Re: [PATCH] block: export SSD/non-rotational queue flag through sysfs

[Jens Axboe <jens.axboe@oracle.com>]

On Mon, Jan 05 2009, James Bottomley wrote:
> On Mon, 2009-01-05 at 20:02 +0100, Bartlomiej Zolnierkiewicz wrote:
> > On Monday 05 January 2009, Jens Axboe wrote:
> > > On Mon, Jan 05 2009, Bartlomiej Zolnierkiewicz wrote:
> > > > From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> > > > Subject: [PATCH] block: export SSD/non-rotational queue flag through sysfs
> > > > 
> > > > For some devices (i.e. CFA ATA) we can't reliably detect whether
> > > > the device is of rotational or non-rotational type so we need to
> > > > leave the final decision about this setting to the user-space.
> > > 
> > > I agree with that, was actually planning on doing that myself.
> > > 
> > > > @@ -146,8 +167,8 @@ static ssize_t queue_nomerges_store(stru
> > > >  		queue_flag_set(QUEUE_FLAG_NOMERGES, q);
> > > >  	else
> > > >  		queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
> > > > -
> > > >  	spin_unlock_irq(q->queue_lock);
> > > > +
> > > >  	return ret;
> > > >  }
> > > >  
> > > 
> > > Hmm?
> > 
> > This is just a "bonus". :)
> > 
> > > > @@ -210,6 +231,12 @@ static struct queue_sysfs_entry queue_hw
> > > >  	.show = queue_hw_sector_size_show,
> > > >  };
> > > >  
> > > > +static struct queue_sysfs_entry queue_nonrot_entry = {
> > > > +	.attr = {.name = "nonrot", .mode = S_IRUGO | S_IWUSR },
> > > > +	.show = queue_nonrot_show,
> > > > +	.store = queue_nonrot_store,
> > > > +};
> > > > +
> > > 
> > > Lets please use a better name for export reasons, non-rotational is a
> > > lot better. Nobody will know what nonrot means :-)
> > 
> > Yeah...
> > 
> > From: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> > Subject: [PATCH v2] block: export SSD/non-rotational queue flag through sysfs
> > 
> > For some devices (i.e. CFA ATA) we can't reliably detect whether
> > the device is of rotational or non-rotational type so we need to
> > leave the final decision about this setting to the user-space.
> > 
> > As a bonus do a minor CodingStyle fixup in queue_nomerges_store().
> > 
> > Suggested-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
> > Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
> > ---
> >  block/blk-sysfs.c |   30 +++++++++++++++++++++++++++++-
> >  1 file changed, 29 insertions(+), 1 deletion(-)
> > 
> > Index: b/block/blk-sysfs.c
> > ===================================================================
> > --- a/block/blk-sysfs.c
> > +++ b/block/blk-sysfs.c
> > @@ -130,6 +130,27 @@ static ssize_t queue_max_hw_sectors_show
> >  	return queue_var_show(max_hw_sectors_kb, (page));
> >  }
> >  
> > +static ssize_t queue_nonrot_show(struct request_queue *q, char *page)
> > +{
> > +	return queue_var_show(blk_queue_nonrot(q), page);
> > +}
> > +
> > +static ssize_t queue_nonrot_store(struct request_queue *q, const char *page,
> > +				  size_t count)
> > +{
> > +	unsigned long nm;
> > +	ssize_t ret = queue_var_store(&nm, page, count);
> > +
> > +	spin_lock_irq(q->queue_lock);
> > +	if (nm)
> > +		queue_flag_set(QUEUE_FLAG_NONROT, q);
> > +	else
> > +		queue_flag_clear(QUEUE_FLAG_NONROT, q);
> > +	spin_unlock_irq(q->queue_lock);
> > +
> > +	return ret;
> > +}
> > +
> >  static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
> >  {
> >  	return queue_var_show(blk_queue_nomerges(q), page);
> > @@ -146,8 +167,8 @@ static ssize_t queue_nomerges_store(stru
> >  		queue_flag_set(QUEUE_FLAG_NOMERGES, q);
> >  	else
> >  		queue_flag_clear(QUEUE_FLAG_NOMERGES, q);
> > -
> >  	spin_unlock_irq(q->queue_lock);
> > +
> >  	return ret;
> >  }
> >  
> > @@ -210,6 +231,12 @@ static struct queue_sysfs_entry queue_hw
> >  	.show = queue_hw_sector_size_show,
> >  };
> >  
> > +static struct queue_sysfs_entry queue_nonrot_entry = {
> > +	.attr = {.name = "non-rotational", .mode = S_IRUGO | S_IWUSR },
> > +	.show = queue_nonrot_show,
> > +	.store = queue_nonrot_store,
> > +};
> > +
> >  static struct queue_sysfs_entry queue_nomerges_entry = {
> >  	.attr = {.name = "nomerges", .mode = S_IRUGO | S_IWUSR },
> >  	.show = queue_nomerges_show,
> > @@ -229,6 +256,7 @@ static struct attribute *default_attrs[]
> >  	&queue_max_sectors_entry.attr,
> >  	&queue_iosched_entry.attr,
> >  	&queue_hw_sector_size_entry.attr,
> > +	&queue_nonrot_entry.attr,
> >  	&queue_nomerges_entry.attr,
> >  	&queue_rq_affinity_entry.attr,
> >  	NULL,
> 
> Almost all block devices might find this useful.  Ought not this flag to
> be in the block layer appearing under /sys/block/<dev>?

The block layer only uses it for scheduling purposes, in which case it
fits well in queue/ since you need the io scheduler.

-- 
Jens Axboe