net: Add a new socket option for a future transmit time.

This patch introduces SO_TXTIME. User space enables this option in
order to pass a desired future transmit time in a CMSG when calling
sendmsg(2). The argument to this socket option is a 8-bytes long struct
provided by the uapi header net_tstamp.h defined as:

struct sock_txtime {
clockid_t clockid;
u32 flags;
};

Note that new fields were added to struct sock by filling a 2-bytes
hole found in the struct. For that reason, neither the struct size or
number of cachelines were altered.

Signed-off-by: Richard Cochran <[e-mail]>
Signed-off-by: Jesus Sanchez-Palencia <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

arch/alpha/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/ia64/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* _ASM_IA64_SOCKET_H */

arch/mips/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/parisc/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		0x4035
 
+#define SO_TXTIME		0x4036
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* _UAPI_ASM_SOCKET_H */

arch/s390/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* _ASM_SOCKET_H */

arch/sparc/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		0x003e
 
+#define SO_TXTIME		0x003f
+#define SCM_TXTIME		SO_TXTIME
+
 /* Security levels - as per NRL IPv6 - don't actually do anything */
 #define SO_SECURITY_AUTHENTICATION		0x5001
 #define SO_SECURITY_ENCRYPTION_TRANSPORT	0x5002

arch/xtensa/include/uapi/asm/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif	/* _XTENSA_SOCKET_H */

include/net/sock.h

···
   *	@sk_destruct: called at sock freeing time, i.e. when all refcnt == 0
   *	@sk_reuseport_cb: reuseport group container
   *	@sk_rcu: used during RCU grace period
+  *	@sk_clockid: clockid used by time-based scheduling (SO_TXTIME)
+  *	@sk_txtime_deadline_mode: set deadline mode for SO_TXTIME
+  *	@sk_txtime_unused: unused txtime flags
   */
 struct sock {
 	/*
···
 	u8			sk_shutdown;
 	u32			sk_tskey;
 	atomic_t		sk_zckey;
+
+	u8			sk_clockid;
+	u8			sk_txtime_deadline_mode : 1,
+				sk_txtime_unused : 7;
+
 	struct socket		*sk_socket;
 	void			*sk_user_data;
 #ifdef CONFIG_SECURITY
···
 	SOCK_FILTER_LOCKED, /* Filter cannot be changed anymore */
 	SOCK_SELECT_ERR_QUEUE, /* Wake select on error queue */
 	SOCK_RCU_FREE, /* wait rcu grace period in sk_destruct() */
+	SOCK_TXTIME,
 };
 
 #define SK_FLAGS_TIMESTAMP ((1UL << SOCK_TIMESTAMP) | (1UL << SOCK_TIMESTAMPING_RX_SOFTWARE))
···
 void sk_send_sigurg(struct sock *sk);
 
 struct sockcm_cookie {
+	u64 transmit_time;
 	u32 mark;
 	u16 tsflags;
 };

include/uapi/asm-generic/socket.h

···
 
 #define SO_ZEROCOPY		60
 
+#define SO_TXTIME		61
+#define SCM_TXTIME		SO_TXTIME
+
 #endif /* __ASM_GENERIC_SOCKET_H */

include/uapi/linux/net_tstamp.h

···
 	__u32 reserved[2];
 };
 
+/*
+ * SO_TXTIME gets a struct sock_txtime with flags being an integer bit
+ * field comprised of these values.
+ */
+enum txtime_flags {
+	SOF_TXTIME_DEADLINE_MODE = (1 << 0),
+
+	SOF_TXTIME_FLAGS_MASK = (SOF_TXTIME_DEADLINE_MODE)
+};
+
+struct sock_txtime {
+	clockid_t       clockid;        /* reference clockid */
+	u32             flags;          /* flags defined by enum txtime_flags */
+};
+
 #endif /* _NET_TIMESTAMPING_H */

net/core/sock.c

···
 
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
+#include <asm/unaligned.h>
 #include <linux/capability.h>
 #include <linux/errno.h>
 #include <linux/errqueue.h>
···
 int sock_setsockopt(struct socket *sock, int level, int optname,
 		    char __user *optval, unsigned int optlen)
 {
+	struct sock_txtime sk_txtime;
 	struct sock *sk = sock->sk;
 	int val;
 	int valbool;
···
 		}
 		break;
 
+	case SO_TXTIME:
+		if (!ns_capable(sock_net(sk)->user_ns, CAP_NET_ADMIN)) {
+			ret = -EPERM;
+		} else if (optlen != sizeof(struct sock_txtime)) {
+			ret = -EINVAL;
+		} else if (copy_from_user(&sk_txtime, optval,
+			   sizeof(struct sock_txtime))) {
+			ret = -EFAULT;
+		} else if (sk_txtime.flags & ~SOF_TXTIME_FLAGS_MASK) {
+			ret = -EINVAL;
+		} else {
+			sock_valbool_flag(sk, SOCK_TXTIME, true);
+			sk->sk_clockid = sk_txtime.clockid;
+			sk->sk_txtime_deadline_mode =
+				!!(sk_txtime.flags & SOF_TXTIME_DEADLINE_MODE);
+		}
+		break;
+
 	default:
 		ret = -ENOPROTOOPT;
 		break;
···
 		u64 val64;
 		struct linger ling;
 		struct timeval tm;
+		struct sock_txtime txtime;
 	} v;
 
 	int lv = sizeof(int);
···
 
 	case SO_ZEROCOPY:
 		v.val = sock_flag(sk, SOCK_ZEROCOPY);
+		break;
+
+	case SO_TXTIME:
+		lv = sizeof(v.txtime);
+		v.txtime.clockid = sk->sk_clockid;
+		v.txtime.flags |= sk->sk_txtime_deadline_mode ?
+				  SOF_TXTIME_DEADLINE_MODE : 0;
 		break;
 
 	default:
···
 
 		sockc->tsflags &= ~SOF_TIMESTAMPING_TX_RECORD_MASK;
 		sockc->tsflags |= tsflags;
+		break;
+	case SCM_TXTIME:
+		if (!sock_flag(sk, SOCK_TXTIME))
+			return -EINVAL;
+		if (cmsg->cmsg_len != CMSG_LEN(sizeof(u64)))
+			return -EINVAL;
+		sockc->transmit_time = get_unaligned((u64 *)CMSG_DATA(cmsg));
 		break;
 	/* SCM_RIGHTS and SCM_CREDENTIALS are semantically in SOL_UNIX. */
 	case SCM_RIGHTS: