[PATCH printk v2 5/7] printk: Use struct console_buffers

[John Ogness]

From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

Replace the separately allocated output buffers with a single
instance of struct console_buffers.

Note that the buffer size of devkmsg_user.text_buf, when replaced
with console_buffers.text, reduces from CONSOLE_EXT_LOG_MAX to
CONSOLE_LOG_MAX. However, the buffer is only used to read ringbuffer
records. These records have a maximum size of LOG_LINE_MAX, which
is defined as CONSOLE_LOG_MAX - PREFIX_MAX.

Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: John Ogness <john.ogness@xxxxxxxxxxxxx>
---
 kernel/printk/printk.c | 68 ++++++++++++++++++++----------------------
 1 file changed, 32 insertions(+), 36 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a4854a60e6d8..750559171e30 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -712,11 +712,9 @@ 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 console_buffers cbufs;
 };
 
 static __printf(3, 4) __cold
@@ -798,6 +796,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 			    size_t count, loff_t *ppos)
 {
 	struct devkmsg_user *user = file->private_data;
+	const int ext_text_size = sizeof(user->cbufs.ext_text);
+	char *ext_text = &user->cbufs.ext_text[0];
 	struct printk_record *r = &user->record;
 	size_t len;
 	ssize_t ret;
@@ -839,8 +839,8 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		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,
+	len = info_print_ext_header(ext_text, ext_text_size, r->info);
+	len += msg_print_ext_body(ext_text + len, ext_text_size - len,
 				  &r->text_buf[0], r->info->text_len,
 				  &r->info->dev_info);
 
@@ -851,7 +851,7 @@ static ssize_t devkmsg_read(struct file *file, char __user *buf,
 		goto out;
 	}
 
-	if (copy_to_user(buf, user->buf, len)) {
+	if (copy_to_user(buf, ext_text, len)) {
 		ret = -EFAULT;
 		goto out;
 	}
@@ -950,7 +950,7 @@ 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));
+			&user->cbufs.text[0], sizeof(user->cbufs.text));
 
 	atomic64_set(&user->seq, prb_first_valid_seq(prb));
 
@@ -2007,6 +2007,10 @@ static int console_trylock_spinning(void)
 	return 1;
 }
 
+#if DROPPED_TEXT_MAX > CONSOLE_EXT_LOG_MAX
+#error "DROPPED_TEXT_MAX too large for console_buffers->ext_text"
+#endif
+
 /*
  * Call the specified console driver, asking it to write out the specified
  * text and length. If @dropped_text is non-NULL and any records have been
@@ -2741,36 +2745,32 @@ static void __console_unlock(void)
  * Print one record for the given console. The record printed is whatever
  * record is the next available record for the given console.
  *
- * @text is a buffer of size CONSOLE_LOG_MAX.
+ * @cbufs is the console buffers used to string-print the formatted messages.
  *
- * If extended messages should be printed, @ext_text is a buffer of size
- * CONSOLE_EXT_LOG_MAX. Otherwise @ext_text must be NULL.
- *
- * If dropped messages should be printed, @dropped_text is a buffer of size
- * DROPPED_TEXT_MAX. Otherwise @dropped_text must be NULL.
+ * @cookie is the cookie from entering the SRCU read-side critical section.
  *
  * @handover will be set to true if a printk waiter has taken over the
  * console_lock, in which case the caller is no longer holding both the
  * console_lock and the SRCU read lock. Otherwise it is set to false.
  *
- * @cookie is the cookie from the SRCU read lock.
- *
  * Returns false if the given console has no next record to print, otherwise
  * true.
  *
  * Requires the console_lock and the SRCU read lock.
  */
-static bool console_emit_next_record(struct console *con, char *text, char *ext_text,
-				     char *dropped_text, bool *handover, int cookie)
+static bool console_emit_next_record(struct console *con, struct console_buffers *cbufs,
+				     int cookie, bool *handover)
 {
 	static int panic_console_dropped;
 	struct printk_info info;
 	struct printk_record r;
+	size_t write_text_size;
 	unsigned long flags;
+	char *dropped_text;
 	char *write_text;
 	size_t len;
 
-	prb_rec_init_rd(&r, &info, text, CONSOLE_LOG_MAX);
+	prb_rec_init_rd(&r, &info, &cbufs->text[0], sizeof(cbufs->text));
 
 	*handover = false;
 
@@ -2792,13 +2792,20 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
 		goto skip;
 	}
 
-	if (ext_text) {
-		write_text = ext_text;
-		len = info_print_ext_header(ext_text, CONSOLE_EXT_LOG_MAX, r.info);
-		len += msg_print_ext_body(ext_text + len, CONSOLE_EXT_LOG_MAX - len,
+	if (console_srcu_read_flags(con) & CON_EXTENDED) {
+		/* Extended consoles do not print "dropped messages". */
+		dropped_text = NULL;
+
+		write_text = &cbufs->ext_text[0];
+		write_text_size = sizeof(cbufs->ext_text);
+		len = info_print_ext_header(write_text, write_text_size, r.info);
+		len += msg_print_ext_body(write_text + len, write_text_size - len,
 					  &r.text_buf[0], r.info->text_len, &r.info->dev_info);
 	} else {
-		write_text = text;
+		/* @ext_text is unused. Use it for "dropped messages". */
+		dropped_text = &cbufs->ext_text[0];
+
+		write_text = &cbufs->text[0];
 		len = record_print_text(&r, console_msg_format & MSG_FORMAT_SYSLOG, printk_time);
 	}
 
@@ -2852,9 +2859,7 @@ static bool console_emit_next_record(struct console *con, char *text, char *ext_
  */
 static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handover)
 {
-	static char dropped_text[DROPPED_TEXT_MAX];
-	static char ext_text[CONSOLE_EXT_LOG_MAX];
-	static char text[CONSOLE_LOG_MAX];
+	static struct console_buffers cbufs;
 	bool any_usable = false;
 	struct console *con;
 	bool any_progress;
@@ -2874,16 +2879,7 @@ static bool console_flush_all(bool do_cond_resched, u64 *next_seq, bool *handove
 				continue;
 			any_usable = true;
 
-			if (console_srcu_read_flags(con) & CON_EXTENDED) {
-				/* Extended consoles do not print "dropped messages". */
-				progress = console_emit_next_record(con, &text[0],
-								    &ext_text[0], NULL,
-								    handover, cookie);
-			} else {
-				progress = console_emit_next_record(con, &text[0],
-								    NULL, &dropped_text[0],
-								    handover, cookie);
-			}
+			progress = console_emit_next_record(con, &cbufs, cookie, handover);
 
 			/*
 			 * If a handover has occurred, the SRCU read lock
-- 
2.30.2