tools/libxs: Stop playing with SIGPIPE

It's very rude for a library to play with signals behind the back of the
application, no matter ones views on the default behaviour of SIGPIPE under
POSIX.  Even if the application doesn't care about the xenstored socket, it my
care about others.

This logic has existed since xenstore/xenstored was originally added in commit
29c9e570b1ed ("Add xenstore daemon and library") in 2005.

It's also unnecessary.  Pass MSG_NOSIGNAL when talking to xenstored over a
pipe (to avoid sucumbing to SIGPIPE if xenstored has crashed), and forgo any
playing with the signal disposition.

This has a side benefit of saving 2 syscalls per xenstore request.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Andryuk <jason.andryuk@amd.com>

diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 1dd95397179466eaec11caf5e6106153a6141730..5d9c7151e8bbeef5c6e0740a18d3653d730f2335 100644 (file)
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -604,7 +604,7 @@ static bool sendmsg_exact(int fd, struct iovec *iov, unsigned int nr)
        };
 
        while (hdr.msg_iovlen) {
-               ssize_t res = sendmsg(fd, &hdr, 0);
+               ssize_t res = sendmsg(fd, &hdr, MSG_NOSIGNAL);
 
                if (res < 0 && errno == EINTR)
                        continue;
@@ -664,7 +664,6 @@ static void *xs_talkv(struct xs_handle *h,
        void *ret = NULL;
        int saved_errno;
        unsigned int i, msg_len;
-       struct sigaction ignorepipe, oldact;
 
        /* Element 0 must be xsd_sockmsg */
        assert(num_vecs >= 1);
@@ -681,11 +680,6 @@ static void *xs_talkv(struct xs_handle *h,
 
        msg->len = msg_len;
 
-       ignorepipe.sa_handler = SIG_IGN;
-       sigemptyset(&ignorepipe.sa_mask);
-       ignorepipe.sa_flags = 0;
-       sigaction(SIGPIPE, &ignorepipe, &oldact);
-
        mutex_lock(&h->request_mutex);
 
        if (!write_request(h, iovec, num_vecs))
@@ -697,7 +691,6 @@ static void *xs_talkv(struct xs_handle *h,
 
        mutex_unlock(&h->request_mutex);
 
-       sigaction(SIGPIPE, &oldact, NULL);
        if (reply_type == XS_ERROR) {
                saved_errno = get_error(ret);
                free(ret);
@@ -716,7 +709,6 @@ fail:
        /* We're in a bad state, so close fd. */
        saved_errno = errno;
        mutex_unlock(&h->request_mutex);
-       sigaction(SIGPIPE, &oldact, NULL);
 close_fd:
        close(h->fd);
        h->fd = -1;