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From 6d1ef1fb841a0b3b4c53b560892f3570b3379dc9 Mon Sep 17 00:00:00 2001
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From: Lennart Poettering <lennart@poettering.net>
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Date: Wed, 10 Jun 2015 19:24:58 +0200
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Subject: [PATCH] journald: don't employ inner loop for reading from incoming
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 sockets
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Otherwise, if the socket is constantly busy we will never return to the
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event loop, but we really need to to dispatch other (possibly more
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high-priority) events too. Hence, return after dispatching one message
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to the event handler, and rely on the event loop calling us back
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right-away.
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Fixes #125
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Related: #1318994
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Cherry-picked from: a315ac4e076c4ce7ce3e5c95792cf916d5e918c5
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---
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 src/journal/journald-server.c | 204 +++++++++++++++++-----------------
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 1 file changed, 100 insertions(+), 104 deletions(-)
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diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
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index 1eb1394d1..275224dc9 100644
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--- a/src/journal/journald-server.c
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+++ b/src/journal/journald-server.c
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@@ -1103,6 +1103,42 @@ finish:
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 int server_process_datagram(sd_event_source *es, int fd, uint32_t revents, void *userdata) {
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         Server *s = userdata;
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+        struct ucred *ucred = NULL;
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+        struct timeval *tv = NULL;
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+        struct cmsghdr *cmsg;
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+        char *label = NULL;
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+        size_t label_len = 0, m;
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+        struct iovec iovec;
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+        ssize_t n;
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+        int *fds = NULL, v = 0;
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+        unsigned n_fds = 0;
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+
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+        union {
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+                struct cmsghdr cmsghdr;
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+
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+                /* We use NAME_MAX space for the SELinux label
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+                 * here. The kernel currently enforces no
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+                 * limit, but according to suggestions from
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+                 * the SELinux people this will change and it
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+                 * will probably be identical to NAME_MAX. For
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+                 * now we use that, but this should be updated
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+                 * one day when the final limit is known. */
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+                uint8_t buf[CMSG_SPACE(sizeof(struct ucred)) +
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+                            CMSG_SPACE(sizeof(struct timeval)) +
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+                            CMSG_SPACE(sizeof(int)) + /* fd */
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+                            CMSG_SPACE(NAME_MAX)]; /* selinux label */
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+        } control = {};
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+
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+        union sockaddr_union sa = {};
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+
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+        struct msghdr msghdr = {
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+                .msg_iov = &iovec,
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+                .msg_iovlen = 1,
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+                .msg_control = &control,
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+                .msg_controllen = sizeof(control),
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+                .msg_name = &sa,
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+                .msg_namelen = sizeof(sa),
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+        };
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         assert(s);
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         assert(fd == s->native_fd || fd == s->syslog_fd || fd == s->audit_fd);
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@@ -1112,119 +1148,79 @@ int server_process_datagram(sd_event_source *es, int fd, uint32_t revents, void
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                 return -EIO;
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         }
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-        for (;;) {
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-                struct ucred *ucred = NULL;
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-                struct timeval *tv = NULL;
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-                struct cmsghdr *cmsg;
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-                char *label = NULL;
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-                size_t label_len = 0;
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-                struct iovec iovec;
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-
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-                union {
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-                        struct cmsghdr cmsghdr;
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-
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-                        /* We use NAME_MAX space for the SELinux label
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-                         * here. The kernel currently enforces no
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-                         * limit, but according to suggestions from
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-                         * the SELinux people this will change and it
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-                         * will probably be identical to NAME_MAX. For
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-                         * now we use that, but this should be updated
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-                         * one day when the final limit is known. */
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-                        uint8_t buf[CMSG_SPACE(sizeof(struct ucred)) +
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-                                    CMSG_SPACE(sizeof(struct timeval)) +
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-                                    CMSG_SPACE(sizeof(int)) + /* fd */
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-                                    CMSG_SPACE(NAME_MAX)]; /* selinux label */
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-                } control = {};
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-                union sockaddr_union sa = {};
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-                struct msghdr msghdr = {
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-                        .msg_iov = &iovec,
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-                        .msg_iovlen = 1,
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-                        .msg_control = &control,
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-                        .msg_controllen = sizeof(control),
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-                        .msg_name = &sa,
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-                        .msg_namelen = sizeof(sa),
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-                };
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-
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-                ssize_t n;
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-                int *fds = NULL;
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-                unsigned n_fds = 0;
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-                int v = 0;
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-                size_t m;
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-
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-                /* Try to get the right size, if we can. (Not all
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-                 * sockets support SIOCINQ, hence we just try, but
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-                 * don't rely on it. */
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-                (void) ioctl(fd, SIOCINQ, &v);
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-
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-                /* Fix it up, if it is too small. We use the same fixed value as auditd here. Awful! */
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-                m = PAGE_ALIGN(MAX3((size_t) v + 1,
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-                                    (size_t) LINE_MAX,
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-                                    ALIGN(sizeof(struct nlmsghdr)) + ALIGN((size_t) MAX_AUDIT_MESSAGE_LENGTH)) + 1);
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-
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-                if (!GREEDY_REALLOC(s->buffer, s->buffer_size, m))
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-                        return log_oom();
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-
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-                iovec.iov_base = s->buffer;
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-                iovec.iov_len = s->buffer_size - 1; /* Leave room for trailing NUL we add later */
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-
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-                n = recvmsg(fd, &msghdr, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
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-                if (n < 0) {
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-                        if (errno == EINTR || errno == EAGAIN)
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-                                return 0;
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-
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-                        log_error_errno(errno, "recvmsg() failed: %m");
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-                        return -errno;
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-                }
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+        /* Try to get the right size, if we can. (Not all
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+         * sockets support SIOCINQ, hence we just try, but
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+         * don't rely on it. */
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+        (void) ioctl(fd, SIOCINQ, &v);
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-                CMSG_FOREACH(cmsg, &msghdr) {
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-
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-                        if (cmsg->cmsg_level == SOL_SOCKET &&
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-                            cmsg->cmsg_type == SCM_CREDENTIALS &&
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-                            cmsg->cmsg_len == CMSG_LEN(sizeof(struct ucred)))
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-                                ucred = (struct ucred*) CMSG_DATA(cmsg);
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-                        else if (cmsg->cmsg_level == SOL_SOCKET &&
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-                                 cmsg->cmsg_type == SCM_SECURITY) {
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-                                label = (char*) CMSG_DATA(cmsg);
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-                                label_len = cmsg->cmsg_len - CMSG_LEN(0);
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-                        } else if (cmsg->cmsg_level == SOL_SOCKET &&
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-                                   cmsg->cmsg_type == SO_TIMESTAMP &&
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-                                   cmsg->cmsg_len == CMSG_LEN(sizeof(struct timeval)))
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-                                tv = (struct timeval*) CMSG_DATA(cmsg);
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-                        else if (cmsg->cmsg_level == SOL_SOCKET &&
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-                                 cmsg->cmsg_type == SCM_RIGHTS) {
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-                                fds = (int*) CMSG_DATA(cmsg);
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-                                n_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
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-                        }
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-                }
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+        /* Fix it up, if it is too small. We use the same fixed value as auditd here. Awful! */
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+        m = PAGE_ALIGN(MAX3((size_t) v + 1,
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+                            (size_t) LINE_MAX,
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+                            ALIGN(sizeof(struct nlmsghdr)) + ALIGN((size_t) MAX_AUDIT_MESSAGE_LENGTH)) + 1);
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-                /* And a trailing NUL, just in case */
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-                s->buffer[n] = 0;
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+        if (!GREEDY_REALLOC(s->buffer, s->buffer_size, m))
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+                return log_oom();
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-                if (fd == s->syslog_fd) {
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-                        if (n > 0 && n_fds == 0)
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-                                server_process_syslog_message(s, strstrip(s->buffer), ucred, tv, label, label_len);
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-                        else if (n_fds > 0)
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-                                log_warning("Got file descriptors via syslog socket. Ignoring.");
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+        iovec.iov_base = s->buffer;
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+        iovec.iov_len = s->buffer_size - 1; /* Leave room for trailing NUL we add later */
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-                } else if (fd == s->native_fd) {
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-                        if (n > 0 && n_fds == 0)
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-                                server_process_native_message(s, s->buffer, n, ucred, tv, label, label_len);
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-                        else if (n == 0 && n_fds == 1)
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-                                server_process_native_file(s, fds[0], ucred, tv, label, label_len);
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-                        else if (n_fds > 0)
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-                                log_warning("Got too many file descriptors via native socket. Ignoring.");
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+        n = recvmsg(fd, &msghdr, MSG_DONTWAIT|MSG_CMSG_CLOEXEC);
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+        if (n < 0) {
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+                if (errno == EINTR || errno == EAGAIN)
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+                        return 0;
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-                } else {
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-                        assert(fd == s->audit_fd);
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+                return log_error_errno(errno, "recvmsg() failed: %m");
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+        }
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-                        if (n > 0 && n_fds == 0)
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-                                server_process_audit_message(s, s->buffer, n, ucred, &sa, msghdr.msg_namelen);
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-                        else if (n_fds > 0)
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-                                log_warning("Got file descriptors via audit socket. Ignoring.");
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+        CMSG_FOREACH(cmsg, &msghdr) {
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+
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+                if (cmsg->cmsg_level == SOL_SOCKET &&
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+                    cmsg->cmsg_type == SCM_CREDENTIALS &&
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+                    cmsg->cmsg_len == CMSG_LEN(sizeof(struct ucred)))
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+                        ucred = (struct ucred*) CMSG_DATA(cmsg);
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+                else if (cmsg->cmsg_level == SOL_SOCKET &&
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+                         cmsg->cmsg_type == SCM_SECURITY) {
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+                        label = (char*) CMSG_DATA(cmsg);
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+                        label_len = cmsg->cmsg_len - CMSG_LEN(0);
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+                } else if (cmsg->cmsg_level == SOL_SOCKET &&
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+                           cmsg->cmsg_type == SO_TIMESTAMP &&
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+                           cmsg->cmsg_len == CMSG_LEN(sizeof(struct timeval)))
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+                        tv = (struct timeval*) CMSG_DATA(cmsg);
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+                else if (cmsg->cmsg_level == SOL_SOCKET &&
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+                         cmsg->cmsg_type == SCM_RIGHTS) {
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+                        fds = (int*) CMSG_DATA(cmsg);
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+                        n_fds = (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
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                 }
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+        }
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+
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+        /* And a trailing NUL, just in case */
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+        s->buffer[n] = 0;
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+
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+        if (fd == s->syslog_fd) {
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+                if (n > 0 && n_fds == 0)
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+                        server_process_syslog_message(s, strstrip(s->buffer), ucred, tv, label, label_len);
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+                else if (n_fds > 0)
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+                        log_warning("Got file descriptors via syslog socket. Ignoring.");
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+
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+        } else if (fd == s->native_fd) {
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+                if (n > 0 && n_fds == 0)
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+                        server_process_native_message(s, s->buffer, n, ucred, tv, label, label_len);
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+                else if (n == 0 && n_fds == 1)
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+                        server_process_native_file(s, fds[0], ucred, tv, label, label_len);
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+                else if (n_fds > 0)
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+                        log_warning("Got too many file descriptors via native socket. Ignoring.");
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-                close_many(fds, n_fds);
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+        } else {
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+                assert(fd == s->audit_fd);
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+
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+                if (n > 0 && n_fds == 0)
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+                        server_process_audit_message(s, s->buffer, n, ucred, &sa, msghdr.msg_namelen);
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+                else if (n_fds > 0)
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+                        log_warning("Got file descriptors via audit socket. Ignoring.");
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         }
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+
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+        close_many(fds, n_fds);
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+        return 0;
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 }
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 static int dispatch_sigusr1(sd_event_source *es, const struct signalfd_siginfo *si, void *userdata) {