x/sys/unix: IoctlFileClone takes int for file descriptors and not uintptr

[mitar]

Go version

go version go1.21.3 linux/amd64

Output of go env in your module/workspace:

GO111MODULE=''
GOARCH='amd64'
GOBIN=''
GOCACHE='/home/mitar/.cache/go-build'
GOENV='/home/mitar/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/home/mitar/.go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/mitar/.go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.3'
GCCGO='/usr/bin/gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build4184395022=/tmp/go-build -gno-record-gcc-switches'

What did you do?

I am trying to use unix.IoctlFileClone.

What did you see happen?

I noticed that I have to cast Go file descriptors (file.Fd()) to int.

What did you expect to see?

That I would not have to cast file descriptors (which are in Go uintptr) to int.

[bcmills]

The signatures of the functions in the unix package are intended to match the signatures of the corresponding C system calls.

On Linux, the C signature of ioctl(2) is:

int ioctl(int fd, unsigned long request, ...);

os.File.Fd presumably returns a uintptr because it is designed to be platform-independent. On Windows it refers to a HANDLE, which is typedef'd pointer to void — which corresponds to a uintptr, not an int. On Unix platforms, you may assume that the uintptr returned by os.File.Fd can be safely converted to an int.

(I suppose that it is theoretically possible for uintptr to be smaller than int, but I don't believe that is the case for any platform currently supported by Go.)

[mitar]

Thanks!

On Unix platforms, you may assume that the uintptr returned by os.File.Fd can be safely converted to an int.

Should this be documented maybe for os.File.Fd?