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Re: [Libguestfs] [PATCH 0/4] v2v: simplify driver copying from virtio-win iso



On Mon, Oct 05, 2015 at 06:52:55PM +0300, Roman Kagan wrote:
> On Thu, Oct 01, 2015 at 07:09:02PM +0300, Roman Kagan wrote:
> > On Thu, Oct 01, 2015 at 04:22:14PM +0100, Richard W.M. Jones wrote:
> > > On Thu, Oct 01, 2015 at 06:04:03PM +0300, Roman Kagan wrote:
> > > > On Mon, Aug 10, 2015 at 06:55:28PM +0300, Roman Kagan wrote:
> > > > > Libguestfs supports passing an ISO image as a source of virtio windows
> > > > > drivers to v2v.
> > > > > 
> > > > > That support, however, looks too heavy-weight: in order to access those
> > > > > drivers, a separate guestfs handle is created (and thus a new emulator
> > > > > process is started), which runs until v2v completes.
> > > > > 
> > > > > This series attempts to make it simpler and lighter-weight, by making
> > > > > the relevant code more local, and by hot-adding the image into the main
> > > > > guestfs handle.
> > > > > 
> > > > > Roman Kagan (4):
> > > > >   v2v: drop useless forced gc
> > > > >   v2v: consolidate virtio-win file copying
> > > > >   v2v: copy virtio drivers without guestfs handle leak
> > > > >   v2v: reuse main guestfs for virtio win drivers iso
> > > > > 
> > > > >  v2v/convert_windows.ml | 184 ++++++++++++++++++++--------------------
> > > > >  v2v/utils.ml           | 224 ++++++++++++++++---------------------------------
> > > > >  v2v/v2v.ml             |   8 --
> > > > >  3 files changed, 163 insertions(+), 253 deletions(-)
> > > > 
> > > > I just realized that, although (at least two of) these patches got
> > > > "likely ACK", they are not in the libguestfs tree.
> > > > 
> > > > The patches still apply to master as of today.
> > > > 
> > > > Is there anything I can do to get them merged?
> > > 
> > > Actually better to post them again so I can review them again.
> > 
> > OK will do.
> > 
> > > I spotted a few problems
> > > 
> > > - There's a missing pair of parentheses around the then clause in:
> > > 
> > >          g2#mount_ro "/dev/sda" vio_root;
> > >          let paths = g2#find vio_root in
> > >          Array.iter (
> > >            fun path ->
> > >              let source = vio_root // path in
> > >              if ((g2#is_file source ~followsymlinks:false) &&
> > >                  (match_vio_path_with_os path inspect.i_arch
> > >                      inspect.i_major_version inspect.i_minor_version
> > >                      inspect.i_product_variant)) then
> > >                                                      ^^^
> > > 
> > >   which makes me think this code can't possibly work.
> > 
> > Indeed.  It failed neither in compilation nor in tests, though.  Looks
> > like I need to patch v2v/test-v2v-windows-conversion.sh, too.
> 
> When I replied I didn't already remember for certain how I verified that
> the code did achieve its goal; however now that I have a test for it
> (submitted today, needs fixing the stylistic comments but working
> otherwise) I claim that it passes with this code, i.e. all the drivers
> do get copied into the guest upon conversion.
> 
> So this code does work as intended; being totally clueless in OCaml I'd
> appreciate being explained -- how?

It's like in C.  The following two if statements do different things:

  if foo then (
    stmt_1;
    stmt_2;
  )

  if foo then
    stmt_1;
    stmt_2;

The second one runs stmt_2 unconditionally.

> > > - Calling String.lowercase is unsafe (because the function is just
> > >   broken in OCaml) and unnecessary.  Just remove it.
> 
> I can't figure out why it's unnecessary and how to remove it.  The only
> place where String.lowercase is called is in match_vio_path_with_os()
> which is basically unchanged in the patch, it's only factored out into a
> separate function.  It tries to do case-insensitive comparison of the
> path elements to constant strings; is there a way to do it other than
> downcasing both sides of the comparison?

Oh I see - yes it's broken upstream too :-(
(See the comment "XXX This won't work if paths contain non-ASCII.")

Since String.lowercase assumes the string is ISO-8859-1, it could
actually corrupt UTF-8 paths.

As usual we're in a hard place here because we don't want to add
dependencies on external libraries like Camomile
(https://github.com/yoriyuki/Camomile) which would be the obvious
choice, but no one has written a working replacement for
mllib/common_utils.ml.

Whatever you do, make sure it's obvious that it's still broken and
needs to be fixed.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
Fedora Windows cross-compiler. Compile Windows programs, test, and
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