Add s6_svc_lock_take() and s6_svc_lock_release()

 Allows fixing a race condition in s6-rc-init.
 s6-supervise also creates event/ before supervise/ so that
locking the servicedir ensures event/ can be used.

4 files changed, 34 insertions, 1 deletions

diff --git a/src/include/s6/s6-supervise.h b/src/include/s6/s6-supervise.h
index f0b08e7..541c30d 100644
--- a/src/include/s6/s6-supervise.h
+++ b/src/include/s6/s6-supervise.h
@@ -5,6 +5,7 @@
 
 #include <sys/types.h>
 #include <skalibs/tai.h>
+#include <skalibs/djbunix.h>
 
 #define S6_SUPERVISE_CTLDIR "supervise"
 #define S6_SUPERVISE_EVENTDIR "event"
@@ -17,6 +18,9 @@ extern int s6_svc_write (char const *, char const *, size_t) ;
 extern int s6_svc_writectl (char const *, char const *, char const *, size_t) ;
 extern int s6_svc_main (int, char const *const *, char const *, char const *, char const *) ;
 
+extern int s6_svc_lock_take (char const *) ;
+#define s6_svc_lock_release(fdlock) lock_un(fdlock)
+
 typedef struct s6_svstatus_s s6_svstatus_t, *s6_svstatus_t_ref ;
 struct s6_svstatus_s
 {
diff --git a/src/libs6/deps-lib/s6 b/src/libs6/deps-lib/s6
index ace5a05..5acb672 100644
--- a/src/libs6/deps-lib/s6
+++ b/src/libs6/deps-lib/s6
@@ -26,6 +26,7 @@ s6_accessrules_uidgid_cdb.o
 s6_accessrules_uidgid_fs.o
 s6_supervise_lock.o
 s6_supervise_lock_mode.o
+s6_svc_lock_take.o
 s6_svc_ok.o
 s6_svc_write.o
 s6_svc_writectl.o
diff --git a/src/libs6/s6_svc_lock_take.c b/src/libs6/s6_svc_lock_take.c
new file mode 100644
index 0000000..57830c0
--- /dev/null
+++ b/src/libs6/s6_svc_lock_take.c
@@ -0,0 +1,28 @@
+/* ISC license. */
+
+#include <sys/stat.h>
+#include <string.h>
+#include <errno.h>
+#include <skalibs/djbunix.h>
+#include <s6/s6-supervise.h>
+
+int s6_svc_lock_take (char const *dir)
+{
+  size_t dirlen = strlen(dir) ;
+  int fdlock ;
+  char lock[dirlen + sizeof(S6_SUPERVISE_CTLDIR) + 6] ;
+  memcpy(lock, dir, dirlen) ;
+  memcpy(lock + dirlen, "/" S6_SUPERVISE_CTLDIR, sizeof(S6_SUPERVISE_CTLDIR) + 1) ;
+  if ((mkdir(lock, S_IRWXU) < 0) && (errno != EEXIST)) return -1 ;
+  memcpy(lock + dirlen + sizeof(S6_SUPERVISE_CTLDIR), "/lock", 6) ;
+  fdlock = open_create(lock) ;
+  if (fdlock < 0) return -1 ;
+  if (coe(fdlock) < 0 || lock_ex(fdlock) < 0)
+  {
+    int e = errno ;
+    fd_close(fdlock) ;
+    errno = e ;
+    return -1 ;
+  }
+  return fdlock ;
+}
diff --git a/src/supervision/s6-supervise.c b/src/supervision/s6-supervise.c
index 7527668..71f247e 100644
--- a/src/supervision/s6-supervise.c
+++ b/src/supervision/s6-supervise.c
@@ -599,9 +599,9 @@ int main (int argc, char const *const *argv)
     memcpy(progname + proglen + 1, argv[1], namelen + 1) ;
     PROG = progname ;
     if (!fd_sanitize()) strerr_diefu1sys(111, "sanitize stdin and stdout") ;
-    x[1].fd = s6_supervise_lock(S6_SUPERVISE_CTLDIR) ;
     if (!ftrigw_fifodir_make(S6_SUPERVISE_EVENTDIR, getegid(), 0))
       strerr_diefu2sys(111, "mkfifodir ", S6_SUPERVISE_EVENTDIR) ;
+    x[1].fd = s6_supervise_lock(S6_SUPERVISE_CTLDIR) ;
     x[0].fd = selfpipe_init() ;
     if (x[0].fd == -1) strerr_diefu1sys(111, "init selfpipe") ;
     if (sig_ignore(SIGPIPE) < 0) strerr_diefu1sys(111, "ignore SIGPIPE") ;