linux-kernel - Re: [PATCH v8 2/5] PCI: endpoint: Add BAR subrange mapping support

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Message-ID: <aWkF6rT0Du7iJwHh@ryzen>
Date: Thu, 15 Jan 2026 16:21:21 +0100
From: Niklas Cassel <cassel@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Koichiro Den <den@...inux.co.jp>, jingoohan1@...il.com, mani@...nel.org,
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Subject: Re: [PATCH v8 2/5] PCI: endpoint: Add BAR subrange mapping support

On Thu, Jan 15, 2026 at 09:52:58AM -0500, Frank Li wrote:
> > @@ -127,6 +150,10 @@ struct pci_epf_bar {
> >  	size_t		mem_size;
> >  	enum pci_barno	barno;
> >  	int		flags;
> > +
> > +	/* Optional sub-range mapping */
> > +	unsigned int	num_submap;
> > +	struct pci_epf_bar_submap	*submap;
> 
> struct pci_epf_bar_submap submap[] __counted_by(num_submap);
> 
> Not sure if use this simplify alloc/free.

Your suggestion changes the submap from a pointer to a flexible array
member.

A flexible array member must always be last in the struct,
and you can only have one flexible array member per struct.

Additionally, using a flexible array member requires the struct to
always be allocated on the heap. You can't allocate a struct with a
flexible array member on the stack.

So I'm not sure that if your suggestion is something we want.


Kind regards,
Niklas