Re: [go-nuts] Custom syscall.Sockaddr

[Elliot Morrison-Reed]

I added the SockaddrCAN type to the golang.org/x/sys/unix package, and it
works great.  I create an issue with links the patch and some test code.

https://github.com/golang/go/issues/16188

On Fri, Jun 24, 2016 at 8:57 PM, Elliot Morrison-Reed 
wrote:

> SocketCAN has been part of mainline linux since kernel 2.6.25 (so getting
> close to a decade now), and it is pretty much the standard for all CAN bus
> communication on linux.
>
> Thanks for the hint, I will look into adding support in the
> golang.org/x/sys/unix package.
>
> Regards,
> Elliot
>
> On Fri, Jun 24, 2016 at 7:52 PM, Ian Lance Taylor  wrote:
>
>> On Fri, Jun 24, 2016 at 8:05 AM,   wrote:
>> >
>> > I am trying to set up an interface from Go to SocketCAN
>> > (https://www.kernel.org/doc/Documentation/networking/can.txt).  This
>> > implements the linux socket interface, however it is a completely
>> separate
>> > socket type from the regular AF_INET or AF_UNIX socket types.
>> >
>> > The sockaddr struct for SocketCAN looks like this:
>> >
>> > struct sockaddr_can {
>> > sa_family_t can_family;
>> > int can_ifindex;
>> > union {
>> > /* transport protocol class address info (e.g. ISOTP) */
>> > struct { canid_t rx_id, tx_id; } tp;
>> >
>> > /* reserved for future CAN protocols address information */
>> > } can_addr;
>> > };
>> >
>> >
>> > Since the union only has one possible entry right now, this is easy
>> enough
>> > to write in Go
>> >
>> > type CanID uint32
>> >
>> > type sockaddrCan struct {
>> >Family  uint16
>> >IfIndex int32
>> >TpRxId  CanID
>> >TpTxId  CanID
>> > }
>> >
>> >
>> > Everything is straight forward so far, but now if I want to pass this to
>> > different syscall functions ( syscall.Bind, syscall.Connect, etc.) I
>> have to
>> > implement the syscall.Sockaddr interface, however looking in the code I
>> see
>> > this:
>> >
>> > type Sockaddr interface {
>> > sockaddr() (ptr unsafe.Pointer, len _Socklen, err error) //
>> lowercase;
>> > only we can define Sockaddrs
>> > }
>> >
>> >
>> > So, finally the questions:
>> >
>> > Why is this interface private? It says that it is, but provides no
>> > rationale.
>> > Does this mean that I have to reimplement all the functions syscall
>> > functions using raw syscall.Syscall?  Or is there some clever way around
>> > this so I can use the syscall package to make a Sockaddr type that is
>> not
>> > already defined.
>>
>> If this is going to be a standard thing in future Linux kernels, I
>> suggest that you add support for it to the golang.org/x/sys/unix
>> package.
>>
>> I don't actually know the answer to why Sockaddr has a private method.
>> I agree that it doesn't seem strictly necessary.
>>
>> Ian
>>
>
>

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Re: [go-nuts] Custom syscall.Sockaddr

[Ian Lance Taylor]

On Fri, Jun 24, 2016 at 8:05 AM,   wrote:
>
> I am trying to set up an interface from Go to SocketCAN
> (https://www.kernel.org/doc/Documentation/networking/can.txt).  This
> implements the linux socket interface, however it is a completely separate
> socket type from the regular AF_INET or AF_UNIX socket types.
>
> The sockaddr struct for SocketCAN looks like this:
>
> struct sockaddr_can {
> sa_family_t can_family;
> int can_ifindex;
> union {
> /* transport protocol class address info (e.g. ISOTP) */
> struct { canid_t rx_id, tx_id; } tp;
>
> /* reserved for future CAN protocols address information */
> } can_addr;
> };
>
>
> Since the union only has one possible entry right now, this is easy enough
> to write in Go
>
> type CanID uint32
>
> type sockaddrCan struct {
>Family  uint16
>IfIndex int32
>TpRxId  CanID
>TpTxId  CanID
> }
>
>
> Everything is straight forward so far, but now if I want to pass this to
> different syscall functions ( syscall.Bind, syscall.Connect, etc.) I have to
> implement the syscall.Sockaddr interface, however looking in the code I see
> this:
>
> type Sockaddr interface {
> sockaddr() (ptr unsafe.Pointer, len _Socklen, err error) // lowercase;
> only we can define Sockaddrs
> }
>
>
> So, finally the questions:
>
> Why is this interface private? It says that it is, but provides no
> rationale.
> Does this mean that I have to reimplement all the functions syscall
> functions using raw syscall.Syscall?  Or is there some clever way around
> this so I can use the syscall package to make a Sockaddr type that is not
> already defined.

If this is going to be a standard thing in future Linux kernels, I
suggest that you add support for it to the golang.org/x/sys/unix
package.

I don't actually know the answer to why Sockaddr has a private method.
I agree that it doesn't seem strictly necessary.

Ian

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