[Libguestfs] [PATCH] convert_linux: translate the first CD-ROM's references in boot conf files

[Laszlo Ersek]

If the only CD-ROM in "s_removables" is on an IDE controller, and the
guest kernel represents it with a /dev/hdX device node, then convert
references to this device node, in the boot config files, to /dev/cdrom.
On the destination (after conversion), /dev/cdrom will point to whataver
node we converted the CD-ROM to, masking a potential i440fx -> q35 (IDE ->
SATA) board change.

If the only CD-ROM is not on an IDE controller, or the guest is modern
enough to represent the IDE CD-ROM as /dev/sr0, then perform no
translation. Namely, /dev/sr0 survives a potential i440fx -> q35 (IDE ->
SATA) board change intact.

When multiple CD-ROMs exist, emit a warning, and attempt the conversion on
the first CD-ROM, as a guess. This may be inexact, but we can't do better,
because:

- SATA, SCSI, and (on modern guests) IDE CD-ROMs are lumped together in
  the /dev/sr* namespace, on the source side, and "s_removable_slot" is
  useless for telling them apart, as we don't know the exact controller
  topology (and OS enumeration order);

- after conversion: some OSes don't create /dev/cdrom* symlinks to all
  CD-ROMs, and even if multiple such symlinks are created, their order is
  basically random.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1637857
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 convert/convert_linux.ml      | 25 +++++++++++++++++++++++++
 tests/test-v2v-cdrom.expected |  2 +-
 tests/test-v2v-cdrom.xml.in   |  4 +++-
 tests/test-v2v-i-ova.xml      |  2 +-
 4 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/convert/convert_linux.ml b/convert/convert_linux.ml
index 8dc648169dcb..9ea94b75bfc9 100644
--- a/convert/convert_linux.ml
+++ b/convert/convert_linux.ml
@@ -1020,6 +1020,31 @@ let convert (g : G.guestfs) source inspect keep_serial_console _ =
           "xvd" ^ drive_name i, block_prefix_after_conversion ^ drive_name i
       ) source.s_disks in
 
+    (* Check the first CD-ROM. If its controller is IDE, and the OS is RHEL<=5,
+     * then translate the CD-ROM from "/dev/hd[SLOT]" to "/dev/cdrom". See
+     * RHBZ#1637857 for details.
+     *)
+    let cdroms = List.filter
+                   (fun removable -> removable.s_removable_type = CDROM)
+                   source.s_removables in
+
+    match cdroms with
+    | _ :: _ :: _ -> warning (f_"multiple CD-ROMs found; translation of \
+                                 CD-ROM references may be inexact")
+    | _ -> ();
+
+    let map = map @
+      (match cdroms with
+       | cdrom :: _ ->
+           (match (cdrom.s_removable_controller, cdrom.s_removable_slot,
+                   family, inspect.i_major_version) with
+            | Some Source_IDE, Some slot, `RHEL_family, v when v <= 5 ->
+                [("hd" ^ drive_name slot, "cdrom")]
+            | _ -> []
+           )
+       | [] -> []
+      ) in
+
     if verbose () then (
       eprintf "block device map:\n";
       List.iter (
diff --git a/tests/test-v2v-cdrom.expected b/tests/test-v2v-cdrom.expected
index 34d2bf5961b0..17bd152d8e64 100644
--- a/tests/test-v2v-cdrom.expected
+++ b/tests/test-v2v-cdrom.expected
@@ -4,5 +4,5 @@
     </disk>
     <disk device='cdrom' type='file'>
       <driver name='qemu' type='raw'/>
-      <target dev='hdc' bus='ide'/>
+      <target dev='sdc' bus='sata'/>
     </disk>
diff --git a/tests/test-v2v-cdrom.xml.in b/tests/test-v2v-cdrom.xml.in
index 6bad5eab1cd4..a6e1e3f514d5 100644
--- a/tests/test-v2v-cdrom.xml.in
+++ b/tests/test-v2v-cdrom.xml.in
@@ -35,7 +35,9 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
       <disk type='file' device='cdrom'>
         <driver name='qemu' type='raw'/>
         <source file='@abs_top_builddir@/test-data/phony-guests/blank-disk.img'/>
-        <!-- virt-v2v should preserve the device name and bus -->
+        <!-- virt-v2v should change the bus to sata, due to Windows 7
+             triggering a machine type change from i440fx to q35. Beyond that,
+             virt-v2v should preserve the on-bus index. -->
         <target dev='hdc' bus='ide'/>
       </disk>
     </devices>
diff --git a/tests/test-v2v-i-ova.xml b/tests/test-v2v-i-ova.xml
index d7383905fdc0..9f3c1974243f 100644
--- a/tests/test-v2v-i-ova.xml
+++ b/tests/test-v2v-i-ova.xml
@@ -28,7 +28,7 @@
     </disk>
     <disk device='cdrom' type='file'>
       <driver name='qemu' type='raw'/>
-      <target dev='hda' bus='ide'/>
+      <target dev='sda' bus='sata'/>
     </disk>
     <disk device='floppy' type='file'>
       <driver name='qemu' type='raw'/>
-- 
2.19.1.3.g30247aa5d201