ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU &manvol; VIDIOC_QUERYCTRL VIDIOC_QUERYMENU Enumerate controls and menu control items int ioctl int fd int request struct v4l2_queryctrl *argp int ioctl int fd int request struct v4l2_querymenu *argp fd &fd; request VIDIOC_QUERYCTRL, VIDIOC_QUERYMENU argp To query the attributes of a control applications set the id field of a &v4l2-queryctrl; and call the VIDIOC_QUERYCTRL ioctl with a pointer to this structure. The driver fills the rest of the structure or returns an &EINVAL; when the id is invalid. It is possible to enumerate controls by calling VIDIOC_QUERYCTRL with successive id values starting from V4L2_CID_BASE up to and exclusive V4L2_CID_BASE_LASTP1. Drivers may return EINVAL if a control in this range is not supported. Further applications can enumerate private controls, which are not defined in this specification, by starting at V4L2_CID_PRIVATE_BASE and incrementing id until the driver returns EINVAL. In both cases, when the driver sets the V4L2_CTRL_FLAG_DISABLED flag in the flags field this control is permanently disabled and should be ignored by the application. V4L2_CTRL_FLAG_DISABLED was intended for two purposes: Drivers can skip predefined controls not supported by the hardware (although returning EINVAL would do as well), or disable predefined and private controls after hardware detection without the trouble of reordering control arrays and indices (EINVAL cannot be used to skip private controls because it would prematurely end the enumeration). When the application ORs id with V4L2_CTRL_FLAG_NEXT_CTRL the driver returns the next supported control, or EINVAL if there is none. Drivers which do not support this flag yet always return EINVAL. Additional information is required for menu controls: the names of the menu items. To query them applications set the id and index fields of &v4l2-querymenu; and call the VIDIOC_QUERYMENU ioctl with a pointer to this structure. The driver fills the rest of the structure or returns an &EINVAL; when the id or index is invalid. Menu items are enumerated by calling VIDIOC_QUERYMENU with successive index values from &v4l2-queryctrl; minimum (0) to maximum, inclusive. See also the examples in . &cs-str; __u32 id Identifies the control, set by the application. See for predefined IDs. When the ID is ORed with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns the first control with a higher ID. Drivers which do not support this flag yet always return an &EINVAL;. &v4l2-ctrl-type; type Type of control, see . __u8 name[32] Name of the control, a NUL-terminated ASCII string. This information is intended for the user. __s32 minimum Minimum value, inclusive. This field gives a lower bound for V4L2_CTRL_TYPE_INTEGER controls and the lowest valid index (always 0) for V4L2_CTRL_TYPE_MENU controls. For V4L2_CTRL_TYPE_STRING controls the minimum value gives the minimum length of the string. This length does not include the terminating zero. It may not be valid for any other type of control, including V4L2_CTRL_TYPE_INTEGER64 controls. Note that this is a signed value. __s32 maximum Maximum value, inclusive. This field gives an upper bound for V4L2_CTRL_TYPE_INTEGER controls and the highest valid index for V4L2_CTRL_TYPE_MENU controls. For V4L2_CTRL_TYPE_STRING controls the maximum value gives the maximum length of the string. This length does not include the terminating zero. It may not be valid for any other type of control, including V4L2_CTRL_TYPE_INTEGER64 controls. Note that this is a signed value. __s32 step This field gives a step size for V4L2_CTRL_TYPE_INTEGER controls. For V4L2_CTRL_TYPE_STRING controls this field refers to the string length that has to be a multiple of this step size. It may not be valid for any other type of control, including V4L2_CTRL_TYPE_INTEGER64 controls.Generally drivers should not scale hardware control values. It may be necessary for example when the name or id imply a particular unit and the hardware actually accepts only multiples of said unit. If so, drivers must take care values are properly rounded when scaling, such that errors will not accumulate on repeated read-write cycles.This field gives the smallest change of an integer control actually affecting hardware. Often the information is needed when the user can change controls by keyboard or GUI buttons, rather than a slider. When for example a hardware register accepts values 0-511 and the driver reports 0-65535, step should be 128.Note that although signed, the step value is supposed to be always positive. __s32 default_value The default value of a V4L2_CTRL_TYPE_INTEGER, _BOOLEAN or _MENU control. Not valid for other types of controls. Drivers reset controls only when the driver is loaded, not later, in particular not when the func-open; is called. __u32 flags Control flags, see . __u32 reserved[2] Reserved for future extensions. Drivers must set the array to zero. &cs-str; __u32 id Identifies the control, set by the application from the respective &v4l2-queryctrl; id. __u32 index Index of the menu item, starting at zero, set by the application. __u8 name[32] Name of the menu item, a NUL-terminated ASCII string. This information is intended for the user. __u32 reserved Reserved for future extensions. Drivers must set the array to zero. Type minimum step maximum Description V4L2_CTRL_TYPE_INTEGER any any any An integer-valued control ranging from minimum to maximum inclusive. The step value indicates the increment between values which are actually different on the hardware. V4L2_CTRL_TYPE_BOOLEAN 0 1 1 A boolean-valued control. Zero corresponds to "disabled", and one means "enabled". V4L2_CTRL_TYPE_MENU 0 1 N-1 The control has a menu of N choices. The names of the menu items can be enumerated with the VIDIOC_QUERYMENU ioctl. V4L2_CTRL_TYPE_BUTTON 0 0 0 A control which performs an action when set. Drivers must ignore the value passed with VIDIOC_S_CTRL and return an &EINVAL; on a VIDIOC_G_CTRL attempt. V4L2_CTRL_TYPE_INTEGER64 n/a n/a n/a A 64-bit integer valued control. Minimum, maximum and step size cannot be queried. V4L2_CTRL_TYPE_STRING ≥ 0 ≥ 1 ≥ 0 The minimum and maximum string lengths. The step size means that the string must be (minimum + N * step) characters long for N ≥ 0. These lengths do not include the terminating zero, so in order to pass a string of length 8 to &VIDIOC-S-EXT-CTRLS; you need to set the size field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can set the size field to maximum + 1. Which character encoding is used will depend on the string control itself and should be part of the control documentation. V4L2_CTRL_TYPE_CTRL_CLASS n/a n/a n/a This is not a control. When VIDIOC_QUERYCTRL is called with a control ID equal to a control class code (see ), the ioctl returns the name of the control class and this control type. Older drivers which do not support this feature return an &EINVAL;. &cs-def; V4L2_CTRL_FLAG_DISABLED 0x0001 This control is permanently disabled and should be ignored by the application. Any attempt to change the control will result in an &EINVAL;. V4L2_CTRL_FLAG_GRABBED 0x0002 This control is temporarily unchangeable, for example because another application took over control of the respective resource. Such controls may be displayed specially in a user interface. Attempts to change the control may result in an &EBUSY;. V4L2_CTRL_FLAG_READ_ONLY 0x0004 This control is permanently readable only. Any attempt to change the control will result in an &EINVAL;. V4L2_CTRL_FLAG_UPDATE 0x0008 A hint that changing this control may affect the value of other controls within the same control class. Applications should update their user interface accordingly. V4L2_CTRL_FLAG_INACTIVE 0x0010 This control is not applicable to the current configuration and should be displayed accordingly in a user interface. For example the flag may be set on a MPEG audio level 2 bitrate control when MPEG audio encoding level 1 was selected with another control. V4L2_CTRL_FLAG_SLIDER 0x0020 A hint that this control is best represented as a slider-like element in a user interface. V4L2_CTRL_FLAG_WRITE_ONLY 0x0040 This control is permanently writable only. Any attempt to read the control will result in an &EACCES; error code. This flag is typically present for relative controls or action controls where writing a value will cause the device to carry out a given action (⪚ motor control) but no meaningful value can be returned. &return-value; EINVAL The &v4l2-queryctrl; id is invalid. The &v4l2-querymenu; id or index is invalid. EACCES An attempt was made to read a write-only control.