From owner-freebsd-hackers  Tue May 11  8: 5:40 1999
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From: "Stan Shkolny" <stan@osgroup.com>
To: <hackers@FreeBSD.ORG>
Subject: vmapbuf (was:Which O/S routines are subject to change?)
Date: Tue, 11 May 1999 10:06:00 -0500
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Well, I see that I need to ask a more precise question.

My character device driver receives a pointer to a user data buffer in the
user's address space. I need to DMA those data. For this, I need to bring
the
pages into memory and lock them before initiating the DMA.

My book tells about physio(). However, I found it unconvenient for me.
One reason is that its functionality doesn't fit well into my driver's
architecture. Another reason is that it calls the vmapbuf() to bring the
data buffer into memory. vmapbuf(), in turn, maps the buffer into the kernel
address space. I don't want to do this, since I have no need for the data
buffer in the kernel space since the only thing that touches it is the DMA
engine.

In other words, I want to write my own routine.

In general, physio() looks like this:

if useracc()
    vmapbuf()
    *strategy()
    vunmapbuf()
endif

And vmapbuf() like this:

vm_fault_quick()
vm_page_hold()
pmap_kenter()    // maps the memory into the kernel space

And I want to write something like this in my driver:
if useracc()
    vm_fault_quick()
    vm_page_hold()
    <initiating DMA>
endif

So, is this likely for the above 3 functions to change or disappear in the
next versions? Can they be considered "stable"?




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