Where does printk() print to?
dmesg should display printk messages.
linux-kernel
Using assertion in the Linux kernel
The corresponding kernel macros are BUG_ON and WARN_ON. The former is for when you want to make the kernel panic and bring the system down (i.e., unrecoverable error). The latter is for when you want to log something to the kernel log (viewable via dmesg). As @Michael says, in the kernel, you need to validate … Read more
What restriction is perf_event_paranoid == 1 actually putting on x86 perf?
In this case CPU event refers to monitoring events per CPU rather than per task. For perf tools this restricts the usage of -C, –cpu= Count only on the list of CPUs provided. Multiple CPUs can be provided as a comma-separated list with no space: 0,1. Ranges of CPUs are specified with -: 0-2. In … Read more
What’s the purpose of the UD2 opcode in the Linux kernel?
It’s the BUG() macro from include/asm-i386/bug.h. /* * Tell the user there is some problem. * The offending file and line are encoded after the “officially * undefined” opcode for parsing in the trap handler. */ #ifdef CONFIG_DEBUG_BUGVERBOSE #define BUG() \ __asm__ __volatile__( “ud2\n” \ “\t.word %c0\n” \ “\t.long %c1\n” \ : : “i” (__LINE__), … Read more
buffered asynchronous file I/O on linux
Unless you want to write your own IO thread pool, the glibc implementation is an acceptable solution. It actually works surprisingly well for something that runs entirely in userland. The kernel implementation does not work with buffered IO at all in my experience (though I’ve seen other people say the opposite!). Which is fine if … Read more
Difference between printk and pr_info
The kernel’s printk.h has: #define pr_info(fmt,arg…) \ printk(KERN_INFO fmt,##arg) Just like the name, pr_info() is printk() with the KERN_INFO priority.
Building a kernel module from several source files which one of them has the same name as the module
Proper way to fix in kernel make file would be as: # obj-m+= my_module.o #append other source files except my_module.c which would be include by default my_module-objs+= src1.o src2.o
Change default console loglevel during boot up [closed]
Do I need to recompile the kernel, No. or is there a way I can get the changed value to be persistent across reboot. Yes. Use the kernel command line parameter loglevel: loglevel= All Kernel Messages with a loglevel smaller than the console loglevel will be printed to the console. It can also be changed … Read more
What does ERESTARTSYS used while writing linux driver?
-ERESTARTSYS is connected to the concept of a restartable system call. A restartable system call is one that can be transparently re-executed by the kernel when there is some interruption. For instance the user space process which is sleeping in a system call can get a signal, execute a handler, and then when the handler … Read more