Hello, On Thu, Jan 13, 2011 at 03:49:50PM +0100, Milan Broz wrote: > So listing block device tree using ONE interface (sysfs) to check > and display device tree for ALL subsystems seems to be good idea for > me. In this exactly defined case. > > I am not saying that symlinks are perfect, just that generic > interface here is not superfluous. I'm not saying finding out the current owner is superflous. That actually is useful but what's implemented now doesn't satisfy that in any generic manner. It only works for md/dm and is designed in such way that it can't be used out of that scope. So, it's only useful for md/dm and for those two cases it tries to show information which doesn't really belong there using an overly complex mechanism. Block device open allows _nesting_ by the claiming device. It is never meant to track different nested claimers and it shows in the implementation and interface. The holder tracking doesn't fit anywhere. It's a completely separate piece of logic which doesn't mix with anything else in the block layer. If you consider its only user - dm-table, the whole picture is somewhat uglier. dm-table tracks how it uses block devices but only within a single target, so there are two separate layers of reference counting going on. This again is caused by the above stated design inconsistency. As block device only considers single claimer which doesn't have to be another device, the owner naturally should have been something which only points to single in-kernel entity in a way which doesn't require link to another sysfs entry. Karel pointed out that having different methods between md and dm would be silly; however, that is a problem which should be solved between dm and md and actually is a quite artificial problem (or solution). It only exists because dm and md do very similar things in many cases. A block device can be used by many more things which are way out of the scope which can be represented in the sysfs hierarchy. It simply is impossible to represent that relationship with symlinks under block device sysfs hierarchy. Thank you. -- tejun -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
