[PATCH] seq_buf: add seq_buf_printk() helper

From: Sergey Senozhatsky
Date: Mon Apr 10 2023 - 22:57:36 EST


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@xxxxxxxxxxxx>
---
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