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SubjectRe: [PATCHv2] printk: add console_msg_format command line option
On Tue, 19 Dec 2017 17:42:43 +0900
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> wrote:

> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 8a61d1eda677..543de386e01e 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -642,6 +642,20 @@
> console=brl,ttyS0
> For now, only VisioBraille is supported.
>
> + console_msg_format=
> + [KNL] Change console messages format
> + default
> + By default we print messages on consoles in
> + "[time stamp] text\n" format (time stamp may not be
> + printed, depending on CONFIG_PRINTK_TIME or
> + `printk_time' param).
> + syslog
> + Switch to syslog format: "<%u>[time stamp] text\n"
> + IOW, each message will have a facility and loglevel
> + prefix. The format is similar to one used by syslog()
> + syscall, or to executing "dmesg -S --raw" or to reading
> + from /proc/kmsg.

Just to clarify. This affects all consoles, not just serial?

> +
> consoleblank= [KNL] The console blank (screen saver) timeout in
> seconds. A value of 0 disables the blank timer.
> Defaults to 0.
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index c2e713f6ae2e..16dd91260273 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -277,6 +277,13 @@ EXPORT_SYMBOL(console_set_on_cmdline);
> /* Flag: console code may call schedule() */
> static int console_may_schedule;
>
> +enum con_msg_format {
> + MSG_FORMAT_DEFAULT = 0,
> + MSG_FORMAT_SYSLOG = (1 << 0),
> +};

So the con_msg_format will be a flag (as denoted with the (1<<0)).
Should we call it "con_msg_format_flags" to make it more obvious that
these are treated as flags and not a simple number.


> +
> +static int console_msg_format = MSG_FORMAT_DEFAULT;
> +
> /*
> * The printk log buffer consists of a chain of concatenated variable
> * length records. Every record starts with a record header, containing
> @@ -1913,6 +1920,17 @@ static int __add_preferred_console(char *name, int idx, char *options,
> c->index = idx;
> return 0;
> }
> +
> +static int __init console_msg_format_setup(char *str)
> +{
> + if (!strncmp(str, "syslog", 6))
> + console_msg_format = MSG_FORMAT_SYSLOG;
> + if (!strncmp(str, "default", 7))

You can use strcmp() instead of strncmp(), the init code will nul
terminate the string for you before calling this function. Otherwise if
we add "syslog_special" or "default_extra" they will be confused with
the above.

-- Steve

> + console_msg_format = MSG_FORMAT_DEFAULT;
> + return 1;
> +}
> +__setup("console_msg_format=", console_msg_format_setup);
> +
> /*
> * Set up a console. Called via do_early_param() in init/main.c
> * for each "console=" parameter in the boot command line.
> @@ -2215,7 +2233,10 @@ void console_unlock(void)
> goto skip;
> }
>
> - len += msg_print_text(msg, false, text + len, sizeof(text) - len);
> + len += msg_print_text(msg,
> + console_msg_format & MSG_FORMAT_SYSLOG,
> + text + len,
> + sizeof(text) - len);
> if (nr_ext_console_drivers) {
> ext_len = msg_print_ext_header(ext_text,
> sizeof(ext_text),

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