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>generic_make_request</SPAN
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><H2
>Name</H2
>generic_make_request -- </DIV
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><H2
>Synopsis</H2
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><CODE
><CODE
CLASS="FUNCDEF"
>void <TT
CLASS="FUNCTION"
>generic_make_request </TT
></CODE
>(int <TT
CLASS="PARAMETER"
><I
>rw</I
></TT
>, struct buffer_head * <TT
CLASS="PARAMETER"
><I
>bh</I
></TT
>);</CODE
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><H2
>Arguments</H2
><P
></P
><DIV
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><DL
><DT
><TT
CLASS="PARAMETER"
><I
>rw</I
></TT
></DT
><DD
><P
> READ, WRITE, or READA - what sort of I/O is desired.
</P
></DD
><DT
><TT
CLASS="PARAMETER"
><I
>bh</I
></TT
></DT
><DD
><P
> The buffer head describing the location in memory and on the device.
</P
></DD
></DL
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><A
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></A
><H2
>Description</H2
><P
> <TT
CLASS="FUNCTION"
>generic_make_request</TT
> is used to make I/O requests of block
devices. It is passed a &struct buffer_head and a &rw value. The
<TT
CLASS="CONSTANT"
>READ</TT
> and <TT
CLASS="CONSTANT"
>WRITE</TT
> options are (hopefully) obvious in meaning. The
<TT
CLASS="CONSTANT"
>READA</TT
> value means that a read is required, but that the driver is
free to fail the request if, for example, it cannot get needed
resources immediately.
</P
><P
> <TT
CLASS="FUNCTION"
>generic_make_request</TT
> does not return any status. The
success/failure status of the request, along with notification of
completion, is delivered asynchronously through the bh->b_end_io
function described (one day) else where.
</P
><P
> The caller of generic_make_request must make sure that b_page,
b_addr, b_size are set to describe the memory buffer, that b_rdev
and b_rsector are set to describe the device address, and the
b_end_io and optionally b_private are set to describe how
completion notification should be signaled. BH_Mapped should also
be set (to confirm that b_dev and b_blocknr are valid).
</P
><P
> generic_make_request and the drivers it calls may use b_reqnext,
and may change b_rdev and b_rsector. So the values of these fields
should NOT be depended on after the call to generic_make_request.
Because of this, the caller should record the device address
information in b_dev and b_blocknr.
</P
><P
> Apart from those fields mentioned above, no other fields, and in
particular, no other flags, are changed by generic_make_request or
any lower level drivers.
</P
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