Go Premium for a chance to win a PS4. Enter to Win

x
  • Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 418
  • Last Modified:

Easiest way to read from device inside another kernel driver

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 some kernel driver.

What is the easiest way I can do this?
What should I watch for?
Any hints/examples are welcomed.

Thank you.
0
ineya
Asked:
ineya
  • 3
  • 2
2 Solutions
 
kolrabiCommented:
I never tried it, but this should work:

1. Get a file pointer for the device you want to open using filp_open.
2. Use the vfs_* functions to operate on the file. (See your linux/fs.h for syntax)
3. Close the file using filp_close.

Something like the snippet (which lacks any error checking).

HTH :)
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);

Open in new window

0
 
ineyaAuthor Commented:
Another solution seems to be to rely on EXPORT_SYMBOL of mtd driver:
http://linux.derkeiler.com/Mailing-Lists/Kernel/2003-10/3671.html
0
 
ineyaAuthor Commented:
@kolrabi: Do you know if there is some documentation for that filp_open, vfs_read? I'm failed trying to google it.
0
 
kolrabiCommented:
As far as I can tell from the header files, the syntax for filp_open() is the same as for open() but returning a "struct file" pointer instead of a file descriptor.

The syntax for the vfs_* functions seems to be the same as the syntax for the callbacks specified in the f_op member (struct file_operations) of the file pointer.

The file struct and the file_operations struct are explained in a little bit more detail here:

http://www.moses.uklinux.net/patches/lki-3.html#ss3.4

0
 
ineyaAuthor Commented:
I didn't get to implement it, but it looks promising, thanks for the effort.
0

Featured Post

Concerto's Cloud Advisory Services

Want to avoid the missteps to gaining all the benefits of the cloud? Learn more about the different assessment options from our Cloud Advisory team.

  • 3
  • 2
Tackle projects and never again get stuck behind a technical roadblock.
Join Now