github.com/metacubex/gvisor@v0.0.0-20240320004321-933faba989ec/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  	"unsafe"
    19  
    20  	"golang.org/x/sys/unix"
    21  )
    22  
    23  const (
    24  	sizeofIovec  = unsafe.Sizeof(unix.Iovec{})
    25  	sizeofMsghdr = unsafe.Sizeof(unix.Msghdr{})
    26  )
    27  
    28  func iovecsReadWrite(sysno uintptr, fd int32, iovs []unix.Iovec, offset int64, flags uint32) (uintptr, unix.Errno) {
    29  	var total uintptr
    30  	for start := 0; start < len(iovs); start += MaxReadWriteIov {
    31  		last := true
    32  		size := len(iovs) - start
    33  		if size > MaxReadWriteIov {
    34  			last = false
    35  			size = MaxReadWriteIov
    36  		}
    37  		curOff := offset
    38  		if offset >= 0 {
    39  			curOff = offset + int64(total)
    40  		}
    41  		cur, _, e := unix.Syscall6(sysno, uintptr(fd), uintptr((unsafe.Pointer)(&iovs[start])), uintptr(size), uintptr(curOff), 0 /* pos_h */, uintptr(flags))
    42  		if cur > 0 {
    43  			total += cur
    44  		}
    45  		if e != 0 {
    46  			return total, e
    47  		}
    48  		if last {
    49  			break
    50  		}
    51  		// If this was a short read/write, then break.
    52  		var curTotal uint64
    53  		for i := range iovs[start : start+size] {
    54  			curTotal += iovs[i].Len
    55  		}
    56  		if uint64(cur) < curTotal {
    57  			break
    58  		}
    59  	}
    60  	return total, 0
    61  }