Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
From:   John Ogness <john.ogness@linutronix.de>
To:     Petr Mladek <pmladek@suse.com>
Cc:     Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: [PATCH printk-rework 03/12] printk: consolidate kmsg_dump_get_buffer/syslog_print_all code
Date:   Tue, 26 Jan 2021 22:21:42 +0106
Message-Id: <20210126211551.26536-4-john.ogness@linutronix.de>
In-Reply-To: <20210126211551.26536-1-john.ogness@linutronix.de>
References: <20210126211551.26536-1-john.ogness@linutronix.de>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

The logic for finding records to fit into a buffer is the same for
kmsg_dump_get_buffer() and syslog_print_all(). Introduce a helper
function find_first_fitting_seq() to handle this logic.

Signed-off-by: John Ogness <john.ogness@linutronix.de>
---
 kernel/printk/printk.c | 71 ++++++++++++++++++++++++------------------
 1 file changed, 41 insertions(+), 30 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 1929aa372e7f..ec2174882b8e 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1421,6 +1421,41 @@ static size_t get_record_print_text_size(struct printk_info *info,
 	return ((prefix_len * line_count) + info->text_len + 1);
 }
 
+/*
+ * Beginning with @start_seq, find the first record where it and all following
+ * records up to (but not including) @max_seq fit into @size.
+ */
+static u64 find_first_fitting_seq(u64 start_seq, u64 max_seq, size_t size,
+				  struct printk_info *info, bool syslog, bool time)
+{
+	unsigned int line_count;
+	size_t len = 0;
+	u64 seq;
+
+	/* Determine the size of the records up to @max_seq. */
+	prb_for_each_info(start_seq, prb, seq, info, &line_count) {
+		if (info->seq >= max_seq)
+			break;
+		len += get_record_print_text_size(info, line_count, syslog, time);
+	}
+
+	/*
+	 * Move first record forward until length fits into the buffer. Ignore
+	 * newest messages that were not counted in the above cycle. Messages
+	 * might appear and get lost in the meantime. This is a best effort
+	 * that prevents an infinite loop that could occur with a retry.
+	 */
+	if (seq < max_seq)
+		max_seq = seq;
+	prb_for_each_info(start_seq, prb, seq, info, &line_count) {
+		if (len <= size || info->seq >= max_seq)
+			break;
+		len -= get_record_print_text_size(info, line_count, syslog, time);
+	}
+
+	return seq;
+}
+
 static int syslog_print(char __user *buf, int size)
 {
 	struct printk_info info;
@@ -1492,7 +1527,6 @@ static int syslog_print(char __user *buf, int size)
 static int syslog_print_all(char __user *buf, int size, bool clear)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
 	char *text;
 	int len = 0;
@@ -1509,15 +1543,7 @@ static int syslog_print_all(char __user *buf, int size, bool clear)
 	 * Find first record that fits, including all following records,
 	 * into the user-provided buffer for this dump.
 	 */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count)
-		len += get_record_print_text_size(&info, line_count, true, time);
-
-	/* move first record forward until length fits into the buffer */
-	prb_for_each_info(clear_seq, prb, seq, &info, &line_count) {
-		if (len <= size)
-			break;
-		len -= get_record_print_text_size(&info, line_count, true, time);
-	}
+	seq = find_first_fitting_seq(clear_seq, -1, size, &info, true, time);
 
 	prb_rec_init_rd(&r, &info, text, LOG_LINE_MAX + PREFIX_MAX);
 
@@ -3410,7 +3436,6 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 			  char *buf, size_t size, size_t *len_out)
 {
 	struct printk_info info;
-	unsigned int line_count;
 	struct printk_record r;
 	unsigned long flags;
 	u64 seq;
@@ -3436,26 +3461,12 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog,
 
 	/*
 	 * Find first record that fits, including all following records,
-	 * into the user-provided buffer for this dump.
+	 * into the user-provided buffer for this dump. Pass in size-1
+	 * because this function (by way of record_print_text()) will
+	 * not write more than size-1 bytes of text into @buf.
 	 */
-
-	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
-		if (info.seq >= dumper->next_seq)
-			break;
-		len += get_record_print_text_size(&info, line_count, syslog, time);
-	}
-
-	/*
-	 * Move first record forward until length fits into the buffer. Ignore
-	 * newest messages that were not counted in the above cycle. Messages
-	 * might appear and get lost in the meantime. This is the best effort
-	 * that prevents an infinite loop.
-	 */
-	prb_for_each_info(dumper->cur_seq, prb, seq, &info, &line_count) {
-		if (len < size || info.seq >= dumper->next_seq)
-			break;
-		len -= get_record_print_text_size(&info, line_count, syslog, time);
-	}
+	seq = find_first_fitting_seq(dumper->cur_seq, dumper->next_seq,
+				     size - 1, &info, syslog, time);
 
 	/* Keep track of the last message for the next iteration. */
 	next_seq = seq;
-- 
2.20.1