how to properly wait for completion of NtCreateFile/etc?

Question

I am using native NT API in my application to access files (NtCreateFile/etc). In order to avoid dealing with STATUS_PENDING I am using FILE_SYNCHRONOUS_IO_NONALERT flag when opening related file. So, opening file looks like this:

UNICODE_STRING fname = toNtUnicode(ntpath);

OBJECT_ATTRIBUTES oa;
InitializeObjectAttributes(&oa, &fname, 0, at.handle(), NULL);

HANDLE h;
IO_STATUS_BLOCK io_status;
NTSTATUS r = NtOpenFile(&h, GENERIC_READ|SYNCHRONIZE, &oa, &io_status, 
    FILE_SHARE_READ, FILE_SYNCHRONOUS_IO_NONALERT|FILE_DIRECTORY_FILE);
if (r != STATUS_SUCCESS)
    ...; // error handling

Unfortunately, it causes kernel to serialize all operations on given handle. I.e. if I try to execute multiple reads in parallel (using multiple threads) -- only one request will be processed at any point in time.

I could get rid of serialization:

HANDLE h;
IO_STATUS_BLOCK io_status;
NTSTATUS r = NtOpenFile(&h, GENERIC_READ|SYNCHRONIZE, &oa, &io_status, 
    FILE_SHARE_READ, FILE_DIRECTORY_FILE);
if (r == STATUS_PENDING)
    ...; // what to do here???

but how exactly should I wait for completion -- WaitForSingleObject() on file handle? As far as I know it can change to signaled state due to many reasons -- is there any way to tell that my open file (or dir) operation completed?

Similarly, if I submit multiple reads (from multiple threads) -- how can I tell which one (if any) has finished?

Answer 1

NtOpenFile is synchronous api. it never return STATUS_PENDING to you. even if driver return STATUS_PENDING for IRP_MJ_CREATE i/o sub-system will be wait for IRP complete

https://github.com/Zer0Mem0ry/ntoskrnl/blob/master/Io/iomgr/parse.c#L1404

so you never need check for STATUS_PENDING after NtOpenFile and never need wait (and in principle we can not wait here - we yet not have file handle -so can not wait on it or bind it to say IOCP. we not pass any event or another callback mechanism for NtOpenFile)