Re: Does register_chrdev function make device file under /dev ?
On Tue, 11 Mar 2014 08:01:26 -, Kim Chan said: To my understanding, device file is needed when a user program wants to access the device and we don't need to generate the device file for us to use the device in kernel. Is my understanding correct? Right. You don't need to generate the device file because you shouldn't be accessing the device in a file-like manner from inside the kernel. I am trying to open a shell on my LCD (is it going to be tty2 That's userspace, not kernel access. pgp1FTlZNga7b.pgp Description: PGP signature ___ Kernelnewbies mailing list Kernelnewbies@kernelnewbies.org http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
RE: Does register_chrdev function make device file under /dev ?
Yeah, I know mknod command. I just wanted to know if the register_chrdev makes
the file or not.
To my understanding, device file is needed when a user program wants to access
the device and we don't need to generate the device file for us to use the
device in kernel. Is my understanding correct?
For example, busybox (a user program) starts shell on tty2-4 by default. (as
the assumed default inittab below)
tty2::askfirst:-/bin/sh
tty3::askfirst:-/bin/sh
tty4::askfirst:-/bin/sh
I have had some mknod commands before in /etc/init.d/rcS to make tty2~tty4
device files, but when I remove them for test, I can see busybox (almost sure
it's coming from busybox) complaining that it cannot find the tty2~tty4 device
files.
I am trying to open a shell on my LCD (is it going to be tty2 ? I don't know)
and I'm not sure if I have to make vcs1 vcs2 vcs3 files. And I don't know how
to switch to LCD shell. during the boot, the texts come out on the LCD but I
cannot see the texts (printf) from busybox. and cannot see the shell on LCD.
When I press the keyboad, it looks like it's connected to tty1(I can see using
prints on uart window). Can anybody tell me some direction?
From : Kernel bu.ker...@gmail.com
Sent : 2014-03-11 14:44:09 ( +09:00 )
To : Kim Chan c...@etri.re.kr
Cc : kernelnewbies@kernelnewbies.org kernelnewbies@kernelnewbies.org
Subject : Re: Does register_chrdev function make device file under /dev ?
On Mar 10, 2014, at 10:25 PM, 김찬 c...@etri.re.krmailto:c...@etri.re.kr
wrote:
Hi,
This should be a basic question.
Does the regisetr_chrdev function make the device file under /dev directory?
I am running linux on our embedded system and inside vcs_init, register_chrdev
is called as below.
int __init vcs_init(void)
{
unsigned int i;
if (register_chrdev(VCS_MAJOR, vcs, vcs_fops))
panic(unable to get major %d for vcs device, VCS_MAJOR);
I can see the function is returning ok but I don't see any vcs* file under /dev.
Does it only register the device on /sys or /proc directory and not under /dev?
Thanks in advance.
Chan
You have to create a device file using 'mknod'
Ex: mknod -m 666 /dev/vcs c major no minor no
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Re: Does register_chrdev function make device file under /dev ?
On Tue, Mar 11, 2014 at 1:31 PM, Kim Chan c...@etri.re.kr wrote:
Yeah, I know mknod command. I just wanted to know if the register_chrdev
makes the file or not.
It doesn't. Also note that this is the old way of registering a char
device. New code should use cdev_add() etc.
To my understanding, device file is needed when a user program wants to
access the device and we don't need to generate the device file for us to
use the device in kernel. Is my understanding correct?
Yes, device nodes are needed for userspace code to access a device
(the good ol devices are also files Unix paradigm! :)).
I'm not sure how an in-kernel access will work (maybe via directly
getting the corresponding cdec structure).
For example, busybox (a user program) starts shell on tty2-4 by default. (as
the assumed default inittab below)
tty2::askfirst:-/bin/sh
tty3::askfirst:-/bin/sh
tty4::askfirst:-/bin/sh
I have had some mknod commands before in /etc/init.d/rcS to make tty2~tty4
device files, but when I remove them for test, I can see busybox (almost
sure it's coming from busybox) complaining that it cannot find the tty2~tty4
device files.
Correct. You will have to create those nodes manually.
I am trying to open a shell on my LCD (is it going to be tty2 ? I don't
know) and I'm not sure if I have to make vcs1 vcs2 vcs3 files. And I don't
know how to switch to LCD shell. during the boot, the texts come out on the
LCD but I cannot see the texts (printf) from busybox. and cannot see the
shell on LCD. When I press the keyboad, it looks like it's connected to
tty1(I can see using prints on uart window). Can anybody tell me some
direction?
I think you need to point getty or a shell to the correct tty before
you can see o/p on the screen. Do you know which device file you're
supposed to create for the LCD? If so, just use that in your inittab.
Something like:
::askfirst:-/bin/sh
HTH,
-mandeep
From : Kernel bu.ker...@gmail.com
Sent : 2014-03-11 14:44:09 ( +09:00 )
To : Kim Chan c...@etri.re.kr
Cc : kernelnewbies@kernelnewbies.org kernelnewbies@kernelnewbies.org
Subject : Re: Does register_chrdev function make device file under /dev ?
On Mar 10, 2014, at 10:25 PM, 김찬 c...@etri.re.kr wrote:
Hi,
This should be a basic question.
Does the regisetr_chrdev function make the device file under /dev directory?
I am running linux on our embedded system and inside vcs_init,
register_chrdev is called as below.
int __init vcs_init(void)
{
unsigned int i;
if (register_chrdev(VCS_MAJOR, vcs, vcs_fops))
panic(unable to get major %d for vcs device, VCS_MAJOR);
I can see the function is returning ok but I don't see any vcs* file under
/dev.
Does it only register the device on /sys or /proc directory and not under
/dev?
Thanks in advance.
Chan
You have to create a device file using 'mknod'
Ex: mknod -m 666 /dev/vcs c major no minor no
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RE: Does register_chrdev function make device file under /dev ?
Hi, Mandeep, Thanks for clearing some things for me.
For accessing the device in kernel code, I think maybe we can use the /proc or
/sys file system.
(I remember seeing people saying something like that.. correct me if I'm wrong)
I think you need to point getty or a shell to the correct tty before you
can see o/p on the screen. Do you know which device file you're supposed
to create for the LCD? If so, just use that in your inittab.
Something like:
::askfirst:-/bin/sh
The problem is, after the final sys_execve() which executes /sbin/init of the
ramdisk, I cannot see any shell coming up so I cannot use getty command.
Using some prints on separate uart print routine, I can see from the kbd_event
function the key value is going to current vc which is using tty1. The key
value is then handed to put_queue function where the character is somehow
copied to tty buffer. Flush_to_ldisc is scheduled for it and it will probably
get passed on to the virtual console.
Added to this, there is a notifier_call_chain and the notifier block is
registered by vcs_poll_data_get function which I don't know weather is
necessary or not. So one of my questions is if vcs is necessary for my case.
(I guess not. There is no other notifier blocks registered)
I gathered without inittab (I don't use inittab which should be ok for most
cases) the assumed default inittab
tty2::askfirst:-/bin/sh
tty3::askfirst:-/bin/sh
tty4::askfirst:-/bin/sh
is being applied by the busybox so there maybe 3 shells on tty2,tty3, and tty4
running somewhere.
But even if there are shells running I don't know how to switch to those ttys.
I tried using Ctrl-Alt F2 (or F3, F4) using the USB keyboard to switch to
tty2,3,4 to see if any shell comes up on the LCD but couldn't see it.
I tried using inittab with no avail before.
I hope somebody could point me on what should be checked. Any hint will be
appreciated.
Regards,
Chan
-Original Message-
From: Mandeep Sandhu [mailto:mandeepsandhu@gmail.com]
Sent: Tuesday, March 11, 2014 6:01 PM
To: Chan Kim
Cc: Kernel; kernelnewbies@kernelnewbies.org
Subject: Re: Does register_chrdev function make device file under /dev ?
On Tue, Mar 11, 2014 at 1:31 PM, Kim Chan c...@etri.re.kr wrote:
Yeah, I know mknod command. I just wanted to know if the
register_chrdev makes the file or not.
It doesn't. Also note that this is the old way of registering a char
device. New code should use cdev_add() etc.
To my understanding, device file is needed when a user program wants
to access the device and we don't need to generate the device file for
us to use the device in kernel. Is my understanding correct?
Yes, device nodes are needed for userspace code to access a device (the
good ol devices are also files Unix paradigm! :)).
I'm not sure how an in-kernel access will work (maybe via directly getting
the corresponding cdec structure).
For example, busybox (a user program) starts shell on tty2-4 by
default. (as the assumed default inittab below)
tty2::askfirst:-/bin/sh tty3::askfirst:-/bin/sh
tty4::askfirst:-/bin/sh I have had some mknod commands before in
/etc/init.d/rcS to make tty2~tty4 device files, but when I remove them
for test, I can see busybox (almost sure it's coming from busybox)
complaining that it cannot find the tty2~tty4 device files.
Correct. You will have to create those nodes manually.
I am trying to open a shell on my LCD (is it going to be tty2 ? I
don't
know) and I'm not sure if I have to make vcs1 vcs2 vcs3 files. And I
don't know how to switch to LCD shell. during the boot, the texts come
out on the LCD but I cannot see the texts (printf) from busybox. and
cannot see the shell on LCD. When I press the keyboad, it looks like
it's connected to tty1(I can see using prints on uart window). Can
anybody tell me some direction?
I think you need to point getty or a shell to the correct tty before you
can see o/p on the screen. Do you know which device file you're supposed
to create for the LCD? If so, just use that in your inittab.
Something like:
::askfirst:-/bin/sh
HTH,
-mandeep
From : Kernel bu.ker...@gmail.com
Sent : 2014-03-11 14:44:09 ( +09:00 )
To : Kim Chan c...@etri.re.kr
Cc : kernelnewbies@kernelnewbies.org kernelnewbies@kernelnewbies.org
Subject : Re: Does register_chrdev function make device file under /dev ?
On Mar 10, 2014, at 10:25 PM, 김찬 c...@etri.re.kr wrote:
Hi,
This should be a basic question.
Does the regisetr_chrdev function make the device file under /dev
directory?
I am running linux on our embedded system and inside vcs_init,
register_chrdev is called as below.
int __init vcs_init(void)
{
unsigned int i;
if (register_chrdev(VCS_MAJOR, vcs, vcs_fops))
panic(unable to get major %d for vcs device,
VCS_MAJOR);
I can see the function is returning ok but I don't
Re: Does register_chrdev function make device file under /dev ?
On Mar 10, 2014, at 10:25 PM, 김찬 c...@etri.re.kr wrote:
Hi,
This should be a basic question.
Does the regisetr_chrdev function make the device file under /dev directory?
I am running linux on our embedded system and inside vcs_init,
register_chrdev is called as below.
int __init vcs_init(void)
{
unsigned int i;
if (register_chrdev(VCS_MAJOR, vcs, vcs_fops))
panic(unable to get major %d for vcs device, VCS_MAJOR);
I can see the function is returning ok but I don't see any vcs* file under
/dev.
Does it only register the device on /sys or /proc directory and not under
/dev?
Thanks in advance.
Chan
You have to create a device file using 'mknod'
Ex: mknod -m 666 /dev/vcs c major no minor no
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