Re: [RFC] pci: Rework config space blocking services

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Sep 06, 2011 at 09:18:13AM +0200, Jan Kiszka wrote:
> >> @@ -401,36 +403,58 @@ int pci_vpd_truncate(struct pci_dev *dev, size_t size)
> >>  EXPORT_SYMBOL(pci_vpd_truncate);
> >>
> >>  /**
> >> - * pci_block_user_cfg_access - Block userspace PCI config reads/writes
> >> + * pci_block_cfg_access - Block PCI config reads/writes
> > 
> > This comment seems confusing. We don't in fact block all config
> > reads writes. Instead we block userspace accesses and
> > concurrent block requests.
> 
> I'm open for a better suggestion that summarize the more verbose (and
> hopefully clearer) explanation below.

I think the problem is, it doesn't block config access
and we call it pci_block_cfg_access.

Thinking about it, doesn't this behave somewhat like a lock?
How about

pci_user_cfg_access_trylock
pci_user_cfg_access_lock
pci_user_cfg_access_unlock

And then:
 * pci_user_cfg_access_lock - Lock userspace PCI config access
 *
 * When locked, any userspace reads or writes to config space
 * and concurrent lock requests will sleep, and trylock requests
 * will fail, until pci_user_cfg_access_unlock is called.

I had a brief thought of using an rwsem internally, but
this would make trylock fail if userspace does config read,
changing semantics.

-- 
MST