dtprobed: handle signals hitting dtprobed better

dtprobed is long-running and thus might get hit by signals at almost any
time.  These will cause long-running operations to return -EINTR, which
needs handling.  We were handling -EINTR when a fuse_session_receive_buf()
happened, but dtprobed spends almost all its time blocked on poll() and that
isn't handling -EINTR at all.  This came to light when tests were written
that intentionally hit dtprobed with signals: fix it by checking the poll()
for EINTR too.  (Done in two places because the core FUSE loop is duplicated
for FUSE 2 and 3.)

Signed-off-by: Nick Alcock <nick.alcock@oracle.com>
Reviewed-by: Kris Van Hees <kris.van.hees@oracle.com>

dtprobed/dtprobed.c

@@ -779,8 +779,11 @@ loop(void)
 	fds[0].events = POLLIN;
 
 	while (!fuse_session_exited(cuse_session)) {
-		if ((ret = poll(fds, 1, -1)) < 0)
+		if (poll(fds, 1, -1) < 0) {
+			if (errno == EINTR)
+				continue;
 			break;
+		}
 
 		if (fds[0].revents != 0) {
 			if ((ret = fuse_session_receive_buf(cuse_session,
@@ -822,8 +825,11 @@ loop(void)
 		struct fuse_buf fbuf = { .mem = buf, .size = bufsize };
 		struct fuse_chan *tmpch = cuse_chan;
 
-		if ((ret = poll(fds, 1, -1)) < 0)
+		if (poll(fds, 1, -1) < 0) {
+			if (errno == EINTR)
+				continue;
 			break;
+		}
 
 		if (fds[0].revents != 0) {
 			if ((ret = fuse_session_receive_buf(cuse_session,