IOException *Invalid function* unless I wait a bit before accessing a file

[lostmsu]

I am guessing same as ERROR_INVALID_FUNCTION code 1 Windows System Error. Shows as "INVALID DEVICE REQUEST" in procmon.

This does not happen on Mirror (at least not with trivial repro steps), but does happen on my overlay FS that combines another read-only FS with a regular directory where any writes go.

I try to read a file immediately after mounting the FS (DokanInstanceBuilder.Build call). CreateFile succeeds, but ReadFile fails with this error according to procmon and the IOException. Roughly, the code is:

var dokanInstance = builder.Build(fs);
await using var stream = new FileInfo(path).OpenRead();
await JsonSerializer.DeserializeAsync<SomeClass>(stream, cancel)
                    .ConfigureAwait(false)!;
                    // IOException: Incorrect function

The funky thing is: during this time neither CreateFile nor ReadFile breakpoints in my FS are hit.

Now if I add a 15 seconds delay after mounting, the call succeeds, and my breakpoints in CreateFile and ReadFile also get hit.

var dokanInstance = builder.Build(fs);
await Task.Delay(TimeSpan.FromSeconds(15)).ConfigureAwait(false);
await using var stream = new FileInfo(path).OpenRead();
await JsonSerializer.DeserializeAsync<SomeClass>(stream)
                    .ConfigureAwait(false)!;
                    // OK

Procmon trace: IncorrectFunction.zip

[lostmsu]

UPD.: While failures occur, there are no logs from CreateFileProxy. If I continue retrying, the first one shows up and then everything since that point succeeds.

[LTRData]

You need to wait until the drive is ready. I usually do that in a loop similar to this:

var driveInfo = new DriveInfo(mountPoint);
while (!driveInfo.IsReady)
{
    await Task.Delay(500);
}

[lostmsu]

Does this work for mount points that are directories (as opposed to drives)? AFAIR DriveInfo will only use the drive portion of mountPoint.

UPD. I checked, it does not. IsReady just does Directory.Exists.

[LTRData]

That's correct unfortunately. You would need to find another way for directory mount points. For example, try to enumerate files in the mount points directory. That will throw an exception until it is ready.

Or, try another approach and let your file system implementation notify when it gets first calls and know that way that it is ready.

[lostmsu]

I created https://github.com/dokan-dev/dokan-dotnet/issues/357 because I think this behavior is surprising.