net: report open file and device descriptors ready in select (Cyberpunk 2077 Galaxy RNG seeding)

Co-authored-by: Artyom Zabroda <artyomzabroda@proton.me>

src/kernel/fileSystem.cpp

@@ -410,6 +410,11 @@ std::filesystem::path GetRealFilename(const std::string& mounted_file_name) {
 	return g_mount_points->ResolvePath(mounted_file_name);
 }
 
+bool IsOpenDescriptor(int d) {
+	const auto* file = g_files->GetFile(d);
+	return file != nullptr && file->opened;
+}
+
 // NOLINTNEXTLINE(readability-function-cognitive-complexity)
 int KYTY_SYSV_ABI KernelOpen(const char* path, int flags, uint16_t mode) {
 	PRINT_NAME();

src/kernel/fileSystem.h

@@ -56,6 +56,8 @@ void                  Mount(const std::filesystem::path& folder, const std::stri
 void                  Umount(const std::string& folder_or_point);
 // Returns an empty path when the guest path has no mounted filesystem.
 std::filesystem::path GetRealFilename(const std::string& mounted_file_name);
+// Returns whether d is an open file, directory or device descriptor.
+bool                  IsOpenDescriptor(int d);
 
 int KYTY_SYSV_ABI     KernelOpen(const char* path, int flags, uint16_t mode);
 int KYTY_SYSV_ABI     KernelClose(int d);

src/libs/network.cpp

@@ -30,6 +30,7 @@
 #include "common/emulatorConfig.h"
 #include "common/logging/log.h"
 #include "common/threads.h"
+#include "kernel/fileSystem.h"
 #include "kernel/pthread.h"
 #include "libs/errno.h"
 #include "libs/libs.h"
@@ -2577,6 +2578,7 @@ int KYTY_SYSV_ABI Select(int nfds, void* readfds, void* writefds, void* exceptfd
 
 	std::vector<std::pair<int, NativeSocket>> descriptors;
 	std::vector<std::shared_ptr<SocketTransport>> stream_reads;
+	std::vector<std::pair<void*, int>> ready_files;
 	int host_nfds = 0;
 	for (int fd = 0; fd < nfds; fd++) {
 		const bool read = GuestFdIsSet(readfds, fd);
@@ -2585,6 +2587,16 @@ int KYTY_SYSV_ABI Select(int nfds, void* readfds, void* writefds, void* exceptfd
 		if (!read && !write && !except) {
 			continue;
 		}
+		// FreeBSD polls files and devices ready to read and write at once.
+		if (!IsSocket(fd) && LibKernel::FileSystem::IsOpenDescriptor(fd)) {
+			if (read) {
+				ready_files.emplace_back(readfds, fd);
+			}
+			if (write) {
+				ready_files.emplace_back(writefds, fd);
+			}
+			continue;
+		}
 		NativeSocket                    socket = INVALID_NATIVE_SOCKET;
 		std::shared_ptr<SocketTransport> transport;
 #if !defined(_WIN32)
@@ -2636,6 +2648,10 @@ int KYTY_SYSV_ABI Select(int nfds, void* readfds, void* writefds, void* exceptfd
 		host_timeout.tv_usec = static_cast<decltype(host_timeout.tv_usec)>(guest_timeout->tv_usec);
 		host_timeout_ptr = &host_timeout;
 	}
+	if (!ready_files.empty()) {
+		host_timeout     = {};
+		host_timeout_ptr = &host_timeout;
+	}
 
 	int result = 0;
 #if defined(_WIN32)
@@ -2672,6 +2688,10 @@ int KYTY_SYSV_ABI Select(int nfds, void* readfds, void* writefds, void* exceptfd
 			result++;
 		}
 	}
+	for (const auto& [fds, fd]: ready_files) {
+		GuestFdSet(fds, fd);
+		result++;
+	}
 	return result;
 }
 

tests/KernelFileSystemTests.cpp

@@ -324,6 +324,7 @@ void CheckSaveRename(const std::filesystem::path &root,
 }
 
 void TestRandomDevices() {
+  namespace Net = Libs::Network::Net;
   for (const auto* path : {"/dev/urandom", "/dev/random"}) {
     const int fd = FileSystem::KernelOpen(path, 0, 0);
     FileSystem::FileStat stat {};
@@ -333,7 +334,18 @@ void TestRandomDevices() {
     std::array<uint8_t, 32> entropy {};
     Check(FileSystem::KernelRead(fd, entropy.data(), entropy.size()) == entropy.size(),
           "character device supplies requested entropy");
+    // OpenSSL RAND_poll selects the device before reading it; a null timeout must not block.
+    std::array<uint64_t, 16> readable {};
+    readable[fd / 64] = uint64_t {1} << (fd % 64);
+    auto writable = readable;
+    const auto requested = readable;
+    Check(Net::Select(fd + 1, readable.data(), writable.data(), nullptr, nullptr) == 2 &&
+              readable == requested && writable == requested,
+          "select reports an entropy source ready at once");
     Check(FileSystem::KernelClose(fd) == OK, "close entropy source");
+    Check(Net::Select(fd + 1, readable.data(), nullptr, nullptr, nullptr) == -1 &&
+              *Libs::Posix::GetErrorAddr() == Libs::Posix::POSIX_EBADF,
+          "select rejects a closed descriptor");
   }
 }
 
@@ -2453,8 +2465,8 @@ int main(int argc, char** argv) {
   TestAioBatches();
   CheckSaveRename(temporary.Path(), "first-save");
   CheckSaveRename(temporary.Path(), "replacement-save");
-  FileSystem::Shutdown();
   CheckSocketWakeup();
+  FileSystem::Shutdown();
   CheckEtherAddressFormatting();
 #if defined(__linux__)
   TestNetCtlHostIpv4();