From d783c57507d76ba18d61c3bfb7c867cf3d69d612 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Mon, 20 Oct 2014 18:34:48 +0100
Subject: [PATCH] v2v: vCenter: Adjust readahead parameter between conversion
 and copying phases (RHBZ#1151033) (RHBZ#1153589).

Previously we fixed RHBZ#1151033 by increasing the cURL readahead
parameter to a large value.  Unfortunately this is too large -- and
hence slow -- for the conversion phase, which broke on slow vCenter
servers (RHBZ#1153589).

What we do now is to perform the conversion phase with the default
readahead (2MB) to ensure stability, since performance of the
conversion phase is not critical.  Then before copying we change the
readahead to the larger value (64MB) to ensure efficient copying.

(cherry picked from commit 9281dc7d44b7b02c6470a61425aa177e6525ee88)
---
 v2v/input_libvirt.ml | 29 ++++++++++++++++++++++++++++-
 v2v/vCenter.ml       | 10 +++++++---
 v2v/vCenter.mli      |  2 +-
 3 files changed, 36 insertions(+), 5 deletions(-)

diff --git a/v2v/input_libvirt.ml b/v2v/input_libvirt.ml
index 9d2869f..93d96b7 100644
--- a/v2v/input_libvirt.ml
+++ b/v2v/input_libvirt.ml
@@ -79,6 +79,9 @@ class input_libvirt_vcenter_https
 object
   inherit input_libvirt verbose libvirt_uri guest
 
+  val mutable mapf = fun ?readahead uri format -> uri, format
+  val saved_uri = Hashtbl.create 13
+
   method source () =
     if verbose then printf "input_libvirt_vcenter_https: source()\n%!";
 
@@ -91,7 +94,15 @@ object
     let { s_disks = disks } as source =
       Input_libvirtxml.parse_libvirt_xml ~verbose xml in
 
-    let mapf = VCenter.map_path_to_uri verbose parsed_uri scheme server in
+    (* Save the mapf function and the original s_qemu_uri fields, so
+     * we can get them in the adjust_overlay_parameters method below.
+     *)
+    mapf <- VCenter.map_path_to_uri verbose parsed_uri scheme server;
+    List.iter (
+      fun disk ->
+        Hashtbl.add saved_uri disk.s_disk_id (disk.s_qemu_uri, disk.s_format)
+    ) disks;
+
     let disks = List.map (
       fun ({ s_qemu_uri = uri; s_format = format } as disk) ->
         let uri, format = mapf uri format in
@@ -99,6 +110,22 @@ object
     ) disks in
 
     { source with s_disks = disks }
+
+  (* See RHBZ#1151033 and RHBZ#1153589 for why this is necessary. *)
+  method adjust_overlay_parameters overlay =
+    let orig_uri, orig_format =
+      try Hashtbl.find saved_uri overlay.ov_source.s_disk_id
+      with Not_found -> failwith "internal error in adjust_overlay_parameters" in
+    let backing_file, _ =
+      mapf ~readahead:(64 * 1024 * 1024) orig_uri orig_format in
+
+    (* Rebase the qcow2 overlay to adjust the readahead parameter. *)
+    let cmd =
+      sprintf "qemu-img rebase -u -b %s %s"
+        (quote backing_file) (quote overlay.ov_overlay_file) in
+    if verbose then printf "%s\n%!" cmd;
+    if Sys.command cmd <> 0 then
+      warning ~prog (f_"qemu-img rebase failed, see earlier errors")
 end
 
 (* Subclass specialized for handling Xen over SSH. *)
diff --git a/v2v/vCenter.ml b/v2v/vCenter.ml
index c04247e..dc29863 100644
--- a/v2v/vCenter.ml
+++ b/v2v/vCenter.ml
@@ -44,7 +44,7 @@ let session_cookie = ref ""
  * XXX Need to handle templates.  The file is called "-delta.vmdk" in
  * place of "-flat.vmdk".
  *)
-let rec map_path_to_uri verbose uri scheme server path format =
+let rec map_path_to_uri verbose uri scheme server ?readahead path format =
   if not (Str.string_match esx_re path 0) then
     path, format
   else (
@@ -84,11 +84,15 @@ let rec map_path_to_uri verbose uri scheme server path format =
       "file.driver", JSON.String "https";
       "file.url", JSON.String url;
       "file.timeout", JSON.Int 600;
-      (* Choose a large readahead.  See: RHBZ#1151033 *)
-      "file.readahead", JSON.Int (64 * 1024 * 1024);
     ] in
 
     let json_params =
+      match readahead with
+      | None -> json_params
+      | Some readahead ->
+        ("file.readahead", JSON.Int readahead) :: json_params in
+
+    let json_params =
       if sslverify then json_params
       else ("file.sslverify", JSON.String "off") :: json_params in
 
diff --git a/v2v/vCenter.mli b/v2v/vCenter.mli
index e504098..06ba452 100644
--- a/v2v/vCenter.mli
+++ b/v2v/vCenter.mli
@@ -18,6 +18,6 @@
 
 (** Functions for dealing with ESX. *)
 
-val map_path_to_uri : bool -> Xml.uri -> string -> string -> string -> string option -> string * string option
+val map_path_to_uri : bool -> Xml.uri -> string -> string -> ?readahead:int -> string -> string option -> string * string option
 (** Map a VMware path like "[datastore1] guest/guest.vmdk" to the
     URL where we can fetch the data. *)
-- 
1.8.3.1