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syscall.go
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syscall.go
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package ioengine
import (
"os"
"syscall"
)
// Single-word zero for use when we need a valid pointer to 0 bytes.
var zero uintptr
// simulate writeatv by calling writeat serially and dose not change the file offset.
func genericWriteAtv(fd File, bs [][]byte, off int64) (n int, err error) {
nOffset := off
nw := 0
for _, b := range bs {
nw, err = fd.WriteAt(b, nOffset)
n += nw
nOffset += int64(nw)
if err != nil {
break
}
}
return n, err
}
// simulate writev by calling write serially and it will change the file offset.
func genericWritev(fd File, bs [][]byte) (n int, err error) {
nw := 0
for _, b := range bs {
nw, err = fd.Write(b)
n += nw
if err != nil {
break
}
}
return n, err
}
func genericAppend(fd File, bs [][]byte) (int, error) {
opt := fd.Option()
// open file with O_APPEND not need to seek
if (opt.Flag & os.O_APPEND) > 0 {
return genericWritev(fd, bs)
}
// acquire file size to append write
size, err := fd.Seek(0, os.SEEK_END)
if err != nil {
return 0, err
}
// Because use writeAt to simulate an append write
// it doesn't change the file offset, to keep append semantic
// so that make sure file offset is the file end.
defer fd.Seek(0, os.SEEK_END)
return fd.WriteAtv(bs, size)
}
func bytes2Iovec(bs [][]byte) []syscall.Iovec {
var iovecs []syscall.Iovec
for _, chunk := range bs {
if len(chunk) == 0 {
continue
}
iovecs = append(iovecs, syscall.Iovec{Base: &chunk[0]})
iovecs[len(iovecs)-1].SetLen(len(chunk))
}
return iovecs
}