Re: [Libguestfs] [PATCH] daemon: always provide stdin when running chroot commands (RHBZ#1280029)

Richard W.M. Jones
2015-12-01T16:58:11Z

On Tue, Dec 01, 2015 at 03:59:56PM +0100, Mateusz Guzik
wrote:
> CHROOT_IN/OUT around commandvf are definitely problematic. chroot should be
> done in the child, which also removes the need to chroot out in the
> parent.

The CHROOT_IN/OUT business does need to be rewritten.  Every
instance where we currently do something like:

  CHROOT_IN;
  r = stat (fd, &statbuf);
  CHROOT_OUT

[https://github.com/libguestfs/libguestfs/blob/master/daemon/stat.c#L93-L95]

should instead be forking a subprocess, chrooting in the subprocess,
and doing the system call in the subprocess.

The problem which makes it not so easy is that instead of using a nice
local variable, we would have to pass back the result from a
subprocess to the parent process (the pair (r, statbuf) in the above
example).

So that means .. a pipe, and serializing the result down the pipe.

The good news is that since this all runs on the same machine in the
same compiled program, it's quite acceptable to dump a C struct into
the pipe.

But it's still a lot of work .. patches welcome of course.

Rich.

--
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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