Easiest way to read from device inside another kernel driver

ineya · 06-23-2008, 08:21 AM

I have some data available in /dev/mtd/0ro. I have no problem to get this data from userspace by opening this device and reading from it. But I need to get this data also within one kernel driver.

What is the easiest way I can do this?
What should I watch for?

Thank you.

Mr. C. · 06-25-2008, 07:05 PM

Device drivers manage their own data; unless there is a standard kernel-callable API for a given class of driver, your out of luck. It would be very bad for one device driver to go poking around the data of another device driver.

This can be done from userspace, because the driver provides data via ioctl, or other well-known interface.

What exactly are you trying to get or accomplish ?

ineya · 06-26-2008, 10:15 AM

So far I googled, that my best choice is to rely on EXPORT_SYMBOL and use some of the functionality from mtd driver.

I'm working on project dealing with embedded devices, and I need to change one kernel driver behavior based on hardware type. The hardware type is written on flash of the device, so I need to read it and based on this information I'll make some processing in another kernel driver.

Mr. C. · 06-26-2008, 11:54 AM

Again, its hard to give you a direct answer to a general question. If that is your only option, then you can certainly go munging around the dirty data structures of some driver's data. Use whatever acceptable means you can, and then only as a last resort do the reverse engineering. But you'll have to live with the consequences.

EXPORT_SYMBOL won't help you with a private data structure inside a driver; if it has no intention of making that data public, all bets are off.

dave201 · 06-26-2008, 01:32 PM

how about pipemill? sh script a wrapper around the /dev's and then do some while loops with |

ineya · 06-27-2008, 01:07 AM

I think, that my last post wasn't so general, but OK, I can try to make it more concrete.
The driver for st7529 (32 Gray Scale Dot Matrix LCD Controller/Driver
) needs to set resolution, startLine, endLine,.. for frame buffer in st7529_init(). But these settings depends on hardware type. And to get this information I need to access flash memory.

Also I got suggestion to use filp_open, what do you think about this?

Code:

struct file *f = filp_open("/dev/mtd/0ro", O_RDONLY, 0444);
 
/* seek to the beginning, not sure if this is really needed. */
vfs_llseek(f, 0, 0);
 
/* read some data */
vfs_read(f, buffer, buffer_size, &f->f_pos);
 
/* do something with the data ... */
 
/* close the file pointed to by f. */
filp_close(f, 0);

ineya · 06-27-2008, 06:30 AM

Supposing this works, it could be easy way to read from that device:
http://linux.derkeiler.com/Mailing-L...3-10/3671.html

jayacharan · 09-06-2008, 06:22 AM

Quote:

Originally Posted by Mr. C.

Device drivers manage their own data; unless there is a standard kernel-callable API for a given class of driver, your out of luck. It would be very bad for one device driver to go poking around the data of another device driver.

This can be done from userspace, because the driver provides data via ioctl, or other well-known interface.

What exactly are you trying to get or accomplish ?

hi,

i'm new to linux device drivers i would like to read the book

"Essential Linux Device Drivers by Robbins " pdf

If u hav this book plz send it to my mail id:

jayacharan.rampog@gmail.com

and any suggestions to write dd.

thanks in advance,

Jayacharan.

Mr. C. · 09-06-2008, 10:34 AM

You are asking in a public for for someone to send you an un-purchased copy of an ebook? Have you no scruples?

You can purchase it here: http://safari.oreilly.com/9780132396554