Re: How can I force a read to hit the disk?

[Alan Stern]

On Tue, 9 Sep 2003, Richard B. Johnson wrote:

> On Mon, 8 Sep 2003, Alan Stern wrote:
> 
> > > When your thread code starts up, execute
> > >                 init_rwsem(&current->mm->mmap_sem);
> > >
> > > ... This is in the thread's code, not the module init code.
> >
> > That doesn't work either; it also causes a segmentation violation.  As I
> > said before, current->mm is NULL.  It gets set that way by exit_mm() which
> > is called from daemonize().
> >
> > Alan Stern
> >
> 
> Gawd. I assumed you knew how to initialize a pointer. I just
> located the procedure used to initialize the semaphore.

Shucks, I know how to initialize a pointer.  I even know how to initialize
a read-write semaphore.  The problem here is not _doing_ the
initialization; it's what _value_ to use.  Kernel threads don't have a
userpace memory component, so naturally current->mm is NULL -- there's no
memory map for it to point to.  Without having a memory map, of course
there's no semaphore to initialize, since the semaphore is _part_ of the 
memory map structure.

Alan Stern

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