Re: [PATCH v2 5/6] state: backend_storage_direct: also use cached data on write

[Markus Pargmann <mpa@pengutronix.de>]

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On Tuesday 28 June 2016 08:55:32 Michael Grzeschik wrote:
> On Tue, Jun 28, 2016 at 08:18:47AM +0200, Sascha Hauer wrote:
> > On Fri, Jun 24, 2016 at 12:06:01PM +0200, Markus Pargmann wrote:
> > > From: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > > 
> > > Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
> > > Signed-off-by: Markus Pargmann <mpa@pengutronix.de>
> > > ---
> > >  common/state/backend_bucket_direct.c | 55 ++++++++++++++++++++++++++++++++++++
> > >  1 file changed, 55 insertions(+)
> > 
> > What's the problem this patch tries to solve?
> 
> The backend storage is writing the first correct bucket data it finds
> back to each copy. Therefor every bucket got written on every boot. Even
> if the content did not change. The direct backend was missing an cache
> that represent the current data in the buckets. This patch adds the
> cache and improves the bootup time on systems with direct bucket storage
> like eeproms.

I talked with Sascha. He suggested to use a separate cache that
implements caching for any bucket type. That would remove all the
caching code from bucket-direct and bucket-circular and make it simpler.

Best Regards,

Markus

> 
> Michael
> 
> > Sascha
> > 
> > > 
> > > diff --git a/common/state/backend_bucket_direct.c b/common/state/backend_bucket_direct.c
> > > index 08892f001e25..772267f6dc1d 100644
> > > --- a/common/state/backend_bucket_direct.c
> > > +++ b/common/state/backend_bucket_direct.c
> > > @@ -29,6 +29,10 @@ struct state_backend_storage_bucket_direct {
> > >  
> > >  	int fd;
> > >  
> > > +	/* Cached data of the last read/write */
> > > +	u8 *current_data;
> > > +	ssize_t current_data_len;
> > > +
> > >  	struct device_d *dev;
> > >  };
> > >  
> > > @@ -99,6 +103,29 @@ static int state_backend_bucket_direct_read(struct state_backend_storage_bucket
> > >  	return 0;
> > >  }
> > >  
> > > +
> > > +static int state_backend_bucket_direct_fill_cache(
> > > +		struct state_backend_storage_bucket *bucket)
> > > +{
> > > +	struct state_backend_storage_bucket_direct *direct =
> > > +	    get_bucket_direct(bucket);
> > > +	ssize_t read_len;
> > > +	uint8_t *buf;
> > > +	int ret;
> > > +
> > > +	ret = state_backend_bucket_direct_read(bucket, &buf, &read_len);
> > > +	if (ret < 0) {
> > > +		dev_err(direct->dev, "Failed to read from file, %d\n", ret);
> > > +		free(buf);
> > > +		return ret;
> > > +	}
> > > +
> > > +	direct->current_data = buf;
> > > +	direct->current_data_len = read_len;
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >  static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
> > >  					     *bucket, const uint8_t * buf,
> > >  					     ssize_t len)
> > > @@ -111,6 +138,11 @@ static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
> > >  	if (direct->max_size && len > direct->max_size)
> > >  		return -E2BIG;
> > >  
> > > +	/* Nothing in cache? Then read to see what is on the device currently */
> > > +	if (!direct->current_data) {
> > > +		state_backend_bucket_direct_fill_cache(bucket);
> > > +	}
> > > +
> > >  	ret = lseek(direct->fd, direct->offset, SEEK_SET);
> > >  	if (ret < 0) {
> > >  		dev_err(direct->dev, "Failed to seek file, %d\n", ret);
> > > @@ -119,6 +151,26 @@ static int state_backend_bucket_direct_write(struct state_backend_storage_bucket
> > >  
> > >  	meta.magic = direct_magic;
> > >  	meta.written_length = len;
> > > +
> > > +	/*
> > > +	 * If we would write the same data that is currently on the device, we
> > > +	 * can return successfully without writing.
> > > +	 * Note that the cache may still be empty if the storage is empty or
> > > +	 * errors occured.
> > > +	 */
> > > +	if (direct->current_data) {
> > > +		dev_dbg(direct->dev, "Comparing cached data, writing %zd bytes, cached %zd bytes\n",
> > > +			len, direct->current_data_len);
> > > +		if (len == direct->current_data_len &&
> > > +		    !memcmp(direct->current_data, buf, len)) {
> > > +			dev_dbg(direct->dev, "Data already on device, not writing again\n");
> > > +			return ret;
> > > +		} else {
> > > +			free(direct->current_data);
> > > +			direct->current_data = NULL;
> > > +		}
> > > +	}
> > > +
> > >  	ret = write_full(direct->fd, &meta, sizeof(meta));
> > >  	if (ret < 0) {
> > >  		dev_err(direct->dev, "Failed to write metadata to file, %d\n", ret);
> > > @@ -147,6 +199,9 @@ static void state_backend_bucket_direct_free(struct
> > >  	struct state_backend_storage_bucket_direct *direct =
> > >  	    get_bucket_direct(bucket);
> > >  
> > > +	if (direct->current_data)
> > > +		free(direct->current_data);
> > > +
> > >  	close(direct->fd);
> > >  	free(direct);
> > >  }
> > 
> 
> 

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