On Wed, Mar 28, 2018 at 2:15 PM, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > On Wed, 2018-03-28 at 07:45 +0300, Amir Goldstein wrote: >> On Wed, Mar 28, 2018 at 4:14 AM, Dai Qizhi <qzdai@xxxxxxxxxxxxxxx> >> wrote: >> [...] >> > > >> > > > I tested overlayfs with nfs_export feature , the kernel is >> > > > built by >> > > > ubuntu , 4.16.0-041600rc7, http://kernel.ubuntu.com/~kernel-ppa >> > > > /mainline/v4.16-rc7/ >> > > > >> > > > the problem is , when i export two different overlay mount >> > > > points on >> > > > server side, then mount them use nfs on the client side, the >> > > > client side >> > > > views the two differnet mount points as the same. >> > > > >> > > > >> > > > on server side: >> > > > >> > > > none on /mnt/m1 type overlay >> > > > (rw,relatime,lowerdir=m1/ro,upperdir=m1/rw,workdir= >> > > > m1/w,index=on,nfs_export=on) >> > > > none on /mnt/m2 type overlay >> > > > (rw,relatime,lowerdir=m2/ro,upperdir=m2/rw,workdir= >> > > > m2/w,index=on,nfs_export=on) >> > > > [root@localhost data]# exportfs -rv >> > > > exporting *:/mnt/m4 >> > > > exporting *:/mnt/m3 >> > > > exporting *:/mnt/m2 >> > > > exporting *:/mnt/m1 >> > > > [root@localhost data]# ls /mnt/m1 >> > > > this_is_m1 >> > > > [root@localhost data]# ls /mnt/m2 >> > > > this_is_m2 >> > > > >> > > > >> > > > on client side: >> > > > >> > > > [root@localhost mnt]# mount 192.168.0.1:/mnt/m1 m1 >> > > > [root@localhost mnt]# mount 192.168.0.1:/mnt/m2 m2 >> > > > [root@localhost mnt]# mount |grep 192 >> > > > 192.168.0.1:/mnt/m1 on /mnt/m1 type nfs >> > > > (rw,relatime,vers=3,rsize=524288,wsize=5 >> > > > 24288,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mou >> > > > ntaddr=192.168.0. >> > > > 1,mountvers=3,mountport=20048,mountproto=udp,local_lock=none,ad >> > > > dr=192.168.0.1) >> > > > 192.168.0.1:/mnt/m1 on /mnt/m2 type nfs >> > > > (rw,relatime,vers=3,rsize=524288,wsize=5 >> > > > 24288,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mou >> > > > ntaddr=192.168.0. >> > > > 1,mountvers=3,mountport=20048,mountproto=udp,local_lock=none,ad >> > > > dr=192.168.0.1) >> > > > >> > > > [root@localhost mnt]# ls /mnt/m1 >> > > > this_is_m1 >> > > > [root@localhost mnt]# ls /mnt/m2 >> > > > this_is_m1 >> > > > [root@localhost mnt]# >> > > >> > > >> > > Please refer to the man page of exports(5), the section about >> > > 'fsid' describes >> > > this problem related to exporting file systems that are not on a >> > > block device, >> > > such as overlayfs. >> > >> > yes, export different mount point with different fsid= option works >> > as >> > expected. >> > >> > >> > > >> > > If you are interested to know if there is a way to fix this that >> > > does >> > > not involve manually >> > > configuring different fsid per export, I will have to consult >> > > with the >> > > NFS experts, so please >> > > reply to this message with CC to <linux-unionfs@xxxxxxxxxxxxxxx> >> > > and >> > > <linux-nfs@xxxxxxxxxxxxxxx> >> > >> > when exporting parent directory with crossmnt option and mount >> > differnet overlayfs >> > under that directory, we encounter the same problem on client >> > side.. >> > >> >> I see. Jeff, Bruce, is there a school book solution to this issue? >> >> Is there a way for a non blockdev export to automatically identify >> itself >> to knfsd? After all, the tuple ("overlayfs";<overlay root file >> handle>) should >> be unique on the server. <overlay root file handle> contains (struct >> ovl_fh) >> the upper fs UUID and the upper root dir file handle. >> >> Technically, if there is no out of tree fs on the system that is >> using the >> value OVL_FILEID (0xfb) for file handle type <overlay root file >> handle> >> itself would be unique. >> >> Thanks, >> Amir. > > tl;dr: not currently, which is why when I did the reexport patches a > few years ago, they _required_ that you manually set the fsid= export > option. > > Longer story: > > Long, long ago, the fsid for the export was almost always determined by > the device major/minor tuple. That became really problematic whenever > devices got reordered after adding a disk to the system and rebooting. > So, Neil Brown added the ability to determine the fsid from the > libblkdev uuid (see nfs-utils commit e91ff0175602c, and kernel commits > from around that time). > > In principle, you could do something similar for overlayfs: add a new > FSID_* type for overlayfs that can reliably determine a unique fsid for > different overlays. That would require kernel and userland patches, of > course... > That's good to know, but I guess I won't be doing any of that anytime soon. Thanks! Amir. -- To unsubscribe from this list: send the line "unsubscribe linux-unionfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
