Re: [ndctl PATCHv2] ndctl: Use max_available_extent for namespaces

["Verma, Vishal L" <vishal.l.verma@intel.com>]

On Tue, 2018-06-26 at 11:00 -0600, Keith Busch wrote:
> The available_size attribute returns all the unused regions, but a
> namespace has to use contiguous free regions. This patch uses the
> attribute returning the largest capacity that can be created for
> determining if the namespace can be created.
> 
> If this is used on a kernel that predates the new attribute, ndctl will
> fall back to the previous behavior using available_size. While that may
> still fail, it is more likely to succeed than returning a hard-coded
> value. 
> 
> Signed-off-by: Keith Busch <keith.busch@intel.com>
> ---
> v1 -> v2:
> 
>   Appropriate subject-prefex for ndctl.
> 
>   Added the fallback to the previous behavior if the attribute is not
>   found, and noted this behavior in the changelog.
> 
>  ndctl/lib/libndctl.c   | 31 +++++++++++++++++++++++++++++++
>  ndctl/lib/libndctl.sym |  1 +
>  ndctl/libndctl.h       |  2 ++
>  ndctl/namespace.c      |  2 +-
>  4 files changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/ndctl/lib/libndctl.c b/ndctl/lib/libndctl.c
> index 47e005e..8ff1fa6 100644
> --- a/ndctl/lib/libndctl.c
> +++ b/ndctl/lib/libndctl.c
> @@ -2025,6 +2025,37 @@ NDCTL_EXPORT unsigned long long
> ndctl_region_get_available_size(
>  	return strtoull(buf, NULL, 0);
>  }
>  
> +NDCTL_EXPORT unsigned long long ndctl_region_get_max_available_extent(
> +		struct ndctl_region *region)
> +{
> +	unsigned int nstype = ndctl_region_get_nstype(region);
> +	struct ndctl_ctx *ctx = ndctl_region_get_ctx(region);
> +	char *path = region->region_buf;
> +	int len = region->buf_len;
> +	char buf[SYSFS_ATTR_SIZE];
> +
> +	switch (nstype) {
> +	case ND_DEVICE_NAMESPACE_PMEM:
> +	case ND_DEVICE_NAMESPACE_BLK:
> +		break;
> +	default:
> +		return 0;
> +	}
> +
> +	if (snprintf(path, len,
> +		     "%s/max_available_extent", region->region_path) >=
> len) {
> +		err(ctx, "%s: buffer too small!\n",
> +				ndctl_region_get_devname(region));
> +		return ULLONG_MAX;
> +	}
> +
> +	/* fall back to legacy behavior if max extents is not exported
> */
> +	if (sysfs_read_attr(ctx, path, buf) < 0)
> +		return ndctl_region_get_available_size(region);

Instead of silently falling back to the legacy behavior, perhaps we should
print a dbg() warning here so that the user can be prompted to update their
kernel.

> +
> +	return strtoull(buf, NULL, 0);
> +}
> +
>  NDCTL_EXPORT unsigned int ndctl_region_get_range_index(struct
> ndctl_region *region)
>  {
>  	return region->range_index;
> diff --git a/ndctl/lib/libndctl.sym b/ndctl/lib/libndctl.sym
> index c1228e5..22fd026 100644
> --- a/ndctl/lib/libndctl.sym
> +++ b/ndctl/lib/libndctl.sym
> @@ -123,6 +123,7 @@ global:
>  	ndctl_region_get_mappings;
>  	ndctl_region_get_size;
>  	ndctl_region_get_available_size;
> +	ndctl_region_get_max_available_extent;
>  	ndctl_region_get_type;
>  	ndctl_region_get_namespace_seed;
>  	ndctl_region_get_btt_seed;
> diff --git a/ndctl/libndctl.h b/ndctl/libndctl.h
> index be997ac..624115d 100644
> --- a/ndctl/libndctl.h
> +++ b/ndctl/libndctl.h
> @@ -338,6 +338,8 @@ unsigned int ndctl_region_get_interleave_ways(struct
> ndctl_region *region);
>  unsigned int ndctl_region_get_mappings(struct ndctl_region *region);
>  unsigned long long ndctl_region_get_size(struct ndctl_region *region);
>  unsigned long long ndctl_region_get_available_size(struct ndctl_region
> *region);
> +unsigned long long ndctl_region_get_max_available_extent(
> +		struct ndctl_region *region);
>  unsigned int ndctl_region_get_range_index(struct ndctl_region *region);
>  unsigned int ndctl_region_get_type(struct ndctl_region *region);
>  struct ndctl_namespace *ndctl_region_get_namespace_seed(
> diff --git a/ndctl/namespace.c b/ndctl/namespace.c
> index fe86d82..4a562a2 100644
> --- a/ndctl/namespace.c
> +++ b/ndctl/namespace.c
> @@ -764,7 +764,7 @@ static int namespace_create(struct ndctl_region
> *region)
>  		return -EAGAIN;
>  	}
>  
> -	available = ndctl_region_get_available_size(region);
> +	available = ndctl_region_get_max_available_extent(region);
>  	if (!available || p.size > available) {
>  		debug("%s: insufficient capacity size: %llx avail:
> %llx\n",
>  			devname, p.size, available);
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