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 =======================
 The Userspace I/O HOWTO
 =======================
 
 :Author: Hans-Jürgen Koch Linux developer, Linutronix
 :Date:   2006-12-11
 
 About this document
 ===================
 
 Translations
 ------------
 
 If you know of any translations for this document, or you are interested
 in translating it, please email me hjk@hansjkoch.de.
 
 Preface
 -------
 
 For many types of devices, creating a Linux kernel driver is overkill.
 All that is really needed is some way to handle an interrupt and provide
 access to the memory space of the device. The logic of controlling the
 device does not necessarily have to be within the kernel, as the device
 does not need to take advantage of any of other resources that the
 kernel provides. One such common class of devices that are like this are
 for industrial I/O cards.
 
 To address this situation, the userspace I/O system (UIO) was designed.
 For typical industrial I/O cards, only a very small kernel module is
 needed. The main part of the driver will run in user space. This
 simplifies development and reduces the risk of serious bugs within a
 kernel module.
 
 Please note that UIO is not an universal driver interface. Devices that
 are already handled well by other kernel subsystems (like networking or
 serial or USB) are no candidates for an UIO driver. Hardware that is
 ideally suited for an UIO driver fulfills all of the following:
 
 -  The device has memory that can be mapped. The device can be
    controlled completely by writing to this memory.
 
 -  The device usually generates interrupts.
 
 -  The device does not fit into one of the standard kernel subsystems.
 
 Acknowledgments
 ---------------
 
 I'd like to thank Thomas Gleixner and Benedikt Spranger of Linutronix,
 who have not only written most of the UIO code, but also helped greatly
 writing this HOWTO by giving me all kinds of background information.
 
 Feedback
 --------
 
 Find something wrong with this document? (Or perhaps something right?) I
 would love to hear from you. Please email me at hjk@hansjkoch.de.
 
 About UIO
 =========
 
 If you use UIO for your card's driver, here's what you get:
 
 -  only one small kernel module to write and maintain.
 
 -  develop the main part of your driver in user space, with all the
    tools and libraries you're used to.
 
 -  bugs in your driver won't crash the kernel.
 
 -  updates of your driver can take place without recompiling the kernel.
 
 How UIO works
 -------------
 
 Each UIO device is accessed through a device file and several sysfs
 attribute files. The device file will be called ``/dev/uio0`` for the
 first device, and ``/dev/uio1``, ``/dev/uio2`` and so on for subsequent
 devices.
 
 ``/dev/uioX`` is used to access the address space of the card. Just use
 :c:func:`mmap()` to access registers or RAM locations of your card.
 
 Interrupts are handled by reading from ``/dev/uioX``. A blocking
 :c:func:`read()` from ``/dev/uioX`` will return as soon as an
 interrupt occurs. You can also use :c:func:`select()` on
 ``/dev/uioX`` to wait for an interrupt. The integer value read from
 ``/dev/uioX`` represents the total interrupt count. You can use this
 number to figure out if you missed some interrupts.
 
 For some hardware that has more than one interrupt source internally,
 but not separate IRQ mask and status registers, there might be
 situations where userspace cannot determine what the interrupt source
 was if the kernel handler disables them by writing to the chip's IRQ
 register. In such a case, the kernel has to disable the IRQ completely
 to leave the chip's register untouched. Now the userspace part can
 determine the cause of the interrupt, but it cannot re-enable
 interrupts. Another cornercase is chips where re-enabling interrupts is
 a read-modify-write operation to a combined IRQ status/acknowledge
 register. This would be racy if a new interrupt occurred simultaneously.
 
 To address these problems, UIO also implements a write() function. It is
 normally not used and can be ignored for hardware that has only a single
 interrupt source or has separate IRQ mask and status registers. If you
 need it, however, a write to ``/dev/uioX`` will call the
 :c:func:`irqcontrol()` function implemented by the driver. You have
 to write a 32-bit value that is usually either 0 or 1 to disable or
 enable interrupts. If a driver does not implement
 :c:func:`irqcontrol()`, :c:func:`write()` will return with
 ``-ENOSYS``.
 
 To handle interrupts properly, your custom kernel module can provide its
 own interrupt handler. It will automatically be called by the built-in
 handler.
 
 For cards that don't generate interrupts but need to be polled, there is
 the possibility to set up a timer that triggers the interrupt handler at
 configurable time intervals. This interrupt simulation is done by
 calling :c:func:`uio_event_notify()` from the timer's event
 handler.
 
 Each driver provides attributes that are used to read or write
 variables. These attributes are accessible through sysfs files. A custom
 kernel driver module can add its own attributes to the device owned by
 the uio driver, but not added to the UIO device itself at this time.
 This might change in the future if it would be found to be useful.
 
 The following standard attributes are provided by the UIO framework:
 
 -  ``name``: The name of your device. It is recommended to use the name
    of your kernel module for this.
 
 -  ``version``: A version string defined by your driver. This allows the
    user space part of your driver to deal with different versions of the
    kernel module.
 
 -  ``event``: The total number of interrupts handled by the driver since
    the last time the device node was read.
 
 These attributes appear under the ``/sys/class/uio/uioX`` directory.
 Please note that this directory might be a symlink, and not a real
 directory. Any userspace code that accesses it must be able to handle
 this.
 
 Each UIO device can make one or more memory regions available for memory
 mapping. This is necessary because some industrial I/O cards require
 access to more than one PCI memory region in a driver.
 
 Each mapping has its own directory in sysfs, the first mapping appears
 as ``/sys/class/uio/uioX/maps/map0/``. Subsequent mappings create
 directories ``map1/``, ``map2/``, and so on. These directories will only
 appear if the size of the mapping is not 0.
 
 Each ``mapX/`` directory contains four read-only files that show
 attributes of the memory:
 
 -  ``name``: A string identifier for this mapping. This is optional, the
    string can be empty. Drivers can set this to make it easier for
    userspace to find the correct mapping.
 
 -  ``addr``: The address of memory that can be mapped.
 
 -  ``size``: The size, in bytes, of the memory pointed to by addr.
 
 -  ``offset``: The offset, in bytes, that has to be added to the pointer
    returned by :c:func:`mmap()` to get to the actual device memory.
    This is important if the device's memory is not page aligned.
    Remember that pointers returned by :c:func:`mmap()` are always
    page aligned, so it is good style to always add this offset.
 
 From userspace, the different mappings are distinguished by adjusting
 the ``offset`` parameter of the :c:func:`mmap()` call. To map the
 memory of mapping N, you have to use N times the page size as your
 offset::
 
     offset = N * getpagesize();
 
 Sometimes there is hardware with memory-like regions that can not be
 mapped with the technique described here, but there are still ways to
 access them from userspace. The most common example are x86 ioports. On
 x86 systems, userspace can access these ioports using
 :c:func:`ioperm()`, :c:func:`iopl()`, :c:func:`inb()`,
 :c:func:`outb()`, and similar functions.
 
 Since these ioport regions can not be mapped, they will not appear under
 ``/sys/class/uio/uioX/maps/`` like the normal memory described above.
 Without information about the port regions a hardware has to offer, it
 becomes difficult for the userspace part of the driver to find out which
 ports belong to which UIO device.
 
 To address this situation, the new directory
 ``/sys/class/uio/uioX/portio/`` was added. It only exists if the driver
 wants to pass information about one or more port regions to userspace.
 If that is the case, subdirectories named ``port0``, ``port1``, and so
 on, will appear underneath ``/sys/class/uio/uioX/portio/``.
 
 Each ``portX/`` directory contains four read-only files that show name,
 start, size, and type of the port region:
 
 -  ``name``: A string identifier for this port region. The string is
    optional and can be empty. Drivers can set it to make it easier for
    userspace to find a certain port region.
 
 -  ``start``: The first port of this region.
 
 -  ``size``: The number of ports in this region.
 
 -  ``porttype``: A string describing the type of port.
 
 Writing your own kernel module
 ==============================
 
 Please have a look at ``uio_cif.c`` as an example. The following
 paragraphs explain the different sections of this file.
 
 struct uio_info
 ---------------
 
 This structure tells the framework the details of your driver, Some of
 the members are required, others are optional.
 
 -  ``const char *name``: Required. The name of your driver as it will
    appear in sysfs. I recommend using the name of your module for this.
 
 -  ``const char *version``: Required. This string appears in
    ``/sys/class/uio/uioX/version``.
 
 -  ``struct uio_mem mem[ MAX_UIO_MAPS ]``: Required if you have memory
    that can be mapped with :c:func:`mmap()`. For each mapping you
    need to fill one of the ``uio_mem`` structures. See the description
    below for details.
 
 -  ``struct uio_port port[ MAX_UIO_PORTS_REGIONS ]``: Required if you
    want to pass information about ioports to userspace. For each port
    region you need to fill one of the ``uio_port`` structures. See the
    description below for details.
 
 -  ``long irq``: Required. If your hardware generates an interrupt, it's
    your modules task to determine the irq number during initialization.
    If you don't have a hardware generated interrupt but want to trigger
    the interrupt handler in some other way, set ``irq`` to
    ``UIO_IRQ_CUSTOM``. If you had no interrupt at all, you could set
    ``irq`` to ``UIO_IRQ_NONE``, though this rarely makes sense.
 
 -  ``unsigned long irq_flags``: Required if you've set ``irq`` to a
    hardware interrupt number. The flags given here will be used in the
    call to :c:func:`request_irq()`.
 
 -  ``int (*mmap)(struct uio_info *info, struct vm_area_struct *vma)``:
    Optional. If you need a special :c:func:`mmap()`
    function, you can set it here. If this pointer is not NULL, your
    :c:func:`mmap()` will be called instead of the built-in one.
 
 -  ``int (*open)(struct uio_info *info, struct inode *inode)``:
    Optional. You might want to have your own :c:func:`open()`,
    e.g. to enable interrupts only when your device is actually used.
 
 -  ``int (*release)(struct uio_info *info, struct inode *inode)``:
    Optional. If you define your own :c:func:`open()`, you will
    probably also want a custom :c:func:`release()` function.
 
 -  ``int (*irqcontrol)(struct uio_info *info, s32 irq_on)``:
    Optional. If you need to be able to enable or disable interrupts
    from userspace by writing to ``/dev/uioX``, you can implement this
    function. The parameter ``irq_on`` will be 0 to disable interrupts
    and 1 to enable them.
 
 Usually, your device will have one or more memory regions that can be
 mapped to user space. For each region, you have to set up a
 ``struct uio_mem`` in the ``mem[]`` array. Here's a description of the
 fields of ``struct uio_mem``:
 
 -  ``const char *name``: Optional. Set this to help identify the memory
    region, it will show up in the corresponding sysfs node.
 
 -  ``int memtype``: Required if the mapping is used. Set this to
    ``UIO_MEM_PHYS`` if you have physical memory on your card to be
    mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated
    with :c:func:`__get_free_pages()` but not kmalloc()). There's also
    ``UIO_MEM_VIRTUAL`` for virtual memory.
 
 -  ``phys_addr_t addr``: Required if the mapping is used. Fill in the
    address of your memory block. This address is the one that appears in
    sysfs.
 
 -  ``resource_size_t size``: Fill in the size of the memory block that
    ``addr`` points to. If ``size`` is zero, the mapping is considered
    unused. Note that you *must* initialize ``size`` with zero for all
    unused mappings.
 
 -  ``void *internal_addr``: If you have to access this memory region
    from within your kernel module, you will want to map it internally by
    using something like :c:func:`ioremap()`. Addresses returned by
    this function cannot be mapped to user space, so you must not store
    it in ``addr``. Use ``internal_addr`` instead to remember such an
    address.
 
 Please do not touch the ``map`` element of ``struct uio_mem``! It is
 used by the UIO framework to set up sysfs files for this mapping. Simply
 leave it alone.
 
 Sometimes, your device can have one or more port regions which can not
 be mapped to userspace. But if there are other possibilities for
 userspace to access these ports, it makes sense to make information
 about the ports available in sysfs. For each region, you have to set up
 a ``struct uio_port`` in the ``port[]`` array. Here's a description of
 the fields of ``struct uio_port``:
 
 -  ``char *porttype``: Required. Set this to one of the predefined
    constants. Use ``UIO_PORT_X86`` for the ioports found in x86
    architectures.
 
 -  ``unsigned long start``: Required if the port region is used. Fill in
    the number of the first port of this region.
 
 -  ``unsigned long size``: Fill in the number of ports in this region.
    If ``size`` is zero, the region is considered unused. Note that you
    *must* initialize ``size`` with zero for all unused regions.
 
 Please do not touch the ``portio`` element of ``struct uio_port``! It is
 used internally by the UIO framework to set up sysfs files for this
 region. Simply leave it alone.
 
 Adding an interrupt handler
 ---------------------------
 
 What you need to do in your interrupt handler depends on your hardware
 and on how you want to handle it. You should try to keep the amount of
 code in your kernel interrupt handler low. If your hardware requires no
 action that you *have* to perform after each interrupt, then your
 handler can be empty.
 
 If, on the other hand, your hardware *needs* some action to be performed
 after each interrupt, then you *must* do it in your kernel module. Note
 that you cannot rely on the userspace part of your driver. Your
 userspace program can terminate at any time, possibly leaving your
 hardware in a state where proper interrupt handling is still required.
 
 There might also be applications where you want to read data from your
 hardware at each interrupt and buffer it in a piece of kernel memory
 you've allocated for that purpose. With this technique you could avoid
 loss of data if your userspace program misses an interrupt.
 
 A note on shared interrupts: Your driver should support interrupt
 sharing whenever this is possible. It is possible if and only if your
 driver can detect whether your hardware has triggered the interrupt or
 not. This is usually done by looking at an interrupt status register. If
 your driver sees that the IRQ bit is actually set, it will perform its
 actions, and the handler returns IRQ_HANDLED. If the driver detects
 that it was not your hardware that caused the interrupt, it will do
 nothing and return IRQ_NONE, allowing the kernel to call the next
 possible interrupt handler.
 
 If you decide not to support shared interrupts, your card won't work in
 computers with no free interrupts. As this frequently happens on the PC
 platform, you can save yourself a lot of trouble by supporting interrupt
 sharing.
 
 Using uio_pdrv for platform devices
 -----------------------------------
 
 In many cases, UIO drivers for platform devices can be handled in a
 generic way. In the same place where you define your
 ``struct platform_device``, you simply also implement your interrupt
 handler and fill your ``struct uio_info``. A pointer to this
 ``struct uio_info`` is then used as ``platform_data`` for your platform
 device.
 
 You also need to set up an array of ``struct resource`` containing
 addresses and sizes of your memory mappings. This information is passed
 to the driver using the ``.resource`` and ``.num_resources`` elements of
 ``struct platform_device``.
 
 You now have to set the ``.name`` element of ``struct platform_device``
 to ``"uio_pdrv"`` to use the generic UIO platform device driver. This
 driver will fill the ``mem[]`` array according to the resources given,
 and register the device.
 
 The advantage of this approach is that you only have to edit a file you
 need to edit anyway. You do not have to create an extra driver.
 
 Using uio_pdrv_genirq for platform devices
 ------------------------------------------
 
 Especially in embedded devices, you frequently find chips where the irq
 pin is tied to its own dedicated interrupt line. In such cases, where
 you can be really sure the interrupt is not shared, we can take the
 concept of ``uio_pdrv`` one step further and use a generic interrupt
 handler. That's what ``uio_pdrv_genirq`` does.
 
 The setup for this driver is the same as described above for
 ``uio_pdrv``, except that you do not implement an interrupt handler. The
 ``.handler`` element of ``struct uio_info`` must remain ``NULL``. The
 ``.irq_flags`` element must not contain ``IRQF_SHARED``.
 
 You will set the ``.name`` element of ``struct platform_device`` to
 ``"uio_pdrv_genirq"`` to use this driver.
 
 The generic interrupt handler of ``uio_pdrv_genirq`` will simply disable
 the interrupt line using :c:func:`disable_irq_nosync()`. After
 doing its work, userspace can reenable the interrupt by writing
 0x00000001 to the UIO device file. The driver already implements an
 :c:func:`irq_control()` to make this possible, you must not
 implement your own.
 
 Using ``uio_pdrv_genirq`` not only saves a few lines of interrupt
 handler code. You also do not need to know anything about the chip's
 internal registers to create the kernel part of the driver. All you need
 to know is the irq number of the pin the chip is connected to.
 
 When used in a device-tree enabled system, the driver needs to be
 probed with the ``"of_id"`` module parameter set to the ``"compatible"``
 string of the node the driver is supposed to handle. By default, the
 node's name (without the unit address) is exposed as name for the
 UIO device in userspace. To set a custom name, a property named
 ``"linux,uio-name"`` may be specified in the DT node.
 
 Using uio_dmem_genirq for platform devices
 ------------------------------------------
 
 In addition to statically allocated memory ranges, they may also be a
 desire to use dynamically allocated regions in a user space driver. In
 particular, being able to access memory made available through the
 dma-mapping API, may be particularly useful. The ``uio_dmem_genirq``
 driver provides a way to accomplish this.
 
 This driver is used in a similar manner to the ``"uio_pdrv_genirq"``
 driver with respect to interrupt configuration and handling.
 
 Set the ``.name`` element of ``struct platform_device`` to
 ``"uio_dmem_genirq"`` to use this driver.
 
 When using this driver, fill in the ``.platform_data`` element of
 ``struct platform_device``, which is of type
 ``struct uio_dmem_genirq_pdata`` and which contains the following
 elements:
 
 -  ``struct uio_info uioinfo``: The same structure used as the
    ``uio_pdrv_genirq`` platform data
 
 -  ``unsigned int *dynamic_region_sizes``: Pointer to list of sizes of
    dynamic memory regions to be mapped into user space.
 
 -  ``unsigned int num_dynamic_regions``: Number of elements in
    ``dynamic_region_sizes`` array.
 
 The dynamic regions defined in the platform data will be appended to the
 `` mem[] `` array after the platform device resources, which implies
 that the total number of static and dynamic memory regions cannot exceed
 ``MAX_UIO_MAPS``.
 
 The dynamic memory regions will be allocated when the UIO device file,
 ``/dev/uioX`` is opened. Similar to static memory resources, the memory
 region information for dynamic regions is then visible via sysfs at
 ``/sys/class/uio/uioX/maps/mapY/*``. The dynamic memory regions will be
 freed when the UIO device file is closed. When no processes are holding
 the device file open, the address returned to userspace is ~0.
 
 Writing a driver in userspace
 =============================
 
 Once you have a working kernel module for your hardware, you can write
 the userspace part of your driver. You don't need any special libraries,
 your driver can be written in any reasonable language, you can use
 floating point numbers and so on. In short, you can use all the tools
 and libraries you'd normally use for writing a userspace application.
 
 Getting information about your UIO device
 -----------------------------------------
 
 Information about all UIO devices is available in sysfs. The first thing
 you should do in your driver is check ``name`` and ``version`` to make
 sure you're talking to the right device and that its kernel driver has
 the version you expect.
 
 You should also make sure that the memory mapping you need exists and
 has the size you expect.
 
 There is a tool called ``lsuio`` that lists UIO devices and their
 attributes. It is available here:
 
 http://www.osadl.org/projects/downloads/UIO/user/
 
 With ``lsuio`` you can quickly check if your kernel module is loaded and
 which attributes it exports. Have a look at the manpage for details.
 
 The source code of ``lsuio`` can serve as an example for getting
 information about an UIO device. The file ``uio_helper.c`` contains a
 lot of functions you could use in your userspace driver code.
 
 mmap() device memory
 --------------------
 
 After you made sure you've got the right device with the memory mappings
 you need, all you have to do is to call :c:func:`mmap()` to map the
 device's memory to userspace.
 
 The parameter ``offset`` of the :c:func:`mmap()` call has a special
 meaning for UIO devices: It is used to select which mapping of your
 device you want to map. To map the memory of mapping N, you have to use
 N times the page size as your offset::
 
         offset = N * getpagesize();
 
 N starts from zero, so if you've got only one memory range to map, set
 ``offset = 0``. A drawback of this technique is that memory is always
 mapped beginning with its start address.
 
 Waiting for interrupts
 ----------------------
 
 After you successfully mapped your devices memory, you can access it
 like an ordinary array. Usually, you will perform some initialization.
 After that, your hardware starts working and will generate an interrupt
 as soon as it's finished, has some data available, or needs your
 attention because an error occurred.
 
 ``/dev/uioX`` is a read-only file. A :c:func:`read()` will always
 block until an interrupt occurs. There is only one legal value for the
 ``count`` parameter of :c:func:`read()`, and that is the size of a
 signed 32 bit integer (4). Any other value for ``count`` causes
 :c:func:`read()` to fail. The signed 32 bit integer read is the
 interrupt count of your device. If the value is one more than the value
 you read the last time, everything is OK. If the difference is greater
 than one, you missed interrupts.
 
 You can also use :c:func:`select()` on ``/dev/uioX``.
 
 Generic PCI UIO driver
 ======================
 
 The generic driver is a kernel module named uio_pci_generic. It can
 work with any device compliant to PCI 2.3 (circa 2002) and any compliant
 PCI Express device. Using this, you only need to write the userspace
 driver, removing the need to write a hardware-specific kernel module.
 
 Making the driver recognize the device
 --------------------------------------
 
 Since the driver does not declare any device ids, it will not get loaded
 automatically and will not automatically bind to any devices, you must
 load it and allocate id to the driver yourself. For example::
 
      modprobe uio_pci_generic
      echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id
 
 If there already is a hardware specific kernel driver for your device,
 the generic driver still won't bind to it, in this case if you want to
 use the generic driver (why would you?) you'll have to manually unbind
 the hardware specific driver and bind the generic driver, like this::
 
         echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind
         echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind
 
 You can verify that the device has been bound to the driver by looking
 for it in sysfs, for example like the following::
 
         ls -l /sys/bus/pci/devices/0000:00:19.0/driver
 
 Which if successful should print::
 
       .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic
 
 Note that the generic driver will not bind to old PCI 2.2 devices. If
 binding the device failed, run the following command::
 
       dmesg
 
 and look in the output for failure reasons.
 
 Things to know about uio_pci_generic
 ------------------------------------
 
 Interrupts are handled using the Interrupt Disable bit in the PCI
 command register and Interrupt Status bit in the PCI status register.
 All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI
 Express devices should support these bits. uio_pci_generic detects
 this support, and won't bind to devices which do not support the
 Interrupt Disable Bit in the command register.
 
 On each interrupt, uio_pci_generic sets the Interrupt Disable bit.
 This prevents the device from generating further interrupts until the
 bit is cleared. The userspace driver should clear this bit before
 blocking and waiting for more interrupts.
 
 Writing userspace driver using uio_pci_generic
 ------------------------------------------------
 
 Userspace driver can use pci sysfs interface, or the libpci library that
 wraps it, to talk to the device and to re-enable interrupts by writing
 to the command register.
 
 Example code using uio_pci_generic
 ----------------------------------
 
 Here is some sample userspace driver code using uio_pci_generic::
 
     #include <stdlib.h>
     #include <stdio.h>
     #include <unistd.h>
     #include <sys/types.h>
     #include <sys/stat.h>
     #include <fcntl.h>
     #include <errno.h>
 
     int main()
     {
         int uiofd;
         int configfd;
         int err;
         int i;
         unsigned icount;
         unsigned char command_high;
 
         uiofd = open("/dev/uio0", O_RDONLY);
         if (uiofd < 0) {
             perror("uio open:");
             return errno;
         }
         configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);
         if (configfd < 0) {
             perror("config open:");
             return errno;
         }
 
         /* Read and cache command value */
         err = pread(configfd, &command_high, 1, 5);
         if (err != 1) {
             perror("command config read:");
             return errno;
         }
         command_high &= ~0x4;
 
         for(i = 0;; ++i) {
             /* Print out a message, for debugging. */
             if (i == 0)
                 fprintf(stderr, "Started uio test driver.\n");
             else
                 fprintf(stderr, "Interrupts: %d\n", icount);
 
             /****************************************/
             /* Here we got an interrupt from the
                device. Do something to it. */
             /****************************************/
 
             /* Re-enable interrupts. */
             err = pwrite(configfd, &command_high, 1, 5);
             if (err != 1) {
                 perror("config write:");
                 break;
             }
 
             /* Wait for next interrupt. */
             err = read(uiofd, &icount, 4);
             if (err != 4) {
                 perror("uio read:");
                 break;
             }
 
         }
         return errno;
     }
 
 Generic Hyper-V UIO driver
 ==========================
 
 The generic driver is a kernel module named uio_hv_generic. It
 supports devices on the Hyper-V VMBus similar to uio_pci_generic on
 PCI bus.
 
 Making the driver recognize the device
 --------------------------------------
 
 Since the driver does not declare any device GUID's, it will not get
 loaded automatically and will not automatically bind to any devices, you
 must load it and allocate id to the driver yourself. For example, to use
 the network device class GUID::
 
      modprobe uio_hv_generic
      echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id
 
 If there already is a hardware specific kernel driver for the device,
 the generic driver still won't bind to it, in this case if you want to
 use the generic driver for a userspace library you'll have to manually unbind
 the hardware specific driver and bind the generic driver, using the device specific GUID
 like this::
 
           echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind
           echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind
 
 You can verify that the device has been bound to the driver by looking
 for it in sysfs, for example like the following::
 
         ls -l /sys/bus/vmbus/devices/ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver
 
 Which if successful should print::
 
       .../ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic
 
 Things to know about uio_hv_generic
 -----------------------------------
 
 On each interrupt, uio_hv_generic sets the Interrupt Disable bit. This
 prevents the device from generating further interrupts until the bit is
 cleared. The userspace driver should clear this bit before blocking and
 waiting for more interrupts.
 
 When host rescinds a device, the interrupt file descriptor is marked down
 and any reads of the interrupt file descriptor will return -EIO. Similar
 to a closed socket or disconnected serial device.
 
 The vmbus device regions are mapped into uio device resources:
     0) Channel ring buffers: guest to host and host to guest
     1) Guest to host interrupt signalling pages
     2) Guest to host monitor page
     3) Network receive buffer region
     4) Network send buffer region
 
 If a subchannel is created by a request to host, then the uio_hv_generic
 device driver will create a sysfs binary file for the per-channel ring buffer.
 For example::
 
         /sys/bus/vmbus/devices/3811fe4d-0fa0-4b62-981a-74fc1084c757/channels/21/ring
 
 Further information
 ===================
 
 -  `OSADL homepage. <http://www.osadl.org>`_
 
 -  `Linutronix homepage. <http://www.linutronix.de>`_

This page was automatically generated by the 2.1.0 LXR engine. The LXR team