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DragonFly kernel List (threaded) for 2005-11
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Re: Copyout to XIO

From: Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>
Date: Wed, 30 Nov 2005 10:16:15 -0800 (PST)

:I have a question regarding the use of XIO's. It seems that XIO's let
:a thread without process context read another processes's user buffer
:(which should be very handy), but there doesn't seem to be a way for
:that thread to write back into the process's address space, unless 
:that process happens to be switched in and we use copyout() the old
:fashioned way.
:How would a new-style device driver or filesystem implement READ for
:a user process from within its own thread?

    All device I/O is eventually going to be converted to a vm_page array
    on entry.  We're about half way along that goal.  Certain higher level
    system calls, such as read and write, will have to break large I/O's
    into smaller chunks that can be page-listed.

    The current use of alternative PMAPs to access another processes address
    space will eventually be removed, since its impossible to abstract
    that sort of access across a cluster.

					Matthew Dillon 

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