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| >Video for Linux Two API Specification: Revision 0.24</TH |
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| ><H1 |
| ><A |
| NAME="VIDIOC-REQBUFS" |
| ></A |
| >ioctl VIDIOC_REQBUFS</H1 |
| ><DIV |
| CLASS="REFNAMEDIV" |
| ><A |
| NAME="AEN13700" |
| ></A |
| ><H2 |
| >Name</H2 |
| >VIDIOC_REQBUFS -- Initiate Memory Mapping or User Pointer I/O</DIV |
| ><DIV |
| CLASS="REFSYNOPSISDIV" |
| ><A |
| NAME="AEN13703" |
| ></A |
| ><H2 |
| >Synopsis</H2 |
| ><DIV |
| CLASS="FUNCSYNOPSIS" |
| ><P |
| ></P |
| ><A |
| NAME="AEN13704" |
| ></A |
| ><P |
| ><CODE |
| ><CODE |
| CLASS="FUNCDEF" |
| >int ioctl</CODE |
| >(int fd, int request, struct v4l2_requestbuffers *argp);</CODE |
| ></P |
| ><P |
| ></P |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13714" |
| ></A |
| ><H2 |
| >Arguments</H2 |
| ><P |
| ></P |
| ><DIV |
| CLASS="VARIABLELIST" |
| ><DL |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >fd</CODE |
| ></DT |
| ><DD |
| ><P |
| >File descriptor returned by <A |
| HREF="r14090.htm" |
| ><CODE |
| CLASS="FUNCTION" |
| >open()</CODE |
| ></A |
| >.</P |
| ></DD |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >request</CODE |
| ></DT |
| ><DD |
| ><P |
| >VIDIOC_REQBUFS</P |
| ></DD |
| ><DT |
| ><CODE |
| CLASS="PARAMETER" |
| >argp</CODE |
| ></DT |
| ><DD |
| ><P |
| ></P |
| ></DD |
| ></DL |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13734" |
| ></A |
| ><H2 |
| >Description</H2 |
| ><P |
| >This ioctl is used to initiate <A |
| HREF="x5791.htm" |
| >memory |
| mapped</A |
| > or <A |
| HREF="x5884.htm" |
| >user pointer</A |
| > |
| I/O. Memory mapped buffers are located in device memory and must be |
| allocated with this ioctl before they can be mapped into the |
| application's address space. User buffers are allocated by |
| applications themselves, and this ioctl is merely used to switch the |
| driver into user pointer I/O mode.</P |
| ><P |
| >To allocate device buffers applications initialize three |
| fields of a <CODE |
| CLASS="STRUCTNAME" |
| >v4l2_requestbuffers</CODE |
| > structure. |
| They set the <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > field to the respective |
| stream or buffer type, the <CODE |
| CLASS="STRUCTFIELD" |
| >count</CODE |
| > field to |
| the desired number of buffers, and <CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| > |
| must be set to <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_MMAP</CODE |
| >. When the ioctl |
| is called with a pointer to this structure the driver attempts to |
| allocate the requested number of buffers and stores the actual number |
| allocated in the <CODE |
| CLASS="STRUCTFIELD" |
| >count</CODE |
| > field. It can be |
| smaller than the number requested, even zero, when the driver runs out |
| of free memory. A larger number is possible when the driver requires |
| more buffers to function correctly.<A |
| NAME="AEN13746" |
| HREF="r13696.htm#FTN.AEN13746" |
| ><SPAN |
| CLASS="footnote" |
| >[1]</SPAN |
| ></A |
| > When memory mapping I/O is not supported the ioctl |
| returns an <SPAN |
| CLASS="ERRORCODE" |
| >EINVAL</SPAN |
| > error code.</P |
| ><P |
| >Applications can call <CODE |
| CLASS="CONSTANT" |
| >VIDIOC_REQBUFS</CODE |
| > |
| again to change the number of buffers, however this cannot succeed |
| when any buffers are still mapped. A <CODE |
| CLASS="STRUCTFIELD" |
| >count</CODE |
| > |
| value of zero frees all buffers, after aborting or finishing any DMA |
| in progress, an implicit <A |
| HREF="r13817.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_STREAMOFF</CODE |
| ></A |
| >. </P |
| ><P |
| >To negotiate user pointer I/O, applications initialize only |
| the <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > field and set |
| <CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| > to |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_USERPTR</CODE |
| >. When the ioctl is called |
| with a pointer to this structure the driver prepares for user pointer |
| I/O, when this I/O method is not supported the ioctl returns an |
| <SPAN |
| CLASS="ERRORCODE" |
| >EINVAL</SPAN |
| > error code.</P |
| ><DIV |
| CLASS="TABLE" |
| ><A |
| NAME="V4L2-REQUESTBUFFERS" |
| ></A |
| ><P |
| ><B |
| >Table 1. struct <CODE |
| CLASS="STRUCTNAME" |
| >v4l2_requestbuffers</CODE |
| ></B |
| ></P |
| ><TABLE |
| BORDER="0" |
| FRAME="void" |
| WIDTH="100%" |
| CLASS="CALSTABLE" |
| ><COL |
| WIDTH="25%" |
| TITLE="C1"><COL |
| WIDTH="25%" |
| TITLE="C2"><COL |
| WIDTH="50%" |
| TITLE="C3"><TBODY |
| VALIGN="TOP" |
| ><TR |
| ><TD |
| >__u32</TD |
| ><TD |
| ><CODE |
| CLASS="STRUCTFIELD" |
| >count</CODE |
| ></TD |
| ><TD |
| >The number of buffers requested or granted. This |
| field is only used when <CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| > is set to |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_MMAP</CODE |
| >.</TD |
| ></TR |
| ><TR |
| ><TD |
| >enum <A |
| HREF="x5953.htm#V4L2-BUF-TYPE" |
| >v4l2_buf_type</A |
| ></TD |
| ><TD |
| ><CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| ></TD |
| ><TD |
| >Type of the stream or buffers, this is the same |
| as the struct <A |
| HREF="r10944.htm#V4L2-FORMAT" |
| >v4l2_format</A |
| > <CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > field. See <A |
| HREF="x5953.htm#V4L2-BUF-TYPE" |
| >Table 3-2</A |
| > for valid values.</TD |
| ></TR |
| ><TR |
| ><TD |
| >enum <A |
| HREF="x5953.htm#V4L2-MEMORY" |
| >v4l2_memory</A |
| ></TD |
| ><TD |
| ><CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| ></TD |
| ><TD |
| >Applications set this field to |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_MMAP</CODE |
| > or |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_MEMORY_USERPTR</CODE |
| >.</TD |
| ></TR |
| ><TR |
| ><TD |
| >__u32</TD |
| ><TD |
| ><CODE |
| CLASS="STRUCTFIELD" |
| >reserved</CODE |
| >[2]</TD |
| ><TD |
| >A place holder for future extensions and custom |
| (driver defined) buffer types <CODE |
| CLASS="CONSTANT" |
| >V4L2_BUF_TYPE_PRIVATE</CODE |
| > and |
| higher.</TD |
| ></TR |
| ></TBODY |
| ></TABLE |
| ></DIV |
| ></DIV |
| ><DIV |
| CLASS="REFSECT1" |
| ><A |
| NAME="AEN13798" |
| ></A |
| ><H2 |
| >Return Value</H2 |
| ><P |
| >On success <SPAN |
| CLASS="RETURNVALUE" |
| >0</SPAN |
| > is returned, on error <SPAN |
| CLASS="RETURNVALUE" |
| >-1</SPAN |
| > and the <CODE |
| CLASS="VARNAME" |
| >errno</CODE |
| > variable is set appropriately:</P |
| ><P |
| ></P |
| ><DIV |
| CLASS="VARIABLELIST" |
| ><DL |
| ><DT |
| ><SPAN |
| CLASS="ERRORCODE" |
| >EBUSY</SPAN |
| ></DT |
| ><DD |
| ><P |
| >The driver supports multiple opens and I/O is already |
| in progress, or reallocation of buffers was attempted although one or |
| more are still mapped.</P |
| ></DD |
| ><DT |
| ><SPAN |
| CLASS="ERRORCODE" |
| >EINVAL</SPAN |
| ></DT |
| ><DD |
| ><P |
| >The buffer type (<CODE |
| CLASS="STRUCTFIELD" |
| >type</CODE |
| > field) or the |
| requested I/O method (<CODE |
| CLASS="STRUCTFIELD" |
| >memory</CODE |
| >) is not |
| supported.</P |
| ></DD |
| ></DL |
| ></DIV |
| ></DIV |
| ><H2 |
| CLASS="FOOTNOTES" |
| >Notes</H2 |
| ><TABLE |
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| ><A |
| NAME="FTN.AEN13746" |
| HREF="r13696.htm#AEN13746" |
| ><SPAN |
| CLASS="footnote" |
| >[1]</SPAN |
| ></A |
| ></TD |
| ><TD |
| ALIGN="LEFT" |
| VALIGN="TOP" |
| WIDTH="95%" |
| ><P |
| >For example video output requires at least two buffers, |
| one displayed and one filled by the application.</P |
| ></TD |
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