doc: better explain the need for IO::Splice::F_NONBLOCK

1 files changed, 9 insertions, 3 deletions

diff --git a/ext/io_splice/io_splice_ext.c b/ext/io_splice/io_splice_ext.c
index 9531633..fdb3397 100644
--- a/ext/io_splice/io_splice_ext.c
+++ b/ext/io_splice/io_splice_ext.c
@@ -345,9 +345,15 @@ void Init_io_splice_ext(void)
         rb_define_const(mSplice, "F_MOVE", UINT2NUM(SPLICE_F_MOVE));
 
         /*
-         * Do not block on I/O.  This flag only affects the pipe(s) being
-         * spliced from/to and has no effect on the non-pipe descriptor
-         * (which requires non-blocking operation to be set explicitly).
+         * Do not block on pipe I/O.  This flag only affects the pipe(s)
+         * being spliced from/to and has no effect on the non-pipe
+         * descriptor (which requires non-blocking operation to be set
+         * explicitly).
+         *
+         * The non-blocking flag (O_NONBLOCK) on the pipe descriptors
+         * themselves are ignored by this family of functions, and
+         * using this flag is the only way to get non-blocking operation
+         * out of them.
          */
         rb_define_const(mSplice, "F_NONBLOCK", UINT2NUM(SPLICE_F_NONBLOCK));