static ssize_t msg_print_ext_body(char *buf, size_t size, 
	return len;

}



static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,

				    bool is_extended, bool may_supress);



/* /dev/kmsg - userspace message inject/listen interface */

struct devkmsg_user {

	atomic64_t seq;

	struct ratelimit_state rs;

	struct mutex lock;

	char buf[CONSOLE_EXT_LOG_MAX];



	struct printk_info info;

	char text_buf[CONSOLE_EXT_LOG_MAX];

	struct printk_record record;

	struct printk_buffers pbufs;

};



static __printf(3, 4) __cold
@@ -786,8 +785,10 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
			    size_t count, loff_t *ppos)

{

	struct devkmsg_user *user = file->private_data;

	struct printk_record *r = &user->record;

	size_t len;

	char *outbuf = &user->pbufs.outbuf[0];

	struct printk_message pmsg = {

		.pbufs = &user->pbufs,

	};

	ssize_t ret;



	if (!user)
@@ -797,7 +798,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
	if (ret)

		return ret;



	if (!prb_read_valid(prb, atomic64_read(&user->seq), r)) {

	if (!printk_get_next_message(&pmsg, atomic64_read(&user->seq), true, false)) {

		if (file->f_flags & O_NONBLOCK) {

			ret = -EAGAIN;

			goto out;
@@ -814,36 +815,31 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf, 
		 * This pairs with __wake_up_klogd:A.

		 */

		ret = wait_event_interruptible(log_wait,

				prb_read_valid(prb,

					atomic64_read(&user->seq), r)); /* LMM(devkmsg_read:A) */

				printk_get_next_message(&pmsg, atomic64_read(&user->seq), true,

							false)); /* LMM(devkmsg_read:A) */

		if (ret)

			goto out;

	}



	if (r->info->seq != atomic64_read(&user->seq)) {

	if (pmsg.dropped) {

		/* our last seen message is gone, return error and reset */

		atomic64_set(&user->seq, r->info->seq);

		atomic64_set(&user->seq, pmsg.seq);

		ret = -EPIPE;

		goto out;

	}



	len = info_print_ext_header(user->buf, sizeof(user->buf), r->info);

	len += msg_print_ext_body(user->buf + len, sizeof(user->buf) - len,

				  &r->text_buf[0], r->info->text_len,

				  &r->info->dev_info);



	atomic64_set(&user->seq, r->info->seq + 1);

	atomic64_set(&user->seq, pmsg.seq + 1);



	if (len > count) {

	if (pmsg.outbuf_len > count) {

		ret = -EINVAL;

		goto out;

	}



	if (copy_to_user(buf, user->buf, len)) {

	if (copy_to_user(buf, outbuf, pmsg.outbuf_len)) {

		ret = -EFAULT;

		goto out;

	}

	ret = len;

	ret = pmsg.outbuf_len;

out:

	mutex_unlock(&user->lock);

	return ret;
@@ -937,9 +933,6 @@ static int devkmsg_open(struct inode *inode, struct file *file) 


	mutex_init(&user->lock);



	prb_rec_init_rd(&user->record, &user->info,

			&user->text_buf[0], sizeof(user->text_buf));



	atomic64_set(&user->seq, prb_first_valid_seq(prb));



	file->private_data = user;
@@ -2762,12 +2755,14 @@ static void console_prepend_dropped(struct printk_message *pmsg, unsigned long d 
 * @is_extended specifies if the message should be formatted for extended

 * console output.

 *

 * @may_supress specifies if records may be skipped based on loglevel.

 *

 * Returns false if no record is available. Otherwise true and all fields

 * of @pmsg are valid. (See the documentation of struct printk_message

 * for information about the @pmsg fields.)

 */

static bool printk_get_next_message(struct printk_message *pmsg, u64 seq,

				    bool is_extended)

				    bool is_extended, bool may_suppress)

{

	static int panic_console_dropped;
@@ -2810,7 +2805,7 @@ static bool printk_get_next_message(struct printk_message *pmsg, u64 seq, 
	}



	/* Skip record that has level above the console loglevel. */

	if (suppress_message_printing(r.info->level))

	if (may_suppress && suppress_message_printing(r.info->level))

		goto out;



	if (is_extended) {
@@ -2853,7 +2848,7 @@ static bool console_emit_next_record(struct console *con, bool *handover, int co 


	*handover = false;



	if (!printk_get_next_message(&pmsg, con->seq, is_extended))

	if (!printk_get_next_message(&pmsg, con->seq, is_extended, true))

		return false;



	con->dropped += pmsg.dropped;