[Libguestfs] [PATCH virt-v2v] convert: If listing RPM applications fails, rebuild DB and retry

[Laszlo Ersek]

On 05/26/22 11:23, Richard W.M. Jones wrote:
> On Thu, May 26, 2022 at 10:53:59AM +0200, Laszlo Ersek wrote:
>> On 05/25/22 18:02, Richard W.M. Jones wrote:
>>> In libguestfs we didn't bother to check the return values from any
>>> librpm calls.  In some cases where possibly the RPM database is
>>> faulty, this caused us to return a zero-length list of installed
>>> applications (but no error indication).  Libguestfs has subsequently
>>> been fixed so now it returns an error if the RPM database is corrupt.
>>>
>>> This commit changes virt-v2v behaviour so that if either
>>> guestfs_inspect_list_applications2 returns a zero-length list (ie. old
>>> libguestfs) or it throws an error (new libguestfs) then we attempt to
>>> rebuild the RPM database and retry the operation.  Rebuilding the
>>> database can recover from some but not all RPM DB corruption.
>>>
>>> See-also: https://bugzilla.redhat.com/show_bug.cgi?id=2089623#c12
>>
>> What an absolutely horrific error mode. Great job debugging it!
>>
>>> Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2089623
>>> Reported-by: Xiaodai Wang
>>> Reported-by: Ming Xie
>>> ---
>>>  convert/inspect_source.ml | 26 ++++++++++++++++++++++++--
>>>  1 file changed, 24 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/convert/inspect_source.ml b/convert/inspect_source.ml
>>> index 1736009629..16058de644 100644
>>> --- a/convert/inspect_source.ml
>>> +++ b/convert/inspect_source.ml
>>> @@ -34,6 +34,7 @@ let rec inspect_source root_choice g =
>>>    reject_if_not_installed_image g root;
>>>  
>>>    let typ = g#inspect_get_type root in
>>> +  let package_format = g#inspect_get_package_format root in
>>>  
>>>    (* Mount up the filesystems. *)
>>>    let mps = g#inspect_get_mountpoints root in
>>> @@ -71,7 +72,7 @@ let rec inspect_source root_choice g =
>>>    ) mps;
>>>  
>>>    (* Get list of applications/packages installed. *)
>>> -  let apps = g#inspect_list_applications2 root in
>>> +  let apps = list_applications g root package_format in
>>>    let apps = Array.to_list apps in
>>>  
>>>    (* A map of app2_name -> application2, for easier lookups.  Note
>>> @@ -106,7 +107,7 @@ let rec inspect_source root_choice g =
>>>      i_arch = g#inspect_get_arch root;
>>>      i_major_version = g#inspect_get_major_version root;
>>>      i_minor_version = g#inspect_get_minor_version root;
>>> -    i_package_format = g#inspect_get_package_format root;
>>> +    i_package_format = package_format;
>>>      i_package_management = g#inspect_get_package_management root;
>>>      i_product_name = g#inspect_get_product_name root;
>>>      i_product_variant = g#inspect_get_product_variant root;
>>> @@ -186,6 +187,27 @@ and reject_if_not_installed_image g root =
>>>    if fmt <> "installed" then
>>>      error (f_"libguestfs thinks this is not an installed operating system (it might be, for example, an installer disk or live CD).  If this is wrong, it is probably a bug in libguestfs.  root=%s fmt=%s") root fmt
>>>  
>>> +(* Wrapper around g#inspect_list_applications2 which, for RPM
>>> + * guests, on failure tries to rebuild the RPM database before
>>> + * repeating the operation.
>>> + *)
>>> +and list_applications g root = function
>>> +  | "rpm" ->
>>> +     (* RPM guest. *)
>>> +     (try
>>
>> [*]
>>
>>> +        let apps = g#inspect_list_applications2 root in
>>> +        if apps = [||] then raise (G.Error "no applications returned");
>>> +        apps
>>> +      with G.Error msg ->
>>> +        debug "%s" msg;
>>> +        debug "rebuilding RPM database and retrying ...";
>>> +        ignore (g#sh "rpmdb --rebuilddb");
>>> +        g#inspect_list_applications2 root
>>> +     )
>>> +  | _ ->
>>> +     (* Non-RPM guest, just do it. *)
>>> +     g#inspect_list_applications2 root
>>> +
>>>  (* See if this guest could use UEFI to boot.  It should use GPT and
>>>   * it should have an EFI System Partition (ESP).
>>>   *
>>>
>>
>> The commit message explains well why the "g#inspect_list_applications2"
>> method call that is at the top of each "match" pattern cannot be
>> factored out (to a common call just before the "match"). However,
>> looking at the code, it's not easy to understand.
>>
>> Can you please:
>>
>> (1) Commit the libguestfs patch,
>>
>> (2) insert a comment at [*], saying that either of the two lines just
>> below may raise an exception, and which one does depends on libguestfs
>> having the commit <HASH> from point (1)?
>>
>> With that:
>>
>> Reviewed-by: Laszlo Ersek <lersek at redhat.com>
> 
> Sure thing, thanks!
> 
> So ...
> 
> libguestfs commit: 488245ed6c0c5db282ec7fed646e8bc00ce0d487
> 
> virt-v2v commit with additional commentary referencing libguestfs
> commit: 31bf5db25bcfd8a9f5a48cc0523abae28861de9a

Thank you, that's a very good comment in there.
Laszlo