Improve SendMsg performance.

SendMsg before this change would copy all the data over into a
new slice even if the underlying socket could only accept a
small amount of data. This is really inefficient with non-blocking
sockets and under high throughput where large writes could get
ErrWouldBlock or if there was say a timeout associated with the sendmsg()
syscall.

With this change we delay copying bytes in till they are needed and only
copy what can be potentially sent/held in the socket buffer. Reducing
the need to repeatedly copy data over.

Also a minor fix to change state FIN-WAIT-1 when shutdown(..., SHUT_WR) is called
instead of when we transmit the actual FIN. Otherwise the socket could remain in
CONNECTED state even though the user has called shutdown() on the socket.

Updates #627

PiperOrigin-RevId: 263430505

2 files changed, 114 insertions, 0 deletions

diff --git a/test/syscalls/linux/BUILD b/test/syscalls/linux/BUILD
index 16666e772..d28ce4ba1 100644
--- a/test/syscalls/linux/BUILD
+++ b/test/syscalls/linux/BUILD
@@ -1252,10 +1252,14 @@ cc_binary(
     srcs = ["partial_bad_buffer.cc"],
     linkstatic = 1,
     deps = [
+        "//test/syscalls/linux:socket_test_util",
+        "//test/util:file_descriptor",
         "//test/util:fs_util",
+        "//test/util:posix_error",
         "//test/util:temp_path",
         "//test/util:test_main",
         "//test/util:test_util",
+        "@com_google_absl//absl/time",
         "@com_google_googletest//:gtest",
     ],
 )
diff --git a/test/syscalls/linux/partial_bad_buffer.cc b/test/syscalls/linux/partial_bad_buffer.cc
index 83b1ad4e4..33822ee57 100644
--- a/test/syscalls/linux/partial_bad_buffer.cc
+++ b/test/syscalls/linux/partial_bad_buffer.cc
@@ -14,13 +14,20 @@
 
 #include <errno.h>
 #include <fcntl.h>
+#include <netinet/in.h>
+#include <netinet/tcp.h>
 #include <sys/mman.h>
+#include <sys/socket.h>
 #include <sys/syscall.h>
 #include <sys/uio.h>
 #include <unistd.h>
 
 #include "gtest/gtest.h"
+#include "absl/time/clock.h"
+#include "test/syscalls/linux/socket_test_util.h"
+#include "test/util/file_descriptor.h"
 #include "test/util/fs_util.h"
+#include "test/util/posix_error.h"
 #include "test/util/temp_path.h"
 #include "test/util/test_util.h"
 
@@ -299,6 +306,109 @@ TEST_F(PartialBadBufferTest, WriteEfaultIsntPartial) {
   EXPECT_STREQ(buf, kMessage);
 }
 
+PosixErrorOr<sockaddr_storage> InetLoopbackAddr(int family) {
+  struct sockaddr_storage addr;
+  memset(&addr, 0, sizeof(addr));
+  addr.ss_family = family;
+  switch (family) {
+    case AF_INET:
+      reinterpret_cast<struct sockaddr_in*>(&addr)->sin_addr.s_addr =
+          htonl(INADDR_LOOPBACK);
+      break;
+    case AF_INET6:
+      reinterpret_cast<struct sockaddr_in6*>(&addr)->sin6_addr =
+          in6addr_loopback;
+      break;
+    default:
+      return PosixError(EINVAL,
+                        absl::StrCat("unknown socket family: ", family));
+  }
+  return addr;
+}
+
+// SendMsgTCP verifies that calling sendmsg with a bad address returns an
+// EFAULT. It also verifies that passing a buffer which is made up of 2
+// pages one valid and one guard page succeeds as long as the write is
+// for exactly the size of 1 page.
+TEST_F(PartialBadBufferTest, SendMsgTCP) {
+  auto listen_socket =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_INET, SOCK_STREAM, IPPROTO_TCP));
+
+  // Initialize address to the loopback one.
+  sockaddr_storage addr = ASSERT_NO_ERRNO_AND_VALUE(InetLoopbackAddr(AF_INET));
+  socklen_t addrlen = sizeof(addr);
+
+  // Bind to some port then start listening.
+  ASSERT_THAT(bind(listen_socket.get(),
+                   reinterpret_cast<struct sockaddr*>(&addr), addrlen),
+              SyscallSucceeds());
+
+  ASSERT_THAT(listen(listen_socket.get(), SOMAXCONN), SyscallSucceeds());
+
+  // Get the address we're listening on, then connect to it. We need to do this
+  // because we're allowing the stack to pick a port for us.
+  ASSERT_THAT(getsockname(listen_socket.get(),
+                          reinterpret_cast<struct sockaddr*>(&addr), &addrlen),
+              SyscallSucceeds());
+
+  auto send_socket =
+      ASSERT_NO_ERRNO_AND_VALUE(Socket(AF_INET, SOCK_STREAM, IPPROTO_TCP));
+
+  ASSERT_THAT(
+      RetryEINTR(connect)(send_socket.get(),
+                          reinterpret_cast<struct sockaddr*>(&addr), addrlen),
+      SyscallSucceeds());
+
+  // Accept the connection.
+  auto recv_socket =
+      ASSERT_NO_ERRNO_AND_VALUE(Accept(listen_socket.get(), nullptr, nullptr));
+
+  // TODO(gvisor.dev/issue/674): Update this once Netstack matches linux
+  //   behaviour on a setsockopt of SO_RCVBUF/SO_SNDBUF.
+  //
+  // Set SO_SNDBUF for socket to exactly kPageSize+1.
+  //
+  // gVisor does not double the value passed in SO_SNDBUF like linux does so we
+  // just increase it by 1 byte here for gVisor so that we can test writing 1
+  // byte past the valid page and check that it triggers an EFAULT
+  // correctly. Otherwise in gVisor the sendmsg call will just return with no
+  // error with kPageSize bytes written successfully.
+  const uint32_t buf_size = kPageSize + 1;
+  ASSERT_THAT(setsockopt(send_socket.get(), SOL_SOCKET, SO_SNDBUF, &buf_size,
+                         sizeof(buf_size)),
+              SyscallSucceedsWithValue(0));
+
+  struct msghdr hdr = {};
+  struct iovec iov = {};
+  iov.iov_base = bad_buffer_;
+  iov.iov_len = kPageSize;
+  hdr.msg_iov = &iov;
+  hdr.msg_iovlen = 1;
+
+  ASSERT_THAT(RetryEINTR(sendmsg)(send_socket.get(), &hdr, 0),
+              SyscallFailsWithErrno(EFAULT));
+
+  // Now assert that writing kPageSize from addr_ succeeds.
+  iov.iov_base = addr_;
+  ASSERT_THAT(RetryEINTR(sendmsg)(send_socket.get(), &hdr, 0),
+              SyscallSucceedsWithValue(kPageSize));
+  // Read all the data out so that we drain the socket SND_BUF on the sender.
+  std::vector<char> buffer(kPageSize);
+  ASSERT_THAT(RetryEINTR(read)(recv_socket.get(), buffer.data(), kPageSize),
+              SyscallSucceedsWithValue(kPageSize));
+
+  // Sleep for a shortwhile to ensure that we have time to process the
+  // ACKs. This is not strictly required unless running under gotsan which is a
+  // lot slower and can result in the next write to write only 1 byte instead of
+  // our intended kPageSize + 1.
+  absl::SleepFor(absl::Milliseconds(50));
+
+  // Now assert that writing > kPageSize results in EFAULT.
+  iov.iov_len = kPageSize + 1;
+  ASSERT_THAT(RetryEINTR(sendmsg)(send_socket.get(), &hdr, 0),
+              SyscallFailsWithErrno(EFAULT));
+}
+
 }  // namespace
 
 }  // namespace testing