Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760031AbaGPR1I (ORCPT ); Wed, 16 Jul 2014 13:27:08 -0400 Received: from mail-ig0-f181.google.com ([209.85.213.181]:61042 "EHLO mail-ig0-f181.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758862AbaGPR1E (ORCPT ); Wed, 16 Jul 2014 13:27:04 -0400 From: Alex Elder To: akpm@linux-foundation.org Cc: pmladek@suse.cz, bp@suse.de, john.stultz@linaro.org, jack@suse.cz, linux-kernel@vger.kernel.org Subject: [PATCH 1/4] printk: LOG_CONT and LOG_NEWLINE are separate Date: Wed, 16 Jul 2014 12:26:57 -0500 Message-Id: <1405531620-9983-2-git-send-email-elder@linaro.org> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1405531620-9983-1-git-send-email-elder@linaro.org> References: <1405531620-9983-1-git-send-email-elder@linaro.org> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Two log record flags--LOG_CONT and LOG_NEWLINE--are never both set at the same time in a log record flags field. What follows is a great deal of explanation that aims to prove this assertion. Having that knowledge allows us to simplify a bit of logic though, and with a little more work (in follow-on patches) it allows us to do without some flag values, considerably simplifying things. So this patch leverages the one-or-the-other nature of these two flags to simplify a small bit of logic. It makes a some other small changes to make it obvious that a few things in surrounding (and related) code are invariant. Log record flags are held in the "cont" continuation buffer, as well as in "syslog_prev" and "console_prev". Those are discussed later. Other than that, log record flags are only set in log_store(): msg->flags = flags & 0x1f; There are 5 places log_store() is called: twice from cont_flush(); and three times from vprintk_emit(). Only two single-flag values are ever passed to cont_flush(): LOG_CONT; and LOG_NEWLINE. That passed-in value is provided by cont_flush() to log_store() either as-is, or modified to include LOG_NOCONS. There are thus four possible flag combinations supplied to log_store() by cont_flush(): LOG_CONT; LOG_NEWLINE; LOG_CONT|LOG_NOCONS; or LOG_NEWLINE|LOG_NOCONS. The first call vprintk_emit() makes to log_store() passes a flags value of LOG_PREFIX|LOG_NEWLINE. The second and third calls pass a computed "lflags" value, possibly with LOG_CONT added. The only possible flag combinations held in "lflags" are: 0; LOG_NEWLINE; LOG_PREFIX; or LOG_NEWLINE|LOG_PREFIX. And the LOG_CONT flag is added only when LOG_NEWLINE is not set. So there are six possible flag combinations supplied by cont_flush(): 0; LOG_NEWLINE; LOG_PREFIX; LOG_CONT; LOG_PREFIX|LOG_CONT; or LOG_PREFIX|LOG_NEWLINE. Therefore log_store() is never provided (so never records) a flag value that contains both LOG_CONT and LOG_NEWLINE. Meanwhile, the "cont" flags field is only ever assigned value 0, or a value passed to cont_flush(). As mentioned above, cont_flush() is never provided more than one flag value. The only values assigned to "syslog_prev" and "console_prev" are 0 or the flags value from a log record. So none of these ever hold LOG_CONT and LOG_NEWLINE at the same time. This proves that at most one of LOG_CONT and LOG_NEWLINE will ever be set in a log record flags field. And as a result, we know that LOG_CONT being set implies LOG_NEWLINE is not set (and vice versa). This patch makes the following changes: - Changes two spots in msg_print_txt() so they no longer bother checking for LOG_NEWLINE once its known that LOG_CONT is set. - Changes two |= assignments in vprintk_emit() to be simple assignments instead, because the result is known to be the same and it makes it obvious no other flags are involved. - Explicitly pass NULL rather than "dict" (and 0 as its length) to log_store() in one spot in vprintk_emit(), because we know the value of dict at that point is always NULL. Signed-off-by: Alex Elder --- kernel/printk/printk.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 13e839d..301ade3 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -1006,11 +1006,9 @@ static size_t msg_print_text(const struct printk_log *msg, enum log_flags prev, prefix = false; if (msg->flags & LOG_CONT) { - if ((prev & LOG_CONT) && !(prev & LOG_NEWLINE)) + if (prev & LOG_CONT) prefix = false; - - if (!(msg->flags & LOG_NEWLINE)) - newline = false; + newline = false; } do { @@ -1642,7 +1640,7 @@ asmlinkage int vprintk_emit(int facility, int level, /* mark and strip a trailing newline */ if (text_len && text[text_len-1] == '\n') { text_len--; - lflags |= LOG_NEWLINE; + lflags = LOG_NEWLINE; } /* strip kernel syslog prefix and extract log level or control flags */ @@ -1672,7 +1670,7 @@ asmlinkage int vprintk_emit(int facility, int level, level = default_message_loglevel; if (dict) - lflags |= LOG_PREFIX|LOG_NEWLINE; + lflags = LOG_PREFIX|LOG_NEWLINE; if (!(lflags & LOG_NEWLINE)) { /* @@ -1688,7 +1686,7 @@ asmlinkage int vprintk_emit(int facility, int level, else printed_len += log_store(facility, level, lflags | LOG_CONT, 0, - dict, dictlen, text, text_len); + NULL, 0, text, text_len); } else { bool stored = false; -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/