1 files changed, 107 insertions, 0 deletions
diff --git a/pkg/sentry/hostfd/hostfd_unsafe.go b/pkg/sentry/hostfd/hostfd_unsafe.go
new file mode 100644
index 000000000..5e9e60fc4
--- /dev/null
+++ b/pkg/sentry/hostfd/hostfd_unsafe.go
@@ -0,0 +1,107 @@
+// Copyright 2020 The gVisor Authors.
+//
+// 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.
+
+package hostfd
+
+import (
+	"io"
+	"syscall"
+	"unsafe"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/safemem"
+)
+
+// Preadv2 reads up to dsts.NumBytes() bytes from host file descriptor fd into
+// dsts. offset and flags are interpreted as for preadv2(2).
+//
+// Preconditions: !dsts.IsEmpty().
+func Preadv2(fd int32, dsts safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
+	// No buffering is necessary regardless of safecopy; host syscalls will
+	// return EFAULT if appropriate, instead of raising SIGBUS.
+	var (
+		n uintptr
+		e syscall.Errno
+	)
+	// Avoid preadv2(2) if possible, since it's relatively new and thus least
+	// likely to be supported by the host kernel.
+	if flags == 0 {
+		if dsts.NumBlocks() == 1 {
+			// Use read() or pread() to avoid iovec allocation and copying.
+			dst := dsts.Head()
+			if offset == -1 {
+				n, _, e = syscall.Syscall(unix.SYS_READ, uintptr(fd), dst.Addr(), uintptr(dst.Len()))
+			} else {
+				n, _, e = syscall.Syscall6(unix.SYS_PREAD64, uintptr(fd), dst.Addr(), uintptr(dst.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
+			}
+		} else {
+			iovs := safemem.IovecsFromBlockSeq(dsts)
+			if offset == -1 {
+				n, _, e = syscall.Syscall(unix.SYS_READV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)))
+			} else {
+				n, _, e = syscall.Syscall6(unix.SYS_PREADV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
+			}
+		}
+	} else {
+		iovs := safemem.IovecsFromBlockSeq(dsts)
+		n, _, e = syscall.Syscall6(unix.SYS_PREADV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
+	}
+	if e != 0 {
+		return 0, e
+	}
+	if n == 0 {
+		return 0, io.EOF
+	}
+	return uint64(n), nil
+}
+
+// Pwritev2 writes up to srcs.NumBytes() from srcs into host file descriptor
+// fd. offset and flags are interpreted as for pwritev2(2).
+//
+// Preconditions: !srcs.IsEmpty().
+func Pwritev2(fd int32, srcs safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
+	// No buffering is necessary regardless of safecopy; host syscalls will
+	// return EFAULT if appropriate, instead of raising SIGBUS.
+	var (
+		n uintptr
+		e syscall.Errno
+	)
+	// Avoid pwritev2(2) if possible, since it's relatively new and thus least
+	// likely to be supported by the host kernel.
+	if flags == 0 {
+		if srcs.NumBlocks() == 1 {
+			// Use write() or pwrite() to avoid iovec allocation and copying.
+			src := srcs.Head()
+			if offset == -1 {
+				n, _, e = syscall.Syscall(unix.SYS_WRITE, uintptr(fd), src.Addr(), uintptr(src.Len()))
+			} else {
+				n, _, e = syscall.Syscall6(unix.SYS_PWRITE64, uintptr(fd), src.Addr(), uintptr(src.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
+			}
+		} else {
+			iovs := safemem.IovecsFromBlockSeq(srcs)
+			if offset == -1 {
+				n, _, e = syscall.Syscall(unix.SYS_WRITEV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)))
+			} else {
+				n, _, e = syscall.Syscall6(unix.SYS_PWRITEV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
+			}
+		}
+	} else {
+		iovs := safemem.IovecsFromBlockSeq(srcs)
+		n, _, e = syscall.Syscall6(unix.SYS_PWRITEV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
+	}
+	if e != 0 {
+		return 0, e
+	}
+	return uint64(n), nil
+}