Hi Greg,
After your previous reply on this thread we started considering to provide this interface and framework/functionality through a userspace service instead of a kernel interface.
The latest iteration on this evolving patch-set doesn’t have strong reasons for living in the kernel anymore - the only objectively strong advantage would be easier driving of ecosystem integration; but I am not sure that's a good enough reason to create a new kernel interface.
I am now looking into adding this through Systemd. Either as a pluggable service or maybe even a systemd builtin offering.
What are your thoughts on it?
Thanks,
Adrian.
On 23/03/2021, 14:57, "Greg KH" <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
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On Mon, Mar 08, 2021 at 05:03:58PM +0100, Alexander Graf wrote:
>
>
> On 08.03.21 15:36, Greg KH wrote:
> >
> > On Mon, Mar 08, 2021 at 04:18:03PM +0200, Adrian Catangiu wrote:
> > > +static struct miscdevice sysgenid_misc = {
> > > + .minor = MISC_DYNAMIC_MINOR,
> > > + .name = "sysgenid",
> > > + .fops = &fops,
> > > +};
> >
> > Much cleaner, but:
> >
> > > +static int __init sysgenid_init(void)
> > > +{
> > > + int ret;
> > > +
> > > + sysgenid_data.map_buf = get_zeroed_page(GFP_KERNEL);
> > > + if (!sysgenid_data.map_buf)
> > > + return -ENOMEM;
> > > +
> > > + atomic_set(&sysgenid_data.generation_counter, 0);
> > > + atomic_set(&sysgenid_data.outdated_watchers, 0);
> > > + init_waitqueue_head(&sysgenid_data.read_waitq);
> > > + init_waitqueue_head(&sysgenid_data.outdated_waitq);
> > > + spin_lock_init(&sysgenid_data.lock);
> > > +
> > > + ret = misc_register(&sysgenid_misc);
> > > + if (ret < 0) {
> > > + pr_err("misc_register() failed for sysgenid\n");
> > > + goto err;
> > > + }
> > > +
> > > + return 0;
> > > +
> > > +err:
> > > + free_pages(sysgenid_data.map_buf, 0);
> > > + sysgenid_data.map_buf = 0;
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static void __exit sysgenid_exit(void)
> > > +{
> > > + misc_deregister(&sysgenid_misc);
> > > + free_pages(sysgenid_data.map_buf, 0);
> > > + sysgenid_data.map_buf = 0;
> > > +}
> > > +
> > > +module_init(sysgenid_init);
> > > +module_exit(sysgenid_exit);
> >
> > So you do this for any bit of hardware that happens to be out there?
> > Will that really work? You do not have any hwid to trigger off of to
> > know that this is a valid device you can handle?
>
> The interface is already useful in a pure container context where the
> generation change request is triggered by software.
>
> And yes, there are hardware triggers, but Michael was quite unhappy about
> potential races between VMGenID change and SysGenID change and thus wanted
> to ideally separate the interfaces. So we went ahead and isolated the
> SysGenID one, as it's already useful as is.
>
> Hardware drivers to inject change events into SysGenID can then follow
> later, for all different hardware platforms. But SysGenID as in this patch
> is a completely hardware agnostic concept.
Ok, this is going to play havoc with fuzzers and other "automated
testers", should be fun to watch! :)
Let's queue this up and see what happens...
thanks,
greg k-h
Amazon Development Center (Romania) S.R.L. registered office: 27A Sf. Lazar Street, UBC5, floor 2, Iasi, Iasi County, 700045, Romania. Registered in Romania. Registration number J22/2621/2005.
