From b9b353db4be5b78da8d89909904f4ca8638c24f8 Mon Sep 17 00:00:00 2001
From: Harshavardhana <harsha@minio.io>
Date: Tue, 11 Dec 2018 16:22:56 -0800
Subject: [PATCH] Add env to support synchronous ops for all calls (#6877)

---
 cmd/posix.go          | 20 ++++++++++++++++++--
 docs/config/README.md | 17 ++++++++++++++---
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/cmd/posix.go b/cmd/posix.go
index 6eb6ac267..004684c86 100644
--- a/cmd/posix.go
+++ b/cmd/posix.go
@@ -71,6 +71,7 @@ type posix struct {
 	connected bool
 
 	diskMount bool // indicates if the path is an actual mount.
+	driveSync bool // indicates if the backend is synchronous.
 
 	// Disk usage metrics
 	stopUsageCh chan struct{}
@@ -191,6 +192,15 @@ func newPosix(path string) (*posix, error) {
 		diskMount:   mountinfo.IsLikelyMountPoint(path),
 	}
 
+	var pf BoolFlag
+	if driveSync := os.Getenv("MINIO_DRIVE_SYNC"); driveSync != "" {
+		pf, err = ParseBoolFlag(driveSync)
+		if err != nil {
+			return nil, err
+		}
+		p.driveSync = bool(pf)
+	}
+
 	if !p.diskMount {
 		go p.diskUsage(globalServiceDoneCh)
 	}
@@ -1013,8 +1023,14 @@ func (s *posix) AppendFile(volume, path string, buf []byte) (err error) {
 		return errFaultyDisk
 	}
 
-	// Create file if not found
-	w, err := s.openFile(volume, path, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
+	var w *os.File
+	// Create file if not found, additionally also enables synchronous
+	// operation if asked by the user.
+	if s.driveSync {
+		w, err = s.openFile(volume, path, os.O_CREATE|os.O_SYNC|os.O_APPEND|os.O_WRONLY)
+	} else {
+		w, err = s.openFile(volume, path, os.O_CREATE|os.O_APPEND|os.O_WRONLY)
+	}
 	if err != nil {
 		return err
 	}
diff --git a/docs/config/README.md b/docs/config/README.md
index 742c64af5..40232d505 100644
--- a/docs/config/README.md
+++ b/docs/config/README.md
@@ -132,9 +132,9 @@ By default, parity for objects with standard storage class is set to `N/2`, and
 
 ## Environment only settings
 
-#### Browser
+### Browser
 
-Enable or disable access to web UI. By default it is set to `on`. You may override this field with ``MINIO_BROWSER`` environment variable.
+Enable or disable access to web UI. By default it is set to `on`. You may override this field with `MINIO_BROWSER` environment variable.
 
 Example:
 
@@ -145,7 +145,7 @@ minio server /data
 
 ### Domain
 
-By default, Minio supports path-style requests that are of the format http://mydomain.com/bucket/object. MINIO_DOMAIN environment variable is used to enable virtual-host-style requests. If the request `Host` header matches with `(.+).mydomain.com` then the matched pattern `$1` is used as bucket and the path is used as object. More information on path-style and virtual-host-style [here](http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAPI.html)
+By default, Minio supports path-style requests that are of the format http://mydomain.com/bucket/object. `MINIO_DOMAIN` environment variable is used to enable virtual-host-style requests. If the request `Host` header matches with `(.+).mydomain.com` then the matched pattern `$1` is used as bucket and the path is used as object. More information on path-style and virtual-host-style [here](http://docs.aws.amazon.com/AmazonS3/latest/dev/RESTAPI.html)
 Example:
 
 ```sh
@@ -153,6 +153,17 @@ export MINIO_DOMAIN=mydomain.com
 minio server /data
 ```
 
+### Drive Sync
+
+By default, Minio writes to disk in synchronous mode for all metadata operations. Set `MINIO_DRIVE_SYNC` environment variable to enable synchronous mode for all data operations as well.
+
+Example:
+
+```sh
+export MINIO_DRIVE_SYNC=on
+minio server /data
+```
+
 ## Explore Further
 
 * [Minio Quickstart Guide](https://docs.minio.io/docs/minio-quickstart-guide)