On Mon, Nov 22, 2010 at 04:48:54PM -0800, Yehuda Sadeh Weinraub wrote: > On Mon, Nov 22, 2010 at 4:14 PM, Greg KH <greg@xxxxxxxxx> wrote: > > On Fri, Nov 19, 2010 at 12:42:51PM -0800, Yehuda Sadeh Weinraub wrote: > >> On Thu, Nov 18, 2010 at 6:08 PM, Greg KH <greg@xxxxxxxxx> wrote: > >> > On Thu, Nov 18, 2010 at 02:53:35PM -0800, Yehuda Sadeh Weinraub wrote: > >> >> Yes, pretty much. One problem that I do see is that if we define the > >> >> snaps/ as a device (and not just as a kobj) as you suggested before, > >> >> it'll automatically create a 'uevent' entry under it which can be a > >> >> real issue in the case we have a snapshot named like that. Shouldn't > >> >> we just create it as a kobj in that case? > >> > > >> > No. Just use the subdirectory option of an attribute group to handle > >> > that and you will not need to create any device or kobject with that > >> > name, the driver core will handle it all automatically for you. > >> > > >> > >> One issue with using the groups name, is that it's not nested (unless > >> I'm missing something), so we can't have it done for the entire > >> planned hierarchy without holding a kobject on the way. Just a > >> reminder, the device-specific hierarchy would look like this: > >> > >> 1. /sys/bus/rbd/devices/<id>/ > >> 2. /sys/bus/rbd/devices/<id>/<device_attrs> > >> 3. /sys/bus/rbd/devices/<id>/snaps/ > >> 4. /sys/bus/rbd/devices/<id>/snaps/<snap_name>/ > >> 5. /sys/bus/rbd/devices/<id>/snaps/<snap_name>/<snap_attrs> > >> > >> One solution would be to create kobjects for (3) and for (4), without > >> using a group name. > > > > Ick, no. > > > >> Another way, we can create groups for (2), and (3) > >> under (1), but that's about it, > > > > attribute group for 2 is fine. > > > >> you can't create the snap specific directory this way without > >> resorting to some internal sysfs directory creation, which will be > >> horribly wrong. At that point we don't have anything for 'snaps', and > >> we don't really need to do any operations under that directory, we > >> just need it to exist so that it contains the snapshot-specific > >> directories. > > > > But you need to do something with those snapshots, right? So, why even > > have "snaps" be a subdir? Why not just make <snap_name> a struct device > > with <id> being the parent, and it living on the same bus_type, but > > being a different device_type (like partitions and block devices are), > > The reason we keep snapshots in a separate subdirectory is that they > can have arbitrary name. So either we prefix them and put them in a > common namespace with the devices, or we put them down the hierarchy. Do either one. I would suggest a prefix. > In any case we don't do any operations on them, we just have them for > informational use and we put them there so that we don't have one big > file that lists them all. But something cares about them, so treat them properly. > >> Another way would be to create a group for (2) under (1) and create a > >> kobject for (3), for which you can create group per snapshot. > >> > >> Am I missing something? We already have the first solution (kobjects > >> only) implemented, is there some real benefit for using the third > >> method? We'll have to manually add remove groups anyway, as snapshots > >> can be removed and new snapshots can be added. > > > > Never add kobjects to a struct device, that is showing you that > > something is wrong, and that userspace really will want to get that > > create/destroy event of the sub child. > > > > But they're there as information device attributes, it's nothing like > partitions in block devices. So we want to just be able to list them > and their attributes easily (and nicely), without having to put them > in one big file. Then use a prefix and put everything in the same subdirectory underneath the id and you should be fine, right? thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
