Re: [PATCH] s390: Hypervisor File System

[Kyle Moffett <mrmacman_g4@mac.com>]

On May 2, 2006, at 17:49:08, Kay Sievers wrote:
> If you can assume that processes accessing the values are  
> cooperative, it already works without any changes:
>
>   $ time flock /sys/class/firmware echo 1 > /sys/class/firmware/ 
> timeout
>   real    0m0.005s
>
>   $ flock /sys/class/firmware sleep 5&
>   [1] 6468
>
>   $ time flock /sys/class/firmware echo 1 > /sys/class/firmware/ 
> timeout
>   real    0m3.558s

But that doesn't solve the problem for framebuffer devices or for the  
s390 code.  Such transactions have one or more of the following  
properties:

(1)  A read operation is _expensive_ or adds unacceptable latencies  
and should be done as rarely as possible
(2)  The data must be all written to hardware simultaneously by the  
kernel; a partial update does not make sense and would cause  
undesired operation from the hardware.

The idea with the transactions would be to create a kernel-memory  
buffer-layer of sorts on top of the underlying sysfs tree to cache  
the read data and collect writes for an atomic commit.  I'll see if I  
can make something work.

Cheers,
Kyle Moffett
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