[Libguestfs] [PATCH] v2v: fixed file_owner function

[Richard W.M. Jones]

On Wed, Aug 03, 2016 at 12:51:24PM +0200, Tomáš Golembiovský wrote:
> On Wed, 3 Aug 2016 11:14:26 +0100
> "Richard W.M. Jones" <rjones at redhat.com> wrote:
> 
> > On Mon, Aug 01, 2016 at 02:46:14PM +0200, Tomáš Golembiovský wrote:
> > > What was happening in file_owner function did not match the description
> > > in the comment. When a path is owned by multiple packages the returned
> > > string was in fact a concatenation of the names of all packages that own
> > > it. E.g. for `Linux.is_file_owned g inspect "/etc"` the returned value
> > > was "filesystemyum" (i.e. "filesystem" + "yum").
> > > 
> > > Signed-off-by: Tomáš Golembiovský <tgolembi at redhat.com>
> > > ---
> > >  v2v/linux.ml | 8 ++++++--
> > >  1 file changed, 6 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/v2v/linux.ml b/v2v/linux.ml
> > > index d20194b..aeff5c5 100644
> > > --- a/v2v/linux.ml
> > > +++ b/v2v/linux.ml
> > > @@ -99,14 +99,18 @@ let rec file_owner g inspect path =
> > >        (* Although it is possible in RPM for multiple packages to own
> > >         * a file, this deliberately only returns one package.
> > >         *)
> > > -      let cmd = [| "rpm"; "-qf"; "--qf"; "%{NAME}"; path |] in
> > > +      let cmd = [| "rpm"; "-qf"; "--qf"; "%{NAME}\\n"; path |] in
> > >        debug "%s" (String.concat " " (Array.to_list cmd));
> > > -      (try g#command cmd
> > > +      (try
> > > +         let pkgs = g#command_lines cmd in
> > > +         pkgs.(0)
> > >         with Guestfs.Error msg as exn ->
> > >           if String.find msg "is not owned" >= 0 then
> > >             raise Not_found
> > >           else
> > >             raise exn
> > > +       | Invalid_argument msg ->
> > > +           raise Not_found  
> > 
> > My concern/confusion about this patch is what raises Invalid_argument?
> > 
> > I'm assuming it's the array index, which could raise `Invalid_argument
> > "index out of bounds"' if the g#command_lines returns a zero-length
> > list, but then my question would be why is the rpm command not
> > returning any lines?
> > 
> > Even if this can happen, the exception shouldn't be converted to
> > Not_found.  It should be an internal error or the exception should be
> > left unchanged.
> 
> Yes, it is to catch the case when rpm reports nothing. Don't know
> if/when this can happen. Do you prefer an error in the exception handler
> (instead of raise Not_found), or should I check the array length (and
> report error)  before accessing it?

Since this should never happen, something like this:

  | Invalid_argument "index out of bounds" ->
      error (f_"internal error: file_owner: rpm command returned no output")

which will immediately exit with a clear error if this case happens.

Rich.

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