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+<refentry id="vidioc-g-ext-ctrls">
+ <refmeta>
+ <refentrytitle>ioctl VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
+VIDIOC_TRY_EXT_CTRLS</refentrytitle>
+ &manvol;
+ </refmeta>
+
+ <refnamediv>
+ <refname>VIDIOC_G_EXT_CTRLS</refname>
+ <refname>VIDIOC_S_EXT_CTRLS</refname>
+ <refname>VIDIOC_TRY_EXT_CTRLS</refname>
+ <refpurpose>Get or set the value of several controls, try control
+values</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <funcsynopsis>
+ <funcprototype>
+ <funcdef>int <function>ioctl</function></funcdef>
+ <paramdef>int <parameter>fd</parameter></paramdef>
+ <paramdef>int <parameter>request</parameter></paramdef>
+ <paramdef>struct v4l2_ext_controls
+*<parameter>argp</parameter></paramdef>
+ </funcprototype>
+ </funcsynopsis>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Arguments</title>
+
+ <variablelist>
+ <varlistentry>
+ <term><parameter>fd</parameter></term>
+ <listitem>
+ <para>&fd;</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>request</parameter></term>
+ <listitem>
+ <para>VIDIOC_G_EXT_CTRLS, VIDIOC_S_EXT_CTRLS,
+VIDIOC_TRY_EXT_CTRLS</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><parameter>argp</parameter></term>
+ <listitem>
+ <para></para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>These ioctls allow the caller to get or set multiple
+controls atomically. Control IDs are grouped into control classes (see
+<xref linkend="ctrl-class" />) and all controls in the control array
+must belong to the same control class.</para>
+
+ <para>Applications must always fill in the
+<structfield>count</structfield>,
+<structfield>ctrl_class</structfield>,
+<structfield>controls</structfield> and
+<structfield>reserved</structfield> fields of &v4l2-ext-controls;, and
+initialize the &v4l2-ext-control; array pointed to by the
+<structfield>controls</structfield> fields.</para>
+
+ <para>To get the current value of a set of controls applications
+initialize the <structfield>id</structfield>,
+<structfield>size</structfield> and <structfield>reserved2</structfield> fields
+of each &v4l2-ext-control; and call the
+<constant>VIDIOC_G_EXT_CTRLS</constant> ioctl. String controls controls
+must also set the <structfield>string</structfield> field.</para>
+
+ <para>If the <structfield>size</structfield> is too small to
+receive the control result (only relevant for pointer-type controls
+like strings), then the driver will set <structfield>size</structfield>
+to a valid value and return an &ENOSPC;. You should re-allocate the
+string memory to this new size and try again. It is possible that the
+same issue occurs again if the string has grown in the meantime. It is
+recommended to call &VIDIOC-QUERYCTRL; first and use
+<structfield>maximum</structfield>+1 as the new <structfield>size</structfield>
+value. It is guaranteed that that is sufficient memory.
+</para>
+
+ <para>To change the value of a set of controls applications
+initialize the <structfield>id</structfield>, <structfield>size</structfield>,
+<structfield>reserved2</structfield> and
+<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
+call the <constant>VIDIOC_S_EXT_CTRLS</constant> ioctl. The controls
+will only be set if <emphasis>all</emphasis> control values are
+valid.</para>
+
+ <para>To check if a set of controls have correct values applications
+initialize the <structfield>id</structfield>, <structfield>size</structfield>,
+<structfield>reserved2</structfield> and
+<structfield>value/string</structfield> fields of each &v4l2-ext-control; and
+call the <constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctl. It is up to
+the driver whether wrong values are automatically adjusted to a valid
+value or if an error is returned.</para>
+
+ <para>When the <structfield>id</structfield> or
+<structfield>ctrl_class</structfield> is invalid drivers return an
+&EINVAL;. When the value is out of bounds drivers can choose to take
+the closest valid value or return an &ERANGE;, whatever seems more
+appropriate. In the first case the new value is set in
+&v4l2-ext-control;. If the new control value is inappropriate (e.g. the
+given menu index is not supported by the menu control), then this will
+also result in an &EINVAL; error.</para>
+
+ <para>The driver will only set/get these controls if all control
+values are correct. This prevents the situation where only some of the
+controls were set/get. Only low-level errors (&eg; a failed i2c
+command) can still cause this situation.</para>
+
+ <table pgwide="1" frame="none" id="v4l2-ext-control">
+ <title>struct <structname>v4l2_ext_control</structname></title>
+ <tgroup cols="4">
+ &cs-ustr;
+ <tbody valign="top">
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>id</structfield></entry>
+ <entry></entry>
+ <entry>Identifies the control, set by the
+application.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>size</structfield></entry>
+ <entry></entry>
+ <entry>The total size in bytes of the payload of this
+control. This is normally 0, but for pointer controls this should be
+set to the size of the memory containing the payload, or that will
+receive the payload. If <constant>VIDIOC_G_EXT_CTRLS</constant> finds
+that this value is less than is required to store
+the payload result, then it is set to a value large enough to store the
+payload result and ENOSPC is returned. Note that for string controls
+this <structfield>size</structfield> field should not be confused with the length of the string.
+This field refers to the size of the memory that contains the string.
+The actual <emphasis>length</emphasis> of the string may well be much smaller.
+</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>reserved2</structfield>[1]</entry>
+ <entry></entry>
+ <entry>Reserved for future extensions. Drivers and
+applications must set the array to zero.</entry>
+ </row>
+ <row>
+ <entry>union</entry>
+ <entry>(anonymous)</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>__s32</entry>
+ <entry><structfield>value</structfield></entry>
+ <entry>New value or current value.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>__s64</entry>
+ <entry><structfield>value64</structfield></entry>
+ <entry>New value or current value.</entry>
+ </row>
+ <row>
+ <entry></entry>
+ <entry>char *</entry>
+ <entry><structfield>string</structfield></entry>
+ <entry>A pointer to a string.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table pgwide="1" frame="none" id="v4l2-ext-controls">
+ <title>struct <structname>v4l2_ext_controls</structname></title>
+ <tgroup cols="3">
+ &cs-str;
+ <tbody valign="top">
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>ctrl_class</structfield></entry>
+ <entry>The control class to which all controls belong, see
+<xref linkend="ctrl-class" />. Drivers that use a kernel framework for handling
+controls will also accept a value of 0 here, meaning that the controls can
+belong to any control class. Whether drivers support this can be tested by setting
+<structfield>ctrl_class</structfield> to 0 and calling <constant>VIDIOC_TRY_EXT_CTRLS</constant>
+with a <structfield>count</structfield> of 0. If that succeeds, then the driver
+supports this feature.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>count</structfield></entry>
+ <entry>The number of controls in the controls array. May
+also be zero.</entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>error_idx</structfield></entry>
+ <entry><para>Set by the driver in case of an error. If the error is
+associated with a particular control, then <structfield>error_idx</structfield>
+is set to the index of that control. If the error is not related to a specific
+control, or the validation step failed (see below), then
+<structfield>error_idx</structfield> is set to <structfield>count</structfield>.
+The value is undefined if the ioctl returned 0 (success).</para>
+
+<para>Before controls are read from/written to hardware a validation step
+takes place: this checks if all controls in the list are valid controls,
+if no attempt is made to write to a read-only control or read from a write-only
+control, and any other up-front checks that can be done without accessing the
+hardware. The exact validations done during this step are driver dependent
+since some checks might require hardware access for some devices, thus making
+it impossible to do those checks up-front. However, drivers should make a
+best-effort to do as many up-front checks as possible.</para>
+
+<para>This check is done to avoid leaving the hardware in an inconsistent state due
+to easy-to-avoid problems. But it leads to another problem: the application needs to
+know whether an error came from the validation step (meaning that the hardware
+was not touched) or from an error during the actual reading from/writing to hardware.</para>
+
+<para>The, in hindsight quite poor, solution for that is to set <structfield>error_idx</structfield>
+to <structfield>count</structfield> if the validation failed. This has the
+unfortunate side-effect that it is not possible to see which control failed the
+validation. If the validation was successful and the error happened while
+accessing the hardware, then <structfield>error_idx</structfield> is less than
+<structfield>count</structfield> and only the controls up to
+<structfield>error_idx-1</structfield> were read or written correctly, and the
+state of the remaining controls is undefined.</para>
+
+<para>Since <constant>VIDIOC_TRY_EXT_CTRLS</constant> does not access hardware
+there is also no need to handle the validation step in this special way,
+so <structfield>error_idx</structfield> will just be set to the control that
+failed the validation step instead of to <structfield>count</structfield>.
+This means that if <constant>VIDIOC_S_EXT_CTRLS</constant> fails with
+<structfield>error_idx</structfield> set to <structfield>count</structfield>,
+then you can call <constant>VIDIOC_TRY_EXT_CTRLS</constant> to try to discover
+the actual control that failed the validation step. Unfortunately, there
+is no <constant>TRY</constant> equivalent for <constant>VIDIOC_G_EXT_CTRLS</constant>.
+</para></entry>
+ </row>
+ <row>
+ <entry>__u32</entry>
+ <entry><structfield>reserved</structfield>[2]</entry>
+ <entry>Reserved for future extensions. Drivers and
+applications must set the array to zero.</entry>
+ </row>
+ <row>
+ <entry>&v4l2-ext-control; *</entry>
+ <entry><structfield>controls</structfield></entry>
+ <entry>Pointer to an array of
+<structfield>count</structfield> v4l2_ext_control structures. Ignored
+if <structfield>count</structfield> equals zero.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ <table pgwide="1" frame="none" id="ctrl-class">
+ <title>Control classes</title>
+ <tgroup cols="3">
+ &cs-def;
+ <tbody valign="top">
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_USER</constant></entry>
+ <entry>0x980000</entry>
+ <entry>The class containing user controls. These controls
+are described in <xref linkend="control" />. All controls that can be set
+using the &VIDIOC-S-CTRL; and &VIDIOC-G-CTRL; ioctl belong to this
+class.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_MPEG</constant></entry>
+ <entry>0x990000</entry>
+ <entry>The class containing MPEG compression controls.
+These controls are described in <xref
+ linkend="mpeg-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_CAMERA</constant></entry>
+ <entry>0x9a0000</entry>
+ <entry>The class containing camera controls.
+These controls are described in <xref
+ linkend="camera-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_FM_TX</constant></entry>
+ <entry>0x9b0000</entry>
+ <entry>The class containing FM Transmitter (FM TX) controls.
+These controls are described in <xref
+ linkend="fm-tx-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_FLASH</constant></entry>
+ <entry>0x9c0000</entry>
+ <entry>The class containing flash device controls.
+These controls are described in <xref
+ linkend="flash-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_JPEG</constant></entry>
+ <entry>0x9d0000</entry>
+ <entry>The class containing JPEG compression controls.
+These controls are described in <xref
+ linkend="jpeg-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_IMAGE_SOURCE</constant></entry>
+ <entry>0x9e0000</entry> <entry>The class containing image
+ source controls. These controls are described in <xref
+ linkend="image-source-controls" />.</entry>
+ </row>
+ <row>
+ <entry><constant>V4L2_CTRL_CLASS_IMAGE_PROC</constant></entry>
+ <entry>0x9f0000</entry> <entry>The class containing image
+ processing controls. These controls are described in <xref
+ linkend="image-process-controls" />.</entry>
+ </row>
+ </tbody>
+ </tgroup>
+ </table>
+
+ </refsect1>
+
+ <refsect1>
+ &return-value;
+
+ <variablelist>
+ <varlistentry>
+ <term><errorcode>EINVAL</errorcode></term>
+ <listitem>
+ <para>The &v4l2-ext-control; <structfield>id</structfield>
+is invalid, the &v4l2-ext-controls;
+<structfield>ctrl_class</structfield> is invalid, or the &v4l2-ext-control;
+<structfield>value</structfield> was inappropriate (e.g. the given menu
+index is not supported by the driver). This error code is
+also returned by the <constant>VIDIOC_S_EXT_CTRLS</constant> and
+<constant>VIDIOC_TRY_EXT_CTRLS</constant> ioctls if two or more
+control values are in conflict.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>ERANGE</errorcode></term>
+ <listitem>
+ <para>The &v4l2-ext-control; <structfield>value</structfield>
+is out of bounds.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EBUSY</errorcode></term>
+ <listitem>
+ <para>The control is temporarily not changeable, possibly
+because another applications took over control of the device function
+this control belongs to.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>ENOSPC</errorcode></term>
+ <listitem>
+ <para>The space reserved for the control's payload is insufficient.
+The field <structfield>size</structfield> is set to a value that is enough
+to store the payload and this error code is returned.</para>
+ </listitem>
+ </varlistentry>
+ <varlistentry>
+ <term><errorcode>EACCES</errorcode></term>
+ <listitem>
+ <para>Attempt to try or set a read-only control or to get a
+ write-only control.</para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </refsect1>
+</refentry>
+