Re: [PATCH 2/2] pnfs/blocklayout: cap total parse operations in volume topology

[Christoph Hellwig <hch@lst.de>]

On Tue, Apr 21, 2026 at 10:03:44AM +0000, Werner Kasselman wrote:
> The recursive-descent volume parser materializes a separate device
> tree node for every volume reference.  When CONCAT or STRIPE volumes
> reference the same child index, the parser re-parses that subtree for
> each reference, causing work exponential in nesting depth.
> 
> Cap the total number of bl_parse_deviceid() calls at
> PNFS_BLOCK_MAX_PARSE_OPS (1024) to bound CPU and memory consumption
> from server-controlled GETDEVICEINFO topologies.

The OPS naming is a bit odd, these are called 'volumes' in the specs.
Which isn't a great name, but it generally helps to stick to the
spec terms.  So maybe rename the constant, and also add a comment
explaining the limit to the code?

> +		int depth, int *remaining, gfp_t gfp_mask);

Also use unsigned here as well.  And maybe we should group the depth
and ops into a struct instead of adding more and more parameters?

Otherwise this looks good.