Windows System Software -- Consulting, Training, Development -- Unique Expertise, Guaranteed Results

Sept/Oct 2019 Issue of The NT Insider available

Download PDF here:

It’s a particularly BIG issue, too: 40 pages of technical goodness, ranging from WDF to Minifilters. Check it out.
Before Posting...
Please check out the Community Guidelines in the Announcements and Administration Category.


Jorgen_LundmanJorgen_Lundman Member - All Emails Posts: 47

Real basic question here, my apologies. So when I get IRP_MJ_CREATE with NULL name, and NULL relativeObject, it is known as a "volume open".

I used to simply grab the root "\" object, and return that. But this is causing some issues, in that I now have two Fileobjects with FsContext pointing to one vnode of "\". (Open of literal "\" and volume open).

So, what IS a volume open anyway? What operations is generally performed on a volume handle? Are read/writes done, and if so, what data is expected? Is it perhaps like opening the raw disk? (then, why not just open the disk, instead of via the filesystem)


  • Scott_Noone_(OSR)Scott_Noone_(OSR) Administrator Posts: 3,173

    A volume is a logical grouping of one or more partitions. So, opening the disk is not equivalent.

    Yes, you can read and write the volume (e.g. this is how format works). Normally you see queries for volume level information (free space, etc) but there are a bunch other requests that require a volume handle (defrag comes to mind). The FASTFAT source should give you a good baseline of what the file system is supposed to do with a volume open. Note that there are some special semantics around what it means to open a volume with no share. Again see FASTFAT.


  • Jorgen_LundmanJorgen_Lundman Member - All Emails Posts: 47

    "A volume is a logical grouping of one or more partitions." that sounds almost like opening the raw device on Unix, as opposed to a slice/partition.

    Following the thread of Volume Open in FASTFAT sources was not easy, but I will attempt it again. I guess I need to decide what to do with Volume Opens in ZFS, since there isn't (always) a single physical device under the mount (mirror/raids) but it does sound that, besides the disk-size requests and similar things, I can just return zero data on READ requests, and "make up" correctish looking partitions for the dataset that is open. I don't anticipate working with defrag or format.

Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!

Upcoming OSR Seminars
Writing WDF Drivers 21 Oct 2019 OSR Seminar Space & ONLINE
Internals & Software Drivers 18 Nov 2019 Dulles, VA
Kernel Debugging 30 Mar 2020 OSR Seminar Space
Developing Minifilters 27 Apr 2020 OSR Seminar Space & ONLINE