From 3063d84e9c0162ba74670f4eb6ef276ceb03c644 Mon Sep 17 00:00:00 2001
From: Grzegorz Jaszczyk <jaszczyk@google.com>
Date: Thu, 6 Jun 2024 15:27:08 +0000
Subject: [PATCH] libmodprobe: add support for dynamic module options

Hitherto libmodprobe was supporting modules.options which allows passing
extra module options. This commit extends that support and beside
`options`, modules.options can now contain `dyn_options` entries.

Syntax example:
dyn_options snd_sof_pci system "/vendor/bin/mod_options --sof-fw"

This allows to determine extra module options, with help of external
program, at runtime which can be useful for unibuilds, supporting
various device flavors and therefore requiring different module options.

Using external program to customize modules parameters are inspired by
Android's external firmware handler:
https://android.googlesource.com/platform/system/core/+/master/init/README.ueventd.md#firmware-loading
and the same RunExternalHandler is reused for both dynamic module
handling and firmware handling.

Bug: 335619610
Test: Test audio on systems using snd_sof_pci module and verify
correctness of custom module parameters.

Change-Id: Ibd1a942d4ea022519676435ed525cd7c3e720d31
---
 libmodprobe/include/modprobe/modprobe.h |  1 +
 libmodprobe/libmodprobe.cpp             | 61 +++++++++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/libmodprobe/include/modprobe/modprobe.h b/libmodprobe/include/modprobe/modprobe.h
index d7a90c488..7b691b13a 100644
--- a/libmodprobe/include/modprobe/modprobe.h
+++ b/libmodprobe/include/modprobe/modprobe.h
@@ -59,6 +59,7 @@ class Modprobe {
     bool ParseSoftdepCallback(const std::vector<std::string>& args);
     bool ParseLoadCallback(const std::vector<std::string>& args);
     bool ParseOptionsCallback(const std::vector<std::string>& args);
+    bool ParseDynOptionsCallback(const std::vector<std::string>& args);
     bool ParseBlocklistCallback(const std::vector<std::string>& args);
     void ParseKernelCmdlineOptions();
     void ParseCfg(const std::string& cfg, std::function<bool(const std::vector<std::string>&)> f);
diff --git a/libmodprobe/libmodprobe.cpp b/libmodprobe/libmodprobe.cpp
index 8cc0b9b2e..bdd114c4b 100644
--- a/libmodprobe/libmodprobe.cpp
+++ b/libmodprobe/libmodprobe.cpp
@@ -17,8 +17,11 @@
 #include <modprobe/modprobe.h>
 
 #include <fnmatch.h>
+#include <grp.h>
+#include <pwd.h>
 #include <sys/stat.h>
 #include <sys/syscall.h>
+#include <sys/wait.h>
 
 #include <algorithm>
 #include <map>
@@ -30,9 +33,12 @@
 #include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
+#include <android-base/parseint.h>
 #include <android-base/strings.h>
 #include <android-base/unique_fd.h>
 
+#include "exthandler/exthandler.h"
+
 std::string Modprobe::MakeCanonical(const std::string& module_path) {
     auto start = module_path.find_last_of('/');
     if (start == std::string::npos) {
@@ -164,6 +170,10 @@ bool Modprobe::ParseOptionsCallback(const std::vector<std::string>& args) {
     auto it = args.begin();
     const std::string& type = *it++;
 
+    if (type == "dyn_options") {
+        return ParseDynOptionsCallback(std::vector<std::string>(it, args.end()));
+    }
+
     if (type != "options") {
         LOG(ERROR) << "non-options line encountered in modules.options";
         return false;
@@ -197,6 +207,57 @@ bool Modprobe::ParseOptionsCallback(const std::vector<std::string>& args) {
     return true;
 }
 
+bool Modprobe::ParseDynOptionsCallback(const std::vector<std::string>& args) {
+    auto it = args.begin();
+    int arg_size = 3;
+
+    if (args.size() < arg_size) {
+        LOG(ERROR) << "dyn_options lines in modules.options must have at least" << arg_size
+                   << " entries, not " << args.size();
+        return false;
+    }
+
+    const std::string& module = *it++;
+
+    const std::string& canonical_name = MakeCanonical(module);
+    if (canonical_name.empty()) {
+        return false;
+    }
+
+    const std::string& pwnam = *it++;
+    passwd* pwd = getpwnam(pwnam.c_str());
+    if (!pwd) {
+        LOG(ERROR) << "invalid handler uid'" << pwnam << "'";
+        return false;
+    }
+
+    std::string handler_with_args =
+            android::base::Join(std::vector<std::string>(it, args.end()), ' ');
+    handler_with_args.erase(std::remove(handler_with_args.begin(), handler_with_args.end(), '\"'),
+                            handler_with_args.end());
+
+    LOG(DEBUG) << "Launching external module options handler: '" << handler_with_args
+               << " for module: " << module;
+
+    // There is no need to set envs for external module options handler - pass
+    // empty map.
+    std::unordered_map<std::string, std::string> envs_map;
+    auto result = RunExternalHandler(handler_with_args, pwd->pw_uid, 0, envs_map);
+    if (!result.ok()) {
+        LOG(ERROR) << "External module handler failed: " << result.error();
+        return false;
+    }
+
+    LOG(INFO) << "Dynamic options for module: " << module << " are '" << *result << "'";
+
+    auto [unused, inserted] = this->module_options_.emplace(canonical_name, *result);
+    if (!inserted) {
+        LOG(ERROR) << "multiple options lines present for module " << module;
+        return false;
+    }
+    return true;
+}
+
 bool Modprobe::ParseBlocklistCallback(const std::vector<std::string>& args) {
     auto it = args.begin();
     const std::string& type = *it++;