On Thu, Dec 30, 2010 at 05:05:22AM -0600, Rob Landley wrote: > On Thu, Dec 30, 2010 at 4:44 AM, Kirill A. Shutemov <kas@xxxxxxxxxx> wrote: > > On Thu, Dec 30, 2010 at 04:05:07AM -0600, Rob Landley wrote: > >> On 12/30/2010 03:44 AM, Kirill A. Shutemov wrote: > >> >>> If no rpcmount mountoption, no rpc_pipefs was found at > >> >>> '/var/lib/nfs/rpc_pipefs' and we are in init's mount namespace, we use > >> >>> init_rpc_pipefs. > >> >> > >> >> It's the "we are in init's mount namespace" that I was wondering about. > >> >> > >> >> So if I naievely chroot, nfs mount stops working the way it did before I > >> >> chrooted unless I do an extra setup step? > >> > > >> > No. It will work as before since you are still in init's mount namespace. > >> > Creating new mount namespace changes rules. > >> > >> Ah, CLONE_NEWNS and then you need /var/lib/nfs/rpc_pipefs. Got it. > >> > >> I'm kind of surprised that the kernel cares about a specific path under > >> /var/lib. (Seems like policy in the kernel somehow.) > > > > Yep. It's bad, but there is way to overwrite the default. > > > > Other way is to leave 'rpcmount' mountoption without default. > > get_rpc_pipefs(NULL) in init's mount namespace will always return > > init_rpc_pipefs, without filesystem lookup. > > get_rpc_pipefs(NULL) in non-init's mount namespace will always return > > error. > > > > So you will have to specify 'rpcmount' mountoption for every nfs mount in > > container. Hmm, I guess, it may confuse user. > > > > Or we can try to move the default to userspace. /sbin/mount.nfs? > > /proc/sys/kernel/hotplug exists to tell the kernel where to find the hotplug > binary. Once upon a time /sys/hotplug was the default value, and that was > there to overwrite it. (They changed the default to blank (disabled) not due > to policy reasons, but due to adding the netlink hotplug notification > mechanism and making that the default.) > > I bring that up to point out that the general consensus about policy in the > kernel seems to be "when you really really can't avoid having any, make a > sane default the user can override". > > (Of course adding another entry to the crawling horror of /proc may not > be an improvement. But individual overrides at the mount -o level seem > like a non-optimal granularity for this...) Do you propose to implement default as sysctl parameter? > >> Can't it just > >> check the current process's mount list to see if an instance of > >> rpc_pipefs is mounted in the current namespace the way lxc looks for > >> cgroups? Or are there potential performance/scalability issues with that? > > > > What should we do if we have several rpc_pipefs mounts in the namespace? > > You mean more than one inside a given process's view of the filesystem, taking > into account chroot like /proc/mounts does? > > Before this patch series, there was one instance systemwide. The patch changed > that to look a fixed location in the filesystem relative to the > current chroot. Either > way, there was one instance available to a given process doing an nfs mount. > > What's the use case for having more than one visible to a given process? > (NUMA scalability? Some sort of multipath/VPN routing context?) It's no so obvious for me why we should restrict it. ;) Currently, there is no association between rpc_pipefs and mount namespace, so I don't see simple way to restrict number of rpc_pipefs per mount namespace. Associating mount namespace with rpc_pipefs is not a good idea, I think. -- Kirill A. Shutemov -- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
