Re: userspace block driver?

Avi Kivity
2005-11-09T08:37:07Z

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.