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// Copyright 2018 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 host
import (
"syscall"
"gvisor.googlesource.com/gvisor/pkg/abi/linux"
"gvisor.googlesource.com/gvisor/pkg/syserror"
)
// maxIovs is the maximum number of iovecs to pass to the host.
var maxIovs = linux.UIO_MAXIOV
// copyToMulti copies as many bytes from src to dst as possible.
func copyToMulti(dst [][]byte, src []byte) {
for _, d := range dst {
done := copy(d, src)
src = src[done:]
if len(src) == 0 {
break
}
}
}
// copyFromMulti copies as many bytes from src to dst as possible.
func copyFromMulti(dst []byte, src [][]byte) {
for _, s := range src {
done := copy(dst, s)
dst = dst[done:]
if len(dst) == 0 {
break
}
}
}
// buildIovec builds an iovec slice from the given []byte slice.
//
// If truncate, truncate bufs > maxlen. Otherwise, immediately return an error.
//
// If length < the total length of bufs, err indicates why, even when returning
// a truncated iovec.
//
// If intermediate != nil, iovecs references intermediate rather than bufs and
// the caller must copy to/from bufs as necessary.
func buildIovec(bufs [][]byte, maxlen int, truncate bool) (length uintptr, iovecs []syscall.Iovec, intermediate []byte, err error) {
var iovsRequired int
for _, b := range bufs {
length += uintptr(len(b))
if len(b) > 0 {
iovsRequired++
}
}
stopLen := length
if length > uintptr(maxlen) {
if truncate {
stopLen = uintptr(maxlen)
err = syserror.EAGAIN
} else {
return 0, nil, nil, syserror.EMSGSIZE
}
}
if iovsRequired > maxIovs {
// The kernel will reject our call if we pass this many iovs.
// Use a single intermediate buffer instead.
b := make([]byte, stopLen)
return stopLen, []syscall.Iovec{{
Base: &b[0],
Len: uint64(stopLen),
}}, b, err
}
var total uintptr
iovecs = make([]syscall.Iovec, 0, iovsRequired)
for i := range bufs {
l := len(bufs[i])
if l == 0 {
continue
}
stop := l
if total+uintptr(stop) > stopLen {
stop = int(stopLen - total)
}
iovecs = append(iovecs, syscall.Iovec{
Base: &bufs[i][0],
Len: uint64(stop),
})
total += uintptr(stop)
if total >= stopLen {
break
}
}
return total, iovecs, nil, err
}
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