Binder: Split OS to Android and Unix part, abstract GetThreadId out

Bug: 302723053
Test: mma in binder folder
Test: aosp/2616196
Change-Id: I73df8fc453df0edf496960853cb0004f1c3a6a43
diff --git a/libs/binder/OS_unix_base.cpp b/libs/binder/OS_unix_base.cpp
new file mode 100644
index 0000000..81933d5
--- /dev/null
+++ b/libs/binder/OS_unix_base.cpp
@@ -0,0 +1,165 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "OS.h"
+
+#include <android-base/file.h>
+#include <binder/RpcTransportRaw.h>
+#include <log/log.h>
+#include <string.h>
+
+using android::base::ErrnoError;
+using android::base::Result;
+
+namespace android::binder::os {
+
+// Linux kernel supports up to 253 (from SCM_MAX_FD) for unix sockets.
+constexpr size_t kMaxFdsPerMsg = 253;
+
+Result<void> setNonBlocking(android::base::borrowed_fd fd) {
+    int flags = TEMP_FAILURE_RETRY(fcntl(fd.get(), F_GETFL));
+    if (flags == -1) {
+        return ErrnoError() << "Could not get flags for fd";
+    }
+    if (int ret = TEMP_FAILURE_RETRY(fcntl(fd.get(), F_SETFL, flags | O_NONBLOCK)); ret == -1) {
+        return ErrnoError() << "Could not set non-blocking flag for fd";
+    }
+    return {};
+}
+
+status_t getRandomBytes(uint8_t* data, size_t size) {
+    int ret = TEMP_FAILURE_RETRY(open("/dev/urandom", O_RDONLY | O_CLOEXEC | O_NOFOLLOW));
+    if (ret == -1) {
+        return -errno;
+    }
+
+    base::unique_fd fd(ret);
+    if (!base::ReadFully(fd, data, size)) {
+        return -errno;
+    }
+    return OK;
+}
+
+status_t dupFileDescriptor(int oldFd, int* newFd) {
+    int ret = fcntl(oldFd, F_DUPFD_CLOEXEC, 0);
+    if (ret < 0) {
+        return -errno;
+    }
+
+    *newFd = ret;
+    return OK;
+}
+
+std::unique_ptr<RpcTransportCtxFactory> makeDefaultRpcTransportCtxFactory() {
+    return RpcTransportCtxFactoryRaw::make();
+}
+
+ssize_t sendMessageOnSocket(
+        const RpcTransportFd& socket, iovec* iovs, int niovs,
+        const std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds) {
+    if (ancillaryFds != nullptr && !ancillaryFds->empty()) {
+        if (ancillaryFds->size() > kMaxFdsPerMsg) {
+            errno = EINVAL;
+            return -1;
+        }
+
+        // CMSG_DATA is not necessarily aligned, so we copy the FDs into a buffer and then
+        // use memcpy.
+        int fds[kMaxFdsPerMsg];
+        for (size_t i = 0; i < ancillaryFds->size(); i++) {
+            fds[i] = std::visit([](const auto& fd) { return fd.get(); }, ancillaryFds->at(i));
+        }
+        const size_t fdsByteSize = sizeof(int) * ancillaryFds->size();
+
+        alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(int) * kMaxFdsPerMsg)];
+
+        msghdr msg{
+                .msg_iov = iovs,
+                .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+                .msg_control = msgControlBuf,
+                .msg_controllen = sizeof(msgControlBuf),
+        };
+
+        cmsghdr* cmsg = CMSG_FIRSTHDR(&msg);
+        cmsg->cmsg_level = SOL_SOCKET;
+        cmsg->cmsg_type = SCM_RIGHTS;
+        cmsg->cmsg_len = CMSG_LEN(fdsByteSize);
+        memcpy(CMSG_DATA(cmsg), fds, fdsByteSize);
+
+        msg.msg_controllen = CMSG_SPACE(fdsByteSize);
+        return TEMP_FAILURE_RETRY(sendmsg(socket.fd.get(), &msg, MSG_NOSIGNAL | MSG_CMSG_CLOEXEC));
+    }
+
+    msghdr msg{
+            .msg_iov = iovs,
+            // posix uses int, glibc uses size_t.  niovs is a
+            // non-negative int and can be cast to either.
+            .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+    };
+    return TEMP_FAILURE_RETRY(sendmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+}
+
+ssize_t receiveMessageFromSocket(
+        const RpcTransportFd& socket, iovec* iovs, int niovs,
+        std::vector<std::variant<base::unique_fd, base::borrowed_fd>>* ancillaryFds) {
+    if (ancillaryFds != nullptr) {
+        int fdBuffer[kMaxFdsPerMsg];
+        alignas(struct cmsghdr) char msgControlBuf[CMSG_SPACE(sizeof(fdBuffer))];
+
+        msghdr msg{
+                .msg_iov = iovs,
+                .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+                .msg_control = msgControlBuf,
+                .msg_controllen = sizeof(msgControlBuf),
+        };
+        ssize_t processSize = TEMP_FAILURE_RETRY(recvmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+        if (processSize < 0) {
+            return -1;
+        }
+
+        for (cmsghdr* cmsg = CMSG_FIRSTHDR(&msg); cmsg != nullptr; cmsg = CMSG_NXTHDR(&msg, cmsg)) {
+            if (cmsg->cmsg_level == SOL_SOCKET && cmsg->cmsg_type == SCM_RIGHTS) {
+                // NOTE: It is tempting to reinterpret_cast, but cmsg(3) explicitly asks
+                // application devs to memcpy the data to ensure memory alignment.
+                size_t dataLen = cmsg->cmsg_len - CMSG_LEN(0);
+                LOG_ALWAYS_FATAL_IF(dataLen > sizeof(fdBuffer)); // validity check
+                memcpy(fdBuffer, CMSG_DATA(cmsg), dataLen);
+                size_t fdCount = dataLen / sizeof(int);
+                ancillaryFds->reserve(ancillaryFds->size() + fdCount);
+                for (size_t i = 0; i < fdCount; i++) {
+                    ancillaryFds->emplace_back(base::unique_fd(fdBuffer[i]));
+                }
+                break;
+            }
+        }
+
+        if (msg.msg_flags & MSG_CTRUNC) {
+            errno = EPIPE;
+            return -1;
+        }
+        return processSize;
+    }
+    msghdr msg{
+            .msg_iov = iovs,
+            // posix uses int, glibc uses size_t.  niovs is a
+            // non-negative int and can be cast to either.
+            .msg_iovlen = static_cast<decltype(msg.msg_iovlen)>(niovs),
+    };
+
+    return TEMP_FAILURE_RETRY(recvmsg(socket.fd.get(), &msg, MSG_NOSIGNAL));
+}
+
+} // namespace android::binder::os