Examples get "permission denied" on macOS

[goldsborough]

I tried to run the examples from godoc.org for the go-fuse/v2/fs package on macOS but they failed pretty much out of the box for me. My steps:

1. brew cask install osxfuse
2. sudo reboot
3. mkdir x && go mod init example.com/x
4. Copy https://godoc.org/github.com/hanwen/go-fuse/fs#example-package--Dynamic into main.go
5. go mod vendor

go: finding module for package github.com/hanwen/go-fuse/v2/fs
go: finding module for package github.com/hanwen/go-fuse/v2/fuse
go: found github.com/hanwen/go-fuse/v2/fs in github.com/hanwen/go-fuse/v2 v2.0.3
go: found github.com/hanwen/go-fuse/v2/fuse in github.com/hanwen/go-fuse/v2 v2.0.3

5. go run main.go

2020/09/20 19:41:37 rx 2: INIT i0 {7.19 Ra 0x100000 ATOMIC_O_TRUNC,VOL_RENAME,CASE_INSENSITIVE,XTIMES,0x18000000}
2020/09/20 19:41:37 tx 2:     OK, {7.8 Ra 0x100000  0/0 Wr 0x10000 Tg 0x0}
2020/09/20 19:41:37 rx 3: STATFS i1
2020/09/20 19:41:37 rx 2: STATFS i1
2020/09/20 19:41:37 tx 3:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 tx 2:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 rx 3: STATFS i1
2020/09/20 19:41:37 tx 3:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 rx 2: STATFS i1
2020/09/20 19:41:37 tx 2:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 rx 3: STATFS i1
2020/09/20 19:41:37 tx 3:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 rx 2: STATFS i1
2020/09/20 19:41:37 tx 2:     OK, {blocks (0,0)/0 files 0/0 bs0 nl0 frs0}
2020/09/20 19:41:37 rx 3: ACCESS i1 {u=501 g=20 x}
2020/09/20 19:41:37 tx 3:     OK
2020/09/20 19:41:37 rx 2: LOOKUP i1 [".go-fuse-epoll-hack"] 20b
2020/09/20 19:41:37 tx 2:     2=no such file or directory, {i0 g0 tE=0s tA=0s {M00 SZ=0 L=0 0:0 0 0:0 A 0.000000 M 0.000000 C 0.000000}}
2020/09/20 19:41:37 rx 3: ACCESS i1 {u=501 g=20 w}
2020/09/20 19:41:37 tx 3:     13=permission denied
2020/09/20 19:41:37 permission denied
panic: permission denied

goroutine 1 [running]:
log.Panic(0xc00017fea8, 0x1, 0x1)
	/usr/local/Cellar/go/1.15/libexec/src/log/log.go:351 +0xae
main.main()
	/Users/goldsborough/Documents/Projects/x/main.go:118 +0x125
exit status 2

Interestingly, the unionfs example works. From what I can see it uses the old nodefs/pathfs APIs while the example above used the new fs API. Any thoughts on why the new API is resulting in permission errors?

More hints: It does work if I sudo go run main.go but then subsequently I can only access the mounted filesystem as root too. I also tried changing the directory from /tmp/ to a local folder and that made no difference.

[hanwen]

2020/09/20 19:41:37 rx 3: ACCESS i1 {u=501 g=20 w}
2020/09/20 19:41:37 tx 3:     13=permission denied

have you tried implementing the Access operation?

[hanwen]

oh, wait it's the example, so it should provide the access function.

[YoSev]

I can confirm running into the same problem on MacOS 10.15.6

[YoSev]

Adding the follwing solves the problem for me:

// Implement (handleless) Access
var _ = (fs.NodeAccesser)((*bytesNode)(nil))

func (bn *bytesNode) Access(ctx context.Context, input uint32) (errno syscall.Errno) {
	return 0
}

[hanwen]

sorry for the delay.

I had a closer look. So, for some reason OSX is checking access(W_OK), on mount ie.

2020/09/20 19:41:37 rx 3: ACCESS i1 {u=501 g=20 w}
2020/09/20 19:41:37 tx 3:     13=permission denied

that is actually correct, as the Dynamic example is not a writable filesystem. It's unclear to me why OSXFUSE insists on having a writable root for the mount directory.

[hanwen]

I had a brief look at the OSXFUSE project page on github, but with the project being taken closed-source, it's not clear where to report bugs. Is there someone here who could post the bugreport in the appropriate queue?