On Sun, 22 Feb 2004, Chris Bergmann wrote:
Greets,
I've been trying to open/read/write/etc a file from within a KEXT,
This is generally considered to be a *bad* idea.
using the vnode interface. I keep running myself into locking trouble
because I lack a thorough understanding of the correct procedures for
dealing with vnodes. I've tried a few different solutions, however
(apart from the odd case where it "just worked" for a while) they all
end up either deadlocking the vfs or causing a (locking-related) panic.
Generally if you need to read/write to files from a KEXT in mass, you use the IOKit messages or sockets or sysctl depending on what you're doing to a user daemon to do file IO.
As a basic background to where i'm coming from- I've converted Apple's
HFS+ code to compile with C++ and made the necessary modifications to
run as a KEXT; now i'm trying to create some additional "system" files.
I'm baffled why you converted this to C++, file systems are not IOKit objects, and are generally C only entities.
Apple's existing system files (extents tree, etc) are treated rather
specially by the filesystem and I don't want to go down the same path-
instead I would like to open a file in much the same way as a userland
process would (except using the vfs directly since i'm in a KEXT.)
This is generally considered a bad thing to do. The locking issues are complex in a file system and you can easily bypass a lot of the locking rules by accessing these functions out of context. Its incredably easy to leave a vnode locked somewhere and not have the system panic till much later on.
I'm looking for any suggestions on how to go about this task.. or any
good references such as books describing the usage of the vfs would be
great (i purchased McKusick's 4.4 BSD OS book but it's not overly
helpful in this area.) Pointers to existing source from which I can
learn by example would also be helpful.
What are you trying to accomplish anyways? If you really are trying to add another file to the "special" area of HFS+ in CNID's 2 though 15 then I'd imagine you'd probably have to make your own HFS+ file system and build that into a new kernel, or try to make it a loadable file system and put it at a higher priority for HFS in the filesystem bundles. Either way this can get quite annoying pretty quickly. --- Marek Kozubal marek@portents.com _______________________________________________ darwin-kernel mailing list | darwin-kernel@lists.apple.com Help/Unsubscribe/Archives: http://www.lists.apple.com/mailman/listinfo/darwin-kernel Do not post admin requests to the list. They will be ignored.