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Fixed MTP to work with TWRP
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awab228
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165
Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
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165
Documentation/DocBook/media/v4l/vidioc-create-bufs.xml
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<refentry id="vidioc-create-bufs">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_CREATE_BUFS</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_CREATE_BUFS</refname>
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<refpurpose>Create buffers for Memory Mapped or User Pointer or DMA Buffer
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I/O</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_create_buffers *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_CREATE_BUFS</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental"> experimental </link>
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interface and may change in the future.</para>
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</note>
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<para>This ioctl is used to create buffers for <link linkend="mmap">memory
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mapped</link> or <link linkend="userp">user pointer</link> or <link
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linkend="dmabuf">DMA buffer</link> I/O. It can be used as an alternative or in
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addition to the <constant>VIDIOC_REQBUFS</constant> ioctl, when a tighter
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control over buffers is required. This ioctl can be called multiple times to
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create buffers of different sizes.</para>
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<para>To allocate the device buffers applications must initialize the
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relevant fields of the <structname>v4l2_create_buffers</structname> structure.
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The <structfield>count</structfield> field must be set to the number of
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requested buffers, the <structfield>memory</structfield> field specifies the
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requested I/O method and the <structfield>reserved</structfield> array must be
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zeroed.</para>
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<para>The <structfield>format</structfield> field specifies the image format
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that the buffers must be able to handle. The application has to fill in this
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&v4l2-format;. Usually this will be done using the
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<constant>VIDIOC_TRY_FMT</constant> or <constant>VIDIOC_G_FMT</constant> ioctl()
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to ensure that the requested format is supported by the driver. Unsupported
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formats will result in an error.</para>
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<para>The buffers created by this ioctl will have as minimum size the size
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defined by the <structfield>format.pix.sizeimage</structfield> field. If the
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<structfield>format.pix.sizeimage</structfield> field is less than the minimum
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required for the given format, then <structfield>sizeimage</structfield> will be
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increased by the driver to that minimum to allocate the buffers. If it is
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larger, then the value will be used as-is. The same applies to the
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<structfield>sizeimage</structfield> field of the
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<structname>v4l2_plane_pix_format</structname> structure in the case of
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multiplanar formats.</para>
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<para>When the ioctl is called with a pointer to this structure the driver
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will attempt to allocate up to the requested number of buffers and store the
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actual number allocated and the starting index in the
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<structfield>count</structfield> and the <structfield>index</structfield> fields
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respectively. On return <structfield>count</structfield> can be smaller than
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the number requested. The driver may also increase buffer sizes if required,
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however, it will not update <structfield>sizeimage</structfield> field values.
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The user has to use <constant>VIDIOC_QUERYBUF</constant> to retrieve that
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information.</para>
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<table pgwide="1" frame="none" id="v4l2-create-buffers">
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<title>struct <structname>v4l2_create_buffers</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>index</structfield></entry>
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<entry>The starting buffer index, returned by the driver.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>count</structfield></entry>
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<entry>The number of buffers requested or granted. If count == 0, then
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<constant>VIDIOC_CREATE_BUFS</constant> will set <structfield>index</structfield>
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to the current number of created buffers, and it will check the validity of
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<structfield>memory</structfield> and <structfield>format.type</structfield>.
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If those are invalid -1 is returned and errno is set to &EINVAL;,
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otherwise <constant>VIDIOC_CREATE_BUFS</constant> returns 0. It will
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never set errno to &EBUSY; in this particular case.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>memory</structfield></entry>
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<entry>Applications set this field to
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<constant>V4L2_MEMORY_MMAP</constant>,
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<constant>V4L2_MEMORY_DMABUF</constant> or
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<constant>V4L2_MEMORY_USERPTR</constant>. See <xref linkend="v4l2-memory"
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/></entry>
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</row>
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<row>
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<entry>&v4l2-format;</entry>
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<entry><structfield>format</structfield></entry>
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<entry>Filled in by the application, preserved by the driver.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[8]</entry>
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<entry>A place holder for future extensions.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>ENOMEM</errorcode></term>
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<listitem>
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<para>No memory to allocate buffers for <link linkend="mmap">memory
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mapped</link> I/O.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The buffer type (<structfield>format.type</structfield> field),
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requested I/O method (<structfield>memory</structfield>) or format
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(<structfield>format</structfield> field) is not valid.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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