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Re: [Libguestfs] Transform and "Lenses xx and xx could be used to load this file"



Hi Rich,

On Thu, Nov 3, 2016 at 7:27 AM, Richard W.M. Jones <rjones redhat com> wrote:
However if the Augeas lens happens to contain that path already,
things go wrong:

  augtool> transform passwd incl /etc/passwd
  augtool> load
  # /etc/passwd is not parsed by the passwd lens
  augtool> get /augeas/files/etc/passwd/error/message
  /augeas/files/etc/passwd/error/message = Lenses @Passwd and passwd.lns could be used to load this file

This is specifically a problem when libguestfs adds a call to
aug_transform to cater for a file that is not covered by an existing
lens, but then Augeas adds that file, and then we get the error above
until libguestfs removes the call to aug_transform.  We cannot control
when Augeas and libguestfs are released in different Linux distros.

That's a good point that I hadn't thought about before.
 
There are workarounds for this involving fishing out the existing
transform and working out if it covers the file or not, but that's
pretty tedious.

It seems to be that Augeas could be cleverer here and could just
ignore the case where two identical transforms apply to the same file
and DWIM.

I just put up a PR[1] that makes it ok for multiple transforms to handle the same file as long as they use the same lens. I'll wait with making the release that I was going to make today until I hear back from you - could you make sure you run this patch through whatever Augeas-relevant tests you have in libguestfs ? I want to make sure I don't have some unintentional screwup in there that might break loading or saving where it used to work. (and hearing back some time next week is  early enough; there's nothing requiring a release be made right now)

David

[1] https://github.com/hercules-team/augeas/pull/425


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