[PATCH] Add a function for dumping iovec in msghdr used in sendmsg and recvmsg

[Masatake YAMATO]

* syscall.c (dumpio): Call dumpiov_in_msghdr if
the target function is recvmsg or sendmsg.

* net.c (extractmsghdr): New function derived from
`printmsghdr'.
(printmsghdr): Use `extractmsghdr'.
(dumpiov_in_msghdr): New function.

* defs.h: Add a declaration for `dumpiov_in_msghdr'.

Here is an example session:

    $ ./strace -e write=all ip link change dev enp0s25 mtu 1501 > /dev/null
    sendmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"(...
     * 40 bytes in buffer 0
     | 00000  28 00 00 00 10 00 05 00  d0 d9 aa 53 00 00 00 00  (..........S.... |
     | 00010  00 00 00 00 02 00 00 00  00 00 00 00 00 00 00 00  ................ |
     | 00020  08 00 04 00 dd 05 00 00                           ........         |
    ...

    $ ./strace -e read=all ip link show > /dev/null
    recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"...
     * 8192 bytes in buffer 0
     | 00000  34 00 00 00 02 00 00 00  00 00 00 00 ff 23 00 00  4............#.. |
     | 00010  ff ff ff ff 20 00 00 00  10 00 05 00 00 00 00 00  .... ........... |
    ...

Signed-off-by: Masatake YAMATO <yamato at redhat.com>
---
 defs.h    |  1 +
 net.c     | 45 +++++++++++++++++++++++++++++++--------------
 syscall.c |  4 ++++
 3 files changed, 36 insertions(+), 14 deletions(-)

diff --git a/defs.h b/defs.h
index 1a3b483..39eb1be 100644
--- a/defs.h
+++ b/defs.h
@@ -676,6 +676,7 @@ extern int printargs_ld(struct tcb *);
 extern void addflags(const struct xlat *, int);
 extern int printflags(const struct xlat *, int, const char *);
 extern const char *sprintflags(const char *, const struct xlat *, int);
+extern void dumpiov_in_msghdr(struct tcb *, long);
 extern void dumpiov(struct tcb *, int, long);
 extern void dumpstr(struct tcb *, long, int);
 extern void printstr(struct tcb *, long, long);
diff --git a/net.c b/net.c
index 08341ad..36ab8cc 100644
--- a/net.c
+++ b/net.c
@@ -392,29 +392,46 @@ struct mmsghdr32 {
 	uint32_t /* unsigned */ msg_len;
 };
 
-static void
-printmsghdr(struct tcb *tcp, long addr, unsigned long data_size)
+static int
+extractmsghdr(struct tcb *tcp, long addr, struct msghdr *msg)
 {
-	struct msghdr msg;
-
 #if SUPPORTED_PERSONALITIES > 1 && SIZEOF_LONG > 4
 	if (current_wordsize == 4) {
 		struct msghdr32 msg32;
 
 		if (umove(tcp, addr, &msg32) < 0) {
-			tprintf("%#lx", addr);
-			return;
+			return -1;
 		}
-		msg.msg_name       = (void*)(long)msg32.msg_name;
-		msg.msg_namelen    =              msg32.msg_namelen;
-		msg.msg_iov        = (void*)(long)msg32.msg_iov;
-		msg.msg_iovlen     =              msg32.msg_iovlen;
-		msg.msg_control    = (void*)(long)msg32.msg_control;
-		msg.msg_controllen =              msg32.msg_controllen;
-		msg.msg_flags      =              msg32.msg_flags;
+		msg->msg_name       = (void*)(long)msg32.msg_name;
+		msg->msg_namelen    =              msg32.msg_namelen;
+		msg->msg_iov        = (void*)(long)msg32.msg_iov;
+		msg->msg_iovlen     =              msg32.msg_iovlen;
+		msg->msg_control    = (void*)(long)msg32.msg_control;
+		msg->msg_controllen =              msg32.msg_controllen;
+		msg->msg_flags      =              msg32.msg_flags;
 	} else
 #endif
-	if (umove(tcp, addr, &msg) < 0) {
+	if (umove(tcp, addr, msg) < 0) {
+			return -1;
+		}
+	return 0;
+}
+
+void
+dumpiov_in_msghdr(struct tcb *tcp, long addr)
+{
+	struct msghdr msg;
+
+	if (extractmsghdr(tcp, addr, &msg) >= 0)
+		dumpiov(tcp, msg.msg_iovlen, (long)msg.msg_iov);
+}
+
+static void
+printmsghdr(struct tcb *tcp, long addr, unsigned long data_size)
+{
+	struct msghdr msg;
+
+	if (extractmsghdr(tcp, addr, &msg) < 0) {
 		tprintf("%#lx", addr);
 		return;
 	}
diff --git a/syscall.c b/syscall.c
index b0ad47e..518ef13 100644
--- a/syscall.c
+++ b/syscall.c
@@ -2494,6 +2494,8 @@ dumpio(struct tcb *tcp)
 			dumpstr(tcp, tcp->u_arg[1], tcp->u_rval);
 		else if (func == sys_readv)
 			dumpiov(tcp, tcp->u_arg[2], tcp->u_arg[1]);
+		else if (func == sys_recvmsg)
+			dumpiov_in_msghdr(tcp, tcp->u_arg[1]);
 		return;
 	}
 	if (qual_flags[tcp->u_arg[0]] & QUAL_WRITE) {
@@ -2504,6 +2506,8 @@ dumpio(struct tcb *tcp)
 			dumpstr(tcp, tcp->u_arg[1], tcp->u_arg[2]);
 		else if (func == sys_writev)
 			dumpiov(tcp, tcp->u_arg[2], tcp->u_arg[1]);
+		else if (func == sys_sendmsg)
+			dumpiov_in_msghdr(tcp, tcp->u_arg[1]);
 		return;
 	}
 }
-- 
1.9.0