[dm-devel] [PATCH v2] dax: fix for do not print error message for non-persistent memory block device

[Pankaj Gupta]

> When calling __generic_fsdax_supported(), a dax-unsupported device may
> not have dax_dev as NULL, e.g. the dax related code block is not enabled
> by Kconfig.
>
> Therefore in __generic_fsdax_supported(), to check whether a device
> supports DAX or not, the following order should be performed,
> - If dax_dev pointer is NULL, it means the device driver explicitly
>   announce it doesn't support DAX. Then it is OK to directly return
>   false from __generic_fsdax_supported().
> - If dax_dev pointer is NOT NULL, it might be because the driver doesn't
>   support DAX and not explicitly initialize related data structure. Then
>   bdev_dax_supported() should be called for further check.
>
> IMHO if device driver desn't explicitly set its dax_dev pointer to NULL,
> this is not a bug. Calling bdev_dax_supported() makes sure they can be
> recognized as dax-unsupported eventually.
>
> This patch does the following change for the above purpose,
>     -       if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
>     +       if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
>
>
> Fixes: c2affe920b0e ("dax: do not print error message for non-persistent memory block device")
> Signed-off-by: Coly Li <colyli at suse.de>
> Reviewed-and-Tested-by: Adrian Huang <ahuang12 at lenovo.com>
> Cc: Ira Weiny <ira.weiny at intel.com>
> Cc: Jan Kara <jack at suse.com>
> Cc: Mike Snitzer <snitzer at redhat.com>
> Cc: Pankaj Gupta <pankaj.gupta.linux at gmail.com>
> Cc: Vishal Verma <vishal.l.verma at intel.com>
> ---
> Changelog:
> v2: add Reviewed-and-Tested-by from Adrian Huang.
> v1: initial version.
>
>  drivers/dax/super.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> index 32642634c1bb..e5767c83ea23 100644
> --- a/drivers/dax/super.c
> +++ b/drivers/dax/super.c
> @@ -100,7 +100,7 @@ bool __generic_fsdax_supported(struct dax_device *dax_dev,
>                 return false;
>         }
>
> -       if (!dax_dev && !bdev_dax_supported(bdev, blocksize)) {
> +       if (!dax_dev || !bdev_dax_supported(bdev, blocksize)) {
>                 pr_debug("%s: error: dax unsupported by block device\n",
>                                 bdevname(bdev, buf));
>                 return false;
> --

Looks good.
Reviewed-by: Pankaj Gupta <pankaj.gupta.linux at gmail.com>