Re: [RFC PATCH 1/5] fs: introduce notifier list for vfs inode

[Chengguang Xu <cgxu519@mykernel.net>]

 ---- 在 星期四, 2020-10-15 12:57:41 Al Viro <viro@zeniv.linux.org.uk> 撰写 ----
 > 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@zeniv.linux.org.uk> 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...
 > 

Hi AI, Jack, Amir

Based on your feedback, I would to change the inode dirty notification
something like below, is it acceptable? 


diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index 1492271..48473d9 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -2249,6 +2249,14 @@ void __mark_inode_dirty(struct inode *inode, int flags)
 
        trace_writeback_mark_inode_dirty(inode, flags);
 
+       if (inode->state & I_OVL_INUSE) {
+               struct inode *ovl_inode;
+
+               ovl_inode = ilookup5(NULL, (unsigned long)inode, ovl_inode_test, inode);
+               if (ovl_inode)
+                       __mark_inode_dirty(ovl_inode, flags);
+       }
+
        /*
         * Don't do this for I_DIRTY_PAGES - that doesn't actually
         * dirty the inode itself
diff --git a/fs/inode.c b/fs/inode.c
index 72c4c34..ed6c85e 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -820,7 +820,7 @@ static struct inode *find_inode(struct super_block *sb,
 
 repeat:
        hlist_for_each_entry(inode, head, i_hash) {
-               if (inode->i_sb != sb)
+               if (sb && inode->i_sb != sb)
                        continue;
                if (!test(inode, data))
                        continue;


Thanks,
Chengguang