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1=======================2The Userspace I/O HOWTO3=======================4 5:Author: Hans-Jürgen Koch Linux developer, Linutronix6:Date: 2006-12-117 8About this document9===================10 11Translations12------------13 14If you know of any translations for this document, or you are interested15in translating it, please email me hjk@hansjkoch.de.16 17Preface18-------19 20For many types of devices, creating a Linux kernel driver is overkill.21All that is really needed is some way to handle an interrupt and provide22access to the memory space of the device. The logic of controlling the23device does not necessarily have to be within the kernel, as the device24does not need to take advantage of any of other resources that the25kernel provides. One such common class of devices that are like this are26for industrial I/O cards.27 28To address this situation, the userspace I/O system (UIO) was designed.29For typical industrial I/O cards, only a very small kernel module is30needed. The main part of the driver will run in user space. This31simplifies development and reduces the risk of serious bugs within a32kernel module.33 34Please note that UIO is not an universal driver interface. Devices that35are already handled well by other kernel subsystems (like networking or36serial or USB) are no candidates for an UIO driver. Hardware that is37ideally suited for an UIO driver fulfills all of the following:38 39- The device has memory that can be mapped. The device can be40 controlled completely by writing to this memory.41 42- The device usually generates interrupts.43 44- The device does not fit into one of the standard kernel subsystems.45 46Acknowledgments47---------------48 49I'd like to thank Thomas Gleixner and Benedikt Spranger of Linutronix,50who have not only written most of the UIO code, but also helped greatly51writing this HOWTO by giving me all kinds of background information.52 53Feedback54--------55 56Find something wrong with this document? (Or perhaps something right?) I57would love to hear from you. Please email me at hjk@hansjkoch.de.58 59About UIO60=========61 62If you use UIO for your card's driver, here's what you get:63 64- only one small kernel module to write and maintain.65 66- develop the main part of your driver in user space, with all the67 tools and libraries you're used to.68 69- bugs in your driver won't crash the kernel.70 71- updates of your driver can take place without recompiling the kernel.72 73How UIO works74-------------75 76Each UIO device is accessed through a device file and several sysfs77attribute files. The device file will be called ``/dev/uio0`` for the78first device, and ``/dev/uio1``, ``/dev/uio2`` and so on for subsequent79devices.80 81``/dev/uioX`` is used to access the address space of the card. Just use82:c:func:`mmap()` to access registers or RAM locations of your card.83 84Interrupts are handled by reading from ``/dev/uioX``. A blocking85:c:func:`read()` from ``/dev/uioX`` will return as soon as an86interrupt occurs. You can also use :c:func:`select()` on87``/dev/uioX`` to wait for an interrupt. The integer value read from88``/dev/uioX`` represents the total interrupt count. You can use this89number to figure out if you missed some interrupts.90 91For some hardware that has more than one interrupt source internally,92but not separate IRQ mask and status registers, there might be93situations where userspace cannot determine what the interrupt source94was if the kernel handler disables them by writing to the chip's IRQ95register. In such a case, the kernel has to disable the IRQ completely96to leave the chip's register untouched. Now the userspace part can97determine the cause of the interrupt, but it cannot re-enable98interrupts. Another cornercase is chips where re-enabling interrupts is99a read-modify-write operation to a combined IRQ status/acknowledge100register. This would be racy if a new interrupt occurred simultaneously.101 102To address these problems, UIO also implements a write() function. It is103normally not used and can be ignored for hardware that has only a single104interrupt source or has separate IRQ mask and status registers. If you105need it, however, a write to ``/dev/uioX`` will call the106:c:func:`irqcontrol()` function implemented by the driver. You have107to write a 32-bit value that is usually either 0 or 1 to disable or108enable interrupts. If a driver does not implement109:c:func:`irqcontrol()`, :c:func:`write()` will return with110``-ENOSYS``.111 112To handle interrupts properly, your custom kernel module can provide its113own interrupt handler. It will automatically be called by the built-in114handler.115 116For cards that don't generate interrupts but need to be polled, there is117the possibility to set up a timer that triggers the interrupt handler at118configurable time intervals. This interrupt simulation is done by119calling :c:func:`uio_event_notify()` from the timer's event120handler.121 122Each driver provides attributes that are used to read or write123variables. These attributes are accessible through sysfs files. A custom124kernel driver module can add its own attributes to the device owned by125the uio driver, but not added to the UIO device itself at this time.126This might change in the future if it would be found to be useful.127 128The following standard attributes are provided by the UIO framework:129 130- ``name``: The name of your device. It is recommended to use the name131 of your kernel module for this.132 133- ``version``: A version string defined by your driver. This allows the134 user space part of your driver to deal with different versions of the135 kernel module.136 137- ``event``: The total number of interrupts handled by the driver since138 the last time the device node was read.139 140These attributes appear under the ``/sys/class/uio/uioX`` directory.141Please note that this directory might be a symlink, and not a real142directory. Any userspace code that accesses it must be able to handle143this.144 145Each UIO device can make one or more memory regions available for memory146mapping. This is necessary because some industrial I/O cards require147access to more than one PCI memory region in a driver.148 149Each mapping has its own directory in sysfs, the first mapping appears150as ``/sys/class/uio/uioX/maps/map0/``. Subsequent mappings create151directories ``map1/``, ``map2/``, and so on. These directories will only152appear if the size of the mapping is not 0.153 154Each ``mapX/`` directory contains four read-only files that show155attributes of the memory:156 157- ``name``: A string identifier for this mapping. This is optional, the158 string can be empty. Drivers can set this to make it easier for159 userspace to find the correct mapping.160 161- ``addr``: The address of memory that can be mapped.162 163- ``size``: The size, in bytes, of the memory pointed to by addr.164 165- ``offset``: The offset, in bytes, that has to be added to the pointer166 returned by :c:func:`mmap()` to get to the actual device memory.167 This is important if the device's memory is not page aligned.168 Remember that pointers returned by :c:func:`mmap()` are always169 page aligned, so it is good style to always add this offset.170 171From userspace, the different mappings are distinguished by adjusting172the ``offset`` parameter of the :c:func:`mmap()` call. To map the173memory of mapping N, you have to use N times the page size as your174offset::175 176 offset = N * getpagesize();177 178Sometimes there is hardware with memory-like regions that can not be179mapped with the technique described here, but there are still ways to180access them from userspace. The most common example are x86 ioports. On181x86 systems, userspace can access these ioports using182:c:func:`ioperm()`, :c:func:`iopl()`, :c:func:`inb()`,183:c:func:`outb()`, and similar functions.184 185Since these ioport regions can not be mapped, they will not appear under186``/sys/class/uio/uioX/maps/`` like the normal memory described above.187Without information about the port regions a hardware has to offer, it188becomes difficult for the userspace part of the driver to find out which189ports belong to which UIO device.190 191To address this situation, the new directory192``/sys/class/uio/uioX/portio/`` was added. It only exists if the driver193wants to pass information about one or more port regions to userspace.194If that is the case, subdirectories named ``port0``, ``port1``, and so195on, will appear underneath ``/sys/class/uio/uioX/portio/``.196 197Each ``portX/`` directory contains four read-only files that show name,198start, size, and type of the port region:199 200- ``name``: A string identifier for this port region. The string is201 optional and can be empty. Drivers can set it to make it easier for202 userspace to find a certain port region.203 204- ``start``: The first port of this region.205 206- ``size``: The number of ports in this region.207 208- ``porttype``: A string describing the type of port.209 210Writing your own kernel module211==============================212 213Please have a look at ``uio_cif.c`` as an example. The following214paragraphs explain the different sections of this file.215 216struct uio_info217---------------218 219This structure tells the framework the details of your driver, Some of220the members are required, others are optional.221 222- ``const char *name``: Required. The name of your driver as it will223 appear in sysfs. I recommend using the name of your module for this.224 225- ``const char *version``: Required. This string appears in226 ``/sys/class/uio/uioX/version``.227 228- ``struct uio_mem mem[ MAX_UIO_MAPS ]``: Required if you have memory229 that can be mapped with :c:func:`mmap()`. For each mapping you230 need to fill one of the ``uio_mem`` structures. See the description231 below for details.232 233- ``struct uio_port port[ MAX_UIO_PORTS_REGIONS ]``: Required if you234 want to pass information about ioports to userspace. For each port235 region you need to fill one of the ``uio_port`` structures. See the236 description below for details.237 238- ``long irq``: Required. If your hardware generates an interrupt, it's239 your modules task to determine the irq number during initialization.240 If you don't have a hardware generated interrupt but want to trigger241 the interrupt handler in some other way, set ``irq`` to242 ``UIO_IRQ_CUSTOM``. If you had no interrupt at all, you could set243 ``irq`` to ``UIO_IRQ_NONE``, though this rarely makes sense.244 245- ``unsigned long irq_flags``: Required if you've set ``irq`` to a246 hardware interrupt number. The flags given here will be used in the247 call to :c:func:`request_irq()`.248 249- ``int (*mmap)(struct uio_info *info, struct vm_area_struct *vma)``:250 Optional. If you need a special :c:func:`mmap()`251 function, you can set it here. If this pointer is not NULL, your252 :c:func:`mmap()` will be called instead of the built-in one.253 254- ``int (*open)(struct uio_info *info, struct inode *inode)``:255 Optional. You might want to have your own :c:func:`open()`,256 e.g. to enable interrupts only when your device is actually used.257 258- ``int (*release)(struct uio_info *info, struct inode *inode)``:259 Optional. If you define your own :c:func:`open()`, you will260 probably also want a custom :c:func:`release()` function.261 262- ``int (*irqcontrol)(struct uio_info *info, s32 irq_on)``:263 Optional. If you need to be able to enable or disable interrupts264 from userspace by writing to ``/dev/uioX``, you can implement this265 function. The parameter ``irq_on`` will be 0 to disable interrupts266 and 1 to enable them.267 268Usually, your device will have one or more memory regions that can be269mapped to user space. For each region, you have to set up a270``struct uio_mem`` in the ``mem[]`` array. Here's a description of the271fields of ``struct uio_mem``:272 273- ``const char *name``: Optional. Set this to help identify the memory274 region, it will show up in the corresponding sysfs node.275 276- ``int memtype``: Required if the mapping is used. Set this to277 ``UIO_MEM_PHYS`` if you have physical memory on your card to be278 mapped. Use ``UIO_MEM_LOGICAL`` for logical memory (e.g. allocated279 with :c:func:`__get_free_pages()` but not kmalloc()). There's also280 ``UIO_MEM_VIRTUAL`` for virtual memory.281 282- ``phys_addr_t addr``: Required if the mapping is used. Fill in the283 address of your memory block. This address is the one that appears in284 sysfs.285 286- ``resource_size_t size``: Fill in the size of the memory block that287 ``addr`` points to. If ``size`` is zero, the mapping is considered288 unused. Note that you *must* initialize ``size`` with zero for all289 unused mappings.290 291- ``void *internal_addr``: If you have to access this memory region292 from within your kernel module, you will want to map it internally by293 using something like :c:func:`ioremap()`. Addresses returned by294 this function cannot be mapped to user space, so you must not store295 it in ``addr``. Use ``internal_addr`` instead to remember such an296 address.297 298Please do not touch the ``map`` element of ``struct uio_mem``! It is299used by the UIO framework to set up sysfs files for this mapping. Simply300leave it alone.301 302Sometimes, your device can have one or more port regions which can not303be mapped to userspace. But if there are other possibilities for304userspace to access these ports, it makes sense to make information305about the ports available in sysfs. For each region, you have to set up306a ``struct uio_port`` in the ``port[]`` array. Here's a description of307the fields of ``struct uio_port``:308 309- ``char *porttype``: Required. Set this to one of the predefined310 constants. Use ``UIO_PORT_X86`` for the ioports found in x86311 architectures.312 313- ``unsigned long start``: Required if the port region is used. Fill in314 the number of the first port of this region.315 316- ``unsigned long size``: Fill in the number of ports in this region.317 If ``size`` is zero, the region is considered unused. Note that you318 *must* initialize ``size`` with zero for all unused regions.319 320Please do not touch the ``portio`` element of ``struct uio_port``! It is321used internally by the UIO framework to set up sysfs files for this322region. Simply leave it alone.323 324Adding an interrupt handler325---------------------------326 327What you need to do in your interrupt handler depends on your hardware328and on how you want to handle it. You should try to keep the amount of329code in your kernel interrupt handler low. If your hardware requires no330action that you *have* to perform after each interrupt, then your331handler can be empty.332 333If, on the other hand, your hardware *needs* some action to be performed334after each interrupt, then you *must* do it in your kernel module. Note335that you cannot rely on the userspace part of your driver. Your336userspace program can terminate at any time, possibly leaving your337hardware in a state where proper interrupt handling is still required.338 339There might also be applications where you want to read data from your340hardware at each interrupt and buffer it in a piece of kernel memory341you've allocated for that purpose. With this technique you could avoid342loss of data if your userspace program misses an interrupt.343 344A note on shared interrupts: Your driver should support interrupt345sharing whenever this is possible. It is possible if and only if your346driver can detect whether your hardware has triggered the interrupt or347not. This is usually done by looking at an interrupt status register. If348your driver sees that the IRQ bit is actually set, it will perform its349actions, and the handler returns IRQ_HANDLED. If the driver detects350that it was not your hardware that caused the interrupt, it will do351nothing and return IRQ_NONE, allowing the kernel to call the next352possible interrupt handler.353 354If you decide not to support shared interrupts, your card won't work in355computers with no free interrupts. As this frequently happens on the PC356platform, you can save yourself a lot of trouble by supporting interrupt357sharing.358 359Using uio_pdrv for platform devices360-----------------------------------361 362In many cases, UIO drivers for platform devices can be handled in a363generic way. In the same place where you define your364``struct platform_device``, you simply also implement your interrupt365handler and fill your ``struct uio_info``. A pointer to this366``struct uio_info`` is then used as ``platform_data`` for your platform367device.368 369You also need to set up an array of ``struct resource`` containing370addresses and sizes of your memory mappings. This information is passed371to the driver using the ``.resource`` and ``.num_resources`` elements of372``struct platform_device``.373 374You now have to set the ``.name`` element of ``struct platform_device``375to ``"uio_pdrv"`` to use the generic UIO platform device driver. This376driver will fill the ``mem[]`` array according to the resources given,377and register the device.378 379The advantage of this approach is that you only have to edit a file you380need to edit anyway. You do not have to create an extra driver.381 382Using uio_pdrv_genirq for platform devices383------------------------------------------384 385Especially in embedded devices, you frequently find chips where the irq386pin is tied to its own dedicated interrupt line. In such cases, where387you can be really sure the interrupt is not shared, we can take the388concept of ``uio_pdrv`` one step further and use a generic interrupt389handler. That's what ``uio_pdrv_genirq`` does.390 391The setup for this driver is the same as described above for392``uio_pdrv``, except that you do not implement an interrupt handler. The393``.handler`` element of ``struct uio_info`` must remain ``NULL``. The394``.irq_flags`` element must not contain ``IRQF_SHARED``.395 396You will set the ``.name`` element of ``struct platform_device`` to397``"uio_pdrv_genirq"`` to use this driver.398 399The generic interrupt handler of ``uio_pdrv_genirq`` will simply disable400the interrupt line using :c:func:`disable_irq_nosync()`. After401doing its work, userspace can reenable the interrupt by writing4020x00000001 to the UIO device file. The driver already implements an403:c:func:`irq_control()` to make this possible, you must not404implement your own.405 406Using ``uio_pdrv_genirq`` not only saves a few lines of interrupt407handler code. You also do not need to know anything about the chip's408internal registers to create the kernel part of the driver. All you need409to know is the irq number of the pin the chip is connected to.410 411When used in a device-tree enabled system, the driver needs to be412probed with the ``"of_id"`` module parameter set to the ``"compatible"``413string of the node the driver is supposed to handle. By default, the414node's name (without the unit address) is exposed as name for the415UIO device in userspace. To set a custom name, a property named416``"linux,uio-name"`` may be specified in the DT node.417 418Using uio_dmem_genirq for platform devices419------------------------------------------420 421In addition to statically allocated memory ranges, they may also be a422desire to use dynamically allocated regions in a user space driver. In423particular, being able to access memory made available through the424dma-mapping API, may be particularly useful. The ``uio_dmem_genirq``425driver provides a way to accomplish this.426 427This driver is used in a similar manner to the ``"uio_pdrv_genirq"``428driver with respect to interrupt configuration and handling.429 430Set the ``.name`` element of ``struct platform_device`` to431``"uio_dmem_genirq"`` to use this driver.432 433When using this driver, fill in the ``.platform_data`` element of434``struct platform_device``, which is of type435``struct uio_dmem_genirq_pdata`` and which contains the following436elements:437 438- ``struct uio_info uioinfo``: The same structure used as the439 ``uio_pdrv_genirq`` platform data440 441- ``unsigned int *dynamic_region_sizes``: Pointer to list of sizes of442 dynamic memory regions to be mapped into user space.443 444- ``unsigned int num_dynamic_regions``: Number of elements in445 ``dynamic_region_sizes`` array.446 447The dynamic regions defined in the platform data will be appended to the448`` mem[] `` array after the platform device resources, which implies449that the total number of static and dynamic memory regions cannot exceed450``MAX_UIO_MAPS``.451 452The dynamic memory regions will be allocated when the UIO device file,453``/dev/uioX`` is opened. Similar to static memory resources, the memory454region information for dynamic regions is then visible via sysfs at455``/sys/class/uio/uioX/maps/mapY/*``. The dynamic memory regions will be456freed when the UIO device file is closed. When no processes are holding457the device file open, the address returned to userspace is ~0.458 459Writing a driver in userspace460=============================461 462Once you have a working kernel module for your hardware, you can write463the userspace part of your driver. You don't need any special libraries,464your driver can be written in any reasonable language, you can use465floating point numbers and so on. In short, you can use all the tools466and libraries you'd normally use for writing a userspace application.467 468Getting information about your UIO device469-----------------------------------------470 471Information about all UIO devices is available in sysfs. The first thing472you should do in your driver is check ``name`` and ``version`` to make473sure you're talking to the right device and that its kernel driver has474the version you expect.475 476You should also make sure that the memory mapping you need exists and477has the size you expect.478 479There is a tool called ``lsuio`` that lists UIO devices and their480attributes. It is available here:481 482http://www.osadl.org/projects/downloads/UIO/user/483 484With ``lsuio`` you can quickly check if your kernel module is loaded and485which attributes it exports. Have a look at the manpage for details.486 487The source code of ``lsuio`` can serve as an example for getting488information about an UIO device. The file ``uio_helper.c`` contains a489lot of functions you could use in your userspace driver code.490 491mmap() device memory492--------------------493 494After you made sure you've got the right device with the memory mappings495you need, all you have to do is to call :c:func:`mmap()` to map the496device's memory to userspace.497 498The parameter ``offset`` of the :c:func:`mmap()` call has a special499meaning for UIO devices: It is used to select which mapping of your500device you want to map. To map the memory of mapping N, you have to use501N times the page size as your offset::502 503 offset = N * getpagesize();504 505N starts from zero, so if you've got only one memory range to map, set506``offset = 0``. A drawback of this technique is that memory is always507mapped beginning with its start address.508 509Waiting for interrupts510----------------------511 512After you successfully mapped your devices memory, you can access it513like an ordinary array. Usually, you will perform some initialization.514After that, your hardware starts working and will generate an interrupt515as soon as it's finished, has some data available, or needs your516attention because an error occurred.517 518``/dev/uioX`` is a read-only file. A :c:func:`read()` will always519block until an interrupt occurs. There is only one legal value for the520``count`` parameter of :c:func:`read()`, and that is the size of a521signed 32 bit integer (4). Any other value for ``count`` causes522:c:func:`read()` to fail. The signed 32 bit integer read is the523interrupt count of your device. If the value is one more than the value524you read the last time, everything is OK. If the difference is greater525than one, you missed interrupts.526 527You can also use :c:func:`select()` on ``/dev/uioX``.528 529Generic PCI UIO driver530======================531 532The generic driver is a kernel module named uio_pci_generic. It can533work with any device compliant to PCI 2.3 (circa 2002) and any compliant534PCI Express device. Using this, you only need to write the userspace535driver, removing the need to write a hardware-specific kernel module.536 537Making the driver recognize the device538--------------------------------------539 540Since the driver does not declare any device ids, it will not get loaded541automatically and will not automatically bind to any devices, you must542load it and allocate id to the driver yourself. For example::543 544 modprobe uio_pci_generic545 echo "8086 10f5" > /sys/bus/pci/drivers/uio_pci_generic/new_id546 547If there already is a hardware specific kernel driver for your device,548the generic driver still won't bind to it, in this case if you want to549use the generic driver (why would you?) you'll have to manually unbind550the hardware specific driver and bind the generic driver, like this::551 552 echo -n 0000:00:19.0 > /sys/bus/pci/drivers/e1000e/unbind553 echo -n 0000:00:19.0 > /sys/bus/pci/drivers/uio_pci_generic/bind554 555You can verify that the device has been bound to the driver by looking556for it in sysfs, for example like the following::557 558 ls -l /sys/bus/pci/devices/0000:00:19.0/driver559 560Which if successful should print::561 562 .../0000:00:19.0/driver -> ../../../bus/pci/drivers/uio_pci_generic563 564Note that the generic driver will not bind to old PCI 2.2 devices. If565binding the device failed, run the following command::566 567 dmesg568 569and look in the output for failure reasons.570 571Things to know about uio_pci_generic572------------------------------------573 574Interrupts are handled using the Interrupt Disable bit in the PCI575command register and Interrupt Status bit in the PCI status register.576All devices compliant to PCI 2.3 (circa 2002) and all compliant PCI577Express devices should support these bits. uio_pci_generic detects578this support, and won't bind to devices which do not support the579Interrupt Disable Bit in the command register.580 581On each interrupt, uio_pci_generic sets the Interrupt Disable bit.582This prevents the device from generating further interrupts until the583bit is cleared. The userspace driver should clear this bit before584blocking and waiting for more interrupts.585 586Writing userspace driver using uio_pci_generic587------------------------------------------------588 589Userspace driver can use pci sysfs interface, or the libpci library that590wraps it, to talk to the device and to re-enable interrupts by writing591to the command register.592 593Example code using uio_pci_generic594----------------------------------595 596Here is some sample userspace driver code using uio_pci_generic::597 598 #include <stdlib.h>599 #include <stdio.h>600 #include <unistd.h>601 #include <sys/types.h>602 #include <sys/stat.h>603 #include <fcntl.h>604 #include <errno.h>605 606 int main()607 {608 int uiofd;609 int configfd;610 int err;611 int i;612 unsigned icount;613 unsigned char command_high;614 615 uiofd = open("/dev/uio0", O_RDONLY);616 if (uiofd < 0) {617 perror("uio open:");618 return errno;619 }620 configfd = open("/sys/class/uio/uio0/device/config", O_RDWR);621 if (configfd < 0) {622 perror("config open:");623 return errno;624 }625 626 /* Read and cache command value */627 err = pread(configfd, &command_high, 1, 5);628 if (err != 1) {629 perror("command config read:");630 return errno;631 }632 command_high &= ~0x4;633 634 for(i = 0;; ++i) {635 /* Print out a message, for debugging. */636 if (i == 0)637 fprintf(stderr, "Started uio test driver.\n");638 else639 fprintf(stderr, "Interrupts: %d\n", icount);640 641 /****************************************/642 /* Here we got an interrupt from the643 device. Do something to it. */644 /****************************************/645 646 /* Re-enable interrupts. */647 err = pwrite(configfd, &command_high, 1, 5);648 if (err != 1) {649 perror("config write:");650 break;651 }652 653 /* Wait for next interrupt. */654 err = read(uiofd, &icount, 4);655 if (err != 4) {656 perror("uio read:");657 break;658 }659 660 }661 return errno;662 }663 664Generic Hyper-V UIO driver665==========================666 667The generic driver is a kernel module named uio_hv_generic. It668supports devices on the Hyper-V VMBus similar to uio_pci_generic on669PCI bus.670 671Making the driver recognize the device672--------------------------------------673 674Since the driver does not declare any device GUID's, it will not get675loaded automatically and will not automatically bind to any devices, you676must load it and allocate id to the driver yourself. For example, to use677the network device class GUID::678 679 modprobe uio_hv_generic680 echo "f8615163-df3e-46c5-913f-f2d2f965ed0e" > /sys/bus/vmbus/drivers/uio_hv_generic/new_id681 682If there already is a hardware specific kernel driver for the device,683the generic driver still won't bind to it, in this case if you want to684use the generic driver for a userspace library you'll have to manually unbind685the hardware specific driver and bind the generic driver, using the device specific GUID686like this::687 688 echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/hv_netvsc/unbind689 echo -n ed963694-e847-4b2a-85af-bc9cfc11d6f3 > /sys/bus/vmbus/drivers/uio_hv_generic/bind690 691You can verify that the device has been bound to the driver by looking692for it in sysfs, for example like the following::693 694 ls -l /sys/bus/vmbus/devices/ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver695 696Which if successful should print::697 698 .../ed963694-e847-4b2a-85af-bc9cfc11d6f3/driver -> ../../../bus/vmbus/drivers/uio_hv_generic699 700Things to know about uio_hv_generic701-----------------------------------702 703On each interrupt, uio_hv_generic sets the Interrupt Disable bit. This704prevents the device from generating further interrupts until the bit is705cleared. The userspace driver should clear this bit before blocking and706waiting for more interrupts.707 708When host rescinds a device, the interrupt file descriptor is marked down709and any reads of the interrupt file descriptor will return -EIO. Similar710to a closed socket or disconnected serial device.711 712The vmbus device regions are mapped into uio device resources:713 0) Channel ring buffers: guest to host and host to guest714 1) Guest to host interrupt signalling pages715 2) Guest to host monitor page716 3) Network receive buffer region717 4) Network send buffer region718 719If a subchannel is created by a request to host, then the uio_hv_generic720device driver will create a sysfs binary file for the per-channel ring buffer.721For example::722 723 /sys/bus/vmbus/devices/3811fe4d-0fa0-4b62-981a-74fc1084c757/channels/21/ring724 725Further information726===================727 728- `OSADL homepage. <http://www.osadl.org>`_729 730- `Linutronix homepage. <http://www.linutronix.de>`_731