Update printk.c

[invicnaper]

Adding new function , int type_printk(int type, const char *fmt, ...) , it will print an output and adding type , 1 : [error] . 2 [log] 3 [action] . TODO : other types

[hitmoon]

Does we need a 'break' statement at the end of 'case 0' block?

[invicnaper]

yes it's been added . others types will be added

[kjenova]

Why does in case 1 sprintf() need to be called before local_irq_save()? Since there is no 'undefined type' for which we don't do anything, local_irq_save() and some other routines are going to be used anyway, why not leave repeated statements out of the switch?

int printk_type(int type, const char *fmt, ...)
{
unsigned long flags;
va_list args;
char *buf;
int r;

local_irq_save(flags);
buf = __get_cpu_var(printk_sched_buf);

switch(type){
    case 0:
        va_start(args, fmt);
        r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);
        break;
    case 1:
        const char *all_fmt;
        sprintf(all_fmt, "[Error] : %s", fmt);
        va_start(args, all_fmt)
        r = vsnprintf(buf, PRINTK_BUF_SIZE, all_fmt, args);
        break;
}

va_end(args);
__this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);
irq_work_queue(&__get_cpu_var(wake_up_klogd_work));
local_irq_restore(flags);

return r;

}

[invicnaper]

Yes it's been added to , and also the default case .

[kjenova]

Also, if you want the function to be visible inside the kernel API (as printk() is) you should add this underneath the closing brace of the function:

EXPORT_SYMBOL(type_printk);

[chest-rockwell]

This is exactly why Linus doesn't support pull requests via GitHub. Your willingness to contribute to an open source project is appreciated, but you can't just send pull requests to a major project with broken, untested code. Read the docs, go through the proper vetting process, and THEN submit your pull requests (but not here).

[kjenova]

OP's current code doesn't work. I made a working version, for educational purposes. Applying this commit (https://github.com/kjenova/linux/commit/26eb273d60d91a0979468e094ea0718348599d65) to the latest kernel (3.15.0-rc7), building the kernel, running it, compiling this module against the kernel and running this module:

#include "/where_your_3.15rc-7_kernel_source_is/linux/module.h"
#include "/where_your_3.15rc-7_kernel_source_is/linux/kernel.h"

int init_module()
{
printk(KERN_INFO "using printk() with KERN_INFO macro.");
printk(KERN_WARNING "using printk() with KERN_WARNING macro.");
printk(KERN_ERR "using printk() with KERN_ERR macro.");

printk(KERN_INFO "switching to type_printk().");

type_printk(0, "using type_printk() with normal type.");
type_printk(1, "using type_printk() with error type.");
type_printk(2. "using type_printk() with action type.");
type_printk(-1, "using type_printk() with unsupported type.");

return 0;

}

void exit_module(void)
{

}

produces this output on the /usr/var/kern.log of my machine (my .config is http://pastebin.com/BcZCkp8i):

/begin

May 31 17:07:28 kje-desktop kernel: [ 177.015377] test_type_printk: module license 'unspecified' taints kernel.
May 31 17:07:28 kje-desktop kernel: [ 177.015382] Disabling lock debugging due to kernel taint
May 31 17:07:28 kje-desktop kernel: [ 177.015461] using printk() with KERN_INFO macro.
May 31 17:07:28 kje-desktop kernel: [ 177.015463] using printk() with KERN_WARNING macro.using printk() with KERN_ERR macro.
May 31 17:07:56 kje-desktop kernel: [ 177.015472] switching to type_printk().using type_printk() with normal type.[Error] : using type_printk() with error type.[Action] : using type_printk() with action type.using type_printk() with unsupported type.
May 31 17:07:56 kje-desktop kernel: [ 205.352376] general protection fault: 0000 [#1] SMP
May 31 17:07:56 kje-desktop kernel: [ 205.352385] Modules linked in: test_type_printk(PO)

/end

I don't see a reason, why to add this change to the kernel. If there is a reason, go with it through the above mentioned process.

[nizqsut]

ocal_irq_save(flags); --> should be "local_irq_save(flags);"?
Is it a spelling wrong?

[kjenova]

Well, the reason your code didn't work is, that you should've put it under the declaration of wake_up_klogd() (as printk_sched(), on which your code is based on, is).

[invicnaper]

thank you guys for you comments , i have updated the code

[kjenova]

Don't forget to add this line to include/linux/printk.h

/begin

asmlinkage __printf(2, 3) __cold
int type_printk(int type, char *fmt, ...);

/end

The macro __printf(2, 3) tells us, that the second (we don't start counting at zero here, zero means argument not supplied) argument will be the format string and the third the va_list. __cold is a compiler hint, it tells us to optimise (but not so "agressively", it's "cold" because of that) this functions and place it near other "cold" functions (from: http://axon.cs.byu.edu/~adam/gatheredinfo/tips/tips_gcc.php).

On a side note: your original function also compiles and works (you should put that func at the very end, however), if you add kmalloc(). You can also use the printk_sched() function (I used it in type_printk_using_printk_sched() function).

The full code:

/include/linux/printk.h

add this:

asmlinkage __printf(2, 3) __cold
int type_printk(int type, char *fmt, ...);

asmlinkage __printf(2, 3) __cold
int type_printk_using_printk_sched(int type, char *fmt, ...);

/kernel/printk.c

add this:

asmlinkage __visible int type_printk(int type, char *fmt, ...)
{
va_list args;
char *buf;
char *all_fmt;
int r;
unsigned long flags;

local_irq_save(flags);
buf = __get_cpu_var(printk_sched_buf);

switch(type) {
    default:
        va_start(args, fmt);
        r = vsnprintf(buf, PRINTK_BUF_SIZE, fmt, args);
        break;
    case 1:
        all_fmt = kmalloc(sizeof(fmt)+11*sizeof(char), GFP_KERNEL);
        sprintf(all_fmt, "[Error] : %s", fmt);
        va_start(args, all_fmt);
        r = vsnprintf(buf, PRINTK_BUF_SIZE, all_fmt, args);
        kfree(all_fmt);
        break;
    case 2:
        all_fmt = kmalloc(sizeof(fmt)+12*sizeof(char), GFP_KERNEL);
        sprintf(all_fmt, "[Action] : %s", fmt);
        va_start(args, all_fmt);
        r = vsnprintf(buf, PRINTK_BUF_SIZE, all_fmt, args);
        kfree(all_fmt);
        break;
}
va_end(args);
__this_cpu_or(printk_pending, PRINTK_PENDING_SCHED);
irq_work_queue(&__get_cpu_var(wake_up_klogd_work));
local_irq_restore(flags);
return r;

}
EXPORT_SYMBOL(type_printk);

asmlinkage __visible int type_printk_using_printk_sched(int type, char *fmt, ...)
{
va_list args;
char *all_fmt;
int r;

switch(type) {
    default:
        va_start(args, fmt);
        r = printk_sched(fmt, args);
    case 1:
        all_fmt = kmalloc(sizeof(fmt)+11*sizeof(char), GFP_KERNEL);
        sprintf(all_fmt, "[Error] : %s\n", fmt);
        va_start(args, all_fmt);
        r = printk_sched(all_fmt, args);
        kfree(all_fmt);
        break;
    case 2:
        all_fmt = kmalloc(sizeof(fmt)+12*sizeof(char), GFP_KERNEL);
        sprintf(all_fmt, "[Action] : %s\n", fmt);
        va_start(args, all_fmt);
        r = printk_sched(all_fmt, args);
        kfree(all_fmt);
        break;
}
return r;

}
EXPORT_SYMBOL(type_printk_using_printk_sched);

/begin

Jun 1 20:20:15 kje-desktop kernel: [ 67.877502] test_type_printk: module license 'unspecified' taints kernel.
Jun 1 20:20:15 kje-desktop kernel: [ 67.877506] Disabling lock debugging due to kernel taint
Jun 1 20:20:15 kje-desktop kernel: [ 67.877569] using printk() with KERN_INFO macro.
Jun 1 20:20:15 kje-desktop kernel: [ 67.877570] using printk() with KERN_WARNING macro.using printk() with KERN_ERR macro.
Jun 1 20:20:15 kje-desktop kernel: [ 67.877572] switching to type_printk().switching to type_printk_using_printk_sched().
Jun 1 20:20:15 kje-desktop kernel: [ 67.877765] [sched_delayed] [Error] : using type_printk_using_printk_sched() with unsupported type.

/end

Important: as seen, only one of the outputs of those functions is seen, due to scheduling. So you're better off with the current version!

[invicnaper]

ok I corrected the code