Re: userspace block driver?

[Avi Kivity]

Oliver Neukum wrote:

> On Wed, 9 Nov 2005, Jeff Garzik wrote:
>
>  
>
> > Has anybody put any thought towards how a userspace block driver would work?
> >
> > Consider a block device implemented via an SSL network connection.  I don't
> > want to put SSL in the kernel, which means the only other alternative is to
> > pass data to/from a userspace daemon.
> >    
>
> I am afraid this is impossible without some heavy infrastructure work.
> You will almost inevitably deadlock. Yes, you can mlock() your driver, but 
> that still will not tell the kernel that GFP_KERNEL must be replaced with 
> GFP_NOIO if it is triggered by syscalls you are doing.
>
>  
A simple patch can help here (in addition to mlockall()):

 http://www.ussg.iu.edu/hypermail/linux/kernel/0407.3/0297.html

you might want to increase the free memory target as well.
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