Driver development question

[Chris Harrer]

Hi John,

Sorry for top posting...

I put a delay in my thread waiting for rootvnode to be set and I'm able to
create a file now.

Thanks!

Chris

-----Original Message-----
From: Chris Harrer [mailto:cjharrer at comcast.net] 
Sent: Wednesday, July 29, 2009 2:51 PM
To: 'Chris Harrer'; 'John Baldwin'
Cc: 'Alfred Perlstein'; 'freebsd-drivers at freebsd.org'
Subject: RE: Driver development question

>The problem is that kernel threads do not have a valid file descriptor
table, 
>hence fd_cdir is NULL.  You could work around this if you create a
dedicated 
>kproc and set fd_cdir to rootvnode (but vref() rootvnode when you do this).

>You should also set fd_rdir and fd_jdir to rootvnode as well (also doing 
>appropriate vref() of rootvnode for each reference).  Something like this:
>
>	struct filedesc *fdp;
>
>	fdp = curthread->td_proc->p_fd;
>	FILEDESC_XLOCK(fdp);
>	fd->fd_rdir = rootvnode;
>	vref(rootvnode);
>	fd->fd_jdir = rootvnode;
>	vref(rootvnode);
>	fd->fd_cdir = rootvnode;
>	vref(rootvnode);
>	FILEDESC_XUNLOCK(fdp);
>
>You should not do this from a callout routine or interrupt handler however.

>You could do this via a TASK to a private taskqueue with a dedicated kernel

>process however.  (i.e. queue a task that does the above during after 
>creating the taskqueue and then queue a task to create the file later).
>
>-- 
>John Baldwin

Hi John,

I tried this and rootvnode = 0x0, so I am still getting a SIGSEGV.  I create
a thread in my "attach" routine via:

	status = kproc_create(sxg_dump_thread, adapter, &adapter->dumpproc,
RFNOWAIT , 0, "sxgdump");
	if (status) {
		SXG_DBG_MSG(adapter->dev, "%s[%p], Cannot create dump
thread, status: %d\n",
					__func__, adapter, status);
		return (status);
	}

Then my thread does:

static void
sxg_dump_thread(void * arg)
{
	adapter_t		*adapter = (adapter_t *)arg;
	struct filedesc	*fdp;
	ulong32			index = 0;

	// Set up some file descriptor stuff so we can
	// actually open/create a dump file.  Kernel 
	// threads, by design, do not have a valid
	// file descriptor table.  So, we're gonna
	// make this thread point to one!
	fdp = curthread->td_proc->p_fd;
	FILEDESC_XLOCK(fdp);
	fdp->fd_rdir = rootvnode;
	vref(rootvnode);       <----- SIGSEGV on this line, rootvnode = 0x0
	fdp->fd_jdir = rootvnode;
	vref(rootvnode);
	fdp->fd_cdir = rootvnode;
	vref(rootvnode);
	FILEDESC_XUNLOCK(fdp);
	for (;;){
		...

Sorry if I'm doing something obviously wrong, I'm trying to come up to speed
as quickly as I can.

Cheers,

Chris