[Libguestfs] [nbdkit PATCH v4 1/4] server: Export nbdkit_set_dlopen_prefix function

[Eric Blake]

On 2/15/20 10:22 PM, Eric Blake wrote:
> At least the VDDK plugin needs a way to load .so files with a custom
> directory prepended.  Asking the user to set LD_LIBRARY_PATH is too
> strong (that would leak into the child process created by --run, and
> makes the user think about issues that we'd rather cover
> automatically).  But overriding dlopen() to make it easier to prepend
> a directory name under our control requires either a separate
> namespace via dlmopen() (which itself is annoying - it messes up gdb
> debugging), or that the override occur prior to any other library that
> also depends on -ldl.  Which means that if we are going to provide
> this functionality, we have to do so from nbdkit proper.
> 
> Note that properly injecting a dlopen shim for all subsequent shared
> library loads requires that the override itself be in a shared
> library.  Thus, nbdkit has to pull it in via a shared library link,
> rather than merely a .o file, and we now have to install something in
> pkglibdir.  What's more, now that we link against a shared library
> instead of just libtool convenience libraries, libtool now creates a
> wrapper app named lt-nbdkit so that it can run an in-tree build that
> still locates the uninstalled shared library; this affects some
> expected output in tests.

The wrapper script also needs a tweak thanks to libtool's behavior; I'll 
have to squash this in:

diff --git i/wrapper.c w/wrapper.c
index 6aef81a1..b0b9c158 100644
--- i/wrapper.c
+++ w/wrapper.c
@@ -1,5 +1,5 @@
  /* nbdkit
- * Copyright (C) 2017-2019 Red Hat Inc.
+ * Copyright (C) 2017-2020 Red Hat Inc.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions are
@@ -148,6 +148,8 @@ main (int argc, char *argv[])
     */
    s = getenv ("NBDKIT_VALGRIND");
    if (s && strcmp (s, "1") == 0) {
+    passthru ("libtool");
+    passthru ("execute");
      passthru (VALGRIND);
      passthru ("--vgdb=no");
      passthru ("--leak-check=full");
@@ -163,6 +165,8 @@ main (int argc, char *argv[])
    else {
      s = getenv ("NBDKIT_GDB");
      if (s && strcmp (s, "1") == 0) {
+      passthru ("libtool");
+      passthru ("execute");
        passthru ("gdb");
        passthru ("--args");
      }



-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org