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

[Laszlo Ersek]

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>


Thanks
Laszlo