vidioc-querycap.rst (10505B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_QUERYCAP: 5 6********************* 7ioctl VIDIOC_QUERYCAP 8********************* 9 10Name 11==== 12 13VIDIOC_QUERYCAP - Query device capabilities 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_QUERYCAP 19 20``int ioctl(int fd, VIDIOC_QUERYCAP, struct v4l2_capability *argp)`` 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28``argp`` 29 Pointer to struct :c:type:`v4l2_capability`. 30 31Description 32=========== 33 34All V4L2 devices support the ``VIDIOC_QUERYCAP`` ioctl. It is used to 35identify kernel devices compatible with this specification and to obtain 36information about driver and hardware capabilities. The ioctl takes a 37pointer to a struct :c:type:`v4l2_capability` which is 38filled by the driver. When the driver is not compatible with this 39specification the ioctl returns an ``EINVAL`` error code. 40 41.. c:type:: v4l2_capability 42 43.. tabularcolumns:: |p{1.4cm}|p{2.8cm}|p{13.1cm}| 44 45.. cssclass:: longtable 46 47.. flat-table:: struct v4l2_capability 48 :header-rows: 0 49 :stub-columns: 0 50 :widths: 3 4 20 51 52 * - __u8 53 - ``driver``\ [16] 54 - Name of the driver, a unique NUL-terminated ASCII string. For 55 example: "bttv". Driver specific applications can use this 56 information to verify the driver identity. It is also useful to 57 work around known bugs, or to identify drivers in error reports. 58 59 Storing strings in fixed sized arrays is bad practice but 60 unavoidable here. Drivers and applications should take precautions 61 to never read or write beyond the end of the array and to make 62 sure the strings are properly NUL-terminated. 63 * - __u8 64 - ``card``\ [32] 65 - Name of the device, a NUL-terminated UTF-8 string. For example: 66 "Yoyodyne TV/FM". One driver may support different brands or 67 models of video hardware. This information is intended for users, 68 for example in a menu of available devices. Since multiple TV 69 cards of the same brand may be installed which are supported by 70 the same driver, this name should be combined with the character 71 device file name (e. g. ``/dev/video2``) or the ``bus_info`` 72 string to avoid ambiguities. 73 * - __u8 74 - ``bus_info``\ [32] 75 - Location of the device in the system, a NUL-terminated ASCII 76 string. For example: "PCI:0000:05:06.0". This information is 77 intended for users, to distinguish multiple identical devices. If 78 no such information is available the field must simply count the 79 devices controlled by the driver ("platform:vivid-000"). The 80 bus_info must start with "PCI:" for PCI boards, "PCIe:" for PCI 81 Express boards, "usb-" for USB devices, "I2C:" for i2c devices, 82 "ISA:" for ISA devices, "parport" for parallel port devices and 83 "platform:" for platform devices. 84 * - __u32 85 - ``version`` 86 - Version number of the driver. 87 88 Starting with kernel 3.1, the version reported is provided by the 89 V4L2 subsystem following the kernel numbering scheme. However, it 90 may not always return the same version as the kernel if, for 91 example, a stable or distribution-modified kernel uses the V4L2 92 stack from a newer kernel. 93 94 The version number is formatted using the ``KERNEL_VERSION()`` 95 macro. For example if the media stack corresponds to the V4L2 96 version shipped with Kernel 4.14, it would be equivalent to: 97 * - :cspan:`2` 98 99 ``#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))`` 100 101 ``__u32 version = KERNEL_VERSION(4, 14, 0);`` 102 103 ``printf ("Version: %u.%u.%u\\n",`` 104 105 ``(version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF);`` 106 * - __u32 107 - ``capabilities`` 108 - Available capabilities of the physical device as a whole, see 109 :ref:`device-capabilities`. The same physical device can export 110 multiple devices in /dev (e.g. /dev/videoX, /dev/vbiY and 111 /dev/radioZ). The ``capabilities`` field should contain a union of 112 all capabilities available around the several V4L2 devices 113 exported to userspace. For all those devices the ``capabilities`` 114 field returns the same set of capabilities. This allows 115 applications to open just one of the devices (typically the video 116 device) and discover whether video, vbi and/or radio are also 117 supported. 118 * - __u32 119 - ``device_caps`` 120 - Device capabilities of the opened device, see 121 :ref:`device-capabilities`. Should contain the available 122 capabilities of that specific device node. So, for example, 123 ``device_caps`` of a radio device will only contain radio related 124 capabilities and no video or vbi capabilities. This field is only 125 set if the ``capabilities`` field contains the 126 ``V4L2_CAP_DEVICE_CAPS`` capability. Only the ``capabilities`` 127 field can have the ``V4L2_CAP_DEVICE_CAPS`` capability, 128 ``device_caps`` will never set ``V4L2_CAP_DEVICE_CAPS``. 129 * - __u32 130 - ``reserved``\ [3] 131 - Reserved for future extensions. Drivers must set this array to 132 zero. 133 134 135.. tabularcolumns:: |p{7.0cm}|p{2.6cm}|p{7.7cm}| 136 137.. _device-capabilities: 138 139.. cssclass:: longtable 140 141.. flat-table:: Device Capabilities Flags 142 :header-rows: 0 143 :stub-columns: 0 144 :widths: 3 1 4 145 146 * - ``V4L2_CAP_VIDEO_CAPTURE`` 147 - 0x00000001 148 - The device supports the single-planar API through the 149 :ref:`Video Capture <capture>` interface. 150 * - ``V4L2_CAP_VIDEO_CAPTURE_MPLANE`` 151 - 0x00001000 152 - The device supports the :ref:`multi-planar API <planar-apis>` 153 through the :ref:`Video Capture <capture>` interface. 154 * - ``V4L2_CAP_VIDEO_OUTPUT`` 155 - 0x00000002 156 - The device supports the single-planar API through the 157 :ref:`Video Output <output>` interface. 158 * - ``V4L2_CAP_VIDEO_OUTPUT_MPLANE`` 159 - 0x00002000 160 - The device supports the :ref:`multi-planar API <planar-apis>` 161 through the :ref:`Video Output <output>` interface. 162 * - ``V4L2_CAP_VIDEO_M2M`` 163 - 0x00008000 164 - The device supports the single-planar API through the Video 165 Memory-To-Memory interface. 166 * - ``V4L2_CAP_VIDEO_M2M_MPLANE`` 167 - 0x00004000 168 - The device supports the :ref:`multi-planar API <planar-apis>` 169 through the Video Memory-To-Memory interface. 170 * - ``V4L2_CAP_VIDEO_OVERLAY`` 171 - 0x00000004 172 - The device supports the :ref:`Video Overlay <overlay>` 173 interface. A video overlay device typically stores captured images 174 directly in the video memory of a graphics card, with hardware 175 clipping and scaling. 176 * - ``V4L2_CAP_VBI_CAPTURE`` 177 - 0x00000010 178 - The device supports the :ref:`Raw VBI Capture <raw-vbi>` 179 interface, providing Teletext and Closed Caption data. 180 * - ``V4L2_CAP_VBI_OUTPUT`` 181 - 0x00000020 182 - The device supports the :ref:`Raw VBI Output <raw-vbi>` 183 interface. 184 * - ``V4L2_CAP_SLICED_VBI_CAPTURE`` 185 - 0x00000040 186 - The device supports the :ref:`Sliced VBI Capture <sliced>` 187 interface. 188 * - ``V4L2_CAP_SLICED_VBI_OUTPUT`` 189 - 0x00000080 190 - The device supports the :ref:`Sliced VBI Output <sliced>` 191 interface. 192 * - ``V4L2_CAP_RDS_CAPTURE`` 193 - 0x00000100 194 - The device supports the :ref:`RDS <rds>` capture interface. 195 * - ``V4L2_CAP_VIDEO_OUTPUT_OVERLAY`` 196 - 0x00000200 197 - The device supports the :ref:`Video Output Overlay <osd>` (OSD) 198 interface. Unlike the *Video Overlay* interface, this is a 199 secondary function of video output devices and overlays an image 200 onto an outgoing video signal. When the driver sets this flag, it 201 must clear the ``V4L2_CAP_VIDEO_OVERLAY`` flag and vice 202 versa. [#f1]_ 203 * - ``V4L2_CAP_HW_FREQ_SEEK`` 204 - 0x00000400 205 - The device supports the 206 :ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl 207 for hardware frequency seeking. 208 * - ``V4L2_CAP_RDS_OUTPUT`` 209 - 0x00000800 210 - The device supports the :ref:`RDS <rds>` output interface. 211 * - ``V4L2_CAP_TUNER`` 212 - 0x00010000 213 - The device has some sort of tuner to receive RF-modulated video 214 signals. For more information about tuner programming see 215 :ref:`tuner`. 216 * - ``V4L2_CAP_AUDIO`` 217 - 0x00020000 218 - The device has audio inputs or outputs. It may or may not support 219 audio recording or playback, in PCM or compressed formats. PCM 220 audio support must be implemented as ALSA or OSS interface. For 221 more information on audio inputs and outputs see :ref:`audio`. 222 * - ``V4L2_CAP_RADIO`` 223 - 0x00040000 224 - This is a radio receiver. 225 * - ``V4L2_CAP_MODULATOR`` 226 - 0x00080000 227 - The device has some sort of modulator to emit RF-modulated 228 video/audio signals. For more information about modulator 229 programming see :ref:`tuner`. 230 * - ``V4L2_CAP_SDR_CAPTURE`` 231 - 0x00100000 232 - The device supports the :ref:`SDR Capture <sdr>` interface. 233 * - ``V4L2_CAP_EXT_PIX_FORMAT`` 234 - 0x00200000 235 - The device supports the struct 236 :c:type:`v4l2_pix_format` extended fields. 237 * - ``V4L2_CAP_SDR_OUTPUT`` 238 - 0x00400000 239 - The device supports the :ref:`SDR Output <sdr>` interface. 240 * - ``V4L2_CAP_META_CAPTURE`` 241 - 0x00800000 242 - The device supports the :ref:`metadata` capture interface. 243 * - ``V4L2_CAP_READWRITE`` 244 - 0x01000000 245 - The device supports the :c:func:`read()` and/or 246 :c:func:`write()` I/O methods. 247 * - ``V4L2_CAP_ASYNCIO`` 248 - 0x02000000 249 - The device supports the :ref:`asynchronous <async>` I/O methods. 250 * - ``V4L2_CAP_STREAMING`` 251 - 0x04000000 252 - The device supports the :ref:`streaming <mmap>` I/O method. 253 * - ``V4L2_CAP_META_OUTPUT`` 254 - 0x08000000 255 - The device supports the :ref:`metadata` output interface. 256 * - ``V4L2_CAP_TOUCH`` 257 - 0x10000000 258 - This is a touch device. 259 * - ``V4L2_CAP_IO_MC`` 260 - 0x20000000 261 - There is only one input and/or output seen from userspace. The whole 262 video topology configuration, including which I/O entity is routed to 263 the input/output, is configured by userspace via the Media Controller. 264 See :ref:`media_controller`. 265 * - ``V4L2_CAP_DEVICE_CAPS`` 266 - 0x80000000 267 - The driver fills the ``device_caps`` field. This capability can 268 only appear in the ``capabilities`` field and never in the 269 ``device_caps`` field. 270 271Return Value 272============ 273 274On success 0 is returned, on error -1 and the ``errno`` variable is set 275appropriately. The generic error codes are described at the 276:ref:`Generic Error Codes <gen-errors>` chapter. 277 278.. [#f1] 279 The struct :c:type:`v4l2_framebuffer` lacks an 280 enum :c:type:`v4l2_buf_type` field, therefore the 281 type of overlay is implied by the driver capabilities.