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<p class=MsoNormal>Hello,<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>at our institute we are experiencing some problems
concerning unionfs in combination with NFS.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>The scenario is the following:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>We have a server with an NFSv3-export (set to ro). Clients mount
this nfs-export (ro as well) and unionfs is used to merge it with a tmpfs.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Adding and deleting files works as expected. However, if a
file is opened (which according to ls –l has write permission) which only
exists in the ro branch it is recognized as readonly. Only forcing a write can
make changes to the file. For “echo >” or “echo
>>” on an existing files I receive a “Permission
denied”.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Here an example:<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>> cd /root/unionfs_test/union/usr<o:p></o:p></p>
<p class=MsoNormal>> ls –l test<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>-rwxrwxrwx 1 root root 8 Jul 24 15:45 test<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>> strace -e file /bin/bash -c 'echo > test'<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>execve("/bin/bash", ["/bin/bash",
"-c", "echo > test"], [/* 48 vars */]) = 0<o:p></o:p></p>
<p class=MsoNormal>access("/etc/ld.so.preload",
R_OK) = -1 ENOENT (No such file or directory)<o:p></o:p></p>
<p class=MsoNormal>open("/etc/ld.so.cache",
O_RDONLY) = 3<o:p></o:p></p>
<p class=MsoNormal>open("/lib/libncurses.so.5", O_RDONLY) = 3<o:p></o:p></p>
<p class=MsoNormal>open("/lib/libdl.so.2",
O_RDONLY) = 3<o:p></o:p></p>
<p class=MsoNormal>open("/lib/libc.so.6",
O_RDONLY) = 3<o:p></o:p></p>
<p class=MsoNormal>open("/dev/tty", O_RDWR|O_NONBLOCK|O_LARGEFILE) =
3<o:p></o:p></p>
<p class=MsoNormal>open("/proc/meminfo",
O_RDONLY) = 3<o:p></o:p></p>
<p class=MsoNormal>stat64("/root/unionfs_test/union/usr", {st_mode=S_IFDIR|0755,
st_size=40, ...}) = 0<o:p></o:p></p>
<p class=MsoNormal>stat64(".", {st_mode=S_IFDIR|0755, st_size=40,
...}) = 0<o:p></o:p></p>
<p class=MsoNormal>open("test", O_WRONLY|O_CREAT|O_TRUNC|O_LARGEFILE,
0666) = -1 EACCES (Permission denied)<o:p></o:p></p>
<p class=MsoNormal>/bin/bash: test: Permission denied<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>After I first forced a write, did a chmod, touch, etc.
everything works fine. Also if the file does not exist beforehand. So I guess
this is again one of those problems where no copy-up is triggered because NFS
is answering EACCES instead of EROFS? However, I have marked the branch as ro
and the mount is ro as well. Can this problem still occur?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Here my system setup, an expert from the /etc/exports on the
server and the commands to reproduce the effect on the clients.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Server: Gentoo linux, 64 Bit, gentoo kernel
2.6.26-hardened-r9, export using NFSv3<o:p></o:p></p>
<p class=MsoNormal>Client: Gentoo linux, 32 Bit, vanilla kernel
2.6.29.4 with unionfs 2.5.2 patch and ipipe patch<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Exports (excerpt):<o:p></o:p></p>
<p class=MsoNormal>/lb/diskless/rootfs
xxx.xxx.xxx.0/24(ro,fsid=100,mp=/lb,async,no_root_squash,no_subtree_check) <o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>cat /proc/mounts (on server, excerpt)<o:p></o:p></p>
<p class=MsoNormal>/dev/sdc1 /lb ext3 rw,noatime,errors=continue,data=ordered 0
0<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Mount commands on client:<o:p></o:p></p>
<p class=MsoNormal>mkdir nfs tmpfs union<o:p></o:p></p>
<p class=MsoNormal>mount -nt nfs -o ro,nolock server:/lb/diskless/rootfs
/root/unionfs_test/nfs<o:p></o:p></p>
<p class=MsoNormal>mount -nt tmpfs tmpfs /root/unionfs_test/tmpfs<o:p></o:p></p>
<p class=MsoNormal>mount -nt unionfs -o rw,dirs=/root/unionfs_test/tmpfs=rw:
/root/unionfs_test/nfs=ro unionfs /root/unionfs_test/union<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>This seems to be the same problem as reported in Bugzilla
Bug 624 <a href="https://bugzilla.filesystems.org/show_bug.cgi?id=624">https://bugzilla.filesystems.org/show_bug.cgi?id=624</a>.
I did some tests and found out that, also for me, the problem is
“solved” if the export is set to rw. However, exporting the
filesystem as rw doesn’t seem like an alternative, mainly for security
reasons, i.e. unionfs is currently not usable for us. So for the moment we are
stuck with unionfs-fuse which does not have this problem but obviously has a
huge impact on performance.<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal>Is there a plan to solve this issue or is there any workaround?<o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:Consolas'>Regards,<o:p></o:p></span></p>
<p class=MsoNormal><span style='font-size:10.5pt;font-family:Consolas'>Thomas</span><o:p></o:p></p>
<p class=MsoNormal><o:p> </o:p></p>
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