> Hi sandeep, > > On Tue, May 17, 2011 at 12:52 AM, sandeep kumar > <coolsandyforyou@xxxxxxxxx> wrote: > > > > Hi , > > Here is my question. > > when we put 'printk's in kernel code the logs will go to the log_buffer.(i observed that from implementation) > > But when UART is enabled(in the bootloader), the same printk logs?are going to the serial console. > > As per my study printk doesnot implementing anything that writes to the UART console. > > > > Now here are?my questions, > > how this is being achieved??Where this is implemented?(which file) > > When you register your UART driver there is typically an option to > register a console driver at the same time. > > For example, let's take a look at the 8250 serial driver. We'll look > at the file drivers/serial/8250.c Think the file has changed, its now in drivers/tty/serial/8250.c > Search for the function serial8250_console_init, which has a call to > register_console. > > That's the starting point that sets up the console driver. You can > have other drivers call register_console and get your console messages > sent out whatever bizarre device you may have connected to your > system. > You can also have multiple consoles registered at the same time. If so, you can see the output in all the registered ports. > > Where wil be the parsing of the cmdline string sent from the bootloader is done? > > The function console_setup is called when the console= parameter is > passed on the kernel command line. > <http://lxr.linux.no/linux+v2.6.38/kernel/printk.c#L904> In the console_setup function, the struct console's address in stored in a char pointer. If you want to know how the parsing is done, if (str[0] >= '0' && str[0] <= '9') { strcpy(buf, "ttyS"); strncpy(buf + 4, str, sizeof(buf) - 5); } else { strncpy(buf, str, sizeof(buf) - 1); } buf[sizeof(buf) - 1] = 0; if ((options = strchr(str, ',')) != NULL) *(options++) = 0; I they check the str[0], the first element in the received char array, it corresponds to char name[16] // from linux/console.h the name parameter in the static struct console serial8250_console is "ttyS". Basically what the first line does is that, the console device's name should not start with numbers. If not actual name is copied. > The __setup just after the end of the function is what causes it to > call that function when the console= parameter is passed. /harper _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
