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Message-ID: <ZnQEPjcLnolJFi6n@pathway.suse.cz>
Date: Thu, 20 Jun 2024 12:28:14 +0200
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
Steven Rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v2 10/18] printk: Provide helper for message
prepending
On Tue 2024-06-04 01:30:45, John Ogness wrote:
> In order to support prepending different texts to printk
> messages, split out the prepending code into a helper
> function.
>
> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> ---
> kernel/printk/printk.c | 38 +++++++++++++++++++++++++++-----------
> 1 file changed, 27 insertions(+), 11 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 4613f9145a8e..fcbf794a0aaf 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2806,30 +2806,25 @@ static void __console_unlock(void)
> #ifdef CONFIG_PRINTK
>
> /*
> - * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This
> - * is achieved by shifting the existing message over and inserting the dropped
> - * message.
> + * Prepend the message in @pmsg->pbufs->outbuf with the message in
> + * @pmsg->pbufs->scratchbuf. This is achieved by shifting the existing message
> + * over and inserting the scratchbuf message.
> *
> * @pmsg is the printk message to prepend.
> *
> - * @dropped is the dropped count to report in the dropped message.
> + * @len is the length of the message in @pmsg->pbufs->scratchbuf.
> *
> * If the message text in @pmsg->pbufs->outbuf does not have enough space for
> - * the dropped message, the message text will be sufficiently truncated.
> + * the scratchbuf message, the message text will be sufficiently truncated.
> *
> * If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
> */
> -void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
> +static void __console_prepend_scratch(struct printk_message *pmsg, size_t len)
> {
> struct printk_buffers *pbufs = pmsg->pbufs;
> - const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
> const size_t outbuf_sz = sizeof(pbufs->outbuf);
> char *scratchbuf = &pbufs->scratchbuf[0];
> char *outbuf = &pbufs->outbuf[0];
> - size_t len;
> -
> - len = scnprintf(scratchbuf, scratchbuf_sz,
> - "** %lu printk messages dropped **\n", dropped);
>
> /*
> * Make sure outbuf is sufficiently large before prepending.
> @@ -2851,6 +2846,27 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
> pmsg->outbuf_len += len;
> }
>
> +/*
> + * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message".
> + * @pmsg->outbuf_len is updated appropriately.
> + *
> + * @pmsg is the printk message to prepend.
> + *
> + * @dropped is the dropped count to report in the dropped message.
> + */
> +void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
> +{
> + struct printk_buffers *pbufs = pmsg->pbufs;
> + const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
> + char *scratchbuf = &pbufs->scratchbuf[0];
> + size_t len;
> +
> + len = scnprintf(scratchbuf, scratchbuf_sz,
> + "** %lu printk messages dropped **\n", dropped);
> +
> + __console_prepend_scratch(pmsg, len);
> +}
There is a lot of boilerplate code around the custom part. A better
solution might be to allow passing a printf format to the function
prepending the existing message.
I have tried how it would look like. Here is the patch. Note that it
is only compile-only tested:
>From 853a3761f4e0f13970ffc71d9463f79eaa06fca1 Mon Sep 17 00:00:00 2001
From: John Ogness <john.ogness@...utronix.de>
Date: Tue, 4 Jun 2024 01:30:45 +0206
Subject: [PATCH] printk: Provide helper for message prepending
In order to support prepending different texts to printk
messages, split out the prepending code into a helper
function.
Signed-off-by: John Ogness <john.ogness@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
kernel/printk/printk.c | 36 +++++++++++++++++++++++++-----------
1 file changed, 25 insertions(+), 11 deletions(-)
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 3e07e9884907..b0a6aab792fc 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2806,30 +2806,31 @@ static void __console_unlock(void)
#ifdef CONFIG_PRINTK
/*
- * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message". This
- * is achieved by shifting the existing message over and inserting the dropped
- * message.
+ * Prepend the message in @pmsg->pbufs->outbuf. This is achieved by shifting
+ * the existing message over and inserting the scratchbuf message.
*
- * @pmsg is the printk message to prepend.
+ * @pmsg is the original printk message.
+ * @fmt is the printf format of the message which will prepend the existing one.
*
- * @dropped is the dropped count to report in the dropped message.
- *
- * If the message text in @pmsg->pbufs->outbuf does not have enough space for
- * the dropped message, the message text will be sufficiently truncated.
+ * If there is not enough space in @pmsg->pbufs->outbuf, the existing
+ * message text will be sufficiently truncated.
*
* If @pmsg->pbufs->outbuf is modified, @pmsg->outbuf_len is updated.
*/
-void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+__printf(2, 3)
+static void console_prepend_message(struct printk_message *pmsg, const char *fmt, ...)
{
struct printk_buffers *pbufs = pmsg->pbufs;
const size_t scratchbuf_sz = sizeof(pbufs->scratchbuf);
const size_t outbuf_sz = sizeof(pbufs->outbuf);
char *scratchbuf = &pbufs->scratchbuf[0];
char *outbuf = &pbufs->outbuf[0];
+ va_list args;
size_t len;
- len = scnprintf(scratchbuf, scratchbuf_sz,
- "** %lu printk messages dropped **\n", dropped);
+ va_start(args, fmt);
+ len = vscnprintf(scratchbuf, scratchbuf_sz, fmt, args);
+ va_end(args);
/*
* Make sure outbuf is sufficiently large before prepending.
@@ -2851,6 +2852,19 @@ void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
pmsg->outbuf_len += len;
}
+/*
+ * Prepend the message in @pmsg->pbufs->outbuf with a "dropped message".
+ * @pmsg->outbuf_len is updated appropriately.
+ *
+ * @pmsg is the printk message to prepend.
+ *
+ * @dropped is the dropped count to report in the dropped message.
+ */
+void console_prepend_dropped(struct printk_message *pmsg, unsigned long dropped)
+{
+ console_prepend_message(pmsg, "** %lu printk messages dropped **\n", dropped);
+}
+
/*
* Read and format the specified record (or a later record if the specified
* record is not available).
--
2.45.2
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