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Date: Mon, 20 Apr 2015 14:50:16 +0200
From: Petr Mladek <pmladek@...e.cz>
To: Tejun Heo <tj@...nel.org>
Cc: akpm@...ux-foundation.org, davem@...emloft.net,
linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
Kay Sievers <kay@...y.org>
Subject: Re: [PATCH 03/16] printk: move LOG_NOCONS skipping into
call_console_drivers()
On Thu 2015-04-16 19:03:40, Tejun Heo wrote:
> When a line is printed by multiple printk invocations, each chunk is
> directly sent out to console drivers so that they don't get lost.
> When the line is completed and stored in the log buffer, the line is
> suppressed from going out to consoles as that'd lead to duplicate
> outputs. This is tracked with LOG_NOCONS flag.
>
> The suppression is currently implemented in console_unlock() which
> skips invoking call_console_drivers() for LOG_NOCONS messages. This
> patch moves the filtering into call_console_drivers() in preparation
> of the planned extended console drivers which will deal with the
> duplicate messages themselves.
>
> While this makes call_console_drivers() iterate over LOG_NOCONS
> messages, this is extremely unlikely to matter especially given that
> continuation lines aren't that common and also simplifies
> console_unlock() a bit.
>
> Signed-off-by: Tejun Heo <tj@...nel.org>
> Cc: Kay Sievers <kay@...y.org>
> Cc: Petr Mladek <pmladek@...e.cz>
> ---
> kernel/printk/printk.c | 46 ++++++++++++++++++++++++----------------------
> 1 file changed, 24 insertions(+), 22 deletions(-)
>
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index 5ea6709..0175c46 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -1417,7 +1417,8 @@ SYSCALL_DEFINE3(syslog, int, type, char __user *, buf, int, len)
> * log_buf[start] to log_buf[end - 1].
> * The console_lock must be held.
> */
> -static void call_console_drivers(int level, const char *text, size_t len)
> +static void call_console_drivers(int level, bool nocons,
> + const char *text, size_t len)
> {
> struct console *con;
>
> @@ -1438,6 +1439,13 @@ static void call_console_drivers(int level, const char *text, size_t len)
> if (!cpu_online(smp_processor_id()) &&
> !(con->flags & CON_ANYTIME))
> continue;
> + /*
> + * Skip record we have buffered and already printed
> + * directly to the console when we received it.
> + */
> + if (nocons)
> + continue;
> +
> con->write(con, text, len);
> }
> }
> @@ -1919,7 +1927,8 @@ static struct cont {
> } cont;
> static struct printk_log *log_from_idx(u32 idx) { return NULL; }
> static u32 log_next(u32 idx) { return 0; }
> -static void call_console_drivers(int level, const char *text, size_t len) {}
> +static void call_console_drivers(int level, bool nocons,
> + const char *text, size_t len) {}
> static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev,
> bool syslog, char *buf, size_t size) { return 0; }
> static size_t cont_print_text(char *text, size_t size) { return 0; }
> @@ -2190,7 +2199,7 @@ static void console_cont_flush(char *text, size_t size)
> len = cont_print_text(text, size);
> raw_spin_unlock(&logbuf_lock);
> stop_critical_timings();
> - call_console_drivers(cont.level, text, len);
> + call_console_drivers(cont.level, false, text, len);
> start_critical_timings();
> local_irq_restore(flags);
> return;
> @@ -2234,6 +2243,7 @@ again:
> struct printk_log *msg;
> size_t len;
> int level;
> + bool nocons;
>
> raw_spin_lock_irqsave(&logbuf_lock, flags);
> if (seen_seq != log_next_seq) {
> @@ -2252,38 +2262,30 @@ again:
> } else {
> len = 0;
> }
> -skip:
> +
> if (console_seq == log_next_seq)
> break;
>
> msg = log_from_idx(console_idx);
> - if (msg->flags & LOG_NOCONS) {
> - /*
> - * Skip record we have buffered and already printed
> - * directly to the console when we received it.
> - */
> - console_idx = log_next(console_idx);
> - console_seq++;
> - /*
> - * We will get here again when we register a new
> - * CON_PRINTBUFFER console. Clear the flag so we
> - * will properly dump everything later.
> - */
> - msg->flags &= ~LOG_NOCONS;
> - console_prev = msg->flags;
> - goto skip;
> - }
> -
> level = msg->level;
> + nocons = msg->flags & LOG_NOCONS;
> len += msg_print_text(msg, console_prev, false,
> text + len, sizeof(text) - len);
> console_idx = log_next(console_idx);
> console_seq++;
> console_prev = msg->flags;
> +
> + /*
> + * The log will be processed again when we register a new
> + * CON_PRINTBUFFER console. Clear the flag so we will
> + * properly dump everything later.
> + */
> + msg->flags &= ~LOG_NOCONS;
The previous code cleared LOG_NOCONS before saving flags into
console_prev. Well, the change does not have any real effect.
And the new order makes more sense.
This patch looks fine to me.
Reviewed-by: Petr Mladek <pmladek@...e.cz>
Best Regards,
Petr
> raw_spin_unlock(&logbuf_lock);
>
> stop_critical_timings(); /* don't trace print latency */
> - call_console_drivers(level, text, len);
> + call_console_drivers(level, nocons, text, len);
> start_critical_timings();
> local_irq_restore(flags);
> }
> --
> 2.1.0
>
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