FIX: enhanced nbdkit command detection and usage

lib/config.ml.in

@@ -23,5 +23,6 @@ let package_version_full = "@PACKAGE_VERSION_FULL@"
 let prefix = "@prefix@"
 let datadir = prefix ^ "/share"
 let host_cpu = "@host_cpu@"
+let nbdkit = if "@NBDKIT@" = "" then None else Some "@NBDKIT@"
 let nbdcopy = "@NBDCOPY@"
 let nbdinfo = "@NBDINFO@"

lib/config.mli

@@ -34,6 +34,9 @@ val datadir : string
 val host_cpu : string
 (** The configure value [@host_cpu@] *)
 
+val nbdkit : string option
+(** The location of the nbdkit program, from configure value [@NBDKIT@] *)
+
 val nbdcopy : string
 (** The location of the nbdcopy program, from configure value [@NBDCOPY@] *)
 

lib/nbdkit.ml

@@ -26,14 +26,22 @@ open Unix_utils
 
 open Utils
 
+let nbdkit_cmd : string ref = ref ""
+
 let is_installed =
-  let test = lazy (Sys.command "nbdkit --version >/dev/null 2>&1" = 0) in
-  fun () -> Lazy.force test
+  match Config.nbdkit with
+  | Some path -> begin
+      nbdkit_cmd := path;
+      let cmd = sprintf "%s --version >/dev/null 2>&1" path in
+      let test = lazy (Sys.command cmd = 0) in
+      fun () -> Lazy.force test
+    end
+  | None -> fun () -> false
 
 type config = (string * string) list
 
 let get_config = lazy (
-  let cmd = "nbdkit --dump-config" in
+  let cmd = !nbdkit_cmd ^ " --dump-config" in
   let lines = external_command cmd in
   List.map (String.split "=") lines
 )
@@ -54,30 +62,30 @@ let get_version = lazy (
   and release = int_of_string (PCRE.sub 3) in
   if verbose () then (
     eprintf "info: nbdkit version:\n%!";
-    ignore (Sys.command "nbdkit --version >&2");
+    ignore (Sys.command (!nbdkit_cmd ^ " --version >&2"));
     eprintf "parsed version: %d.%d.%d\n%!" major minor release
   );
   (major, minor, release)
 )
 let version () = Lazy.force get_version
 
 let probe_plugin name =
-  let cmd = sprintf "nbdkit %s --version >/dev/null 2>&1" (quote name) in
+  let cmd = sprintf "%s %s --version >/dev/null 2>&1" !nbdkit_cmd (quote name) in
   Sys.command cmd = 0
 
 let probe_plugin_parameter name regex =
-  let cmd = sprintf "nbdkit %s --help | grep -sq %s"
-              (quote name) (quote regex) in
+  let cmd = sprintf "%s %s --help | grep -sq %s"
+              !nbdkit_cmd (quote name) (quote regex) in
   Sys.command cmd = 0
 
 let probe_filter name =
-  let cmd = sprintf "nbdkit null --filter=%s --version >/dev/null 2>&1"
-              (quote name) in
+  let cmd = sprintf "%s null --filter=%s --version >/dev/null 2>&1"
+              !nbdkit_cmd (quote name) in
   Sys.command cmd = 0
 
 let probe_filter_parameter name regex =
-  let cmd = sprintf "nbdkit null --filter=%s --help | grep -sq %s"
-              (quote name) (quote regex) in
+  let cmd = sprintf "%s null --filter=%s --help | grep -sq %s"
+              !nbdkit_cmd (quote name) (quote regex) in
   Sys.command cmd = 0
 
 type cmd = {
@@ -132,7 +140,7 @@ let run_unix socket cmd =
     add_arg, add_args_reversed, get_args
   in
 
-  add_arg "nbdkit";
+  add_arg !nbdkit_cmd;
   add_arg "--exit-with-parent";
   add_arg "--foreground";
   add_arg "--pidfile"; add_arg pidfile;
@@ -173,7 +181,7 @@ let run_unix socket cmd =
   if pid = 0 then (
     (* Child process (nbdkit). *)
     List.iter (fun (k, v) -> putenv k v) cmd.env;
-    execvp "nbdkit" args
+    execvp !nbdkit_cmd args
   );
 
   (* Wait for the pidfile to appear so we know that nbdkit

m4/guestfs-progs.m4

@@ -60,6 +60,11 @@ AM_CONDITIONAL([HAVE_ZIP],[test "x$ZIP" != "xno"])
 AC_PATH_PROGS([UNZIP],[unzip],[no])
 AC_DEFINE_UNQUOTED([UNZIP],["$UNZIP"],[Name of unzip program.])
 
+dnl Detect nbdkit also under /usr/sbin or /sbin in case they're not on $PATH
+AC_PATH_PROG(NBDKIT,[nbdkit], [no], [/usr/sbin$PATH_SEPARATOR/sbin$PATH_SEPARATOR$PATH])
+AS_IF([test "x$NBDKIT" = "xno"],
+      [AC_MSG_WARN([nbdkit binary (from nbdkit) not found, some runtime functionality will be missing])])
+
 dnl nbdinfo, nbdcopy, required by virt-v2v
 AC_CHECK_PROG([NBDINFO], [nbdinfo], [nbdinfo], [no])
 AC_CHECK_PROG([NBDCOPY], [nbdcopy], [nbdcopy], [no])