From 0baafb158f6dc5abc5b6180cb1d1fa7f9b56be5b Mon Sep 17 00:00:00 2001
From: Nick Craig-Wood <nick@craig-wood.com>
Date: Sat, 14 Sep 2019 13:11:21 +0100
Subject: [PATCH] mount: allow files of unkown size to be read properly

Before this change, files of unknown size (eg Google Docs) would
appear in file listings with 0 size and would only allow 0 bytes to be
read.

This change sets the direct_io flag in the FUSE return which bypasses
the cache for these files.  This means that they can be read properly.

This is compatible with some, but not all applications.
---
 cmd/cmount/fs.go             | 3 +++
 cmd/mount/file.go            | 5 +++++
 docs/content/drive.md        | 9 ++++++---
 docs/content/googlephotos.md | 9 +++++----
 4 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/cmd/cmount/fs.go b/cmd/cmount/fs.go
index 9d732be34..1ae98cc96 100644
--- a/cmd/cmount/fs.go
+++ b/cmd/cmount/fs.go
@@ -299,6 +299,9 @@ func (fsys *FS) Open(path string, flags int) (errc int, fh uint64) {
 		return translateError(err), fhUnset
 	}
 
+	// FIXME add support for unknown length files setting direct_io
+	// See: https://github.com/billziss-gh/cgofuse/issues/38
+
 	return 0, fsys.openHandle(handle)
 }
 
diff --git a/cmd/mount/file.go b/cmd/mount/file.go
index 6a26af1fa..4bc7c3d45 100644
--- a/cmd/mount/file.go
+++ b/cmd/mount/file.go
@@ -73,6 +73,11 @@ func (f *File) Open(ctx context.Context, req *fuse.OpenRequest, resp *fuse.OpenR
 		return nil, translateError(err)
 	}
 
+	// If size unknown then use direct io to read
+	if handle.Node().DirEntry().Size() < 0 {
+		resp.Flags |= fuse.OpenDirectIO
+	}
+
 	return &FileHandle{handle}, nil
 }
 
diff --git a/docs/content/drive.md b/docs/content/drive.md
index bb58a7327..3e094b2ce 100644
--- a/docs/content/drive.md
+++ b/docs/content/drive.md
@@ -882,9 +882,12 @@ without downloading them.
 Google docs will transfer correctly with `rclone sync`, `rclone copy`
 etc as rclone knows to ignore the size when doing the transfer.
 
-However an unfortunate consequence of this is that you can't download
-Google docs using `rclone mount` - you will get a 0 sized file.  If
-you try again the doc may gain its correct size and be downloadable.
+However an unfortunate consequence of this is that you may not be able
+to download Google docs using `rclone mount`. If it doesn't work you
+will get a 0 sized file.  If you try again the doc may gain its
+correct size and be downloadable. Whther it will work on not depends
+on the application accessing the mount and the OS you are running -
+experiment to find out if it does work for you!
 
 ### Duplicated files ###
 
diff --git a/docs/content/googlephotos.md b/docs/content/googlephotos.md
index ed2f24341..6a66d69a4 100644
--- a/docs/content/googlephotos.md
+++ b/docs/content/googlephotos.md
@@ -277,13 +277,14 @@ that when syncing to Google Photos, rclone can only do a file
 existence check.
 
 It is possible to read the size of the media, but this needs an extra
-HTTP HEAD request per media item so is very slow and uses up a lot of
+HTTP HEAD request per media item so is **very slow** and uses up a lot of
 transactions.  This can be enabled with the `--gphotos-read-size`
 option or the `read_size = true` config parameter.
 
-If you want to use the backend with `rclone mount` you will need to
-enable this flag otherwise you will not be able to read media off the
-mount.
+If you want to use the backend with `rclone mount` you may need to
+enable this flag (depending on your OS and application using the
+photos) otherwise you may not be able to read media off the mount.
+You'll need to experiment to see if it works for you without the flag.
 
 ### Albums