[Libguestfs] [PATCH 2/3] v2v: linux: check also kernel config for modules

[Pino Toscano]

When checking whether a kernel supports virtio or it is Xen-based, it is
assumed that the feature has the kernel module for it; this will fail if
the feature is built-in in the kernel, misrepresenting it.

The solution is to check the kernel configuration (/boot/config-$kver)
whether the feature is built-in, in case there is no module available.

This fixes the virtio detection on Ubuntu kernels, where virtio is
built in and not as module.
---
 v2v/linux_kernels.ml | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/v2v/linux_kernels.ml b/v2v/linux_kernels.ml
index b292921..c197f78 100644
--- a/v2v/linux_kernels.ml
+++ b/v2v/linux_kernels.ml
@@ -53,6 +53,21 @@ let detect_kernels (g : G.guestfs) inspect family bootloader =
   (* What kernel/kernel-like packages are installed on the current guest? *)
   let installed_kernels : kernel_info list =
     let rex_ko = Str.regexp ".*\\.k?o\\(\\.xz\\)?$" in
+    let check_config version feature =
+      let prefix = "^CONFIG_" ^ String.uppercase_ascii feature ^ "=" in
+      let lines = g#grep ~extended:true prefix ("/boot/config-" ^ version) in
+      let lines = Array.to_list lines in
+      match lines with
+      | [] -> false
+      | line :: _ ->
+        let kind = snd (String.split "=" line) in
+        (match kind with
+        | "m" (* Theoretically this should not be needed, since the module
+               * would be found. *)
+        | "y" -> true
+        | _ -> false
+        )
+    in
     let rex_ko_extract = Str.regexp ".*/\\([^/]+\\)\\.k?o\\(\\.xz\\)?$" in
     let rex_initrd =
       if family = `Debian_family then
@@ -156,7 +171,10 @@ let detect_kernels (g : G.guestfs) inspect family bootloader =
              ) modules in
              assert (List.length modules > 0);
 
-             let supports_virtio = List.mem "virtio_net" modules in
+             let kernel_supports what kconf =
+               List.mem what modules || check_config version kconf in
+
+             let supports_virtio = kernel_supports "virtio_net" "VIRTIO_NET" in
              let is_xen_kernel = List.mem "xennet" modules in
 
              (* If the package name is like "kernel-debug", then it's
-- 
2.7.4