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[86.9.19.6]) by smtp.gmail.com with ESMTPSA id u4-v6sm7659356wro.47.2018.08.31.13.52.30 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Fri, 31 Aug 2018 13:52:31 -0700 (PDT) From: Daniel Thompson To: Jason Wessel Cc: Daniel Thompson , kgdb-bugreport@lists.sourceforge.net, linux-kernel@vger.kernel.org, patches@linaro.org Subject: [PATCH 2/5] kdb: Simplify code to fetch characters from console Date: Fri, 31 Aug 2018 21:51:39 +0100 Message-Id: <20180831205142.23609-3-daniel.thompson@linaro.org> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20180831205142.23609-1-daniel.thompson@linaro.org> References: <20180831205142.23609-1-daniel.thompson@linaro.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently kdb_read_get_key() contains complex control flow that, on close inspection, turns out to be unnecessary. In particular: 1. It is impossible to enter the branch conditioned on (escape_delay == 1) except when the loop enters with (escape_delay == 2) allowing us to combine the branches. 2. Most of the code conditioned on (escape_delay == 2) simply modifies local data and then breaks out of the loop causing the function to return escape_data[0]. 3. Based on #2 there is not actually any need to ever explicitly set escape_delay to 2 because we it is much simpler to directly return escape_data[0] instead. 4. escape_data[0] is, for all but one exit path, known to be '\e'. Simplify the code based on these observations. There is a subtle (and harmless) change of behaviour resulting from this simplification: instead of letting the escape timeout after ~1998 milliseconds we now timeout after ~2000 milliseconds Signed-off-by: Daniel Thompson --- kernel/debug/kdb/kdb_io.c | 38 ++++++++++++++------------------------ 1 file changed, 14 insertions(+), 24 deletions(-) diff --git a/kernel/debug/kdb/kdb_io.c b/kernel/debug/kdb/kdb_io.c index e54e1e185c47..0ba490728459 100644 --- a/kernel/debug/kdb/kdb_io.c +++ b/kernel/debug/kdb/kdb_io.c @@ -122,25 +122,18 @@ static int kdb_read_get_key(char *buffer, size_t bufsize) touch_nmi_watchdog(); f = &kdb_poll_funcs[0]; } - if (escape_delay == 2) { - *ped = '\0'; - ped = escape_data; - --escape_delay; - } - if (escape_delay == 1) { - key = *ped++; - if (!*ped) - --escape_delay; - break; - } + key = (*f)(); + if (key == -1) { if (escape_delay) { udelay(ESCAPE_UDELAY); - --escape_delay; + if (--escape_delay == 0) + return '\e'; } continue; } + if (bufsize <= 2) { if (key == '\r') key = '\n'; @@ -148,28 +141,25 @@ static int kdb_read_get_key(char *buffer, size_t bufsize) *buffer = '\0'; return -1; } + if (escape_delay == 0 && key == '\e') { escape_delay = ESCAPE_DELAY; ped = escape_data; f_escape = f; } if (escape_delay) { - *ped++ = key; - if (f_escape != f) { - escape_delay = 2; - continue; - } + if (f_escape != f) + return '\e'; + *ped++ = key; key = kdb_read_handle_escape(escape_data, ped - escape_data); - if (key > 0) { - escape_data[0] = key; - escape_data[1] = '\0'; - } - if (key) - escape_delay = 2; - continue; + if (key < 0) + return '\e'; + if (key == 0) + continue; } + break; /* A key to process */ } return key; -- 2.17.1