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>blk_init_queue</SPAN
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><H2
>Name</H2
>blk_init_queue -- prepare a request queue for use with a block device
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>Synopsis</H2
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><P
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><P
><CODE
><CODE
CLASS="FUNCDEF"
>void <TT
CLASS="FUNCTION"
>blk_init_queue </TT
></CODE
>(request_queue_t * <TT
CLASS="PARAMETER"
><I
>q</I
></TT
>, request_fn_proc * <TT
CLASS="PARAMETER"
><I
>rfn</I
></TT
>);</CODE
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><H2
>Arguments</H2
><P
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><DIV
CLASS="VARIABLELIST"
><DL
><DT
><TT
CLASS="PARAMETER"
><I
>q</I
></TT
></DT
><DD
><P
> The &request_queue_t to be initialised
</P
></DD
><DT
><TT
CLASS="PARAMETER"
><I
>rfn</I
></TT
></DT
><DD
><P
> The function to be called to process requests that have been
placed on the queue.
</P
></DD
></DL
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><A
NAME="AEN11646"
></A
><H2
>Description</H2
><P
> If a block device wishes to use the standard request handling procedures,
which sorts requests and coalesces adjacent requests, then it must
call <TT
CLASS="FUNCTION"
>blk_init_queue</TT
>. The function <TT
CLASS="PARAMETER"
><I
>rfn</I
></TT
> will be called when there
are requests on the queue that need to be processed. If the device
supports plugging, then <TT
CLASS="PARAMETER"
><I
>rfn</I
></TT
> may not be called immediately when requests
are available on the queue, but may be called at some time later instead.
Plugged queues are generally unplugged when a buffer belonging to one
of the requests on the queue is needed, or due to memory pressure.
</P
><P
> <TT
CLASS="PARAMETER"
><I
>rfn</I
></TT
> is not required, or even expected, to remove all requests off the
queue, but only as many as it can handle at a time. If it does leave
requests on the queue, it is responsible for arranging that the requests
get dealt with eventually.
</P
><P
> A global spin lock <TT
CLASS="ENVAR"
>$io_request_lock</TT
> must be held while manipulating the
requests on the request queue.
</P
><P
> The request on the head of the queue is by default assumed to be
potentially active, and it is not considered for re-ordering or merging
whenever the given queue is unplugged. This behaviour can be changed with
<TT
CLASS="FUNCTION"
>blk_queue_headactive</TT
>.
</P
></DIV
><DIV
CLASS="REFSECT1"
><A
NAME="AEN11658"
></A
><H2
>Note</H2
><P
> <TT
CLASS="FUNCTION"
>blk_init_queue</TT
> must be paired with a <TT
CLASS="FUNCTION"
>blk_cleanup_queue</TT
> call
when the block device is deactivated (such as at module unload).
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