How do cdev and its associated file operation work? - linux-kernel

Question

Actually working on a PCI driver.
I have two PCIe cards with same device ID and vendor ID.
So to make a difference, I assign these two cards with two different MINOR numbers.
//request for device numbers
error = alloc_chrdev_region(&devt, 0, cards_found, DEVICE_NAME);
if (error == 0)
{
major = MAJOR(devt);
printk(KERN_INFO "(drv_init): MAJOR number is %d\n", major);
printk(KERN_INFO "(drv_init): MINOR number range from 0 to %d\n", cards_found-1);
cdevs = cdev_alloc();
cdevs->owner = THIS_MODULE;
cdev_init(cdevs, fops);
for(i=0;i<cards_found,i++)
{
devt = MKDEV(major, i);
error = cdev_add(cdevs, devt, 1);
if (error == 0)
{
printk(KERN_INFO "(drv_init): cdev_add success for minor number: %d", i);
}
else
{
printk(KERN_ALERT "(drv_init): cdev_add failed for minor number: %d,error code: %d, exit driver\n", i, error);
devt = MKDEV(major, 0);
unregister_chrdev_region(devt, cards_found);
pci_unregister_driver(&my_pci_driver);
return(error);
}
}
} `
I'm doing this because all docs I found on internet suggests that one MINOR number for one device.
But I can't understand how could OS know which card is targeted when I do a fops_open, since the fops is bundled to all devices.
Need your help, Thx everyone.
PS: fops = file operations

Answer 1

Signature of .open operation is
int open(struct inode* inode, struct file* file)
Minor number of device opened can be obtained via
iminor(inode)
Other file operations also may obtain device number using file->f_inode as inode.
Alternatively, .open may store some device-specific data in file->f_private, and other operations may access them that way.