client: make fuse direct I/O strategies explicit

So far the --direct-io-mode option has been presented
as of being Boolean valued. That is however not exact,
as a third behavior is chosen if the option is not
specified.

We accept now the "auto" value as an explicit choice
for the default heuristics, and indicate in the
descriptions of the option (which occur in commandline
help and in the gluterfs / mount.glusterfs man pages)
that auto is the default.

The default heuristics was briefly described in the
commandline help. We are getting rid of that, because:
- it's not the right place to provide such details;
- there is no guarantee of keeping the current heuristics
  so it might go out of sync with reality;
- that is already the case to some degree, because the
  description did not take into account that the default
  heuristics varies between platforms (on Mac, it's just
  "off"), and that xlators can also prescribe direct I/O
  for the file of their choice (see change
  I3fe3312cd96baa4eecfe1247ab7255b4f455f049).

Change-Id: Ia83479c0c67fe66b7fc2e0e8db5b7792d9f44b28
Signed-off-by: Csaba Henk <csaba@redhat.com>

2 files changed, 4 insertions, 4 deletions

diff --git a/doc/glusterfs.8 b/doc/glusterfs.8
index 520150a55e9..985f30a5865 100644
--- a/doc/glusterfs.8
+++ b/doc/glusterfs.8
@@ -118,8 +118,8 @@ Set fuse module's background queue length to N (the default is 64).
 \fB\-\-congestion\-threshold=N\fR
 Set fuse module's congestion threshold to N (the default is 48).
 .TP
-\fB\-\-direct\-io\-mode=BOOL\fR
-Enable/Disable the direct-I/O mode in fuse module (the default is enable).
+\fB\-\-direct\-io\-mode=BOOL|auto\fR
+Specify fuse direct I/O strategy (the default is auto).
 .TP
 \fB\-\-dump-fuse=PATH\f\R
 Dump fuse traffic to PATH
diff --git a/doc/mount.glusterfs.8 b/doc/mount.glusterfs.8
index b77d02551ba..6a51fc9aef0 100644
--- a/doc/mount.glusterfs.8
+++ b/doc/mount.glusterfs.8
@@ -92,8 +92,8 @@ Set negative timeout to SECONDS in fuse kernel module [default: 0]
 Volume name to be used for MOUNT-POINT [default: top most volume in
 VOLUME-FILE]
 .TP
-\fBdirect\-io\-mode=\fRdisable
-Disable direct I/O mode in fuse kernel module
+\fBdirect\-io\-mode=\fRBOOL|auto
+Specify fuse direct I/O strategy [default: auto]
 .TP
 \fBcongestion\-threshold=\fRN
 Set fuse module's congestion threshold to N [default: 48]