journal: guarantee async-signal-safety in sd_journald_sendv

signal(7) provides a list of functions which may be called from a
signal handler. Other functions, which only call those functions and
don't access global memory and are reentrant are also safe.
sd_j_sendv was mostly OK, but would call mkostemp and writev in a
fallback path, which are unsafe.

Being able to call sd_j_sendv in a async-signal-safe way is important
because it allows it be used in signal handlers.

Safety is achieved by replacing mkostemp with open(O_TMPFILE) and an
open-coded writev replacement which uses write. Unfortunately,
O_TMPFILE is only available on kernels >= 3.11. When O_TMPFILE is
unavailable, an open-coded mkostemp is used.

https://bugzilla.gnome.org/show_bug.cgi?id=722889

1 files changed, 3 insertions, 0 deletions

diff --git a/src/shared/util.h b/src/shared/util.h
index 630137a53a..1169864c3a 100644
--- a/src/shared/util.h
+++ b/src/shared/util.h
@@ -850,4 +850,7 @@ bool pid_valid(pid_t pid);
 int getpeercred(int fd, struct ucred *ucred);
 int getpeersec(int fd, char **ret);
 
+int writev_safe(int fd, const struct iovec *w, int j);
+
+int mkostemp_safe(char *pattern, int flags);
 int open_tmpfile(const char *path, int flags);