From c9dccacfccc72c32692eedff4a27a4b0833a2afd Mon Sep 17 00:00:00 2001 From: Vincent Whitchurch Date: Thu, 11 Jul 2019 16:29:37 +0200 Subject: printk: Do not lose last line in kmsg buffer dump kmsg_dump_get_buffer() is supposed to select all the youngest log messages which fit into the provided buffer. It determines the correct start index by using msg_print_text() with a NULL buffer to calculate the size of each entry. However, when performing the actual writes, msg_print_text() only writes the entry to the buffer if the written len is lesser than the size of the buffer. So if the lengths of the selected youngest log messages happen to precisely fill up the provided buffer, the last log message is not included. We don't want to modify msg_print_text() to fill up the buffer and start returning a length which is equal to the size of the buffer, since callers of its other users, such as kmsg_dump_get_line(), depend upon the current behaviour. Instead, fix kmsg_dump_get_buffer() to compensate for this. For example, with the following two final prints: [ 6.427502] AAAAAAAAAAAAA [ 6.427769] BBBBBBBB12345 A dump of a 64-byte buffer filled by kmsg_dump_get_buffer(), before this patch: 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 35 32 32 31 39 37 <0>[ 6.522197 00000010: 5d 20 41 41 41 41 41 41 41 41 41 41 41 41 41 0a ] AAAAAAAAAAAAA. 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ After this patch: 00000000: 3c 30 3e 5b 20 20 20 20 36 2e 34 35 36 36 37 38 <0>[ 6.456678 00000010: 5d 20 42 42 42 42 42 42 42 42 31 32 33 34 35 0a ] BBBBBBBB12345. 00000020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ 00000030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ Link: http://lkml.kernel.org/r/20190711142937.4083-1-vincent.whitchurch@axis.com Fixes: e2ae715d66bf4bec ("kmsg - kmsg_dump() use iterator to receive log buffer content") To: rostedt@goodmis.org Cc: linux-kernel@vger.kernel.org Cc: # v3.5+ Signed-off-by: Vincent Whitchurch Reviewed-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- kernel/printk/printk.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'kernel') diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1888f6a3b694..424abf802f02 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -3274,7 +3274,7 @@ bool kmsg_dump_get_buffer(struct kmsg_dumper *dumper, bool syslog, /* move first record forward until length fits into the buffer */ seq = dumper->cur_seq; idx = dumper->cur_idx; - while (l > size && seq < dumper->next_seq) { + while (l >= size && seq < dumper->next_seq) { struct printk_log *msg = log_from_idx(idx); l -= msg_print_text(msg, true, time, NULL, 0); -- cgit v1.2.3-59-g8ed1b From 35c35493b0e3343522256f6054516f4e2161a6d4 Mon Sep 17 00:00:00 2001 From: Chuhong Yuan Date: Fri, 9 Aug 2019 15:10:34 +0800 Subject: printk: Replace strncmp() with str_has_prefix() strncmp(str, const, len) is error-prone because len is easy to have typo. An example is the hard-coded len has counting error or sizeof(const) forgets - 1. So we prefer using newly introduced str_has_prefix() to substitute such strncmp() to make code better. Link: http://lkml.kernel.org/r/20190809071034.17279-1-hslester96@gmail.com Cc: "Steven Rostedt" Cc: linux-kernel@vger.kernel.org Signed-off-by: Chuhong Yuan Reviewed-by: Sergey Senozhatsky [pmladek@suse.com: Slightly updated and reformatted the commit message.] Signed-off-by: Petr Mladek --- kernel/printk/braille.c | 15 +++++++++++---- kernel/printk/printk.c | 22 ++++++++++++++++------ 2 files changed, 27 insertions(+), 10 deletions(-) (limited to 'kernel') diff --git a/kernel/printk/braille.c b/kernel/printk/braille.c index 1d21ebacfdb8..17a9591e54ff 100644 --- a/kernel/printk/braille.c +++ b/kernel/printk/braille.c @@ -11,11 +11,18 @@ int _braille_console_setup(char **str, char **brl_options) { - if (!strncmp(*str, "brl,", 4)) { + size_t len; + + len = str_has_prefix(*str, "brl,"); + if (len) { *brl_options = ""; - *str += 4; - } else if (!strncmp(*str, "brl=", 4)) { - *brl_options = *str + 4; + *str += len; + return 0; + } + + len = str_has_prefix(*str, "brl="); + if (len) { + *brl_options = *str + len; *str = strchr(*brl_options, ','); if (!*str) { pr_err("need port name after brl=\n"); diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c index 1888f6a3b694..43a31015ec93 100644 --- a/kernel/printk/printk.c +++ b/kernel/printk/printk.c @@ -118,19 +118,29 @@ static unsigned int __read_mostly devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT; static int __control_devkmsg(char *str) { + size_t len; + if (!str) return -EINVAL; - if (!strncmp(str, "on", 2)) { + len = str_has_prefix(str, "on"); + if (len) { devkmsg_log = DEVKMSG_LOG_MASK_ON; - return 2; - } else if (!strncmp(str, "off", 3)) { + return len; + } + + len = str_has_prefix(str, "off"); + if (len) { devkmsg_log = DEVKMSG_LOG_MASK_OFF; - return 3; - } else if (!strncmp(str, "ratelimit", 9)) { + return len; + } + + len = str_has_prefix(str, "ratelimit"); + if (len) { devkmsg_log = DEVKMSG_LOG_MASK_DEFAULT; - return 9; + return len; } + return -EINVAL; } -- cgit v1.2.3-59-g8ed1b