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.chd@xxxxxxxxx] > Sent: Tuesday, March 11, 2014 6:01 PM > To: Chan Kim > Cc: Kernel; kernelnewbies@xxxxxxxxxxxxxxxxx > Subject: Re: Does register_chrdev function make device file under /dev ? > > On Tue, Mar 11, 2014 at 1:31 PM, Kim Chan <ckim@xxxxxxxxxx> 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.kernel@xxxxxxxxx> > > Sent : 2014-03-11 14:44:09 ( +09:00 ) > > To : Kim Chan <ckim@xxxxxxxxxx> > > Cc : kernelnewbies@xxxxxxxxxxxxxxxxx <kernelnewbies@xxxxxxxxxxxxxxxxx> > > Subject : Re: Does register_chrdev function make device file under /dev ? > > > > > > > > On Mar 10, 2014, at 10:25 PM, 김찬 <ckim@xxxxxxxxxx> 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> > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies@xxxxxxxxxxxxxxxxx > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > > > > > _______________________________________________ > > Kernelnewbies mailing list > > Kernelnewbies@xxxxxxxxxxxxxxxxx > > http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies > > _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
