[xen stable-4.18] tools/libxs: Stop playing with SIGPIPE

[patchbot@xxxxxxx]

commit b6aa39f210d42168633a07f1c18f5d65f041ca09
Author:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
AuthorDate: Mon Nov 25 12:11:04 2024 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Mon Nov 25 12:11:04 2024 +0100

    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@xxxxxxxxxx>
    Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
    Reviewed-by: Jason Andryuk <jason.andryuk@xxxxxxx>
    master commit: a17b6db9b00784b409c35e3017dc45aed1ec2bfb
    master date: 2024-07-23 15:11:27 +0100
---
 tools/libs/store/xs.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/tools/libs/store/xs.c b/tools/libs/store/xs.c
index 0b62ec537f..7286a60fd0 100644
--- a/tools/libs/store/xs.c
+++ b/tools/libs/store/xs.c
@@ -613,7 +613,7 @@ 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;
@@ -673,7 +673,6 @@ 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);
@@ -690,11 +689,6 @@ 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))
@@ -706,7 +700,6 @@ 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);
@@ -725,7 +718,6 @@ 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;
--
generated by git-patchbot for /home/xen/git/xen.git#stable-4.18