Actually I'm a beginner and I'm trying to learn the concept of low-level driver and high level driver. I want to know how a module depends on other modules for their operation.
I've done lsmod command. I found these lines in the output.
parport_pc 25962 1
lp 7028 0
parport 32635 3 ppdev,parport_pc,lp
From the above lines, I understood that there exist modules like,
parport_pc
lp
parport
I've found source code parport_pc.c, lp.c, in the directory /usr/src/drivers/parport. But I can't find the source code for parport in my entire file system. Even though I found parpot.ko inside /lib/modules/linux2.6.32-37-generic/kernel/parport.
Also in the directory /usr/src/drivers/parport, I've seen a line in the Makefile like,
obj-$(CONFIG_PARPORT) += parport.o
So where can I find the parport.c file ? I've searched the entire file system using the command
find / -name parport.c
but no result. Why is the file parport.c missing?
The parport.o file is compiled from multiple .c files, including share.c, ieee1284.c, ieee1284_ops.c, and procfs.c, and possibly including daisy.c and probe.c, all under the drivers/parport/ directory of the Linux sources. (This information was taken from Linux 3.5-rc3-00203-g8874e81, which is a bit newer than the kernel you are looking at, but the parallel port drivers don't change much any more).
To find this information, I looked at the same Makefile and noted that the parport-objs variable was initially set to share.o ieee1284.o ieee1284_ops.o procfs.o and daisy.o probe.o was added if CONFIG_PARPORT_1284 was set to y.
Related
I am pretty new to linux kernel.I am trying to generate PWM through linux. The API man talks about a sysfs interface. I want to implement a userspace program in C. But using PWM forces me to use a command line. Furthermore, using read, write is a problem in C as when I am using cd, it is changing path directory.
Thus the path is variable. Is there any way I can pass values to pwm_config() without using sysfs? Perhaps through ioctl? If yes, then what would be the procedure?
Application C code:
void main(){
int export = open("/sys/class/pwm/pmwchip0/export",O_WRONLY);
int period,duty_cycle,enable;
if(export == -1)
{
perror("Export:");
}
and so on for other files like period and duty cycle.
When I try to run my application I get the following error.
Export:: No such file or directory
Export_write: Bad file descriptor
Period_write:: Bad file descriptor
Duty_cycle_write:: Bad file descriptor
Enable_write:: Bad file descriptor
As far as I know, the sysfs is the only standard userspace interface to PWM. But anything you can do from the command line can be done in C (the shell is written in C, after all).
The problem you are having with cd is not actually a problem. Inside sysfs the directories in /sys/class/pwd/* are actually symbolic links to the proper devices. In your case /sys/class/pwm/pwmchip0 is a symlink to /sys/devices/soc0/amba/f8001000.timer/pwm/pwmchip0.
The funny thing is that some shells, when you cd a symbolic link will resolve to the real directory, but other shells will actually keep the symlink name as the current directory.
But that issue with the directory symlinks should not be an issue for you. A C program willing to manage PWM devices should not change the working directory. Instead open the files with the full path:
open("/sys/class/pwm/pwmchip0/npwm", O_RDONLY);
and so on.
I want to add custom syscall to freebsd(school work). I google hundreds of time. there is no right solution for it.
my homework is: "Add custom syscall to freebsd kernel and recompile the kernel and use it".
finally I find that I should follow instructions in these two pages:
1 : http://www.onlamp.com/pub/a/bsd/2003/10/09/adding_system_calls.html
then
2: https://www.freebsd.org/doc/en/books/handbook/kernelconfig-building.html
will it shows errors in compile time:
<sys/parma.h> no such file or directory
<sys/kern.h> no such file or directory
<sys/syscallargs.h> no such file or directory
I removed these three header include form my file then recompile it. now shows other errors like: MAXCPU undeclered in pcpu.h file.
what I missed? how can I do my school work?
NOTE: I use freebsd8 in vbox
Look at what the error messages say; the files don't exist.
The first include file is a typo; it's param.h, not parma.h!
There is no kern.h. Maybe you mean sys/kernel.h?
Idem for syscallargs.h. Do you perhaps mean syscall.h?
You can find header files with e.g:
find /usr/src/sys/ -type f -name '*.h'|grep 'sys/.*kern.*\.h'
/usr/src/sys/ofed/include/linux/kernel.h
/usr/src/sys/dev/netmap/netmap_kern.h
...
Update: More important is determining which includes you actually need.
FreeBSD has pretty good documentation. If you want to use a kernel function or data-structure, it is probably covered in section 9 of the manual pages.
You can list all the manual pages in that section with ls /usr/share/man/man9/ | less. Or you can use the apropos command.
Since you want to implement a syscall, start with e.g.
apropos syscall
It will return:
SYSCALL_MODULE(9) - syscall kernel module declaration macro
syscall(2), __syscall(2) - indirect system call
It seems to me that the first one could be relevant to your assignment. (The second one is how to call a system call from user space.) So read it with man SYSCALL_MODULE. Or read it online.
Note that:
A minimal example for a syscall module can be found in
/usr/share/examples/kld/syscall/module/syscall.c.
That example should be enough to get you started on writing your own system call module...
Well take a look at share/examples/kld/syscall for a complete implementation as a module.
Adding a new file to teh kernel is left as an exercise for the reader.
Here is a hint: find the newest added file within kern/* subdir AND CHECK WHAT COMMITS WERE DONE TO MAKE IT COMPILE.
In fact you could have done exactly the same with syscall: FIND THE NEWEST ADDED SYSCALL AND CHECK HOW IT WAS ACHIEVED.
All this is available in svn/git repository history.
I wrote a basic character driver for beagle-bone which prints two message in 1 second interval via a workqueue and a tasklet using printk.
At first i build it as module driver, generated .ko file, load it using insmod command and the print is coming when viewed via dmesg.
Then i built as inbuilt driver and load the uImage and after bootup i checked the dmesg prints. But there is no prints.
In the .config file
CONFIG_MY_DRIVER=y
So its taken as built in driver i think.
How can i confirm whether its actually built in the final image. No error was reported while building.
Is there any additional steps to be done for loading the build in driver.
Please pardon me if i went wrong on any basics. I am really new to linux.
This means that you added it probably somewhere to Kconfig file:
"CONFIG_MY_DRIVER=y"
but, Have you added it to Makefile? It works like that, then kernel during a building an Image, takes all of this directives "CONFIG_*" and use it to build particular source files from Makefile.
Example:
cat fs/ext2/Makefile
ext2-$(CONFIG_EXT2_FS_SECURITY) += xattr_security.o
cat fs/ext2/Kconfig
config EXT2_FS_SECURITY
bool "Ext2 Security Labels"
depends on EXT2_FS_XATTR
so in this example above if your source file is xattr_security.c then you should get xattr_security.o file in fs/ext2 dir, when this is build. You should also see it if your file is build, during a compilation process.
So I'm working with ucLinux under the NXP LPC1788 processor (ARM-CortexM3, no MMU). The ucLinux port was orignally done by Emcraft Systems.
The 1788 has 512KiB of onboard flash (called eNVM) which is faster to access than the rest of memory connected via the external memory controller. Emcraft's linker script has a portion where you can relocate critical parts of the kernel to this eNVM area. I'm using 80K for the bootloader so I have 432K free to stuff with as much kernel as I can.
So the linker script, vmlinux.lds.S, has a portion that begins like this:
#ifdef CONFIG_KERNEL_IN_ENVM
_envm_loc = .;
.envm ENVM_PHYS_OFFSET + CONFIG_KERNEL_IN_ENVM_OFFSET * 1024 : {
_envm_start = .;
#if CONFIG_KERNEL_IN_ENVM_SIZE>0
__exception_text_start = .;
*(.exception.text*)
*(.exception.rodata*)
__exception_text_end = .;
SCHED_TEXT
LOCK_TEXT
KPROBES_TEXT
usr/built-in.o(.text)
usr/built-in.o(.rodata*)
init/built-in.o(.text)
init/built-in.o(.rodata*)
mm/built-in.o(.text)
mm/built-in.o(.rodata*)
...and so on. As you can see, entire subdirectories are being pulled in via their built-in.o object file.
As I get closer and closer to the end of the flash space, I'd like to have a bit more control over what gets linked here. drivers/built-in.o, for example, won't fit in the free space but if I could get drivers/usb and drivers/input here, that would help a lot.
If I modify the linker script to have just those portions, like this:
drivers/usb/built-in.o(.text)
drivers/usb/built-in.o(.rodata*)
drivers/input/built-in.o(.text)
drivers/input/built-in.o(.rodata*)
then I get duplicate symbol errors when drivers/built-in.o gets linked. I can't see where that happens exactly, so that's part of the problem I think.
So the question: Is there a way to link individual built-in.o files to different regions without linking the master .o built at the top of the directory?
I've put the whole linker file at http://pastebin.com/qcj6rHme if anyone wants to take a look.
Thanks!
If you're going to link usb and input directly, drivers/built-in.o should not include them. Modifying Kbuild to build the subdirs but not include them is a bit tricky; those two elements will have to filtered out of obj-y where drivers/built-in.o is generated -- if they aren't included in obj-y they won't get built at all.
I see that in the directory kernel/arch/arm there are a lot of board files, which I am using as reference for my i2c driver. I have the following code in a directory I made called ./mach-foo and I want to add it to the make file so my driver will work.
Here are the contents:
./mach-foo/foo-dummy.c has module init and exit and a basic i2c struct and probe, does printk's to confirm calls
$ cat ./mach-foo/Makefile
obj-m += foo_dummy.c
Now I need to know how mach-foo will get compiled or built or what ever (my understanding is limited). Looking at the makefile already in place in kernel/arch/arm/Makefile I see that other folders are added via a line similar to
machine-$(CONFIG_FOO_BAR) := foobar
I am familiar with the operation of Kconfig, and that it decideds what come with CONFIG_FOO_BAR
I was hoping that I could just hard-code a line like
machine-m :=foo does this work?
I saw that the Makefile automatically appends mach- to the name here, so are machine-m or machine-y valid?
Also, do I need := or +=?