nodefs API: cannot implement chgrp

[rfjakob]

chgrp(1) actually calls chown(2) with owner set to -1.

Right now, the nodefs code does not handle chgrp at all, but that could be fixed easily. The real problem is that the parameters for Node.Chown() are defined as uint32 instead of int as for syscall.Chown()

How to fix this? Pass 0xFFFFFFFF instead of -1 ?

[rfjakob]

This should do it. If you agree I will submit it together with a test case for loopbackfs.

diff --git a/fuse/nodefs/fsops.go b/fuse/nodefs/fsops.go
index 459b75c..4c3120d 100644
--- a/fuse/nodefs/fsops.go
+++ b/fuse/nodefs/fsops.go
@@ -201,7 +201,15 @@ func (c *rawBridge) SetAttr(input *fuse.SetAttrIn, out *fuse.AttrOut) (code fuse
                code = node.fsInode.Chmod(f, permissions, &input.Context)
        }
        if code.Ok() && (input.Valid&(fuse.FATTR_UID|fuse.FATTR_GID) != 0) {
-               code = node.fsInode.Chown(f, uint32(input.Uid), uint32(input.Gid), &input.Context)
+               var uid uint32 = ^uint32(0) // means "don't care" in chown(2)
+               var gid uint32 = ^uint32(0)
+               if input.Valid&fuse.FATTR_UID != 0 {
+                       uid = input.Uid
+               }
+               if input.Valid&fuse.FATTR_GID != 0 {
+                       gid = input.Gid
+               }
+               code = node.fsInode.Chown(f, uid, gid, &input.Context)
        }
        if code.Ok() && input.Valid&fuse.FATTR_SIZE != 0 {
                code = node.fsInode.Truncate(f, input.Size, &input.Context)