[lxc-devel] [PATCH 1/1] userns: clear and save id_map

[Dwight Engen]

On Mon, 15 Jul 2013 20:58:49 -0500
Serge Hallyn <serge.hallyn at ubuntu.com> wrote:

> Quoting Dwight Engen (dwight.engen at oracle.com):
> > On Mon, 15 Jul 2013 16:45:36 -0500
> > Serge Hallyn <serge.hallyn at ubuntu.com> wrote:
> > 
> > > Quoting Dwight Engen (dwight.engen at oracle.com):
> > > > Starting program: /usr/bin/lxc-clone -s -o ol64-01 -n ol64-04
> > > > [Thread debugging using libthread_db enabled]
> > > > Using host libthread_db library "/lib64/libthread_db.so.1".
> > > > Detaching after fork from child process 28359.
> > > > Detaching after fork from child process 28361.
> > > > 
> > > > Program received signal SIGSEGV, Segmentation fault.
> > > > 0x00007f99e689e08e in write_config (fout=fout at entry=0x1b79670,
> > > > c=0x1b77400) at confile.c:1950
> > > > 1950	confile.c: No such file or directory.
> > > > Missing separate debuginfos, use: debuginfo-install
> > > > lxc-0.9.x-1.fc18.x86_64 (gdb) bt
> > > > #0  0x00007f99e689e08e in write_config
> > > > (fout=fout at entry=0x1b79670, c=0x1b77400) at confile.c:1950
> > > > #1  0x00007f99e68a6c6b in lxcapi_save_config (c=0x1b764d0,
> > > > alt_file=<optimized out>) at lxccontainer.c:1214
> > > > #2  0x00007f99e68a99b8 in lxcapi_clone (c=<optimized out>,
> > > > newname=<optimized out>, lxcpath=<optimized out>,
> > > > flags=<optimized
> > > > out>, bdevtype=0x0, bdevdata=0x0, newsize=0, hookargs=0x0) at
> > > > out>lxccontainer.c:1963
> > > > #3  0x0000000000400d2f in main ()
> > > 
> > > Actually I think that looks a bit different from the segfault I
> > > was getting with my first version - please let me know if v2 still
> > > causes this for you.  (I don't get it with non-snapped clones).
> > 
> > v2 works fine for me with snapshoted clone, thanks! and
> > 
> > Acked-by: Dwight Engen <dwight.engen at oracle.com>
> > Tested-by: Dwight Engen <dwight.engen at oracle.com>
> 
> Great, thanks.
> 
> > I did notice something though: after the clone I ran uidmapshift -r
> > to check the range of uid's in the cloned rootfs and there is one
> > file that was out of range: it is the <rootfs>/etc/hostname that
> > clone_update_rootfs() creates. For templates that already have this
> > file, I think it will be fine but for those that don't the file
> > will be created as the uid of the caller. I think maybe we should
> > just call file_exists(path) before doing the fopen() in that flow,
> > if you agree I can send a patch.
> 
> I think I follow but I'm not 100% sure: are you saying that
> /etc/hostname did not exist in your rootfs before the lxc-clone?
> Presumably then it doesn't need to exist, and you're suggesting
> we check whether it exists before updating?

Exactly. Patch follows, tested both with and without /etc/hostname in
rootfs.

> If so, that sounds good.
> 
> Another option would be to run the clone_update_rootfs in a mapped
> userns, but it doesn't sound like this case warrants that - the files
> simply don't need to be updated.
> 
> -serge