ioctl VIDIOC_QUERYCAP &manvol; VIDIOC_QUERYCAP Query device capabilities int ioctl int fd int request struct v4l2_capability *argp fd &fd; request VIDIOC_QUERYCAP argp All V4L2 devices support the VIDIOC_QUERYCAP ioctl. It is used to identify kernel devices compatible with this specification and to obtain information about driver and hardware capabilities. The ioctl takes a pointer to a &v4l2-capability; which is filled by the driver. When the driver is not compatible with this specification the ioctl returns an &EINVAL;. &cs-str; __u8 driver[16] Name of the driver, a unique NUL-terminated ASCII string. For example: "bttv". Driver specific applications can use this information to verify the driver identity. It is also useful to work around known bugs, or to identify drivers in error reports. The driver version is stored in the version field.Storing strings in fixed sized arrays is bad practice but unavoidable here. Drivers and applications should take precautions to never read or write beyond the end of the array and to make sure the strings are properly NUL-terminated. __u8 card[32] Name of the device, a NUL-terminated ASCII string. For example: "Yoyodyne TV/FM". One driver may support different brands or models of video hardware. This information is intended for users, for example in a menu of available devices. Since multiple TV cards of the same brand may be installed which are supported by the same driver, this name should be combined with the character device file name (⪚ /dev/video2) or the bus_info string to avoid ambiguities. __u8 bus_info[32] Location of the device in the system, a NUL-terminated ASCII string. For example: "PCI Slot 4". This information is intended for users, to distinguish multiple identical devices. If no such information is available the field may simply count the devices controlled by the driver, or contain the empty string (bus_info[0] = 0). __u32 version Version number of the driver. Together with the driver field this identifies a particular driver. The version number is formatted using the KERNEL_VERSION() macro: #define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c)) __u32 version = KERNEL_VERSION(0, 8, 1); printf ("Version: %u.%u.%u\n", (version >> 16) & 0xFF, (version >> 8) & 0xFF, version & 0xFF); __u32 capabilities Device capabilities, see . __u32 reserved[4] Reserved for future extensions. Drivers must set this array to zero. &cs-def; V4L2_CAP_VIDEO_CAPTURE 0x00000001 The device supports the Video Capture interface. V4L2_CAP_VIDEO_OUTPUT 0x00000002 The device supports the Video Output interface. V4L2_CAP_VIDEO_OVERLAY 0x00000004 The device supports the Video Overlay interface. A video overlay device typically stores captured images directly in the video memory of a graphics card, with hardware clipping and scaling. V4L2_CAP_VBI_CAPTURE 0x00000010 The device supports the Raw VBI Capture interface, providing Teletext and Closed Caption data. V4L2_CAP_VBI_OUTPUT 0x00000020 The device supports the Raw VBI Output interface. V4L2_CAP_SLICED_VBI_CAPTURE 0x00000040 The device supports the Sliced VBI Capture interface. V4L2_CAP_SLICED_VBI_OUTPUT 0x00000080 The device supports the Sliced VBI Output interface. V4L2_CAP_RDS_CAPTURE 0x00000100 The device supports the RDS interface. V4L2_CAP_VIDEO_OUTPUT_OVERLAY 0x00000200 The device supports the Video Output Overlay (OSD) interface. Unlike the Video Overlay interface, this is a secondary function of video output devices and overlays an image onto an outgoing video signal. When the driver sets this flag, it must clear the V4L2_CAP_VIDEO_OVERLAY flag and vice versa.The &v4l2-framebuffer; lacks an &v4l2-buf-type; field, therefore the type of overlay is implied by the driver capabilities. V4L2_CAP_HW_FREQ_SEEK 0x00000400 The device supports the &VIDIOC-S-HW-FREQ-SEEK; ioctl for hardware frequency seeking. V4L2_CAP_TUNER 0x00010000 The device has some sort of tuner to receive RF-modulated video signals. For more information about tuner programming see . V4L2_CAP_AUDIO 0x00020000 The device has audio inputs or outputs. It may or may not support audio recording or playback, in PCM or compressed formats. PCM audio support must be implemented as ALSA or OSS interface. For more information on audio inputs and outputs see . V4L2_CAP_RADIO 0x00040000 This is a radio receiver. V4L2_CAP_MODULATOR 0x00080000 The device has some sort of modulator to emit RF-modulated video/audio signals. For more information about modulator programming see . V4L2_CAP_READWRITE 0x01000000 The device supports the read() and/or write() I/O methods. V4L2_CAP_ASYNCIO 0x02000000 The device supports the asynchronous I/O methods. V4L2_CAP_STREAMING 0x04000000 The device supports the streaming I/O method. &return-value; EINVAL The device is not compatible with this specification.