Fix plugin directory.

[aoxy]

What?

This PR fixes a bug in the plugin directory resolution logic in getPluginDir(). Previously, the code attempted to locate plugins in a non-existent core/plugins directory. With certain build setups, this resulted in plugin loading failures, as reported when running ./examples/cpp/nixl_example:

$ NIXL_LOG_LEVEL=DEBUG ./examples/cpp/nixl_example
I0919 19:06:48.573057   96808 nixl_agent.cpp:122] NIXL ETCD is excluded
I0919 19:06:48.573148   96808 nixl_agent.cpp:122] NIXL ETCD is excluded
I0919 19:06:48.573169   96808 nixl_plugin_manager.cpp:197] Loading plugins from file: /home/aoxy/projs/nixl/my_build/pluginlist
I0919 19:06:48.628053   96808 nixl_plugin_manager.cpp:206] Loading plugins from: /home/aoxy/projs/nixl/my_build/examples/cpp/../../src/core/plugins
E0919 19:06:48.628149   96808 nixl_plugin_manager.cpp:297] Error accessing directory("/home/aoxy/projs/nixl/my_build/examples/cpp/../../src/core/plugins"): No such file or directory
...

Why?

The root cause of the bug is the logic for deriving the plugin directory path using std::filesystem::path::parent_path. The code snippet is:

static std::string
getPluginDir() {
    // Environment variable takes precedence
    const char *plugin_dir = getenv("NIXL_PLUGIN_DIR");
    if (plugin_dir) {
        return plugin_dir;
    }
    // By default, use the plugin directory relative to the binary
    Dl_info info;
    int ok = dladdr(reinterpret_cast<void *>(&getPluginDir), &info);
    if (!ok) {
        NIXL_ERROR << "Failed to get plugin directory from dladdr";
        return "";
    }
    return (std::filesystem::path(info.dli_fname).parent_path() / "plugins").string();
}

If info.dli_fname is /home/aoxy/projs/nixl/my_build/examples/cpp/../../src/core/libnixl.so, then std::filesystem::path(info.dli_fname).parent_path() results in /home/aoxy/projs/nixl/my_build/examples/cpp/../../src/core. This means the code searches for plugins under core/plugins, which does not exist.

Reference on how parent_path works:
https://en.cppreference.com/w/cpp/filesystem/path/parent_path

#include <filesystem>
#include <iostream>
namespace fs = std::filesystem;
 
int main()
{
    for (fs::path p : {"/var/tmp/example.txt", "/", "/var/tmp/."})
        std::cout << "The parent path of " << p
                  << " is " << p.parent_path() << '\n';
}
// Output:
// The parent path of "/var/tmp/example.txt" is "/var/tmp"
// The parent path of "/" is "/"
// The parent path of "/var/tmp/." is "/var/tmp"

List of the actual directory structure:

$ ls /home/jerryao/projs/nixl/my_build/examples/cpp/../../src/
api  bindings  core  infra  plugins  utils

The correct plugin directory should be /home/aoxy/projs/nixl/my_build/examples/cpp/../../src/plugins.

How?

The fix is to use parent_path() twice on info.dli_fname before appending "plugins", so that the plugin directory is set to the correct location above core (i.e., directly under src). Specifically, change

return (std::filesystem::path(info.dli_fname).parent_path() / "plugins").string();

to

return (std::filesystem::path(info.dli_fname).parent_path().parent_path() / "plugins").string();

This ensures the resolved path will be /home/aoxy/projs/nixl/my_build/examples/cpp/../../src/plugins, matching the actual project layout and fixing the loading error.

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[github-actions]

👋 Hi aoxy! Thank you for contributing to ai-dynamo/nixl.

Your PR reviewers will review your contribution then trigger the CI to test your changes.

🚀

[aranadive]

/ok to test 76cd8b0

[aranadive]

/build

[ovidiusm]

This will work for build directory, but it will break loading from installation directory

Will break installs

[aranadive]

This will work for build directory, but it will break loading from installation directory

You're right. Blossom CI passed. So we seem to have a testing gap with wheels in CI.