linux-kernel - [PATCH] seq_buf: add seq_buf

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Date:   Tue, 11 Apr 2023 11:55:56 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Yosry Ahmed <yosryahmed@...gle.com>,
        linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: [PATCH] seq_buf: add seq_buf_printk() helper

Sometimes we use seq_buf to format a string buffer, which
we then pass to printk(). However, in certain situations
the seq_buf string buffer can get too big, exceeding the
PRINTKRB_RECORD_MAX bytes limit, and causing printk() to
truncate the string.

Add a new seq_buf helper. This helper prints the seq_buf
string buffer line by line, using \n as a delimiter,
rather than passing the whole string buffer to printk()
at once.

Signed-off-by: Sergey Senozhatsky <senozhatsky@...omium.org>
---
 include/linux/seq_buf.h |  2 ++
 lib/seq_buf.c           | 30 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+)

diff --git a/include/linux/seq_buf.h b/include/linux/seq_buf.h
index 5b31c5147969..80b78df89809 100644
--- a/include/linux/seq_buf.h
+++ b/include/linux/seq_buf.h
@@ -159,4 +159,6 @@ extern int
 seq_buf_bprintf(struct seq_buf *s, const char *fmt, const u32 *binary);
 #endif
 
+void seq_buf_printk(struct seq_buf *s, const char *lvl);
+
 #endif /* _LINUX_SEQ_BUF_H */
diff --git a/lib/seq_buf.c b/lib/seq_buf.c
index 0a68f7aa85d6..9d13004c2324 100644
--- a/lib/seq_buf.c
+++ b/lib/seq_buf.c
@@ -93,6 +93,36 @@ int seq_buf_printf(struct seq_buf *s, const char *fmt, ...)
 }
 EXPORT_SYMBOL_GPL(seq_buf_printf);
 
+/**
+ * seq_buf_printk - printk seq_buf line by line
+ * @s: seq_buf descriptor
+ * @lvl: printk level
+ *
+ * printk()-s a multi-line sequential buffer line by line
+ */
+void seq_buf_printk(struct seq_buf *s, const char *lvl)
+{
+	const char *start, *lf;
+	int len;
+
+	if (s->size == 0)
+		return;
+
+	start = s->buffer;
+	while ((lf = strchr(start, '\n'))) {
+		len = lf - start + 1;
+		printk("%s%.*s", lvl, len, start);
+		start = ++lf;
+	}
+
+	/* No trailing LF */
+	if (start < s->buffer + s->len) {
+		len = s->buffer + s->len - start;
+		printk("%s%.*s\n", lvl, len, start);
+	}
+}
+EXPORT_SYMBOL_GPL(seq_buf_printk);
+
 #ifdef CONFIG_BINARY_PRINTF
 /**
  * seq_buf_bprintf - Write the printf string from binary arguments
-- 
2.40.0.577.gac1e443424-goog