virtio-fs cannot support "cargo bulid"

[XeCycle]

Running cargo build in a typical rust project on virtio-fs mount (something as simple as cargo new helloworld can reproduce it), will fail saying cannot canonicalize paths; mounting to a new drive letter or a junction point makes no difference. I tried cargo build --target-dir=C:\somewhere-else, same error. Seems rust tools insist on using paths with symlinks resolved, but the current implementation based on winfsp does not support that; cmake-based c++ projects work fine, in contrast, however only if build tree is not on virtio-fs. The opposite would fail, too, with some cryptic message I don't understand; no idea whether that's intended.

Versions:

• Windows 10
• virtiofsd as shipped with qemu 5.1.0, packaged by arch
• guest driver 0.1.189

<viofs/w10/amd64 $ ll
.r-xr-xr-x 9.3Ki xecycle 10 Aug 12:17 viofs.cat*
.r-xr-xr-x 2.4Ki xecycle 10 Aug  8:51 viofs.inf*
.r-xr-xr-x 956Ki xecycle 10 Aug  8:51 viofs.pdb*
.r-xr-xr-x  54Ki xecycle 10 Aug 12:17 viofs.sys*
.r-xr-xr-x 117Ki xecycle 10 Aug 12:18 virtiofs.exe*
.r-xr-xr-x 3.1Mi xecycle 10 Aug  8:51 virtiofs.pdb*
<viofs/w10/amd64 $ sha1sum *
2574e91a5d5f9cd4e28f871c90cac8140b0ed9b4  viofs.cat
85a3a16108ea5bf5032d2959e4b460aed3764ed1  viofs.inf
8993fce1cfc6bce7011f0d2d94b35d39076a2e28  viofs.pdb
9819cec611918f9b62500204cc25cdd2948c36a3  viofs.sys
313f7a0c5f8c22a85f5ffeeb567690e5a3d5775d  virtiofs.exe
a896ac7cfaeb7f1a5f93513517e1897d6d685baa  virtiofs.pdb

Btw. a simple test of fio fio-rand-RW.fio (basically the one from fio examples) says virtio-fs is slower than samba, in this random 4k read-write-mixed test. Do we intend to outperform samba?

[hammerg]

Thanks for trying virtio-fs for Windows. Are you sure the cargo failure is a result of unresolved symbolic links? Because at the moment symbolic links are not supported.

The performance comparison and optimization (if required ;-)) are planned after virtio-fs will be more stable and usable.

[XeCycle]

@hammerg Actually my paths contains no symlinks; somehow, if mounted to a junction point, that point looks like a symlink.

Example of error message when mounted at a drive letter (error is similar if on a junction point):

PS Z:\work\test\rust\hello> C:\Users\Administrator\.cargo\bin\cargo build --target-dir=C:\build\rshello                                                       
warning: could not canonicalize path: 'Z:\work\test\rust\hello'                                                                                               
warning: could not canonicalize path: 'Z:\work\test\rust\hello'                                                                                   
warning: could not canonicalize path: 'Z:\work\test\rust'                                                                                                     
warning: could not canonicalize path: 'Z:\work\test'                                                                                              
warning: could not canonicalize path: 'Z:\work'                                                                                                               
warning: could not canonicalize path: 'Z:\'                                                                                                       
   Compiling hello v0.1.0 (Z:\work\test\rust\hello)                                                                                                           
error: could not parse/generate dep info at: C:\build\rshello\debug\deps\hello.d                                                                              
                                                                                                                                                              
Caused by:
  此卷不包含可识别的文件系统。
  请确定所有请求的文件系统驱动程序已加载，且此卷未损坏。 (os error 1005)

and the error code is defined as:

ERROR_UNRECOGNIZED_VOLUME

1005 (0x3ED)

The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted.

[xiagao]

@XeCycle
We have a bug to track this issue in downstream, if there is process, I will update here.

[viktor-prutyanov]

Cargo is a Rust software. Rust's fs::canonicalize has problems with network drives and some filesystems:
rust-lang/rustup#682
rust-lang/rust#86447

This is how fs::canonicalize calls GetFinalPathNameByHandleW with VOLUME_NAME_DOS argument:
https://github.com/rust-lang/rust/blob/7be8693984d32d2f65ce9ded4f65b6b7340bddce/library/std/src/sys/windows/fs.rs#L875

Small sample with GetFinalPathNameByHandle with VOLUME_NAME_DOS invocation:
https://gist.github.com/viktor-prutyanov/1d8680f19e200d0079cb47bf8057bf4a

This is how it reacts to VirtIO-FS path:

PS C:\Users\Administrator\source\repos\GetPath\x64\Debug> .\GetPath.exe X:\testfile.txt
GetFinalPathNameByHandle (error 1005)

ERROR_UNRECOGNIZED_VOLUME (1005):
The volume does not contain a recognized file system. Please make sure that all required file system drivers are loaded and that the volume is not corrupted.

For example, output for NTFS path:

PS C:\Users\Administrator\source\repos\GetPath\x64\Debug> .\GetPath.exe C:\Windows\System32\notepad.exe
The final path is: \\?\C:\Windows\System32\notepad.exe

WinFSP MemFS shows exactly the same behaviour as VirtIO-FS does. Looks like it is WinFSP limitation.

By the way, GetFinalPathNameByHandle with VOLUME_NAME_NT works:

The final path is: \Device\Volume{60e35478-7719-11ec-b332-525400f94cb9}\testfile.txt

[viktor-prutyanov]

Hi @XeCycle,

According to winfsp/winfsp#410, to make GetFinalPathNameByHandle (and thus fs::canonicalize) work with WinFsp one can set mount point \\.\Z: instead of Z:.

For now, it can be done through registry: reg add HKLM\Software\VirtIO-FS /v MountPoint /d \\.\Z:

After that, cargo will work with VirtIO-FS:

Z:\>cargo new helloworld
     Created binary (application) `helloworld` package

Z:\>cd helloworld

Z:\helloworld>cargo run
   Compiling helloworld v0.1.0 (Z:\helloworld)
    Finished dev [unoptimized + debuginfo] target(s) in 0.67s
     Running `target\debug\helloworld.exe`
Hello, world!

[YanVugenfirer]

Hello All,

Please help us understanding you use cases for using virtio-fs, and thus make us virtio-fs support better.
Please participate in the discussion and add your use cases: #726

Thanks a lot,
Yan.

[XeCycle]

Thanks @viktor-prutyanov and @YanVugenfirer, I switched to smb last year and have not found time to verify this. Now that you have verified the fix I think we can just close this!