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pr_debug: fix wrong insmod assertions, document mess of printk(KERN_DEBUG

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Ciro Santilli
2018-05-05 21:42:47 +01:00
parent 22a7b9bf2b
commit 8a826ab16a
2 changed files with 73 additions and 7 deletions
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66
README.adoc
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@@ -409,6 +409,20 @@ which now outputs the `pr_debug` message:
printk debug
....
but TODO: it also shows debug messages even without enabling them explicitly:
....
echo 8 > /proc/sys/kernel/printk
insmod /myprintk.ko
....
and it shows as enabled:
....
# grep myprintk /sys/kernel/debug/dynamic_debug/control
/linux-kernel-module-cheat/out/x86_64/buildroot/build/kernel_module-1.0/./myprintk.c:12 [myprintk]myinit =p "pr_debug\012"
....
Enable `pr_debug` for boot messages as well, before we can reach userland and write to `/proc`:
....
@@ -417,6 +431,58 @@ Enable `pr_debug` for boot messages as well, before we can reach userland and wr
Get ready for the noisiest boot ever, I think it overflows the `printk` buffer and funny things happen.
===== pr_debug != printk(KERN_DEBUG
When `CONFIG_DYNAMIC_DEBUG` is set, `printk(KERN_DEBUG` is not the exact same as `pr_debug(` since `printk(KERN_DEBUG` messages are visible with:
....
./run -e 'initcall_debug logleve=8'
....
which outputs lines of type:
....
<7>[ 1.756680] calling clk_disable_unused+0x0/0x130 @ 1
<7>[ 1.757003] initcall clk_disable_unused+0x0/0x130 returned 0 after 111 usecs
....
which are `printk(KERN_DEBUG` inside `init/main.c` in v4.16.
Mentioned at: https://stackoverflow.com/questions/37272109/how-to-get-details-of-all-modules-drivers-got-initialized-probed-during-kernel-b
This likely comes from the ifdef split at `init/main.c`:
....
/* If you are writing a driver, please use dev_dbg instead */
#if defined(CONFIG_DYNAMIC_DEBUG)
#include <linux/dynamic_debug.h>
/* dynamic_pr_debug() uses pr_fmt() internally so we don't need it here */
#define pr_debug(fmt, ...) \
dynamic_pr_debug(fmt, ##__VA_ARGS__)
#elif defined(DEBUG)
#define pr_debug(fmt, ...) \
printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#else
#define pr_debug(fmt, ...) \
no_printk(KERN_DEBUG pr_fmt(fmt), ##__VA_ARGS__)
#endif
....
==== ignore_loglevel
....
./run -e 'ignore_loglevel'
....
enables all log levels, and is basically the same as:
....
./run -e 'loglevel=8'
....
except that you don't need to know what is the maximum level.
=== Module documentation
....

14
kernel_module/myprintk.c
View File

@@ -3,13 +3,13 @@
static int myinit(void)
{
pr_alert("printk alert\n");
pr_crit("printk crit\n");
pr_err("printk err\n");
pr_warning("printk warning\n");
pr_notice("printk notice\n");
pr_info("printk info\n");
pr_debug("printk debug\n");
pr_alert("pr_alert\n");
pr_crit("pr_crit\n");
pr_err("pr_err");
pr_warning("pr_warning\n");
pr_notice("pr_notice\n");
pr_info("pr_info\n");
pr_debug("pr_debug\n");
return 0;
}