github.com/MerlinKodo/gvisor@v0.0.0-20231110090155-957f62ecf90e/pkg/sentry/hostfd/hostfd_unsafe.go (about)

     1  // Copyright 2020 The gVisor Authors.
     2  //
     3  // Licensed under the Apache License, Version 2.0 (the "License");
     4  // you may not use this file except in compliance with the License.
     5  // You may obtain a copy of the License at
     6  //
     7  //     http://www.apache.org/licenses/LICENSE-2.0
     8  //
     9  // Unless required by applicable law or agreed to in writing, software
    10  // distributed under the License is distributed on an "AS IS" BASIS,
    11  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    12  // See the License for the specific language governing permissions and
    13  // limitations under the License.
    14  
    15  package hostfd
    16  
    17  import (
    18  	"io"
    19  	"unsafe"
    20  
    21  	"github.com/MerlinKodo/gvisor/pkg/log"
    22  	"github.com/MerlinKodo/gvisor/pkg/safemem"
    23  	"golang.org/x/sys/unix"
    24  )
    25  
    26  const (
    27  	sizeofIovec  = unsafe.Sizeof(unix.Iovec{})
    28  	sizeofMsghdr = unsafe.Sizeof(unix.Msghdr{})
    29  )
    30  
    31  // Preadv2 reads up to dsts.NumBytes() bytes from host file descriptor fd into
    32  // dsts. offset and flags are interpreted as for preadv2(2).
    33  //
    34  // Preconditions: !dsts.IsEmpty().
    35  func Preadv2(fd int32, dsts safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
    36  	// No buffering is necessary regardless of safecopy; host syscalls will
    37  	// return EFAULT if appropriate, instead of raising SIGBUS.
    38  	var (
    39  		n uintptr
    40  		e unix.Errno
    41  	)
    42  	if flags == 0 && dsts.NumBlocks() == 1 {
    43  		// Use read() or pread() to avoid iovec allocation and copying.
    44  		dst := dsts.Head()
    45  		if offset == -1 {
    46  			n, _, e = unix.Syscall(unix.SYS_READ, uintptr(fd), dst.Addr(), uintptr(dst.Len()))
    47  		} else {
    48  			n, _, e = unix.Syscall6(unix.SYS_PREAD64, uintptr(fd), dst.Addr(), uintptr(dst.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
    49  		}
    50  	} else {
    51  		iovs := safemem.IovecsFromBlockSeq(dsts)
    52  		if len(iovs) > MaxReadWriteIov {
    53  			log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), MaxReadWriteIov)
    54  			iovs = iovs[:MaxReadWriteIov]
    55  		}
    56  		n, _, e = unix.Syscall6(unix.SYS_PREADV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
    57  	}
    58  	if e != 0 {
    59  		return 0, e
    60  	}
    61  	if n == 0 {
    62  		return 0, io.EOF
    63  	}
    64  	return uint64(n), nil
    65  }
    66  
    67  // Pwritev2 writes up to srcs.NumBytes() from srcs into host file descriptor
    68  // fd. offset and flags are interpreted as for pwritev2(2).
    69  //
    70  // Preconditions: !srcs.IsEmpty().
    71  func Pwritev2(fd int32, srcs safemem.BlockSeq, offset int64, flags uint32) (uint64, error) {
    72  	// No buffering is necessary regardless of safecopy; host syscalls will
    73  	// return EFAULT if appropriate, instead of raising SIGBUS.
    74  	var (
    75  		n uintptr
    76  		e unix.Errno
    77  	)
    78  	if flags == 0 && srcs.NumBlocks() == 1 {
    79  		// Use write() or pwrite() to avoid iovec allocation and copying.
    80  		src := srcs.Head()
    81  		if offset == -1 {
    82  			n, _, e = unix.Syscall(unix.SYS_WRITE, uintptr(fd), src.Addr(), uintptr(src.Len()))
    83  		} else {
    84  			n, _, e = unix.Syscall6(unix.SYS_PWRITE64, uintptr(fd), src.Addr(), uintptr(src.Len()), uintptr(offset), 0 /* pos_h */, 0 /* unused */)
    85  		}
    86  	} else {
    87  		iovs := safemem.IovecsFromBlockSeq(srcs)
    88  		if len(iovs) > MaxReadWriteIov {
    89  			log.Debugf("hostfd.Preadv2: truncating from %d iovecs to %d", len(iovs), MaxReadWriteIov)
    90  			iovs = iovs[:MaxReadWriteIov]
    91  		}
    92  		n, _, e = unix.Syscall6(unix.SYS_PWRITEV2, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[0])), uintptr(len(iovs)), uintptr(offset), 0 /* pos_h */, uintptr(flags))
    93  	}
    94  	if e != 0 {
    95  		return 0, e
    96  	}
    97  	return uint64(n), nil
    98  }