Factor fsimpl/gofer.host{Preadv,Pwritev} out of fsimpl/gofer.

Also fix returning EOF when 0 bytes are read.

PiperOrigin-RevId: 308089875

8 files changed, 218 insertions, 97 deletions

diff --git a/pkg/sentry/fsimpl/gofer/BUILD b/pkg/sentry/fsimpl/gofer/BUILD
index acd061905..b9c4beee4 100644
--- a/pkg/sentry/fsimpl/gofer/BUILD
+++ b/pkg/sentry/fsimpl/gofer/BUILD
@@ -35,7 +35,6 @@ go_library(
         "fstree.go",
         "gofer.go",
         "handle.go",
-        "handle_unsafe.go",
         "p9file.go",
         "pagemath.go",
         "regular_file.go",
@@ -53,6 +52,7 @@ go_library(
         "//pkg/p9",
         "//pkg/safemem",
         "//pkg/sentry/fs/fsutil",
+        "//pkg/sentry/hostfd",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/kernel/time",
         "//pkg/sentry/memmap",
diff --git a/pkg/sentry/fsimpl/gofer/handle.go b/pkg/sentry/fsimpl/gofer/handle.go
index cfe66f797..724a3f1f7 100644
--- a/pkg/sentry/fsimpl/gofer/handle.go
+++ b/pkg/sentry/fsimpl/gofer/handle.go
@@ -20,6 +20,7 @@ import (
 	"gvisor.dev/gvisor/pkg/context"
 	"gvisor.dev/gvisor/pkg/p9"
 	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sentry/hostfd"
 )
 
 // handle represents a remote "open file descriptor", consisting of an opened
@@ -77,7 +78,7 @@ func (h *handle) readToBlocksAt(ctx context.Context, dsts safemem.BlockSeq, offs
 	}
 	if h.fd >= 0 {
 		ctx.UninterruptibleSleepStart(false)
-		n, err := hostPreadv(h.fd, dsts, int64(offset))
+		n, err := hostfd.Preadv2(h.fd, dsts, int64(offset), 0 /* flags */)
 		ctx.UninterruptibleSleepFinish(false)
 		return n, err
 	}
@@ -103,7 +104,7 @@ func (h *handle) writeFromBlocksAt(ctx context.Context, srcs safemem.BlockSeq, o
 	}
 	if h.fd >= 0 {
 		ctx.UninterruptibleSleepStart(false)
-		n, err := hostPwritev(h.fd, srcs, int64(offset))
+		n, err := hostfd.Pwritev2(h.fd, srcs, int64(offset), 0 /* flags */)
 		ctx.UninterruptibleSleepFinish(false)
 		return n, err
 	}
diff --git a/pkg/sentry/fsimpl/gofer/handle_unsafe.go b/pkg/sentry/fsimpl/gofer/handle_unsafe.go
deleted file mode 100644
index 19560ab26..000000000
--- a/pkg/sentry/fsimpl/gofer/handle_unsafe.go
+++ /dev/null
@@ -1,66 +0,0 @@
-// Copyright 2019 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 gofer
-
-import (
-	"syscall"
-	"unsafe"
-
-	"gvisor.dev/gvisor/pkg/safemem"
-)
-
-// Preconditions: !dsts.IsEmpty().
-func hostPreadv(fd int32, dsts safemem.BlockSeq, off int64) (uint64, error) {
-	// No buffering is necessary regardless of safecopy; host syscalls will
-	// return EFAULT if appropriate, instead of raising SIGBUS.
-	if dsts.NumBlocks() == 1 {
-		// Use pread() instead of preadv() to avoid iovec allocation and
-		// copying.
-		dst := dsts.Head()
-		n, _, e := syscall.Syscall6(syscall.SYS_PREAD64, uintptr(fd), dst.Addr(), uintptr(dst.Len()), uintptr(off), 0, 0)
-		if e != 0 {
-			return 0, e
-		}
-		return uint64(n), nil
-	}
-	iovs := safemem.IovecsFromBlockSeq(dsts)
-	n, _, e := syscall.Syscall6(syscall.SYS_PREADV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(off), 0, 0)
-	if e != 0 {
-		return 0, e
-	}
-	return uint64(n), nil
-}
-
-// Preconditions: !srcs.IsEmpty().
-func hostPwritev(fd int32, srcs safemem.BlockSeq, off int64) (uint64, error) {
-	// No buffering is necessary regardless of safecopy; host syscalls will
-	// return EFAULT if appropriate, instead of raising SIGBUS.
-	if srcs.NumBlocks() == 1 {
-		// Use pwrite() instead of pwritev() to avoid iovec allocation and
-		// copying.
-		src := srcs.Head()
-		n, _, e := syscall.Syscall6(syscall.SYS_PWRITE64, uintptr(fd), src.Addr(), uintptr(src.Len()), uintptr(off), 0, 0)
-		if e != 0 {
-			return 0, e
-		}
-		return uint64(n), nil
-	}
-	iovs := safemem.IovecsFromBlockSeq(srcs)
-	n, _, e := syscall.Syscall6(syscall.SYS_PWRITEV, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(off), 0, 0)
-	if e != 0 {
-		return 0, e
-	}
-	return uint64(n), nil
-}
diff --git a/pkg/sentry/fsimpl/host/BUILD b/pkg/sentry/fsimpl/host/BUILD
index 82e1fb74b..44dd9f672 100644
--- a/pkg/sentry/fsimpl/host/BUILD
+++ b/pkg/sentry/fsimpl/host/BUILD
@@ -15,12 +15,11 @@ go_library(
     deps = [
         "//pkg/abi/linux",
         "//pkg/context",
-        "//pkg/fd",
         "//pkg/log",
         "//pkg/refs",
-        "//pkg/safemem",
         "//pkg/sentry/arch",
         "//pkg/sentry/fsimpl/kernfs",
+        "//pkg/sentry/hostfd",
         "//pkg/sentry/kernel",
         "//pkg/sentry/kernel/auth",
         "//pkg/sentry/memmap",
diff --git a/pkg/sentry/fsimpl/host/host.go b/pkg/sentry/fsimpl/host/host.go
index fe14476f1..ae94cfa6e 100644
--- a/pkg/sentry/fsimpl/host/host.go
+++ b/pkg/sentry/fsimpl/host/host.go
@@ -25,11 +25,10 @@ import (
 	"golang.org/x/sys/unix"
 	"gvisor.dev/gvisor/pkg/abi/linux"
 	"gvisor.dev/gvisor/pkg/context"
-	"gvisor.dev/gvisor/pkg/fd"
 	"gvisor.dev/gvisor/pkg/log"
 	"gvisor.dev/gvisor/pkg/refs"
-	"gvisor.dev/gvisor/pkg/safemem"
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/kernfs"
+	"gvisor.dev/gvisor/pkg/sentry/hostfd"
 	"gvisor.dev/gvisor/pkg/sentry/kernel/auth"
 	"gvisor.dev/gvisor/pkg/sentry/memmap"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
@@ -492,19 +491,9 @@ func readFromHostFD(ctx context.Context, hostFD int, dst usermem.IOSequence, off
 	if flags != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}
-
-	var reader safemem.Reader
-	if offset == -1 {
-		reader = safemem.FromIOReader{fd.NewReadWriter(hostFD)}
-	} else {
-		reader = safemem.FromVecReaderFunc{
-			func(srcs [][]byte) (int64, error) {
-				n, err := unix.Preadv(hostFD, srcs, offset)
-				return int64(n), err
-			},
-		}
-	}
+	reader := hostfd.GetReadWriterAt(int32(hostFD), offset, flags)
 	n, err := dst.CopyOutFrom(ctx, reader)
+	hostfd.PutReadWriterAt(reader)
 	return int64(n), err
 }
 
@@ -542,19 +531,9 @@ func writeToHostFD(ctx context.Context, hostFD int, src usermem.IOSequence, offs
 	if flags != 0 {
 		return 0, syserror.EOPNOTSUPP
 	}
-
-	var writer safemem.Writer
-	if offset == -1 {
-		writer = safemem.FromIOWriter{fd.NewReadWriter(hostFD)}
-	} else {
-		writer = safemem.FromVecWriterFunc{
-			func(srcs [][]byte) (int64, error) {
-				n, err := unix.Pwritev(hostFD, srcs, offset)
-				return int64(n), err
-			},
-		}
-	}
+	writer := hostfd.GetReadWriterAt(int32(hostFD), offset, flags)
 	n, err := src.CopyInTo(ctx, writer)
+	hostfd.PutReadWriterAt(writer)
 	return int64(n), err
 }
 
diff --git a/pkg/sentry/hostfd/BUILD b/pkg/sentry/hostfd/BUILD
new file mode 100644
index 000000000..364a78306
--- /dev/null
+++ b/pkg/sentry/hostfd/BUILD
@@ -0,0 +1,17 @@
+load("//tools:defs.bzl", "go_library")
+
+licenses(["notice"])
+
+go_library(
+    name = "hostfd",
+    srcs = [
+        "hostfd.go",
+        "hostfd_unsafe.go",
+    ],
+    visibility = ["//pkg/sentry:internal"],
+    deps = [
+        "//pkg/safemem",
+        "//pkg/sync",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
diff --git a/pkg/sentry/hostfd/hostfd.go b/pkg/sentry/hostfd/hostfd.go
new file mode 100644
index 000000000..70dd9cafb
--- /dev/null
+++ b/pkg/sentry/hostfd/hostfd.go
@@ -0,0 +1,84 @@
+// 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 provides efficient I/O with host file descriptors.
+package hostfd
+
+import (
+	"gvisor.dev/gvisor/pkg/safemem"
+	"gvisor.dev/gvisor/pkg/sync"
+)
+
+// ReadWriterAt implements safemem.Reader and safemem.Writer by reading from
+// and writing to a host file descriptor respectively. ReadWriterAts should be
+// obtained by calling GetReadWriterAt.
+//
+// Clients should usually prefer to use Preadv2 and Pwritev2 directly.
+type ReadWriterAt struct {
+	fd     int32
+	offset int64
+	flags  uint32
+}
+
+var rwpool = sync.Pool{
+	New: func() interface{} {
+		return &ReadWriterAt{}
+	},
+}
+
+// GetReadWriterAt returns a ReadWriterAt that reads from / writes to the given
+// host file descriptor, starting at the given offset and using the given
+// preadv2(2)/pwritev2(2) flags. If offset is -1, the host file descriptor's
+// offset is used instead. Users are responsible for ensuring that fd remains
+// valid for the lifetime of the returned ReadWriterAt, and must call
+// PutReadWriterAt when it is no longer needed.
+func GetReadWriterAt(fd int32, offset int64, flags uint32) *ReadWriterAt {
+	rw := rwpool.Get().(*ReadWriterAt)
+	*rw = ReadWriterAt{
+		fd:     fd,
+		offset: offset,
+		flags:  flags,
+	}
+	return rw
+}
+
+// PutReadWriterAt releases a ReadWriterAt returned by a previous call to
+// GetReadWriterAt that is no longer in use.
+func PutReadWriterAt(rw *ReadWriterAt) {
+	rwpool.Put(rw)
+}
+
+// ReadToBlocks implements safemem.Reader.ReadToBlocks.
+func (rw *ReadWriterAt) ReadToBlocks(dsts safemem.BlockSeq) (uint64, error) {
+	if dsts.IsEmpty() {
+		return 0, nil
+	}
+	n, err := Preadv2(rw.fd, dsts, rw.offset, rw.flags)
+	if rw.offset >= 0 {
+		rw.offset += int64(n)
+	}
+	return n, err
+}
+
+// WriteFromBlocks implements safemem.Writer.WriteFromBlocks.
+func (rw *ReadWriterAt) WriteFromBlocks(srcs safemem.BlockSeq) (uint64, error) {
+	if srcs.IsEmpty() {
+		return 0, nil
+	}
+	n, err := Pwritev2(rw.fd, srcs, rw.offset, rw.flags)
+	if rw.offset >= 0 {
+		rw.offset += int64(n)
+	}
+	return n, err
+}
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
+}