Re: [Haskell-cafe] Genuine Need For Persistent Global State?

alangcarter:

On Fri, Oct 16, 2009 at 9:13 PM, Bryan O'Sullivan wrote:

You don't need anything special for this. A Linux kernel "struct device" has a "void *driver_data" member which is private for your use, and intended for precisely this purpose. Global persistent state makes no more sense for kernel drivers than for most other code: how would it work if you had two mice plugged into your system?

Thanks Bryan - your thought on this is pure and true :-)

Although I'm just making a toy driver, I wanted to exercise the bits a real one would need, and wrongly thought persistent state would matter. You're quite right though - generally, things that matter should go in the per device store, which can easily be kmalloc()ed/kfree()ed on open/close, picked up and passed into Haskell as a Ptr on write/read (so avoiding even the need to understand the C struct in Haskell), then peeked and poked.

My driver can now accumulate data as I wanted, and I don't feel like I've cheated.

So what solution did you pick in the end? Allocate on the C side, and pass a reference back and forth? -- Don