Re: [Libguestfs] [PATCH nbdkit 1/9] server: Add libnbdkit.so.

I believe after a lot of reading around this topic that it should be possible to call from the plugin DLLs into functions in the EXE. One technique is outlined here: https://stackoverflow.com/a/18147774 The idea above is to use DLLTOOL to generate an "import library" (a static linked library containing stubs which are used to resolve at runtime a list of symbols). Import libraries are a normal part of building DLLs on Windows where you always end up building the .DLL and another .LIB containing these stubs. The unusual thing here is only that we generate the import library against an executable rather than a DLL. This would be the simplest technique to use, but I could not make it work in the end. Generating the import library is fine. The problem is actually that libtool doesn't believe it should be possible to add a static .a file when building a DLL and I couldn't work around that. In any case if we did the above we'd still have to hack every plugin and filter so that it links to the import library. But there's a lower-level technique we could use instead: https://nachtimwald.com/2012/07/15/calling-functions-in-exe-from-plugins-... https://stackoverflow.com/questions/770344/visual-c-linking-plugin-dll-ag... This is to use GetProcAddress from the plugin (DLL) to get the address of symbols in nbdkit.exe. It works a bit like dlsym. I hacked together a test plugin to try this: static void load (void) { int (*_nbdkit_parse_int) (const char *what, const char *str, int *r) = GetProcAddress (GetModuleHandle (NULL), "nbdkit_parse_int"); fprintf (stderr, "nbdkit_parse_int addr = %p\n", _nbdkit_parse_int); void (*_nbdkit_debug) (const char *msg, ...) = GetProcAddress (GetModuleHandle (NULL), "nbdkit_debug"); _nbdkit_debug ("calling nbdkit_debug now ..."); } and on loading this plugin into server/nbdkit.exe: nbdkit_parse_int addr = 000000000040BD40 nbdkit: debug: calling nbdkit_debug now ... So it really does work. I'm not quite sure exactly how to integrate this. Perhaps adding some Windows-only code to plugin_init which does the appropriate GetProcAddress calls, initializing some function pointers in the plugin? Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-builder quickly builds VMs from scratch http://libguestfs.org/virt-builder.1.html