First off, I don't know how you are posting your code samples, but they are
unreadable in my Firefox and Chrome on windows.
Second, I would point out that the system you use for converting a "string"
to the buffer will fail if there are any non-ascii characters.
Third, OT, but I wonder why pciDevice is a string pointer, instead of a
string?
Personally, I don't see anything *decisively *incorrect, but there is a lot
of context that is missing. If you wanted to indicate your OS, and provide
a complete working sample, I'm sure I, or someone else could help more.
One thing that jumps out at me is the use of
*uintptr(unsafe.Pointer(&ioctlId))*, in your initial example. It is hidden
by the function *VFIO_GROUP_GET_DEVICE_FD()*, which is not provided, in
your larger example. Are you sure you want the pointer to that value, and
not the actual value? Maybe *uintptr(ioctlId))* instead. Seems more
standard for IOCTL to me.
And, of course the changes you made to create an appropriate string buffer
are necessary.
On Thursday, August 23, 2018 at 11:47:18 AM UTC-4, sbez...@cisco.com wrote:
>
> Hi Max,
>
>
>
> Thanks for the suggestion, unfortunately it did not help, see below:
>
>
>
> func GetGroupFD(group int, pciDevice *string) (int, error) {
>
> fmt.Printf("VFIO_GROUP_GET_DEVICE_FD() returned: %04x\n",
> VFIO_GROUP_GET_DEVICE_FD())
>
> buffer := make([]byte, len(*pciDevice)+1)
>
> for i, c := range *pciDevice {
>
> buffer[i] = uint8(c)
>
> }
>
> buffer[len(*pciDevice)] = 0x0
>
> fmt.Printf("pciDevice: %s\n", string(buffer))
>
> device, _, errno := syscall.Syscall(
>
> syscall.SYS_IOCTL,
>
> uintptr(group),
>
> uintptr(VFIO_GROUP_GET_DEVICE_FD()),
>
> uintptr(unsafe.Pointer(&buffer[0])),
>
> )
>
> if errno != 0 {
>
> return 0, fmt.Errorf("fail to get file descriptor for %d with
> errno: %+v", group, errno)
>
> }
>
> return int(device), nil
>
> }
>
>
>
> Any other suggestions?
>
> Thank you
>
> Serguei
>
>
>
> *From: *<golan...@googlegroups.com <javascript:>> on behalf of Max <
> massimilia...@gmail.com <javascript:>>
> *Date: *Thursday, August 23, 2018 at 10:46 AM
> *To: *golang-nuts <golan...@googlegroups.com <javascript:>>
> *Subject: *Re: [go-nuts] Re: Ioctl Syscall with go and c
>
>
>
> Hi Serguei,
>
>
>
> a Go string or *string do not correspond to a C char *
>
> You must pass the address of the first byte of a sufficiently large buffer:
>
>
>
> func GetGroupFD(group int, pciDevice *string) (int, error) {
>
> const N = 256
>
> var buffer [N]byte
>
> device, _, errno := syscall.Syscall(
> syscall.SYS_IOCTL,
> uintptr(group),
> uintptr(unsafe.Pointer(&ioctlId)),
> &buffer[0],
> )
>
> /* if ioctl() is successful, find '\0' in buffer[] and copy the
> relevant portion in *pciDevice */
>
> }
>
>
> On Thursday, August 23, 2018 at 2:55:29 PM UTC+2, sbez...@cisco.com
> wrote:
>
> I changed code a little bit to be able to examine variables:
>
>
>
> func GetGroupFD(group int, pciDevice *string) (int, error) {
>
> ioctlId := 0x3b6a
>
> var buffer uintptr
>
> buffer = uintptr(unsafe.Pointer(pciDevice))
>
>
>
> --
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