I'm seeing something REALLY weird that I hope someone can explain.
Upon module insertion, I do a bus_for_each_dev to find my device if it's
already plugged in, and note it's location on the bus.
Using that info, I then open it via filp_open, and grab it's ioctl handler
address like this:
typedef int(theirIOCTL)(struct inode *, struct file *, unsigned int,
unsigned long);
static theirIOCTL *oldIoctl;
// Get the original IOCTL function
oldIoctl = file->f_op->ioctl;
I print out the address I get, and when cross checked with kallsyms, it
shows that it belongs to usbfs_ioctl. (As expected).
I then call it a couple of times to take control of the device:
// Send the disconnect command (building of the command buffer omitted here)
retVal = oldIoctl(file->f_dentry->d_inode, file, IOCTL_USB_IOCTL, (unsigned
long)&command);
and
// Send the CLAIM command
retVal = oldIoctl(file->f_dentry->d_inode, file, IOCTL_USB_CLAIMINTF,
(unsigned long)&interface);
Both of these work FINE, telling me that my pointer to the function works.
Then, I register MY fops, which contains my ioctl handler:
// This function gets called when someone calls IOCTL on a USBFS device.
int my_usbdev_ioctl(struct inode *inode, struct file *file, unsigned int
cmd, unsigned long arg)
and when a libusb based app makes ioctl calls, I catch them in my function
as expected.
I print out the inode's i_ino, and it matches what I see on the open calls,
so that's a sanity check, I print out the name from the file pointer, and it
matches what I expect, and my switch on "cmd" doesn't hit the "default"
case, showing me that the data that I'm getting is in the correct order, and
that calling conventions are OK.
The problem is, I only want to handle a couple of IOCTLs. The rest, I want
to pass along to the regular handler like this:
// Call the original handler
ret = oldIoctl(inode, file, cmd, arg);
This, of course calls usbfs_ioctl. And then, promptly crashes. On this
line:
struct dev_state *ps = file->private_data;
struct usb_device *dev = ps->dev; // <---- crashes here
Upon further investigation, I've determined that the REAL issue is that
file->private_data is NULL.
I added this check in my_usbdev_ioctl:
// This should be a ptr to a usb_device struct.
if(file->private_data == NULL)
{
printk("private data is NULL!\n");
return 0;
}
And it gets called EVERYTIME an ioctl is issued after I take control.
What am I doing wrong?
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