os: add a function to construct *File with non-blocking file descriptor #22939
Description
Change
Add a new function to construct a *File with a file descriptor, set non blocking and put it into runtime poller. A naive but working diff:
--- a/src/os/file_unix.go
+++ b/src/os/file_unix.go
@@ -74,14 +74,17 @@ func (f *File) Fd() uintptr {
// NewFile returns a new File with the given file descriptor and
// name. The returned value will be nil if fd is not a valid file
// descriptor.
func NewFile(fd uintptr, name string) *File {
return newFile(fd, name, kindNewFile)
}
+func NewFileNonBlocking(fd uintptr, name string) *File {
+ return newFile(fd, name, kindOpenFile)
+}Benefit
With this, I can make use of the runtime poller and have SetDeadline method on custom network interfaces.
An example (on Linux):
package main
import (
"os"
"syscall"
"time"
"unsafe"
)
const IFF_TUN = 0x0001
func main() {
f, err := syscall.Open("/dev/net/tun", os.O_RDWR, 0)
if err != nil { panic(err) }
fd := uintptr(f)
var req ifreq
req.flags = IFF_TUN
copy(req.name[:], "tun0")
ioctl(fd, syscall.TUNSETIFF, uintptr(unsafe.Pointer(&req)))
conn := os.NewFileNonBlocking(fd, "tun0")
packet := make([]byte, 2000)
for {
err := conn.SetDeadline(time.Now().Add(time.Second * 2))
if err != nil { panic(err) }
n, err := conn.Read(packet)
if err != nil {
println(err.Error())
} else {
println("read a packet with length", n)
}
}
}
func ioctl(fd uintptr, request uintptr, ifreq uintptr) {
_, _, errno := syscall.Syscall(syscall.SYS_IOCTL, fd, request, ifreq)
if errno != 0 { panic(errno) }
}
type ifreq struct {
name [16]byte
flags uint16
}Related issue
#15021
It looks like the main motivations of #15021 are runtime poller and SetDeadline.
Both of them can be solved by this very simple function.