fops question

Vermidias · 12-22-2010, 03:58 AM

I have a little question. I dont realy understand what fops does and what is it good for? Can anybody explain it for me.

static struct file_operations fops = {
.read = device_read,
.write = device_write,
.ioctl = device_ioctl,
...
};

Snark1994 · 12-22-2010, 05:45 AM

The G-man found me this

Vermidias · 12-22-2010, 07:41 AM

not really but thanks for your try. I already know what the functions inside fops does but I have no clue how a request could be made or what the kernel does with fops at initialization.

major = register_chrdev(0, "my_device", &fops);

Snark1994 · 12-22-2010, 04:05 PM

Quote:

Originally Posted by Vermidias

major = register_chrdev(0, "my_device", &fops);

Ah sorry. Is that the line from the kernel whose function you are trying to understand?

EDIT:

AHA! This seems to explain the whole process... I haven't actually read it, but skimming it seems to suggest it explains all the functions in struct which you need. The same tutorial's chapter's "Quick summary" seems to suggest that the register_chrdev() function is deprecated as of Kernel 2.6, so presumably the method they outline is more up-to-date

Vermidias · 12-23-2010, 05:35 AM

Ok if I am right fops is just an abstrakt open file that points to the functions of the driver that a userspace programm can use.

example:
i declare .open and .unlocked_ioctl in the modul
and use open() and ioctl() in a userspace program to use the functions of the modul

ok if i am right that not that hard to understand ... but what is with code like

.name = "helloworld",

is there a way to read this information from Userspace? Thank you anyway for clearing my confused mind.

Snark1994 · 12-24-2010, 12:28 AM

Yes, I think that's more or less the case.

Are you looking at a specific example of a driver? Because I was under the impression you only put pointers to functions in a file_operations struct... Obviously, you request the major/minor numbers for the device (in the driver code itself) then you pass a char* with the driver name in it, but I didn't think it was a member (if that's the right term for it) of the file_operations struct itself.