Apple: Fix AF_SYSTEM and AF_SYS_CONTROL

[siegfried]

Trying to fix the issue #3044

Here is the definition I found:

/*!
 *       @struct sockaddr_ctl
 *       @discussion The controller address structure is used to establish
 *               contact between a user client and a kernel controller. The
 *               sc_id/sc_unit uniquely identify each controller. sc_id is a
 *               unique identifier assigned to the controller. The identifier can
 *               be assigned by the system at registration time or be a 32-bit
 *               creator code obtained from Apple Computer. sc_unit is a unit
 *               number for this sc_id, and is privately used by the kernel
 *               controller to identify several instances of the controller.
 *       @field sc_len The length of the structure.
 *       @field sc_family AF_SYSTEM.
 *       @field ss_sysaddr AF_SYS_KERNCONTROL.
 *       @field sc_id Controller unique identifier.
 *       @field sc_unit Kernel controller private unit number.
 *       @field sc_reserved Reserved, must be set to zero.
 */
struct sockaddr_ctl {
	u_char      sc_len;     /* depends on size of bundle ID string */
	u_char      sc_family;  /* AF_SYSTEM */
	u_int16_t   ss_sysaddr; /* AF_SYS_KERNCONTROL */
	u_int32_t   sc_id;      /* Controller unique identifier  */
	u_int32_t   sc_unit;    /* Developer private unit number */
	u_int32_t   sc_reserved[5];
};

Shall I alias AF_SYS_CONTROL to AF_SYS_KERNCONTROL?

[rustbot]

Thanks for the pull request, and welcome! The Rust team is excited to review your changes, and you should hear from @JohnTitor (or someone else) soon.

Please see the contribution instructions for more information.

[siegfried]

I changed the type of PF_SYSTEM to c_int regarding the man page of SOCKET(2):

NAME
     socket – create an endpoint for communication

SYNOPSIS
     #include <sys/socket.h>

     int
     socket(int domain, int type, int protocol);

DESCRIPTION
     socket() creates an endpoint for communication and returns a descriptor.

     The domain parameter specifies a communications domain within which communication will take place; this selects the protocol family which should be used.  These
     families are defined in the include file ⟨sys/socket.h⟩.  The currently understood formats are

           PF_LOCAL        Host-internal protocols, formerly called PF_UNIX,
           PF_UNIX         Host-internal protocols, deprecated, use PF_LOCAL,
           PF_INET         Internet version 4 protocols,
           PF_ROUTE        Internal Routing protocol,
           PF_KEY          Internal key-management function,
           PF_INET6        Internet version 6 protocols,
           PF_SYSTEM       System domain,
           PF_NDRV         Raw access to network device,
           PF_VSOCK        VM Sockets protocols

     The socket has the indicated type, which specifies the semantics of communication.  Currently defined types are:

           SOCK_STREAM
           SOCK_DGRAM
           SOCK_RAW

     A SOCK_STREAM type provides sequenced, reliable, two-way connection based byte streams.  An out-of-band data transmission mechanism may be supported.  A SOCK_DGRAM
     socket supports datagrams (connectionless, unreliable messages of a fixed (typically small) maximum length).  SOCK_RAW sockets provide access to internal network
     protocols and interfaces.  The type SOCK_RAW, which is available only to the super-user.

[tgross35]

Just change to AF_SYSTEM as c_int rather than duplicating the literal

[siegfried]

The old examples uses the value of AF_SYS_CONTROL for AF_SYS_KERNCONTROL. I can also add AF_SYS_KERNCONTROL and leave AF_SYS_CONTROL untouched.

[siegfried]

Is there anything else needed from me?

[JohnTitor]

Changing types is a breaking change and we don't ship it on minor releases. I'll revisit once we decide to do a major release.

[tgross35]

We have an upcoming major release where we can do breaking changes.

It seems unusual to only change one AF_* type - should they all be changed?

[tgross35]

@rustbot author for the above question

[siegfried]

Updated. Sorry for the delay. Please review.

[tgross35]

Just to clarify; is sc_family only ever set to AF_SYSTEM and ss_sysaddr is only ever AF_SYS_CONTROL? Meaning no other constants are ever used for these fields.

[tgross35]

Suggested change

	pub const AF_SYS_CONTROL: c_ushort = 2;
	pub const AF_SYS_CONTROL: c_ushort = 2;

It looks like the field is u_int16_t, so this can just be u16 https://developer.apple.com/documentation/kernel/sockaddr_ctl/1809252-ss_sysaddr.

[siegfried]

Updated. Waiting on CI.

[siegfried]

The CI test failed after I change AF_SYS_CONTROL to u16. Any idea why? @tgross35

[tgross35]

It doesn't look related, the android CI has been flaky.

[siegfried]

Just to clarify; is sc_family only ever set to AF_SYSTEM and ss_sysaddr is only ever AF_SYS_CONTROL? Meaning no other constants are ever used for these fields.

I think so regarding to the document.

[tgross35]

LGTM, please squash. I think the CI failure is unrelated.

Since this is breaking:

@rustbot label +stable-declined

[siegfried]

Squashed.