A device can support line interrupts, MSI (Message Signaled Interrupts) and MSI-X (Message Signaled Interrupts - Extended). Some devices does support only line interrupts, some support line interrupts and MSI, and some devices support all three types. Operating systems provide functions using which it is possible to find some of the information in the hardware populated by vendors based on standards. Function pci_msi_count() returns the maximum number of supported MSI messages. This maximum number is hardware specific. Some hardware supports upto 32 MSI messages, where as some hardwares supports only 8 and some hardwares doesn't have support for MSI at all. If MSI is not supported by a hardware, this function returns 0. We can also use pci_msi_count() to determine a PCI device's MSI support runtime. If the device has support for MSI, return value from pci_msi_count() will be a number greater than 0.