Hey, Matt. On Tue, Mar 13, 2012 at 02:45:26PM -0700, Matt Helsley wrote: > If you want to spend your time doing archaeology there are some old threads > that touch on this idea (roughly around 2003-2005). One point against the > idea that I distinctly recall: > > Somewhat like configfs, object lifetimes in cgroups are determined > primarily by the user whereas sysfs object lifetimes are primarily > determined by the kernel. I think the closest we come to user-determined > objects in sysfs occur through debugfs, and module loading/unloading. > However those involve mount/umount and modprobe/rmmod rather than > mkdir/rmdir to create and remove the objects. The thing is that sysfs itself has been almost completely rewritten since that time to 1. decouple internal representation from vfs objects and 2. provide proper isolation between the userland and kernel code exposing data through sysfs. #1 began mostly due to the large size of dentries and inodes but, with the benefit of hindsight, I think it just was a bad idea to piggyback on vfs objects for object life-cycle management and locking for stuff which is wholely described in memory with simplistic locking. #2 was necessary to avoid hanging device detach due to open sysfs file from userland. sysfs now has notion of "active access" encompassing only each show/store op invocation and it only guarantees that the associated device doesn't go away while active accesses are in progress. The sysfs heritage is almost recognizable and unfortunately almost the same set of problems (nobody wants show/store ops to be called on unlinked css waiting for references to be drained). As refactoring and sharing sysfs won't be a trivial task, my plan is to first augment cgroupfs as necessary with longer term goal of converging and later sharing the same code with sysfs. Thanks. -- tejun _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/containers
