[Libguestfs] Error in chunked encoding

[Richard W.M. Jones]

On Mon, Dec 09, 2013 at 09:17:28PM -0500, Chris Lalancette wrote:
> Hello,
>      Oz is a program that does automated installation of virtual
> machines.  It is written in python and uses libguestfs pretty heavily
> to manipulate ISOs and disks.
>      Someone reported an error against Oz here:
> 
> https://github.com/clalancette/oz/issues/140
> 
> There are some more details in the issue, but it essentially looks
> like something happened during libguestfs tar_out:
> 
> RuntimeError: /dev/fd/13: error in chunked encoding
> 
> Has anyone seen this before?  Any idea what this is about?  If you
> want to comment, I would appreciate it if you could comment in the
> issue itself.

I'll make a comment here and copy it to the github issue tracker.

When libguestfs sends files over the link between the appliance and
the library (such as when running the guestfs_tar_out call), it sends
8 KByte chunks of data.  If the library cannot read a chunk, it will
print this error.  The normal case would be that system call (eg
read(2)) would fail.  This is likely to be a "should never happen"
issue, and this code is well tested.

Oz calls guestfs_tar_out with the /dev/fd/NN parameter (there's
nothing wrong with that).  This explains why /dev/fd/NN is shown in
the error message.

The bug suggests that strace shows a problem with a file descriptor
being closed, but without the complete strace output, plus the precise
version of libguestfs, this is not useful.

I can't really debug this further without knowing the precise version
of libguestfs, the full strace output, and ideally having a
reproducible bug report.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.
http://people.redhat.com/~rjones/virt-top