From 4898d79241b8d92d15e326b0f267ecd54c133e0c Mon Sep 17 00:00:00 2001
From: Ka-Hing Cheung <kahing.cheung@databricks.com>
Date: Wed, 11 Dec 2019 00:49:03 -0800
Subject: [PATCH] plumb through Fd in setattr (#67)

this allows us to distinguish between truncate vs ftruncate
---
 conversions.go         | 5 +++++
 fuseops/ops.go         | 3 +++
 samples/memfs/memfs.go | 6 ++++++
 3 files changed, 14 insertions(+)

diff --git a/conversions.go b/conversions.go
index fb034e9..6502767 100644
--- a/conversions.go
+++ b/conversions.go
@@ -93,6 +93,11 @@ func convertInMessage(
 			to.Mtime = &t
 		}
 
+		if valid.Handle() {
+			t := fuseops.HandleID(in.Fh)
+			to.Handle = &t
+		}
+
 	case fusekernel.OpForget:
 		type input fusekernel.ForgetIn
 		in := (*input)(inMsg.Consume(unsafe.Sizeof(input{})))
diff --git a/fuseops/ops.go b/fuseops/ops.go
index d09c690..03ab376 100644
--- a/fuseops/ops.go
+++ b/fuseops/ops.go
@@ -145,6 +145,9 @@ type SetInodeAttributesOp struct {
 	// The inode of interest.
 	Inode InodeID
 
+	// If set, this is ftruncate(2), otherwise it's truncate(2)
+	Handle *HandleID
+
 	// The attributes to modify, or nil for attributes that don't need a change.
 	Size  *uint64
 	Mode  *os.FileMode
diff --git a/samples/memfs/memfs.go b/samples/memfs/memfs.go
index 6cbb6bc..e0f2a5b 100644
--- a/samples/memfs/memfs.go
+++ b/samples/memfs/memfs.go
@@ -247,6 +247,12 @@ func (fs *memFS) SetInodeAttributes(
 	fs.mu.Lock()
 	defer fs.mu.Unlock()
 
+	if op.Size != nil && op.Handle == nil && *op.Size != 0 {
+		// require that truncate to non-zero has to be ftruncate()
+		// but allow open(O_TRUNC)
+		err = syscall.EBADF
+	}
+
 	// Grab the inode.
 	inode := fs.getInodeOrDie(op.Inode)