[FUSE API] Hardlink count from st_nlink is not propagated

[mhx]

Bug Report

I believe this is a bug (or missing feature) in the WinFsp FUSE API. It seems that the hardlink count returned from a getattr call isn't propagated to the Windows filesystem layer (i.e. nNumberOfLinks in BY_HANDLE_FILE_INFORMATION always reads 1).

How to Reproduce

Use a filesystem that returns st_nlink > 1 in getattr. Checking with the stat tool I can see that two files share the same inode, but each of them has their link count reported as 1 (even though st_nlink is actually 3):

C:\Users\mhx\git\dwarfs\build-vcpkg\tmp>stat format.sh
  File: format.sh
  Size: 94              Blocks: 4          IO Block: 65536  regular file
Device: 13b1fae8h/330431208d    Inode: 31          Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (197608/     mhx)   Gid: (197121/    None)
Access: 2020-11-24 23:14:05.000000000 +0100
Modify: 2020-11-24 23:14:05.000000000 +0100
Change: 2020-11-24 23:14:05.000000000 +0100
 Birth: -

C:\Users\mhx\git\dwarfs\build-vcpkg\tmp>stat foo\1\fmt.sh
  File: foo\1\fmt.sh
  Size: 94              Blocks: 4          IO Block: 65536  regular file
Device: 13b1fae8h/330431208d    Inode: 31          Links: 1
Access: (0755/-rwxr-xr-x)  Uid: (197608/     mhx)   Gid: (197121/    None)
Access: 2020-11-24 23:14:05.000000000 +0100
Modify: 2020-11-24 23:14:05.000000000 +0100
Change: 2020-11-24 23:14:05.000000000 +0100
 Birth: -

At the same time, logging from the getattr operation shows that st_nlink is returned as 3:

The service dwarfs has been started.
I 19:18:53.286122 op_getattr(/) -> st_nlink = 1
I 19:18:53.295476 op_getattr(/) -> st_nlink = 1
I 19:18:57.275441 op_getattr(/) -> st_nlink = 1
I 19:18:57.284256 op_getattr(/) -> st_nlink = 1
I 19:18:57.292798 op_getattr(/) -> st_nlink = 1
I 19:18:57.305563 op_getattr(/test.py) -> st_nlink = 1
I 19:18:57.316398 op_getattr(/perl-exec.sh) -> st_nlink = 1
I 19:18:57.321562 op_getattr(/format.sh) -> st_nlink = 3
I 19:18:57.327337 op_getattr(/foobar) -> st_nlink = 1
I 19:18:57.330381 op_getattr(/foo) -> st_nlink = 1
I 19:18:57.332785 op_getattr(/foo/bar) -> st_nlink = 1
I 19:18:57.334925 op_getattr(/foo) -> st_nlink = 1
I 19:18:57.337009 op_getattr(/empty) -> st_nlink = 1
I 19:18:57.338977 op_getattr(/dev) -> st_nlink = 1
I 19:18:57.340728 op_getattr(/bench.sh) -> st_nlink = 3
I 19:18:57.349516 op_getattr(/) -> st_nlink = 1
I 19:18:57.351154 op_getattr(/) -> st_nlink = 1
I 19:18:57.362641 op_getattr(/) -> st_nlink = 1
I 19:18:57.364635 op_getattr(/) -> st_nlink = 1
I 19:18:57.371488 op_getattr(/format.sh) -> st_nlink = 3
I 19:18:57.373200 op_getattr(/format.sh) -> st_nlink = 3
I 19:18:57.376306 op_getattr(/format.sh) -> st_nlink = 3
I 19:18:57.377897 op_getattr(/format.sh) -> st_nlink = 3
I 19:18:57.379452 op_getattr(/format.sh) -> st_nlink = 3
I 19:19:00.475283 op_getattr(/) -> st_nlink = 1
I 19:19:00.483435 op_getattr(/) -> st_nlink = 1
I 19:19:00.494293 op_getattr(/) -> st_nlink = 1
I 19:19:00.506619 op_getattr(/test.py) -> st_nlink = 1
I 19:19:00.513854 op_getattr(/perl-exec.sh) -> st_nlink = 1
I 19:19:00.520416 op_getattr(/format.sh) -> st_nlink = 3
I 19:19:00.523694 op_getattr(/foobar) -> st_nlink = 1
I 19:19:00.526209 op_getattr(/foo) -> st_nlink = 1
I 19:19:00.528573 op_getattr(/foo/bar) -> st_nlink = 1
I 19:19:00.530738 op_getattr(/foo) -> st_nlink = 1
I 19:19:00.532787 op_getattr(/empty) -> st_nlink = 1
I 19:19:00.535353 op_getattr(/dev) -> st_nlink = 1
I 19:19:00.537032 op_getattr(/bench.sh) -> st_nlink = 3
I 19:19:00.544552 op_getattr(/) -> st_nlink = 1
I 19:19:00.546592 op_getattr(/) -> st_nlink = 1
I 19:19:00.557711 op_getattr(/) -> st_nlink = 1
I 19:19:00.559188 op_getattr(/) -> st_nlink = 1
I 19:19:00.567073 op_getattr(/foo/1/fmt.sh) -> st_nlink = 3
I 19:19:00.568609 op_getattr(/foo) -> st_nlink = 1
I 19:19:00.570069 op_getattr(/foo/1) -> st_nlink = 1
I 19:19:00.571452 op_getattr(/foo/1/fmt.sh) -> st_nlink = 3
I 19:19:00.573116 op_getattr(/foo/1/fmt.sh) -> st_nlink = 3
I 19:19:00.574943 op_getattr(/foo) -> st_nlink = 1
I 19:19:00.576228 op_getattr(/foo/1) -> st_nlink = 1
I 19:19:00.578614 op_getattr(/foo/1/fmt.sh) -> st_nlink = 3
I 19:19:00.580114 op_getattr(/foo/1/fmt.sh) -> st_nlink = 3

Behaviors

I'd expect stat to report the correct hardlink count.

Environment

• OS version and build: 10.0.22621
• WinFsp version and build: 2.0.23075

[billziss-gh]

WinFsp does not support hard links. Please see NTFS Compatibility / Unsupported features.

Related #28