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// 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
}
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