On Fri, Apr 29, 2016 at 11:31:48PM +0100, Al Viro wrote: > On Fri, Apr 29, 2016 at 01:28:00PM -0500, Goldwyn Rodrigues wrote: > > > Yes, you can register any attribute to sysfs, and most filesystems > > are doing exactly that. They maintain the kobject in their > > <fs>_super_block struct and use it to create /sys/fs/<fstype>/<id> > > entries. So what I propose is this: > > [snip] > > What's really missing here is > > 0. carefully audit the existing sysfs users of that sort - they are _very_ > easy to get wrong, especially wrt lifetime issues and locking. As you have > demonstrated yourself in this patchset, BTW... They don't screw with superblock lifetimes for this very reason. On the XFS side, we create the kset object for /sys/fs/xfs in the XFs module init function, and destroy it in the module exit function. There are also some "global" sysfs objects created/destroyed under /sys/fs/xfs at the same time. The per-superblock objects (e.g. /sys/fs/xfs/<dev>/*) are created inside the struct xfs_mount, which means their life cycle is maintained inside the life of the struct superblock. i.e. they are created inside ->fill_super, and removal (and removal completion) occurs inside ->put_super and hence have no impact on or control over the superblock life cycle. ext4 has the same structure of init and teardown, as does btrfs (though it identifies mounted filesystems by uuid rather than device names). Cheers, Dave. -- Dave Chinner david@xxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
