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A jump-start tutorial on writing a Linux PCI device driver. Originally tested with QEMU v1. Also tested with upstream QEMU v1. References to header files and other sources, e. First things first, it must be emphasized that virtual platforms are not a replacement for physical hardware.
Components of a virtual platform can also be easily added, extended or replaced. This device was selected for a number of reasons including its simplicity and framework that facilitates interfacing and testing with external code on the VM host. This framework emulates MMIO access on a physical device: The ivshmem framework also features a mechanism that allows other ivshmem- enabled guests or some other stand-alone program on the host to send IRQs to the VM by way of the eventfd 2 mechanism.
To view the list of supported devices for a given machine architecture, run for instance:. The ivshmem device emulates a PCI device. The legacy ivshmem device. This device supports two configurations: However, it is supported for backward compatibility. In fact, the device driver test instructions presented in this tutorial still rely on this backward compatibility. The -device ivshmem-plain shared-memory-only device.
This device does not support IRQs at all. The instructions in that section were performed on a:. The legacy -device ivshmem or the -device ivshmem-plain command line switches presented above can be used:. The object will be created if it does not exist and truncated to the specified size.
If the object already exists, QEMU will not resize it but will fast and easy online binary option full bwana that the size of the object matches the size given with the value of the size property. The interpretation of the size property remains the same across the different ivshmem devices.
The default units are in megabytes. The value specified against size must be a power of two; a restriction of PCI memory regions. The instructions presented in this entry have been tested with upstream QEMU v1. Fast and easy online binary option full bwana tuple at the beginning of each entry is interpreted as bus: The following lspci output displays the PCI tree layout.
A PCI domain can host upto buses. Each bus can have a maximum of 32 devices, and each device can feature upto 8 functions. For example, PCI device number 01 has 3 functions. The ivshmem device corresponds to fast and easy online binary option full bwana The vendor then allocates DeviceID values for its devices. Vendor Fast and easy online binary option full bwana Hat, Inc. The ivshmem device has been allocated 1af4: SVendor and SubsystemID i. SDevice values are embedded in the PCI configuration space:.
As shown above, the first two bytes contain the VendorID followed by the DeviceID to form a unique bit identifier for the device. However, note that the PCI configuration space is little endian, i. In this respect, the 3 byte-wide Class Code register starts at offset 0x09, while the bit Subsystem VendorID and SubsystemID registers start at offsets 0x2c and 0x2e, respectively.
Organisation of the registers in the configuration space imposes a specific record structure on the first bytes PCI supports byte config space; PCI-X 2. The config space is divided into a fast and easy online binary option full bwana header region and a device dependent region. The first 64 bytes form the standardized header region.
The Class Code identifies the generic function of the device, and in some cases, a specific register-level programming interface. The byte at offset 0x0b is a base class code which broadly classifies the type of function the device performs. The byte at offset 0x0a is a sub-class code which identifies more specifically the function of the device. The byte at offset 0x09 identifies a specific register-level programming interface if any so that device independent software can interact with the device.
For the ivshmem device, the base class and sub-class codes are:. A bit BAR consumes two consecutive bit locations. Registers are typically used for device control or for obtaining device status.
Device memory, on the other hand, could be used to support, say, a framebuffer for video. Further, a MMIO region may also be prefetchablei. In this case, devices hardwire bit 3 of the BAR to 1. Otherwise, for non-prefetchable mappings, this bit remains reset. For bits 2 and 1, a value of 00 means that the device's memory mapping can be located anywhere in a bit address space; a value of 10 implies a relocation anywhere within a bit address space.
For fast and easy online binary option full bwana, compare the following instances of a graphics device configuration space output:. At minimum, a device will implement at least one BAR for device control operations. Operations on the ivshmem device are similar to those on a frame buffer device. In QEMU, the monitor console interface can also be used to obtain similar info These registers are used for device control and status checks.
QEMU's memory allocation for these registers remains within the private virtual address space of the VM instance and, therefore, these registers are not accessible from a separate process address space. For purposes of this guide, only the first two registers are used. This region can be shared between guests or some other external code on the host. The more interesting details fast and easy online binary option full bwana the ivshmem configuration space of this QEMU instance can be summarised as:.
A userland program can still access a PCI device's configuration space, and regions associated with its BARs, even when the device's driver is absent, or has not yet been loaded. This can be quite convenient for prelimary checks or troubleshooting. Nevertheless, functionality with this mode of device access remains very limited.
The driver name must be unique among all PCI drivers in the kernel. Essential callback methods are probe and remove. Invoking this function initiates probing for the device in the underlying PCI layer. This function returns 0 upon success. Otherwise, if something went wrong, an negative value error code is returned.
Eventually, it invokes the device driver's probe callback. The probe method typically handles the following fast and easy online binary option full bwana steps:. If called for the first time, this function enables the device. It wakes up the device if it was suspended. Otherwise, it simply increments the usage count for the device. It returns 0 on success; a negative value error code otherwise.
Do not access any address inside the PCI regions unless this call returns successfully. To get access to the complete BAR without checking for its length, specify 0.
There exist other less generic mapping functions, e. Pin-based interrupts will be covered here 3. Overlooking device specific semantics such as setting a certain interrupt mask control register, registering a pin-based interrupt is simply a matter of calling:. This function enables the device's interrupt capability. Pin-based interrupts are often shared amongst several devices and so the kernel must call each interrupt handler associated with the interrupt.
This function does not return until the PCI core invokes the driver's remove callback method. With respect to program build, the usual runtime considerations, particularly the guest environment C library and kernel version, must be observed 2.
The simplest and most straightforward approach would be to build the sources in the VM environment. Operations on the ivshmem device are similar to those on graphics memory. While read 2write 2lseek 2ioctl 2etc may be used by a userspace application to access the device's MMIO data region via the corresponding device driver file operationsmmap 2 is used here.
The mmap 2 system call memory maps the ivshmem device's MMIO data region into an area of the calling process' virtual address space. Upon successful mmap 2 completion, operations on this mapped memory region become a simple matter of pointer referencing. In other words, the userspace application is given direct access to the ivshmem MMIO data region. The overhead context switching, kernel-user buffer copies, etc associated with readwriteioctletc operations is now avoided.
This translates to a dramatic improvement in throughput for high performance applications. The code presented here implements the conventional mmap file operation method. A discussion on mmaping device MMIO regions can be found here. To test IRQ generation and handling with an ivshmem device, services of an ivshmem server will be required.
This program will provide centralized management for the ivshmem -enabled QEMU VMs or any other standalone ivshmem client programs on the host. Essentially, the ivshmem server will manage file-descriptor information for the UNIX domain socket Fast and easy online binary option full bwana, eventfd 2 notification and the common region shared among the clients.