linux-kernel - Re: [PATCH 3/3] relay

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Date:	Tue, 23 Sep 2008 22:57:50 -0500
From:	Tom Zanussi <zanussi@...cast.net>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	a.p.zijlstra@...llo.nl, prasad@...ux.vnet.ibm.com,
	mbligh@...gle.com, linux-kernel@...r.kernel.org,
	torvalds@...ux-foundation.org, tglx@...utronix.de,
	compudj@...stal.dyndns.org, rostedt@...dmis.org, od@...ell.com,
	fche@...hat.com, hch@....de, dwilder@...ibm.com
Subject: Re: [PATCH 3/3] relay - add channel flags

Thanks for the comments on these patches - I'll include the changes in
the next go-round.

On Tue, 2008-09-23 at 13:20 -0700, Andrew Morton wrote:
> On Tue, 23 Sep 2008 00:27:56 -0500
> Tom Zanussi <zanussi@...cast.net> wrote:
> 
> > Add channel flags to relay, remove global callback param.
> >     
> > relay should probably have had a flags param from the beginning; it
> > wasn't originally added because it wasn't originally needed - it
> > probably would have helped avoid some of the callback contortions
> > that were added due to a lack of flags.  This adds them and does a
> > small amount of low-hanging cleanup, and is also in preparation for
> > some new flags in future patches.
> > 
> > Signed-off-by: Tom Zanussi <tzanussi@...il.com>
> > 
> > diff --git a/block/blktrace.c b/block/blktrace.c
> > index eb9651c..150c5f7 100644
> > --- a/block/blktrace.c
> > +++ b/block/blktrace.c
> > @@ -356,8 +356,7 @@ static int blk_remove_buf_file_callback(struct dentry *dentry)
> >  static struct dentry *blk_create_buf_file_callback(const char *filename,
> >  						   struct dentry *parent,
> >  						   int mode,
> > -						   struct rchan_buf *buf,
> > -						   int *is_global)
> > +						   struct rchan_buf *buf)
> >  {
> >  	return debugfs_create_file(filename, mode, parent, buf,
> >  					&relay_file_operations);
> > @@ -424,7 +423,7 @@ int do_blk_trace_setup(struct request_queue *q, char *name, dev_t dev,
> >  		goto err;
> >  
> >  	bt->rchan = relay_open("trace", dir, buts->buf_size,
> > -				buts->buf_nr, &blk_relay_callbacks, bt);
> > +			       buts->buf_nr, &blk_relay_callbacks, bt, 0UL);
> >  	if (!bt->rchan)
> >  		goto err;
> >  
> > diff --git a/include/linux/relay.h b/include/linux/relay.h
> > index 52e4d61..18fd269 100644
> > --- a/include/linux/relay.h
> > +++ b/include/linux/relay.h
> > @@ -25,7 +25,13 @@
> >  /*
> >   * Tracks changes to rchan/rchan_buf structs
> >   */
> > -#define RELAYFS_CHANNEL_VERSION		7
> > +#define RELAYFS_CHANNEL_VERSION		8
> 
> What is the significance of this change?  Does it affect the
> kernel<->userspace interface?  Is it back-compatible with existing
> userspace?
> 

No, nothing to do with the kernel-userspace interface.  The channel
version is included in the channel struct and was meant as an aid in
deciphering channel data in crash dumps.

Tom

> 
> > +/*
> > + * relay channel flags
> > + */
> > +#define RCHAN_MODE_OVERWRITE		0x00000001	/* 'flight' mode */
> > +#define RCHAN_GLOBAL_BUFFER		0x00000002	/* not using per-cpu */
> >  
> >
> > ...
> >
> > @@ -480,7 +478,7 @@ static struct rchan_buf *relay_open_buf(struct rchan *chan, unsigned int cpu)
> >   	buf->cpu = cpu;
> >   	__relay_reset(buf, 1);
> >  
> > - 	if(chan->is_global) {
> > +	if(chan->flags & RCHAN_GLOBAL_BUFFER) {
> 	
> Please use checkpatch.  It's a little thing, but it's so easy to fix..
> 
> >   		chan->buf[0] = buf;
> >   		buf->cpu = 0;
> >    	}
> >
> > ...

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