Re: Device node - How does kernel know about it
On Thu, Dec 27, 2007 at 07:27:17PM -0800, Siva Prasad wrote: What is the kernel routine that is first called when there is, for example a read() function call from user program? I would like to start debugging from there and see if any thing at all happens when there is a call. Appreciate your help with this question. I don't generally recommend starting debugging at that level, but I'll try to give you some pointers. Every system call coming into the kernel from a user space program initially runs a little piece of assembly language code that looks up a handler (by number) in the system call table and sets up the proper environment to call the appropriate function that implements that call (which is written in C). Normally, those functions are named with a prefix of sys_ and the name of the system call. For example, the implementation of read(2) is called sys_read. You should be able to find it in fs/read_write.c. Other system call implementations are scattered around to be with code related to that call. Most of the file related ones can be found someplace under the fs directory. Brad Boyer [EMAIL PROTECTED] ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: Device node - How does kernel know about it
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. * Looking further into tty driver, I noticed that call to tty_write() or do_tty_write() is not happening at all. So, somewhere the interface between kernel and user program is lost. * Just to check it out, I tried to write a small kernel module and a test program. - Attached memtest.c module (not really testing memory there. :-)) - Attached testmemtest.c user program, that just open's it and reads the information - Created a device node using mknod /dev/memtest c 168 0 - When I do insmod memtest.ko inside the ramdisk bootup scripts, I could see all the printk's on the console - When I execute testmemtest next in the same script, it does not display the printk inside of memtest.c module. This only indicates that read call did not really go to the kernel side. - Just to check my program's validity, I checked on a similar machine and all the code works fine. - uname -r also matches with what I built. So, chances of exiting from open call because of mismatch is remote. Since userland cannot print, I have no idea what exactly is happening there. The kernel will simply look at the major:minor numbers - so maybe you simply have a wrong major/minor for /dev/ttyS0 ? in that case you will see nothing but other than that most things will go on working. hofrat -BEGIN PGP SIGNATURE- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFHdLY2nU7rXZKfY2oRApFpAKCKfGanKHGuFFJmUFy3aQtjmWNjEACfU7uK hrfpn2RMn5l23ZqCOXV5rd8= =GfsF -END PGP SIGNATURE- ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
RE: Device node - How does kernel know about it
Thank you Jon and Nicholas. I already have console=ttyS0 in the kernel command line. That is not helping me. I looked at the major/minor numbers with a good working system and it looks correct for the nodes created in ramdisk. What is the kernel routine that is first called when there is, for example a read() function call from user program? I would like to start debugging from there and see if any thing at all happens when there is a call. Appreciate your help with this question. Thanks Siva -Original Message- From: Nicholas Mc Guire [mailto:[EMAIL PROTECTED] Sent: Friday, December 28, 2007 12:39 AM To: Siva Prasad Cc: linuxppc-dev@ozlabs.org; [EMAIL PROTECTED] Subject: Re: Device node - How does kernel know about it -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. * Looking further into tty driver, I noticed that call to tty_write() or do_tty_write() is not happening at all. So, somewhere the interface between kernel and user program is lost. * Just to check it out, I tried to write a small kernel module and a test program. - Attached memtest.c module (not really testing memory there. :-)) - Attached testmemtest.c user program, that just open's it and reads the information - Created a device node using mknod /dev/memtest c 168 0 - When I do insmod memtest.ko inside the ramdisk bootup scripts, I could see all the printk's on the console - When I execute testmemtest next in the same script, it does not display the printk inside of memtest.c module. This only indicates that read call did not really go to the kernel side. - Just to check my program's validity, I checked on a similar machine and all the code works fine. - uname -r also matches with what I built. So, chances of exiting from open call because of mismatch is remote. Since userland cannot print, I have no idea what exactly is happening there. The kernel will simply look at the major:minor numbers - so maybe you simply have a wrong major/minor for /dev/ttyS0 ? in that case you will see nothing but other than that most things will go on working. hofrat -BEGIN PGP SIGNATURE- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFHdLY2nU7rXZKfY2oRApFpAKCKfGanKHGuFFJmUFy3aQtjmWNjEACfU7uK hrfpn2RMn5l23ZqCOXV5rd8= =GfsF -END PGP SIGNATURE- ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: Device node - How does kernel know about it
On 12/27/07, Siva Prasad [EMAIL PROTECTED] wrote: Thank you Jon and Nicholas. I already have console=ttyS0 in the kernel command line. That is not helping me. Do you have CONFIG_EARLY_PRINTK=y in .config? I looked at the major/minor numbers with a good working system and it looks correct for the nodes created in ramdisk. What is the kernel routine that is first called when there is, for example a read() function call from user program? I would like to start debugging from there and see if any thing at all happens when there is a call. Appreciate your help with this question. Thanks Siva -Original Message- From: Nicholas Mc Guire [mailto:[EMAIL PROTECTED] Sent: Friday, December 28, 2007 12:39 AM To: Siva Prasad Cc: linuxppc-dev@ozlabs.org; [EMAIL PROTECTED] Subject: Re: Device node - How does kernel know about it -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. * Looking further into tty driver, I noticed that call to tty_write() or do_tty_write() is not happening at all. So, somewhere the interface between kernel and user program is lost. * Just to check it out, I tried to write a small kernel module and a test program. - Attached memtest.c module (not really testing memory there. :-)) - Attached testmemtest.c user program, that just open's it and reads the information - Created a device node using mknod /dev/memtest c 168 0 - When I do insmod memtest.ko inside the ramdisk bootup scripts, I could see all the printk's on the console - When I execute testmemtest next in the same script, it does not display the printk inside of memtest.c module. This only indicates that read call did not really go to the kernel side. - Just to check my program's validity, I checked on a similar machine and all the code works fine. - uname -r also matches with what I built. So, chances of exiting from open call because of mismatch is remote. Since userland cannot print, I have no idea what exactly is happening there. The kernel will simply look at the major:minor numbers - so maybe you simply have a wrong major/minor for /dev/ttyS0 ? in that case you will see nothing but other than that most things will go on working. hofrat -BEGIN PGP SIGNATURE- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFHdLY2nU7rXZKfY2oRApFpAKCKfGanKHGuFFJmUFy3aQtjmWNjEACfU7uK hrfpn2RMn5l23ZqCOXV5rd8= =GfsF -END PGP SIGNATURE- -- Jon Smirl [EMAIL PROTECTED] ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
RE: Device node - How does kernel know about it
Jon, Yes!... I have CONFIG_EARLY_PRINTK=y, and I could see early prints during booting the kernel. Afterwards, printk's also work as expected. Only printf's from user space has problem. - Siva -Original Message- From: Jon Smirl [mailto:[EMAIL PROTECTED] Sent: Thursday, December 27, 2007 8:16 PM To: Siva Prasad Cc: Nicholas Mc Guire; linuxppc-dev@ozlabs.org; [EMAIL PROTECTED] Subject: Re: Device node - How does kernel know about it On 12/27/07, Siva Prasad [EMAIL PROTECTED] wrote: Thank you Jon and Nicholas. I already have console=ttyS0 in the kernel command line. That is not helping me. Do you have CONFIG_EARLY_PRINTK=y in .config? I looked at the major/minor numbers with a good working system and it looks correct for the nodes created in ramdisk. What is the kernel routine that is first called when there is, for example a read() function call from user program? I would like to start debugging from there and see if any thing at all happens when there is a call. Appreciate your help with this question. Thanks Siva -Original Message- From: Nicholas Mc Guire [mailto:[EMAIL PROTECTED] Sent: Friday, December 28, 2007 12:39 AM To: Siva Prasad Cc: linuxppc-dev@ozlabs.org; [EMAIL PROTECTED] Subject: Re: Device node - How does kernel know about it -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. * Looking further into tty driver, I noticed that call to tty_write() or do_tty_write() is not happening at all. So, somewhere the interface between kernel and user program is lost. * Just to check it out, I tried to write a small kernel module and a test program. - Attached memtest.c module (not really testing memory there. :-)) - Attached testmemtest.c user program, that just open's it and reads the information - Created a device node using mknod /dev/memtest c 168 0 - When I do insmod memtest.ko inside the ramdisk bootup scripts, I could see all the printk's on the console - When I execute testmemtest next in the same script, it does not display the printk inside of memtest.c module. This only indicates that read call did not really go to the kernel side. - Just to check my program's validity, I checked on a similar machine and all the code works fine. - uname -r also matches with what I built. So, chances of exiting from open call because of mismatch is remote. Since userland cannot print, I have no idea what exactly is happening there. The kernel will simply look at the major:minor numbers - so maybe you simply have a wrong major/minor for /dev/ttyS0 ? in that case you will see nothing but other than that most things will go on working. hofrat -BEGIN PGP SIGNATURE- Version: GnuPG v1.2.4 (GNU/Linux) iD8DBQFHdLY2nU7rXZKfY2oRApFpAKCKfGanKHGuFFJmUFy3aQtjmWNjEACfU7uK hrfpn2RMn5l23ZqCOXV5rd8= =GfsF -END PGP SIGNATURE- -- Jon Smirl [EMAIL PROTECTED] ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Device node - How does kernel know about it
Hi, I am really interested in finding out how kernel knows about device nodes and how the whole thing work. This is as part of my debugging effort on 8641D based PowerPC board. * It all started with the problem of not printing any thing that comes from ramdisk (echo and printf statements), while kernel printk's work perfectly fine. * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. * Looking further into tty driver, I noticed that call to tty_write() or do_tty_write() is not happening at all. So, somewhere the interface between kernel and user program is lost. * Just to check it out, I tried to write a small kernel module and a test program. - Attached memtest.c module (not really testing memory there. :-)) - Attached testmemtest.c user program, that just open's it and reads the information - Created a device node using mknod /dev/memtest c 168 0 - When I do insmod memtest.ko inside the ramdisk bootup scripts, I could see all the printk's on the console - When I execute testmemtest next in the same script, it does not display the printk inside of memtest.c module. This only indicates that read call did not really go to the kernel side. - Just to check my program's validity, I checked on a similar machine and all the code works fine. - uname -r also matches with what I built. So, chances of exiting from open call because of mismatch is remote. Since userland cannot print, I have no idea what exactly is happening there. Now going back to the original question... How does a kernel know about device nodes and how to link with it. Basically I believe interface between user programs and kernel is lost at device nodes. Appreciate any help in continuing my debugging efforts. Thanks Siva memtest.c Description: memtest.c testmemtest.c Description: testmemtest.c ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
Re: Device node - How does kernel know about it
On 12/26/07, Siva Prasad [EMAIL PROTECTED] wrote: Hi, I am really interested in finding out how kernel knows about device nodes and how the whole thing work. This is as part of my debugging effort on 8641D based PowerPC board. * It all started with the problem of not printing any thing that comes from ramdisk (echo and printf statements), while kernel printk's work perfectly fine. * Ramdisk is also executing fine, just that prints are not coming out of serial. I can see the execution of various user programs with a printk in sys_execve() routine. Ramdisk has all the required files like /dev/console, /dev/ttyS0, etc. Does adding console=ttyS0,baud to the kernel boot command line fix it? -- Jon Smirl [EMAIL PROTECTED] ___ Linuxppc-dev mailing list Linuxppc-dev@ozlabs.org https://ozlabs.org/mailman/listinfo/linuxppc-dev
