Re: readdir returns d_type=DT_UNKNOWN to overlay exported dir (NFSv3)

[Trond Myklebust <trondmy@primarydata.com>]

On Thu, 2018-03-15 at 15:13 +0200, Amir Goldstein wrote:
> On Thu, Mar 15, 2018 at 11:47 AM, Eddie Horng <eddiehorng.tw@gmail.co
> m> wrote:
> > I tried to track the difference between overlay-NFSv3 and ext4-
> > NFSv3
> > of encode_post_op_attr.
> > mount configuration:
> > none /share overlay
> > rw,relatime,lowerdir=/base/lower,upperdir=/base/upper,workdir=/base
> > /work,index=on,nfs_export=on
> > 0 0
> > localhost:/share /mnt/n nfs
> > rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,prot
> > o=tcp,timeo=600,retrans=2,sec=sys,mountaddr=127.0.0.1,mountvers=3,m
> > ountport=40931,mountproto=udp,local_lock=none,addr=127.0.0.1
> > 0 0
> > /dev/loop0 /share2 ext4 rw,relatime,data=ordered 0 0
> > localhost:/share2 /mnt/n2 nfs
> > rw,relatime,vers=3,rsize=1048576,wsize=1048576,namlen=255,hard,prot
> > o=tcp,timeo=600,retrans=2,sec=sys,mountaddr=127.0.0.1,mountvers=3,m
> > ountport=40931,mountproto=udp,local_lock=none,addr=127.0.0.1
> > 0 0
> > 
> > file tree:
> > /mnt/n
> > > -- dirA
> > >   `-- bar
> > > -- dirL
> > >   `-- ro-file
> > 
> > `-- foo
> > 
> > /mnt/n2
> > `-- lost+found
> > 
> > Attached log are dmesg start from "readdir /mnt/n (n2)" with nfs
> > and
> > nfsd log are enabled all by sunrpc.nfs(d)_debug. I also add a
> > dump_stack() in the beginning of encode_post_op_attr.
> > 
> > It seems overlay and ext4 have different call flow after "nfsd:
> > READDIR+", there is no failure in overlay's encode_post_op_attr,
> > nfsd
> > does fill the attrs, same as ext4 but it has additional readdir
> > call
> > to child node of "/". I'm not sure if this is normal to overlay and
> > is
> > the cause of DT_UNKNOWN.
> 
> I tried to follow nfsd readdir code to see where the difference can
> come
> from, but nothing poped at me so far.
> 
> > 
> > In additional, overlay returns DT_UNKNOWN to either lower dir or
> > merged dir.
> 
> Your test is readdir of a merged dir, the behavior could differ when
> readdir of
> an overlayfs non merged dir.
> 
> Please send the output and dmesg of readdir of the non-merged lower
> dir:
> 
> /readdir/a.out /mnt/n/dirL
> 
> Please mount an NFS share of /base and send the output of the same
> dir:
> 
> /readdir/a.out /mnt/n_base/lower/n/dirL
> 
> Right now I speculate that the issue you report is related to
> how merged dirs are iterated, but not sure exactly why.

fs/nfsd has nothing to do with ${SUBJECT}.

If you want to trace where the DT_UNKNOWN is coming from, then you need
to look at the _client_ code in fs/nfs/nfs3xdr.c:nfs3_decode_dirent(). 

-- 
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@primarydata.com