On Tue, Sep 06, 2011 at 10:27:45AM +0200, Jan Kiszka wrote: > On 2011-09-06 10:04, Michael S. Tsirkin wrote: > > 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 > > Except that the "userspace" here is still only half of the truth It's the name of the lock :) > and I > prefer to drop it, the naming locks good to me. OK, I think it's acceptable. > > * > > * 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. > > Also, I bet we would make lockdep unhappy when calling > down_write_trylock from IRQ context. > > Jan I think I did this at some point, should be fine. But whatever. > -- > Siemens AG, Corporate Technology, CT T DE IT 1 > Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
