+ seq_buf-add-seq_buf_do_printk-helper.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: seq_buf: add seq_buf_do_printk() helper
has been added to the -mm mm-unstable branch.  Its filename is
     seq_buf-add-seq_buf_do_printk-helper.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/seq_buf-add-seq_buf_do_printk-helper.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Sergey Senozhatsky <senozhatsky@chromium.org>
Subject: seq_buf: add seq_buf_do_printk() helper
Date: Sat, 15 Apr 2023 19:01:10 +0900

(akpm: temporary addition for
memcg-use-seq_buf_do_printk-with-mem_cgroup_print_oom_meminfo.patch)

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 as a delimiter, rather than passing the whole string
buffer to printk() at once.

Link: https://lkml.kernel.org/r/20230415100110.1419872-1-senozhatsky@chromium.org
Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Cc: Steven Rostedt (Google) <rostedt@goodmis.org>
Cc: Yosry Ahmed <yosryahmed@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 include/linux/seq_buf.h |    2 ++
 lib/seq_buf.c           |   32 ++++++++++++++++++++++++++++++++
 2 files changed, 34 insertions(+)

--- a/include/linux/seq_buf.h~seq_buf-add-seq_buf_do_printk-helper
+++ a/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_do_printk(struct seq_buf *s, const char *lvl);
+
 #endif /* _LINUX_SEQ_BUF_H */
--- a/lib/seq_buf.c~seq_buf-add-seq_buf_do_printk-helper
+++ a/lib/seq_buf.c
@@ -93,6 +93,38 @@ int seq_buf_printf(struct seq_buf *s, co
 }
 EXPORT_SYMBOL_GPL(seq_buf_printf);
 
+/**
+ * seq_buf_do_printk - printk seq_buf line by line
+ * @s: seq_buf descriptor
+ * @lvl: printk level
+ *
+ * printk()-s a multi-line sequential buffer line by line. The function
+ * makes sure that the buffer in @s is nul terminated and safe to read
+ * as a string.
+ */
+void seq_buf_do_printk(struct seq_buf *s, const char *lvl)
+{
+	const char *start, *lf;
+
+	if (s->size == 0 || s->len == 0)
+		return;
+
+	seq_buf_terminate(s);
+
+	start = s->buffer;
+	while ((lf = strchr(start, '\n'))) {
+		int len = lf - start + 1;
+
+		printk("%s%.*s", lvl, len, start);
+		start = ++lf;
+	}
+
+	/* No trailing LF */
+	if (start < s->buffer + s->len)
+		printk("%s%s\n", lvl, start);
+}
+EXPORT_SYMBOL_GPL(seq_buf_do_printk);
+
 #ifdef CONFIG_BINARY_PRINTF
 /**
  * seq_buf_bprintf - Write the printf string from binary arguments
_

Patches currently in -mm which might be from senozhatsky@chromium.org are

seq_buf-add-seq_buf_do_printk-helper.patch