Re: [resend PATCH v2 08/33] dcssblk: add dax_operations support

[Gerald Schaefer]

On Mon, 17 Apr 2017 12:09:32 -0700
Dan Williams <dan.j.williams@xxxxxxxxx> wrote:

> Setup a dax_dev to have the same lifetime as the dcssblk block device
> and add a ->direct_access() method that is equivalent to
> dcssblk_direct_access(). Once fs/dax.c has been converted to use
> dax_operations the old dcssblk_direct_access() will be removed.
> 
> Cc: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>  drivers/s390/block/Kconfig   |    1 +
>  drivers/s390/block/dcssblk.c |   54 +++++++++++++++++++++++++++++++++++-------
>  2 files changed, 46 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/s390/block/Kconfig b/drivers/s390/block/Kconfig
> index 4a3b62326183..0acb8c2f9475 100644
> --- a/drivers/s390/block/Kconfig
> +++ b/drivers/s390/block/Kconfig
> @@ -14,6 +14,7 @@ config BLK_DEV_XPRAM
> 
>  config DCSSBLK
>  	def_tristate m
> +	select DAX
>  	prompt "DCSSBLK support"
>  	depends on S390 && BLOCK
>  	help
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index 415d10a67b7a..682a9eb4934d 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -18,6 +18,7 @@
>  #include <linux/interrupt.h>
>  #include <linux/platform_device.h>
>  #include <linux/pfn_t.h>
> +#include <linux/dax.h>
>  #include <asm/extmem.h>
>  #include <asm/io.h>
> 
> @@ -30,8 +31,10 @@ static int dcssblk_open(struct block_device *bdev, fmode_t mode);
>  static void dcssblk_release(struct gendisk *disk, fmode_t mode);
>  static blk_qc_t dcssblk_make_request(struct request_queue *q,
>  						struct bio *bio);
> -static long dcssblk_direct_access(struct block_device *bdev, sector_t secnum,
> +static long dcssblk_blk_direct_access(struct block_device *bdev, sector_t secnum,
>  			 void **kaddr, pfn_t *pfn, long size);
> +static long dcssblk_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> +		long nr_pages, void **kaddr, pfn_t *pfn);
> 
>  static char dcssblk_segments[DCSSBLK_PARM_LEN] = "\0";
> 
> @@ -40,7 +43,11 @@ static const struct block_device_operations dcssblk_devops = {
>  	.owner   	= THIS_MODULE,
>  	.open    	= dcssblk_open,
>  	.release 	= dcssblk_release,
> -	.direct_access 	= dcssblk_direct_access,
> +	.direct_access 	= dcssblk_blk_direct_access,
> +};
> +
> +static const struct dax_operations dcssblk_dax_ops = {
> +	.direct_access = dcssblk_dax_direct_access,
>  };
> 
>  struct dcssblk_dev_info {
> @@ -57,6 +64,7 @@ struct dcssblk_dev_info {
>  	struct request_queue *dcssblk_queue;
>  	int num_of_segments;
>  	struct list_head seg_list;
> +	struct dax_device *dax_dev;
>  };
> 
>  struct segment_info {
> @@ -389,6 +397,8 @@ dcssblk_shared_store(struct device *dev, struct device_attribute *attr, const ch
>  	}
>  	list_del(&dev_info->lh);
> 
> +	kill_dax(dev_info->dax_dev);
> +	put_dax(dev_info->dax_dev);
>  	del_gendisk(dev_info->gd);
>  	blk_cleanup_queue(dev_info->dcssblk_queue);
>  	dev_info->gd->queue = NULL;
> @@ -525,6 +535,7 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
>  	int rc, i, j, num_of_segments;
>  	struct dcssblk_dev_info *dev_info;
>  	struct segment_info *seg_info, *temp;
> +	struct dax_device *dax_dev;
>  	char *local_buf;
>  	unsigned long seg_byte_size;
> 
> @@ -654,6 +665,11 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
>  	if (rc)
>  		goto put_dev;
> 
> +	dax_dev = alloc_dax(dev_info, dev_info->gd->disk_name,
> +			&dcssblk_dax_ops);
> +	if (!dax_dev)
> +		goto put_dev;
> +

The returned dax_dev should be stored into dev_info->dax_dev, for later use
by kill/put_dax(). This can also be done directly, so that we don't need the
local dax_dev variable here.

Also, in the error case, a proper rc should be set before going to put_dev,
probably -ENOMEM.

I took a quick look at the patches for the other affected drivers, and it
looks like axonram also has the "missing rc" issue, and brd the "missing
brd->dax_dev init" issue, pmem seems to be fine.

>  	get_device(&dev_info->dev);
>  	device_add_disk(&dev_info->dev, dev_info->gd);
> 
> @@ -752,6 +768,8 @@ dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const ch
>  	}
> 
>  	list_del(&dev_info->lh);
> +	kill_dax(dev_info->dax_dev);
> +	put_dax(dev_info->dax_dev);
>  	del_gendisk(dev_info->gd);
>  	blk_cleanup_queue(dev_info->dcssblk_queue);
>  	dev_info->gd->queue = NULL;
> @@ -883,21 +901,39 @@ dcssblk_make_request(struct request_queue *q, struct bio *bio)
>  }
> 
>  static long
> -dcssblk_direct_access (struct block_device *bdev, sector_t secnum,
> +__dcssblk_direct_access(struct dcssblk_dev_info *dev_info, pgoff_t pgoff,
> +		long nr_pages, void **kaddr, pfn_t *pfn)
> +{
> +	resource_size_t offset = pgoff * PAGE_SIZE;
> +	unsigned long dev_sz;
> +
> +	dev_sz = dev_info->end - dev_info->start + 1;
> +	*kaddr = (void *) dev_info->start + offset;
> +	*pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset), PFN_DEV);
> +
> +	return (dev_sz - offset) / PAGE_SIZE;
> +}
> +
> +static long
> +dcssblk_blk_direct_access(struct block_device *bdev, sector_t secnum,
>  			void **kaddr, pfn_t *pfn, long size)
>  {
>  	struct dcssblk_dev_info *dev_info;
> -	unsigned long offset, dev_sz;
> 
>  	dev_info = bdev->bd_disk->private_data;
>  	if (!dev_info)
>  		return -ENODEV;
> -	dev_sz = dev_info->end - dev_info->start + 1;
> -	offset = secnum * 512;
> -	*kaddr = (void *) dev_info->start + offset;
> -	*pfn = __pfn_to_pfn_t(PFN_DOWN(dev_info->start + offset), PFN_DEV);
> +	return __dcssblk_direct_access(dev_info, PHYS_PFN(secnum * 512),
> +			PHYS_PFN(size), kaddr, pfn) * PAGE_SIZE;
> +}
> +
> +static long
> +dcssblk_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> +		long nr_pages, void **kaddr, pfn_t *pfn)
> +{
> +	struct dcssblk_dev_info *dev_info = dax_get_private(dax_dev);
> 
> -	return dev_sz - offset;
> +	return __dcssblk_direct_access(dev_info, pgoff, nr_pages, kaddr, pfn);
>  }
> 
>  static void
>