pci_request_region_exclusive (9)

int pci_request_region_exclusive(struct pci_dev * pdev, int bar, const char * res_name);

pdev

PCI device whose resources are to be reserved

bar

BAR to be reserved

res_name

Name to be associated with resource.

Mark the PCI region associated with PCI device pdev BR bar as being reserved by owner res_name. Do not access any address inside the PCI regions unless this call returns successfully.

Returns 0 on success, or EBUSY on error. A warning message is also printed on failure.

The key difference that _exclusive makes it that userspace is explicitly not allowed to map the resource via /dev/mem or sysfs.