"Access denied" error with FUSE mountpoint created using a sample Dokany Fuse Windows program using MSVC by linking against "dokanfuse2.lib"

[dipujoseph-revenera]

Hi all,
I built a sample Dokany Fuse Windows program using Microsoft Visual C++ by linking against the "dokanfuse2.lib" file (taken from the "C:\Program Files\Dokan\Dokan Library-2.2.0\lib\dokanfuse2.lib" file which got installed as part of "Dokan Library 2.2.0.1000 Bundle").

Then started that sample program using the following command from Administrator-mode Command Prompt (in order to have "W:" as the FUSE mount-point):

.\DokanFuseTest2.exe w -oallow_root -oallow_other -s

I am able to see the "W:" drive but get an "Access denied" error while trying to go inside it. Please find attached the screen-shot.

Also, please find the source code of the sample Dokany Fuse Windows program in the "TestDokanFuse.cpp" file present inside the attached zip file -
DokanFuseTest2.zip
.

What could I be doing wrong?

Is linking against the "dokanfuse2.lib" file (using MSVC) supported?

Or, is it supported only with "cygdokanfuse2.dll" file along with the use of the following Cygwin DLLs?

cygwin1.dll
cygstdc++-6.dll
cyggcc_s-seh-1.dll

Please let me know. Any pointers will be much appreciated.

Thank you.

[Liryna]

Hi @dipujoseph-revenera ,

Have you been able to run the sample without changes ?
https://github.com/dokan-dev/dokany/blob/45021e00ec54e38b936620f339c8fb22c3f999d2/samples/fuse_mirror/fusexmp.c

Getting an "Access denied" error while trying to access it means somewhere in your implementation, you are either returning access denied (or similar) or there is an issue with the communication between your implementation and dokan (callbacks not called).
I would suggest adding logs to see what is happening and use Procmon to monitor the event status when accessing the drive.

Is linking against the "dokanfuse2.lib" file (using MSVC) supported?

yes it is

[dipujoseph-revenera]

Thank you very much @Liryna for responding (including confirmation of support for "dokanfuse2.lib" using MSVC) and for providing your valuable inputs.

I will check regarding the points you mentioned and get back to you soon (after the holiday weekend here in India).
Thank you!

[Liryna]

By the way if you are able to mount, it means the usage of the dokan library works but it is the communication after that has an issue

[dipujoseph-revenera]

Thanks @Liryna for the pointers.

I seem to be having problems with the communication between my implementation and Dokan.

What could be the possible reasons for communication issues?

[dipujoseph-revenera]

In "ProcMon", I see the following event (details pasted below) for the "Explorer.EXE" process while trying to access the drive mounted by the sample "fusexmp" program.

Date: 11/8/2024 3:51:39.4118759 PM
Thread: 81712
Class: File System
Operation: QueryRemoteProtocolInformation
Result: INVALID PARAMETER
Path: C:\Windows
Duration: 0.0000023

Does that give any indications?

Thank you.

[dipujoseph-revenera]

Hi @Liryna,
I ran the following command using the "fusexmp.exe" (built using the ".cpp" file in the attached zip file -
fusexmp.zip
):

C:\Dipu\fusexmp\fusexmp\fusexmp\x64\Debug>.\fusexmp.exe o -d -oallow_root -oallow_other -s > fusexmp.log 2>&1

C:\Dipu\fusexmp\fusexmp\fusexmp\x64\Debug>

Please find the generated debug log file ("fusexmp.log") in the attached zip file -
fusexmp_log.zip

The above-mentioned log file was saved after trying to access (go inside) the mounted drive using Windows Explorer.

Also, please note that the callback function "xmp_statfs()" did not get invoked anytime during the above-mentioned testing (confirmed using a separate debugging session with appropriate breakpoints set using the Visual Studio debugger).

Please let me know if the attached debug log file gives any info or pointers regarding what might be going wrong.

Thanks a lot, in advance, for your valuable inputs.

[dipujoseph-revenera]

The main issue was that the callback functions were getting called with Unix-style paths instead of Windows-style paths in the function arguments. Code was added in the callback functions to convert the Unix-style paths to Windows-style paths before using them in places where Windows-style paths were expected.
After this, the XXX_getattr() function and XXX_open() function are working as expected.

Thanks @Liryna for providing the required pointers.

The list of "Gotchas" from https://www.cs.hmc.edu/~geoff/classes/hmc.cs135.201109/homework/fuse/fuse_doc.html were also very helpful.