RE: [PATCH v4 04/12] dcssblk: Handle alloc_dax() -EOPNOTSUPP failure

[Dan Williams]

Mathieu Desnoyers wrote:
> In preparation for checking whether the architecture has data cache
> aliasing within alloc_dax(), modify the error handling of dcssblk
> dcssblk_add_store() to handle alloc_dax() -EOPNOTSUPP failures.
> 
> Considering that s390 is not a data cache aliasing architecture,
> and considering that DCSSBLK selects DAX, a return value of -EOPNOTSUPP
> from alloc_dax() should make dcssblk_add_store() fail.
> 
> For the transition, consider that alloc_dax() returning NULL is the
> same as returning -EOPNOTSUPP.
> 
> Fixes: d92576f1167c ("dax: does not work correctly with virtual aliasing caches")
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
> Cc: Alasdair Kergon <agk@xxxxxxxxxx>
> Cc: Mike Snitzer <snitzer@xxxxxxxxxx>
> Cc: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
> Cc: Vishal Verma <vishal.l.verma@xxxxxxxxx>
> Cc: Dave Jiang <dave.jiang@xxxxxxxxx>
> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Russell King <linux@xxxxxxxxxxxxxxx>
> Cc: linux-arch@xxxxxxxxxxxxxxx
> Cc: linux-cxl@xxxxxxxxxxxxxxx
> Cc: linux-fsdevel@xxxxxxxxxxxxxxx
> Cc: linux-mm@xxxxxxxxx
> Cc: linux-xfs@xxxxxxxxxxxxxxx
> Cc: dm-devel@xxxxxxxxxxxxxxx
> Cc: nvdimm@xxxxxxxxxxxxxxx
> Cc: linux-s390@xxxxxxxxxxxxxxx
> ---
>  drivers/s390/block/dcssblk.c | 11 ++++++-----
>  1 file changed, 6 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/s390/block/dcssblk.c b/drivers/s390/block/dcssblk.c
> index 4b7ecd4fd431..a3010849bfed 100644
> --- a/drivers/s390/block/dcssblk.c
> +++ b/drivers/s390/block/dcssblk.c
> @@ -549,6 +549,7 @@ 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;
>  
> @@ -677,13 +678,13 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
>  	if (rc)
>  		goto put_dev;
>  
> -	dev_info->dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
> -	if (IS_ERR(dev_info->dax_dev)) {
> -		rc = PTR_ERR(dev_info->dax_dev);
> -		dev_info->dax_dev = NULL;
> +	dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
> +	if (IS_ERR_OR_NULL(dax_dev)) {
> +		rc = IS_ERR(dax_dev) ? PTR_ERR(dax_dev) : -EOPNOTSUPP;

Just another "ditto" on alloc_dax() returning NULL so that the ternary
can be removed, but otherwise this looks good.