Document ExclCreate reasoning

options.go

@@ -109,7 +109,25 @@ func NoAppleXattr() MountOption {
 // ExclCreate causes O_EXCL flag to be set for only "truly" exclusive creates,
 // i.e. create calls for which the initiator explicitly set the O_EXCL flag.
 //
+// OSXFUSE expects all create calls to return EEXIST in case the file
+// already exists, regardless of whether O_EXCL was specified or not.
+// To ensure this behavior, it normally sets OpenExclusive for all
+// Create calls, regardless of whether the original call had it set.
+// For distributed filesystems, that may force every file create to be
+// a distributed consensus action, causing undesirable delays.
+//
+// This option makes the FUSE filesystem see the original flag value,
+// and better decide when to ensure global consensus.
+//
+// Note that returning EEXIST on existing file create is still
+// expected with OSXFUSE, regardless of the presence of the
+// OpenExclusive flag.
+//
+// For more information, see
+// https://github.com/osxfuse/osxfuse/issues/209
+//
 // OS X only. Others ignore this options.
+// Requires OSXFUSE 3.4.1 or newer.
 func ExclCreate() MountOption {
 	return exclCreate
 }