fdbased: Vectorized write for packet; relax writev syscall filter.

Now it calls pkt.Data.ToView() when writing the packet. This may require
copying when the packet is large, which puts the worse case in an even worse
situation.

This sent out in a separate preparation change as it requires syscall filter
changes. This change will be followed by the change for the adoption of the new
PacketHeader API.

PiperOrigin-RevId: 321447003

1 files changed, 4 insertions, 28 deletions

diff --git a/pkg/tcpip/link/rawfile/rawfile_unsafe.go b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
index 69de6eb3e..f4c32c2da 100644
--- a/pkg/tcpip/link/rawfile/rawfile_unsafe.go
+++ b/pkg/tcpip/link/rawfile/rawfile_unsafe.go
@@ -66,38 +66,14 @@ func NonBlockingWrite(fd int, buf []byte) *tcpip.Error {
 	return nil
 }
 
-// NonBlockingWrite3 writes up to three byte slices to a file descriptor in a
-// single syscall. It fails if partial data is written.
-func NonBlockingWrite3(fd int, b1, b2, b3 []byte) *tcpip.Error {
-	// If there is no second and third buffer, issue a regular write.
-	if len(b2) == 0 && len(b3) == 0 {
-		return NonBlockingWrite(fd, b1)
-	}
-
-	// Build the iovec that represents them and issue a writev syscall.
-	iovec := [3]syscall.Iovec{
-		{
-			Base: &b1[0],
-			Len:  uint64(len(b1)),
-		},
-		{
-			Base: &b2[0],
-			Len:  uint64(len(b2)),
-		},
-	}
-	iovecLen := uintptr(2)
-
-	if len(b3) > 0 {
-		iovecLen++
-		iovec[2].Base = &b3[0]
-		iovec[2].Len = uint64(len(b3))
-	}
-
+// NonBlockingWriteIovec writes iovec to a file descriptor in a single syscall.
+// It fails if partial data is written.
+func NonBlockingWriteIovec(fd int, iovec []syscall.Iovec) *tcpip.Error {
+	iovecLen := uintptr(len(iovec))
 	_, _, e := syscall.RawSyscall(syscall.SYS_WRITEV, uintptr(fd), uintptr(unsafe.Pointer(&iovec[0])), iovecLen)
 	if e != 0 {
 		return TranslateErrno(e)
 	}
-
 	return nil
 }