[openib-general] IB Driver Initialization of FMR methods

[Roland Dreier]

>>>>> "Tom" == Tom Tucker <tom at ammasso.com> writes:

    Tom> I've noticed that in the IB driver, the FMR methods are not
    Tom> initialized if the XX_FLAG_FRM bit is not set in the device
    Tom> structure. My assumption at this point is that these methods
    Tom> are not present if they are not supported by the device.

    Tom> What's confusing is that the verbs do not check if the
    Tom> function ptr is null when involking the underlying method. I
    Tom> would have expected, that a method would be initialized that
    Tom> returned ENOSYS in this case. Any explanation as to the
    Tom> intended design point for FMR initialization would be greatly
    Tom> appreciated.

I think you must have looked in the wrong place.  In
drivers/infiniband/core/verbs.c, ib_alloc_fmr() starts with:

	struct ib_fmr *ib_alloc_fmr(struct ib_pd *pd,
				    int mr_access_flags,
				    struct ib_fmr_attr *fmr_attr)
	{
		struct ib_fmr *fmr;
	
		if (!pd->device->alloc_fmr)
			return ERR_PTR(-ENOSYS);

so if alloc_fmr is not set, the caller will get -ENOSYS.

We do assume that if the device implements alloc_fmr(), it will
implement the other FMR methods.  This isn't enforced by any code,
since it doesn't seem worth checking for something that is an obvious
bug, and that will cause an immediate and easy-to-diagnose oops.

 - R.