Writing to a file

[Diomidis Spinellis]

On May 5, 2007, at 9:34 PM, Sonja Milicic wrote:
> I'm working on an IO logging utility for FreeBSD as my GSoC  
> project, and
> I have some questions about writing a kernel functions that would open
> an existing or create a new file (with the file name as a parameter,
> returns a vnode * for the file) and write data to that file (with
> pointer to data as parameter). I've found some functions in existing
> code that do similar things and might help me understand how to  
> solve my
> problem, but as there isn't much documentation out there I still don't
> understand a lot of things. So, could anyone please give me a detailed
> explanation of how to open a file in kernel and write to it - best  
> data
> types to use, functions, what to look out for, maybe a link to  
> tutorial
> or manual that deals with this (if such a thing exists), etc.?

A good strategy for dealing with such questions is to look for code  
that does a task similar to the one you want to implement.  Two  
kernel subsystems that come to my mind is the kernel logging  
facility, which writes data to a user space process via a socket, and  
the process accounting facility, which writes data to an already  
opened file.  There are reasons (performance, flexibility) why these  
two facilities have been designed in this way, and it would be a good  
idea to see whether some of their design decisions are also  
applicable to your problem.

Diomidis Spinellis - http://www.spinellis.gr