Clarify and extend paragraphs on interoperation

of fcntl(2), flock(2), and lockf(3) advisory locks.
Add such a paragraph to the flock(2) manpage for the
sake of consistency.

Reviewed by:	Cyrille Lefevre and Kirk McKusick on -arch
MFC after:	2 weeks

1 files changed, 19 insertions, 3 deletions

diff --git a/lib/libc/sys/fcntl.2 b/lib/libc/sys/fcntl.2
index c888890..92b7440 100644
--- a/lib/libc/sys/fcntl.2
+++ b/lib/libc/sys/fcntl.2
@@ -341,11 +341,26 @@ The
 system call is recommended for applications that want to ensure the integrity
 of their locks when using library routines or wish to pass locks
 to their children.
-Note that
-.Xr flock 2
+.Pp
+The
+.Fn fcntl ,
+.Xr flock 2 ,
 and
+.Xr lockf 3
+locks are compatible.
+Processes using different locking interfaces can cooperate
+over the same file safely.
+However, only one of such interfaces should be used within
+the same process.
+If a file is locked by a process through
+.Xr flock 2 ,
+any record within the file will be seen as locked
+from the viewpoint of another process using
 .Fn fcntl
-locks may be safely used concurrently but
+or
+.Xr lockf 3 ,
+and vice versa.
+Note that
 .Fn fcntl F_GETLK
 returns \-1 in
 .Fa l_pid
@@ -558,6 +573,7 @@ for the reasons as stated in
 .Xr getdtablesize 2 ,
 .Xr open 2 ,
 .Xr sigvec 2 ,
+.Xr lockf 3 ,
 .Xr tcgetpgrp 3 ,
 .Xr tcsetpgrp 3
 .Sh HISTORY