Hi Jeff,
I was recently checking some details of the man page for OFD locks,
and realized that one paragraph is somewhat misleading:
Open file description locks always conflict with traditional
record locks, even when they are acquired by the same process on
the same file descriptor.
This doesn't capture the full story, as far as I can tell. In
particular if we have two processes that take locks on the same region
of a file as follows:
F_OFD_SETLK F_RDLCK
and
F_SETLK F_RDLCK
then those pair of locks are compatible. I assume that's expected
behavior, right? I've drafted the patch below for the man page. Seem
okay?
Cheers,
Michael
diff --git a/man2/fcntl.2 b/man2/fcntl.2
index 59f22ce..03c2ae8 100644
--- a/man2/fcntl.2
+++ b/man2/fcntl.2
@@ -495,7 +495,10 @@ and are only automatically released on the last close
of the open file description,
instead of being released on any close of the file.
.PP
-Open file description locks always conflict with traditional record locks,
+Conflicting lock combinations
+(i.e., a read lock and a write lock or two write locks)
+where one lock is an open file description lock and the other
+is a traditional record lock conflict
even when they are acquired by the same process on the same file descriptor.
Open file description locks placed via the same open file description
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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