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Bypass i/o support query APIs
Dejan_Maksimovic
Member - All Emails Posts: 608
in NTFSD
Hello,
I am trying to query (via API) if both the filter and storage stacks support BypassIo.
However, when only the volume/storage don't support it (no NVMe disk), I get no failure in the API. Neither in the DIOC/FSCTL API return code nor the outputData.Query.Status. I tried using the file handle and the volume handle and also to send IOCTL and not FSCTL on a disk handle.
How do I make the query and get results like fsutil bypassio state does?
Regards, Dejan.
I am trying to query (via API) if both the filter and storage stacks support BypassIo.
However, when only the volume/storage don't support it (no NVMe disk), I get no failure in the API. Neither in the DIOC/FSCTL API return code nor the outputData.Query.Status. I tried using the file handle and the volume handle and also to send IOCTL and not FSCTL on a disk handle.
How do I make the query and get results like fsutil bypassio state does?
Regards, Dejan.
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Comments
Hi Dejan-
Fsutil uses the documented FSCTL_MANAGE_BYPASS_IO IOCTL to query BypassIO support for a given volume. Can you please post the output from
fsutil bypassio state <driveletter> /vfrom the system in question?Thanks in advance,
Dave Buches
Windows CoreFS Dev
This is the output:
BypassIo on "C:\Users\Dejan\Desktop" is supported.
Storage Type: SATA
Storage Driver: Not BypassIo Compatible
Driver Name: volmgr.sys
It is this volmgr.sys that I am curious about. Even BPIO enable IOCTL
succeeds on this system for a file, no errors at all. But obviously it
would not work.
Dejan.
Hi Dejan
There are a couple of things that are contributing to some confusion here.
The first is that the currently available documentation doesn't do a great job of explaining that it is possible to enable bypass-IO on a file hosted on a volume where the filter stack supports bypass-IO, but the underlying storage stack does not. In such a scenario (which I suspect is what you're seeing), reads for bypass-IO enabled files will bypass the filter stack, but still be sent down the volume stack. I will file a documentation bug to better explain this.
The second is that FsUtil wasn't providing much help in understanding this. This has been addressed with more recent builds of Windows (this is output from one of my machines running Windows 11 22H2):
Dave Buches
Windows CoreFS Dev
Thanks, that partially explains the output.
Which API/IOCTL can we use to query the volume stack for BPIO support? I
have tried using the BPIO query IOCTL (not FSCTL) but it does not fail
either.
Regards, Dejan.
Hi Dejan
If the volume stack supports BPIO, you should see the
FSBPIO_OUTFL_COMPATIBLE_STORAGE_DRIVERbit inFS_BPIO_OUTPUT::OutFlagsforFS_BPIO_OP_ENABLE, FS_BPIO_OP_QUERY, andFS_BPIO_OP_GET_INFOoperations.Dave Buches
Windows CoreFS Dev
Had to uninstall it and it works now fully.