binder: Eliminate a data copy in RPC transport operations

Switch RpcTransportRaw to use sendmsg() and recvmsg() over
iovecs to send data from multiple buffers to avoid having
to copy all data into a single large buffer.

Bug: 202878542
Test: atest binderRpcTest
Change-Id: I8ba7fa815040555503160ae41888a0b0efe9e5d2

8 files changed, 185 insertions, 147 deletions

diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index 93ed50e986..ace5cd5052 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -287,8 +287,8 @@ void RpcServer::establishConnection(sp<RpcServer>&& server, base::unique_fd clie
 
     RpcConnectionHeader header;
     if (status == OK) {
-        status = client->interruptableReadFully(server->mShutdownTrigger.get(), &header,
-                                                sizeof(header), {});
+        iovec iov{&header, sizeof(header)};
+        status = client->interruptableReadFully(server->mShutdownTrigger.get(), &iov, 1, {});
         if (status != OK) {
             ALOGE("Failed to read ID for client connecting to RPC server: %s",
                   statusToString(status).c_str());
@@ -301,8 +301,9 @@ void RpcServer::establishConnection(sp<RpcServer>&& server, base::unique_fd clie
         if (header.sessionIdSize > 0) {
             if (header.sessionIdSize == kSessionIdBytes) {
                 sessionId.resize(header.sessionIdSize);
-                status = client->interruptableReadFully(server->mShutdownTrigger.get(),
-                                                        sessionId.data(), sessionId.size(), {});
+                iovec iov{sessionId.data(), sessionId.size()};
+                status =
+                        client->interruptableReadFully(server->mShutdownTrigger.get(), &iov, 1, {});
                 if (status != OK) {
                     ALOGE("Failed to read session ID for client connecting to RPC server: %s",
                           statusToString(status).c_str());
@@ -331,8 +332,8 @@ void RpcServer::establishConnection(sp<RpcServer>&& server, base::unique_fd clie
                     .version = protocolVersion,
             };
 
-            status = client->interruptableWriteFully(server->mShutdownTrigger.get(), &response,
-                                                     sizeof(response), {});
+            iovec iov{&response, sizeof(response)};
+            status = client->interruptableWriteFully(server->mShutdownTrigger.get(), &iov, 1, {});
             if (status != OK) {
                 ALOGE("Failed to send new session response: %s", statusToString(status).c_str());
                 // still need to cleanup before we can return
diff --git a/libs/binder/RpcSession.cpp b/libs/binder/RpcSession.cpp
index a5a2bb1017..b84395e7cb 100644
--- a/libs/binder/RpcSession.cpp
+++ b/libs/binder/RpcSession.cpp
@@ -615,8 +615,9 @@ status_t RpcSession::initAndAddConnection(unique_fd fd, const std::vector<uint8_
         header.options |= RPC_CONNECTION_OPTION_INCOMING;
     }
 
+    iovec headerIov{&header, sizeof(header)};
     auto sendHeaderStatus =
-            server->interruptableWriteFully(mShutdownTrigger.get(), &header, sizeof(header), {});
+            server->interruptableWriteFully(mShutdownTrigger.get(), &headerIov, 1, {});
     if (sendHeaderStatus != OK) {
         ALOGE("Could not write connection header to socket: %s",
               statusToString(sendHeaderStatus).c_str());
@@ -624,9 +625,10 @@ status_t RpcSession::initAndAddConnection(unique_fd fd, const std::vector<uint8_
     }
 
     if (sessionId.size() > 0) {
+        iovec sessionIov{const_cast<void*>(static_cast<const void*>(sessionId.data())),
+                         sessionId.size()};
         auto sendSessionIdStatus =
-                server->interruptableWriteFully(mShutdownTrigger.get(), sessionId.data(),
-                                                sessionId.size(), {});
+                server->interruptableWriteFully(mShutdownTrigger.get(), &sessionIov, 1, {});
         if (sendSessionIdStatus != OK) {
             ALOGE("Could not write session ID ('%s') to socket: %s",
                   base::HexString(sessionId.data(), sessionId.size()).c_str(),
diff --git a/libs/binder/RpcState.cpp b/libs/binder/RpcState.cpp
index 09b3d68626..6286c9c7bc 100644
--- a/libs/binder/RpcState.cpp
+++ b/libs/binder/RpcState.cpp
@@ -19,6 +19,7 @@
 #include "RpcState.h"
 
 #include <android-base/hex.h>
+#include <android-base/macros.h>
 #include <android-base/scopeguard.h>
 #include <binder/BpBinder.h>
 #include <binder/IPCThreadState.h>
@@ -309,22 +310,18 @@ RpcState::CommandData::CommandData(size_t size) : mSize(size) {
 }
 
 status_t RpcState::rpcSend(const sp<RpcSession::RpcConnection>& connection,
-                           const sp<RpcSession>& session, const char* what, const void* data,
-                           size_t size, const std::function<status_t()>& altPoll) {
-    LOG_RPC_DETAIL("Sending %s on RpcTransport %p: %s", what, connection->rpcTransport.get(),
-                   android::base::HexString(data, size).c_str());
-
-    if (size > std::numeric_limits<ssize_t>::max()) {
-        ALOGE("Cannot send %s at size %zu (too big)", what, size);
-        (void)session->shutdownAndWait(false);
-        return BAD_VALUE;
+                           const sp<RpcSession>& session, const char* what, iovec* iovs,
+                           size_t niovs, const std::function<status_t()>& altPoll) {
+    for (size_t i = 0; i < niovs; i++) {
+        LOG_RPC_DETAIL("Sending %s on RpcTransport %p: %s", what, connection->rpcTransport.get(),
+                       android::base::HexString(iovs[i].iov_base, iovs[i].iov_len).c_str());
     }
 
     if (status_t status =
                 connection->rpcTransport->interruptableWriteFully(session->mShutdownTrigger.get(),
-                                                                  data, size, altPoll);
+                                                                  iovs, niovs, altPoll);
         status != OK) {
-        LOG_RPC_DETAIL("Failed to write %s (%zu bytes) on RpcTransport %p, error: %s", what, size,
+        LOG_RPC_DETAIL("Failed to write %s (%zu iovs) on RpcTransport %p, error: %s", what, niovs,
                        connection->rpcTransport.get(), statusToString(status).c_str());
         (void)session->shutdownAndWait(false);
         return status;
@@ -334,34 +331,30 @@ status_t RpcState::rpcSend(const sp<RpcSession::RpcConnection>& connection,
 }
 
 status_t RpcState::rpcRec(const sp<RpcSession::RpcConnection>& connection,
-                          const sp<RpcSession>& session, const char* what, void* data,
-                          size_t size) {
-    if (size > std::numeric_limits<ssize_t>::max()) {
-        ALOGE("Cannot rec %s at size %zu (too big)", what, size);
-        (void)session->shutdownAndWait(false);
-        return BAD_VALUE;
-    }
-
+                          const sp<RpcSession>& session, const char* what, iovec* iovs,
+                          size_t niovs) {
     if (status_t status =
                 connection->rpcTransport->interruptableReadFully(session->mShutdownTrigger.get(),
-                                                                 data, size, {});
+                                                                 iovs, niovs, {});
         status != OK) {
-        LOG_RPC_DETAIL("Failed to read %s (%zu bytes) on RpcTransport %p, error: %s", what, size,
+        LOG_RPC_DETAIL("Failed to read %s (%zu iovs) on RpcTransport %p, error: %s", what, niovs,
                        connection->rpcTransport.get(), statusToString(status).c_str());
         (void)session->shutdownAndWait(false);
         return status;
     }
 
-    LOG_RPC_DETAIL("Received %s on RpcTransport %p: %s", what, connection->rpcTransport.get(),
-                   android::base::HexString(data, size).c_str());
+    for (size_t i = 0; i < niovs; i++) {
+        LOG_RPC_DETAIL("Received %s on RpcTransport %p: %s", what, connection->rpcTransport.get(),
+                       android::base::HexString(iovs[i].iov_base, iovs[i].iov_len).c_str());
+    }
     return OK;
 }
 
 status_t RpcState::readNewSessionResponse(const sp<RpcSession::RpcConnection>& connection,
                                           const sp<RpcSession>& session, uint32_t* version) {
     RpcNewSessionResponse response;
-    if (status_t status =
-                rpcRec(connection, session, "new session response", &response, sizeof(response));
+    iovec iov{&response, sizeof(response)};
+    if (status_t status = rpcRec(connection, session, "new session response", &iov, 1);
         status != OK) {
         return status;
     }
@@ -374,14 +367,15 @@ status_t RpcState::sendConnectionInit(const sp<RpcSession::RpcConnection>& conne
     RpcOutgoingConnectionInit init{
             .msg = RPC_CONNECTION_INIT_OKAY,
     };
-    return rpcSend(connection, session, "connection init", &init, sizeof(init));
+    iovec iov{&init, sizeof(init)};
+    return rpcSend(connection, session, "connection init", &iov, 1);
 }
 
 status_t RpcState::readConnectionInit(const sp<RpcSession::RpcConnection>& connection,
                                       const sp<RpcSession>& session) {
     RpcOutgoingConnectionInit init;
-    if (status_t status = rpcRec(connection, session, "connection init", &init, sizeof(init));
-        status != OK)
+    iovec iov{&init, sizeof(init)};
+    if (status_t status = rpcRec(connection, session, "connection init", &iov, 1); status != OK)
         return status;
 
     static_assert(sizeof(init.msg) == sizeof(RPC_CONNECTION_INIT_OKAY));
@@ -514,17 +508,6 @@ status_t RpcState::transactAddress(const sp<RpcSession::RpcConnection>& connecti
             .flags = flags,
             .asyncNumber = asyncNumber,
     };
-    CommandData transactionData(sizeof(RpcWireHeader) + sizeof(RpcWireTransaction) +
-                                data.dataSize());
-    if (!transactionData.valid()) {
-        return NO_MEMORY;
-    }
-
-    memcpy(transactionData.data() + 0, &command, sizeof(RpcWireHeader));
-    memcpy(transactionData.data() + sizeof(RpcWireHeader), &transaction,
-           sizeof(RpcWireTransaction));
-    memcpy(transactionData.data() + sizeof(RpcWireHeader) + sizeof(RpcWireTransaction), data.data(),
-           data.dataSize());
 
     constexpr size_t kWaitMaxUs = 1000000;
     constexpr size_t kWaitLogUs = 10000;
@@ -550,8 +533,13 @@ status_t RpcState::transactAddress(const sp<RpcSession::RpcConnection>& connecti
         return drainCommands(connection, session, CommandType::CONTROL_ONLY);
     };
 
-    if (status_t status = rpcSend(connection, session, "transaction", transactionData.data(),
-                                  transactionData.size(), drainRefs);
+    iovec iovs[]{
+            {&command, sizeof(RpcWireHeader)},
+            {&transaction, sizeof(RpcWireTransaction)},
+            {const_cast<uint8_t*>(data.data()), data.dataSize()},
+    };
+    if (status_t status =
+                rpcSend(connection, session, "transaction", iovs, arraysize(iovs), drainRefs);
         status != OK) {
         // TODO(b/167966510): need to undo onBinderLeaving - we know the
         // refcount isn't successfully transferred.
@@ -584,8 +572,8 @@ status_t RpcState::waitForReply(const sp<RpcSession::RpcConnection>& connection,
                                 const sp<RpcSession>& session, Parcel* reply) {
     RpcWireHeader command;
     while (true) {
-        if (status_t status = rpcRec(connection, session, "command header (for reply)", &command,
-                                     sizeof(command));
+        iovec iov{&command, sizeof(command)};
+        if (status_t status = rpcRec(connection, session, "command header (for reply)", &iov, 1);
             status != OK)
             return status;
 
@@ -599,8 +587,8 @@ status_t RpcState::waitForReply(const sp<RpcSession::RpcConnection>& connection,
     CommandData data(command.bodySize);
     if (!data.valid()) return NO_MEMORY;
 
-    if (status_t status = rpcRec(connection, session, "reply body", data.data(), command.bodySize);
-        status != OK)
+    iovec iov{data.data(), command.bodySize};
+    if (status_t status = rpcRec(connection, session, "reply body", &iov, 1); status != OK)
         return status;
 
     if (command.bodySize < sizeof(RpcWireReply)) {
@@ -653,11 +641,8 @@ status_t RpcState::sendDecStrongToTarget(const sp<RpcSession::RpcConnection>& co
             .command = RPC_COMMAND_DEC_STRONG,
             .bodySize = sizeof(RpcDecStrong),
     };
-    if (status_t status = rpcSend(connection, session, "dec ref header", &cmd, sizeof(cmd));
-        status != OK)
-        return status;
-
-    return rpcSend(connection, session, "dec ref body", &body, sizeof(body));
+    iovec iovs[]{{&cmd, sizeof(cmd)}, {&body, sizeof(body)}};
+    return rpcSend(connection, session, "dec ref", iovs, arraysize(iovs));
 }
 
 status_t RpcState::getAndExecuteCommand(const sp<RpcSession::RpcConnection>& connection,
@@ -665,8 +650,8 @@ status_t RpcState::getAndExecuteCommand(const sp<RpcSession::RpcConnection>& con
     LOG_RPC_DETAIL("getAndExecuteCommand on RpcTransport %p", connection->rpcTransport.get());
 
     RpcWireHeader command;
-    if (status_t status = rpcRec(connection, session, "command header (for server)", &command,
-                                 sizeof(command));
+    iovec iov{&command, sizeof(command)};
+    if (status_t status = rpcRec(connection, session, "command header (for server)", &iov, 1);
         status != OK)
         return status;
 
@@ -726,9 +711,8 @@ status_t RpcState::processTransact(const sp<RpcSession::RpcConnection>& connecti
     if (!transactionData.valid()) {
         return NO_MEMORY;
     }
-    if (status_t status = rpcRec(connection, session, "transaction body", transactionData.data(),
-                                 transactionData.size());
-        status != OK)
+    iovec iov{transactionData.data(), transactionData.size()};
+    if (status_t status = rpcRec(connection, session, "transaction body", &iov, 1); status != OK)
         return status;
 
     return processTransactInternal(connection, session, std::move(transactionData));
@@ -965,16 +949,12 @@ processTransactInternalTailCall:
             .status = replyStatus,
     };
 
-    CommandData replyData(sizeof(RpcWireHeader) + sizeof(RpcWireReply) + reply.dataSize());
-    if (!replyData.valid()) {
-        return NO_MEMORY;
-    }
-    memcpy(replyData.data() + 0, &cmdReply, sizeof(RpcWireHeader));
-    memcpy(replyData.data() + sizeof(RpcWireHeader), &rpcReply, sizeof(RpcWireReply));
-    memcpy(replyData.data() + sizeof(RpcWireHeader) + sizeof(RpcWireReply), reply.data(),
-           reply.dataSize());
-
-    return rpcSend(connection, session, "reply", replyData.data(), replyData.size());
+    iovec iovs[]{
+            {&cmdReply, sizeof(RpcWireHeader)},
+            {&rpcReply, sizeof(RpcWireReply)},
+            {const_cast<uint8_t*>(reply.data()), reply.dataSize()},
+    };
+    return rpcSend(connection, session, "reply", iovs, arraysize(iovs));
 }
 
 status_t RpcState::processDecStrong(const sp<RpcSession::RpcConnection>& connection,
@@ -985,9 +965,8 @@ status_t RpcState::processDecStrong(const sp<RpcSession::RpcConnection>& connect
     if (!commandData.valid()) {
         return NO_MEMORY;
     }
-    if (status_t status =
-                rpcRec(connection, session, "dec ref body", commandData.data(), commandData.size());
-        status != OK)
+    iovec iov{commandData.data(), commandData.size()};
+    if (status_t status = rpcRec(connection, session, "dec ref body", &iov, 1); status != OK)
         return status;
 
     if (command.bodySize != sizeof(RpcDecStrong)) {
diff --git a/libs/binder/RpcState.h b/libs/binder/RpcState.h
index dba0a43060..5cad394a2f 100644
--- a/libs/binder/RpcState.h
+++ b/libs/binder/RpcState.h
@@ -24,6 +24,8 @@
 #include <optional>
 #include <queue>
 
+#include <sys/uio.h>
+
 namespace android {
 
 struct RpcWireHeader;
@@ -177,12 +179,12 @@ private:
     };
 
     [[nodiscard]] status_t rpcSend(const sp<RpcSession::RpcConnection>& connection,
-                                   const sp<RpcSession>& session, const char* what,
-                                   const void* data, size_t size,
+                                   const sp<RpcSession>& session, const char* what, iovec* iovs,
+                                   size_t niovs,
                                    const std::function<status_t()>& altPoll = nullptr);
     [[nodiscard]] status_t rpcRec(const sp<RpcSession::RpcConnection>& connection,
-                                  const sp<RpcSession>& session, const char* what, void* data,
-                                  size_t size);
+                                  const sp<RpcSession>& session, const char* what, iovec* iovs,
+                                  size_t niovs);
 
     [[nodiscard]] status_t waitForReply(const sp<RpcSession::RpcConnection>& connection,
                                         const sp<RpcSession>& session, Parcel* reply);
diff --git a/libs/binder/RpcTransportRaw.cpp b/libs/binder/RpcTransportRaw.cpp
index 7669518954..2182e1868e 100644
--- a/libs/binder/RpcTransportRaw.cpp
+++ b/libs/binder/RpcTransportRaw.cpp
@@ -43,12 +43,10 @@ public:
         return ret;
     }
 
-    template <typename Buffer, typename SendOrReceive>
-    status_t interruptableReadOrWrite(FdTrigger* fdTrigger, Buffer buffer, size_t size,
+    template <typename SendOrReceive>
+    status_t interruptableReadOrWrite(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                       SendOrReceive sendOrReceiveFun, const char* funName,
                                       int16_t event, const std::function<status_t()>& altPoll) {
-        const Buffer end = buffer + size;
-
         MAYBE_WAIT_IN_FLAKE_MODE;
 
         // Since we didn't poll, we need to manually check to see if it was triggered. Otherwise, we
@@ -57,26 +55,61 @@ public:
             return DEAD_OBJECT;
         }
 
+        // If iovs has one or more empty vectors at the end and
+        // we somehow advance past all the preceding vectors and
+        // pass some or all of the empty ones to sendmsg/recvmsg,
+        // the call will return processSize == 0. In that case
+        // we should be returning OK but instead return DEAD_OBJECT.
+        // To avoid this problem, we make sure here that the last
+        // vector at iovs[niovs - 1] has a non-zero length.
+        while (niovs > 0 && iovs[niovs - 1].iov_len == 0) {
+            niovs--;
+        }
+        if (niovs == 0) {
+            // The vectors are all empty, so we have nothing to send.
+            return OK;
+        }
+
         bool havePolled = false;
         while (true) {
-            ssize_t processSize = TEMP_FAILURE_RETRY(
-                    sendOrReceiveFun(mSocket.get(), buffer, end - buffer, MSG_NOSIGNAL));
+            msghdr msg{
+                    .msg_iov = iovs,
+                    .msg_iovlen = niovs,
+            };
+            ssize_t processSize =
+                    TEMP_FAILURE_RETRY(sendOrReceiveFun(mSocket.get(), &msg, MSG_NOSIGNAL));
 
             if (processSize < 0) {
                 int savedErrno = errno;
 
                 // Still return the error on later passes, since it would expose
                 // a problem with polling
-                if (havePolled ||
-                    (!havePolled && savedErrno != EAGAIN && savedErrno != EWOULDBLOCK)) {
+                if (havePolled || (savedErrno != EAGAIN && savedErrno != EWOULDBLOCK)) {
                     LOG_RPC_DETAIL("RpcTransport %s(): %s", funName, strerror(savedErrno));
                     return -savedErrno;
                 }
             } else if (processSize == 0) {
                 return DEAD_OBJECT;
             } else {
-                buffer += processSize;
-                if (buffer == end) {
+                while (processSize > 0 && niovs > 0) {
+                    auto& iov = iovs[0];
+                    if (static_cast<size_t>(processSize) < iov.iov_len) {
+                        // Advance the base of the current iovec
+                        iov.iov_base = reinterpret_cast<char*>(iov.iov_base) + processSize;
+                        iov.iov_len -= processSize;
+                        break;
+                    }
+
+                    // The current iovec was fully written
+                    processSize -= iov.iov_len;
+                    iovs++;
+                    niovs--;
+                }
+                if (niovs == 0) {
+                    LOG_ALWAYS_FATAL_IF(processSize > 0,
+                                        "Reached the end of iovecs "
+                                        "with %zd bytes remaining",
+                                        processSize);
                     return OK;
                 }
             }
@@ -95,16 +128,16 @@ public:
         }
     }
 
-    status_t interruptableWriteFully(FdTrigger* fdTrigger, const void* data, size_t size,
+    status_t interruptableWriteFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                      const std::function<status_t()>& altPoll) override {
-        return interruptableReadOrWrite(fdTrigger, reinterpret_cast<const uint8_t*>(data), size,
-                                        send, "send", POLLOUT, altPoll);
+        return interruptableReadOrWrite(fdTrigger, iovs, niovs, sendmsg, "sendmsg", POLLOUT,
+                                        altPoll);
     }
 
-    status_t interruptableReadFully(FdTrigger* fdTrigger, void* data, size_t size,
+    status_t interruptableReadFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                     const std::function<status_t()>& altPoll) override {
-        return interruptableReadOrWrite(fdTrigger, reinterpret_cast<uint8_t*>(data), size, recv,
-                                        "recv", POLLIN, altPoll);
+        return interruptableReadOrWrite(fdTrigger, iovs, niovs, recvmsg, "recvmsg", POLLIN,
+                                        altPoll);
     }
 
 private:
diff --git a/libs/binder/RpcTransportTls.cpp b/libs/binder/RpcTransportTls.cpp
index 7f810b17ba..c05ea1512f 100644
--- a/libs/binder/RpcTransportTls.cpp
+++ b/libs/binder/RpcTransportTls.cpp
@@ -275,9 +275,9 @@ public:
     RpcTransportTls(android::base::unique_fd socket, Ssl ssl)
           : mSocket(std::move(socket)), mSsl(std::move(ssl)) {}
     Result<size_t> peek(void* buf, size_t size) override;
-    status_t interruptableWriteFully(FdTrigger* fdTrigger, const void* data, size_t size,
+    status_t interruptableWriteFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                      const std::function<status_t()>& altPoll) override;
-    status_t interruptableReadFully(FdTrigger* fdTrigger, void* data, size_t size,
+    status_t interruptableReadFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                     const std::function<status_t()>& altPoll) override;
 
 private:
@@ -303,68 +303,83 @@ Result<size_t> RpcTransportTls::peek(void* buf, size_t size) {
     return ret;
 }
 
-status_t RpcTransportTls::interruptableWriteFully(FdTrigger* fdTrigger, const void* data,
-                                                  size_t size,
+status_t RpcTransportTls::interruptableWriteFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                                   const std::function<status_t()>& altPoll) {
-    auto buffer = reinterpret_cast<const uint8_t*>(data);
-    const uint8_t* end = buffer + size;
-
     MAYBE_WAIT_IN_FLAKE_MODE;
 
     // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
     // once. The trigger is also checked via triggerablePoll() after every SSL_write().
     if (fdTrigger->isTriggered()) return DEAD_OBJECT;
 
-    while (buffer < end) {
-        size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
-        auto [writeSize, errorQueue] = mSsl.call(SSL_write, buffer, todo);
-        if (writeSize > 0) {
-            buffer += writeSize;
-            errorQueue.clear();
+    size_t size = 0;
+    for (size_t i = 0; i < niovs; i++) {
+        const iovec& iov = iovs[i];
+        if (iov.iov_len == 0) {
             continue;
         }
-        // SSL_write() should never return 0 unless BIO_write were to return 0.
-        int sslError = mSsl.getError(writeSize);
-        // TODO(b/195788248): BIO should contain the FdTrigger, and send(2) / recv(2) should be
-        //   triggerablePoll()-ed. Then additionalEvent is no longer necessary.
-        status_t pollStatus = errorQueue.pollForSslError(mSocket.get(), sslError, fdTrigger,
-                                                         "SSL_write", POLLIN, altPoll);
-        if (pollStatus != OK) return pollStatus;
-        // Do not advance buffer. Try SSL_write() again.
+        size += iov.iov_len;
+
+        auto buffer = reinterpret_cast<const uint8_t*>(iov.iov_base);
+        const uint8_t* end = buffer + iov.iov_len;
+        while (buffer < end) {
+            size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
+            auto [writeSize, errorQueue] = mSsl.call(SSL_write, buffer, todo);
+            if (writeSize > 0) {
+                buffer += writeSize;
+                errorQueue.clear();
+                continue;
+            }
+            // SSL_write() should never return 0 unless BIO_write were to return 0.
+            int sslError = mSsl.getError(writeSize);
+            // TODO(b/195788248): BIO should contain the FdTrigger, and send(2) / recv(2) should be
+            //   triggerablePoll()-ed. Then additionalEvent is no longer necessary.
+            status_t pollStatus = errorQueue.pollForSslError(mSocket.get(), sslError, fdTrigger,
+                                                             "SSL_write", POLLIN, altPoll);
+            if (pollStatus != OK) return pollStatus;
+            // Do not advance buffer. Try SSL_write() again.
+        }
     }
     LOG_TLS_DETAIL("TLS: Sent %zu bytes!", size);
     return OK;
 }
 
-status_t RpcTransportTls::interruptableReadFully(FdTrigger* fdTrigger, void* data, size_t size,
+status_t RpcTransportTls::interruptableReadFully(FdTrigger* fdTrigger, iovec* iovs, size_t niovs,
                                                  const std::function<status_t()>& altPoll) {
-    auto buffer = reinterpret_cast<uint8_t*>(data);
-    uint8_t* end = buffer + size;
-
     MAYBE_WAIT_IN_FLAKE_MODE;
 
     // Before doing any I/O, check trigger once. This ensures the trigger is checked at least
     // once. The trigger is also checked via triggerablePoll() after every SSL_write().
     if (fdTrigger->isTriggered()) return DEAD_OBJECT;
 
-    while (buffer < end) {
-        size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
-        auto [readSize, errorQueue] = mSsl.call(SSL_read, buffer, todo);
-        if (readSize > 0) {
-            buffer += readSize;
-            errorQueue.clear();
+    size_t size = 0;
+    for (size_t i = 0; i < niovs; i++) {
+        const iovec& iov = iovs[i];
+        if (iov.iov_len == 0) {
             continue;
         }
-        if (readSize == 0) {
-            // SSL_read() only returns 0 on EOF.
-            errorQueue.clear();
-            return DEAD_OBJECT;
+        size += iov.iov_len;
+
+        auto buffer = reinterpret_cast<uint8_t*>(iov.iov_base);
+        const uint8_t* end = buffer + iov.iov_len;
+        while (buffer < end) {
+            size_t todo = std::min<size_t>(end - buffer, std::numeric_limits<int>::max());
+            auto [readSize, errorQueue] = mSsl.call(SSL_read, buffer, todo);
+            if (readSize > 0) {
+                buffer += readSize;
+                errorQueue.clear();
+                continue;
+            }
+            if (readSize == 0) {
+                // SSL_read() only returns 0 on EOF.
+                errorQueue.clear();
+                return DEAD_OBJECT;
+            }
+            int sslError = mSsl.getError(readSize);
+            status_t pollStatus = errorQueue.pollForSslError(mSocket.get(), sslError, fdTrigger,
+                                                             "SSL_read", 0, altPoll);
+            if (pollStatus != OK) return pollStatus;
+            // Do not advance buffer. Try SSL_read() again.
         }
-        int sslError = mSsl.getError(readSize);
-        status_t pollStatus = errorQueue.pollForSslError(mSocket.get(), sslError, fdTrigger,
-                                                         "SSL_read", 0, altPoll);
-        if (pollStatus != OK) return pollStatus;
-        // Do not advance buffer. Try SSL_read() again.
     }
     LOG_TLS_DETAIL("TLS: Received %zu bytes!", size);
     return OK;
diff --git a/libs/binder/include/binder/RpcTransport.h b/libs/binder/include/binder/RpcTransport.h
index db8b5e920e..348bfebf15 100644
--- a/libs/binder/include/binder/RpcTransport.h
+++ b/libs/binder/include/binder/RpcTransport.h
@@ -28,6 +28,8 @@
 
 #include <binder/RpcCertificateFormat.h>
 
+#include <sys/uio.h>
+
 namespace android {
 
 class FdTrigger;
@@ -44,6 +46,9 @@ public:
     /**
      * Read (or write), but allow to be interrupted by a trigger.
      *
+     * iovs - array of iovecs to perform the operation on. The elements
+     * of the array may be modified by this method.
+     *
      * altPoll - function to be called instead of polling, when needing to wait
      * to read/write data. If this returns an error, that error is returned from
      * this function.
@@ -53,10 +58,10 @@ public:
      *   error - interrupted (failure or trigger)
      */
     [[nodiscard]] virtual status_t interruptableWriteFully(
-            FdTrigger *fdTrigger, const void *buf, size_t size,
+            FdTrigger *fdTrigger, iovec *iovs, size_t niovs,
             const std::function<status_t()> &altPoll) = 0;
     [[nodiscard]] virtual status_t interruptableReadFully(
-            FdTrigger *fdTrigger, void *buf, size_t size,
+            FdTrigger *fdTrigger, iovec *iovs, size_t niovs,
             const std::function<status_t()> &altPoll) = 0;
 
 protected:
diff --git a/libs/binder/tests/binderRpcTest.cpp b/libs/binder/tests/binderRpcTest.cpp
index 5a96b7835c..ca68b99e35 100644
--- a/libs/binder/tests/binderRpcTest.cpp
+++ b/libs/binder/tests/binderRpcTest.cpp
@@ -1674,8 +1674,8 @@ public:
         static AssertionResult defaultPostConnect(RpcTransport* serverTransport,
                                                   FdTrigger* fdTrigger) {
             std::string message(kMessage);
-            auto status = serverTransport->interruptableWriteFully(fdTrigger, message.data(),
-                                                                   message.size(), {});
+            iovec messageIov{message.data(), message.size()};
+            auto status = serverTransport->interruptableWriteFully(fdTrigger, &messageIov, 1, {});
             if (status != OK) return AssertionFailure() << statusToString(status);
             return AssertionSuccess();
         }
@@ -1706,9 +1706,9 @@ public:
         AssertionResult readMessage(const std::string& expectedMessage = kMessage) {
             LOG_ALWAYS_FATAL_IF(mClientTransport == nullptr, "setUpTransport not called or failed");
             std::string readMessage(expectedMessage.size(), '\0');
-            status_t readStatus =
-                    mClientTransport->interruptableReadFully(mFdTrigger.get(), readMessage.data(),
-                                                             readMessage.size(), {});
+            iovec readMessageIov{readMessage.data(), readMessage.size()};
+            status_t readStatus = mClientTransport->interruptableReadFully(mFdTrigger.get(),
+                                                                           &readMessageIov, 1, {});
             if (readStatus != OK) {
                 return AssertionFailure() << statusToString(readStatus);
             }
@@ -1902,8 +1902,8 @@ TEST_P(RpcTransportTest, Trigger) {
     bool shouldContinueWriting = false;
     auto serverPostConnect = [&](RpcTransport* serverTransport, FdTrigger* fdTrigger) {
         std::string message(RpcTransportTestUtils::kMessage);
-        auto status = serverTransport->interruptableWriteFully(fdTrigger, message.data(),
-                                                               message.size(), {});
+        iovec messageIov{message.data(), message.size()};
+        auto status = serverTransport->interruptableWriteFully(fdTrigger, &messageIov, 1, {});
         if (status != OK) return AssertionFailure() << statusToString(status);
 
         {
@@ -1913,7 +1913,8 @@ TEST_P(RpcTransportTest, Trigger) {
             }
         }
 
-        status = serverTransport->interruptableWriteFully(fdTrigger, msg2.data(), msg2.size(), {});
+        iovec msg2Iov{msg2.data(), msg2.size()};
+        status = serverTransport->interruptableWriteFully(fdTrigger, &msg2Iov, 1, {});
         if (status != DEAD_OBJECT)
             return AssertionFailure() << "When FdTrigger is shut down, interruptableWriteFully "
                                          "should return DEAD_OBJECT, but it is "