On Thu, Oct 15, 2020 at 11:42:51AM +0800, Chengguang Xu wrote: > ---- 在 星期四, 2020-10-15 11:25:01 Al Viro <viro@xxxxxxxxxxxxxxxxxx> 撰写 ---- > > On Sat, Oct 10, 2020 at 10:23:51PM +0800, Chengguang Xu wrote: > > > Currently there is no notification api for kernel about modification > > > of vfs inode, in some use cases like overlayfs, this kind of notification > > > will be very helpful to implement containerized syncfs functionality. > > > As the first attempt, we introduce marking inode dirty notification so that > > > overlay's inode could mark itself dirty as well and then only sync dirty > > > overlay inode while syncfs. > > > > Who's responsible for removing the crap from notifier chain? And how does > > that affect the lifetime of inode? > > In this case, overlayfs unregisters call back from the notifier chain of upper inode > when evicting it's own inode. It will not affect the lifetime of upper inode because > overlayfs inode holds a reference of upper inode that means upper inode will not be > evicted while overlayfs inode is still alive. Let me see if I've got it right: * your chain contains 1 (for upper inodes) or 0 (everything else, i.e. the vast majority of inodes) recepients * recepient pins the inode for as long as the recepient exists That looks like a massive overkill, especially since all you are propagating is dirtying the suckers. All you really need is one bit in your inode + hash table indexed by the address of struct inode (well, middle bits thereof, as usual). With entries embedded into overlayfs-private part of overlayfs inode. And callback to be called stored in that entry...
