95 lines
3.2 KiB
Go
95 lines
3.2 KiB
Go
// Copyright 2020 The gVisor Authors.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package hostfd
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import (
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"io"
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"syscall"
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"unsafe"
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"golang.org/x/sys/unix"
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"gvisor.dev/gvisor/pkg/log"
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"gvisor.dev/gvisor/pkg/safemem"
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)
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// Preadv2 reads up to dsts.NumBytes() bytes from host file descriptor fd into
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// dsts. offset and flags are interpreted as for preadv2(2).
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//
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// Preconditions: !dsts.IsEmpty().
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func Preadv2(fd int32, dsts safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
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// No buffering is necessary regardless of safecopy; host syscalls will
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// return EFAULT if appropriate, instead of raising SIGBUS.
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var (
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n uintptr
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e syscall.Errno
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)
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if flags == 0 && dsts.NumBlocks() == 1 {
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// Use read() or pread() to avoid iovec allocation and copying.
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dst := dsts.Head()
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if offset == -1 {
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n, _, e = syscall.Syscall(unix.SYS_READ, uintptr(fd), dst.Addr(), uintptr(dst.Len()))
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} else {
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n, _, e = syscall.Syscall6(unix.SYS_PREAD64, uintptr(fd), dst.Addr(), uintptr(dst.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
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}
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} else {
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iovs := safemem.IovecsFromBlockSeq(dsts)
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if len(iovs) > maxIov {
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log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), maxIov)
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iovs = iovs[:maxIov]
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}
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n, _, e = syscall.Syscall6(unix.SYS_PREADV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
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}
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if e != 0 {
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return 0, e
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}
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if n == 0 {
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return 0, io.EOF
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}
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return uint64(n), nil
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}
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// Pwritev2 writes up to srcs.NumBytes() from srcs into host file descriptor
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// fd. offset and flags are interpreted as for pwritev2(2).
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//
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// Preconditions: !srcs.IsEmpty().
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func Pwritev2(fd int32, srcs safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
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// No buffering is necessary regardless of safecopy; host syscalls will
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// return EFAULT if appropriate, instead of raising SIGBUS.
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var (
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n uintptr
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e syscall.Errno
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)
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if flags == 0 && srcs.NumBlocks() == 1 {
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// Use write() or pwrite() to avoid iovec allocation and copying.
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src := srcs.Head()
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if offset == -1 {
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n, _, e = syscall.Syscall(unix.SYS_WRITE, uintptr(fd), src.Addr(), uintptr(src.Len()))
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} else {
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n, _, e = syscall.Syscall6(unix.SYS_PWRITE64, uintptr(fd), src.Addr(), uintptr(src.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
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}
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} else {
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iovs := safemem.IovecsFromBlockSeq(srcs)
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if len(iovs) > maxIov {
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log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), maxIov)
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iovs = iovs[:maxIov]
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}
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n, _, e = syscall.Syscall6(unix.SYS_PWRITEV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
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}
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if e != 0 {
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return 0, e
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}
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return uint64(n), nil
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}
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