struct real_dev->f_op would not be made available to the userspace. It's for target/real device bookkeeping. On Mon, Feb 2, 2015 at 4:02 PM, <Valdis.Kletnieks@vt.edu> wrote:

On Mon, 02 Feb 2015 15:24:37 -0600, riya khanna said:

...

Hi,

I'm writing a device driver to to provide a wrapper device around a real device. Is it acceptable to do the following:

wrapper_dev_open(flags) { // do additional bookkeeping real_dev_filp = filp_open(real_device_node_path, flags); }

wrapper_dev_mmap(mmap_parameters) { // do additional checks return real_dev_filp->f_op->mmap(mmap_parameters); }

wrapper_dev_ioctl(ioctl_parameters) { // do additional checks return real_dev_filp->f_op->ioctl(ioctl_parameters); }

Is it safe to do something like this?

Probably not. If you return a struct real_dev->f_op then any further calls will vector through that structure, totally unseen to your wrapper, which means you won't be able to provide whatever added-value extras the wrapper is trying to do (in other words, your wrapper ends up not doing anything).

The real fun starts when something calls real->f_op->close() out from under you... :)