linux-kernel - Re: [PATCH] genalloc: add support of multiple gen

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Date:	Mon, 8 Jun 2015 14:03:51 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>,
	Olof Johansson <olof@...om.net>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] genalloc: add support of multiple gen_pools per device

On Fri, 5 Jun 2015 02:35:30 +0300 Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com> wrote:

> 
> > If there's a pattern, it is "subsytem-identifier_operation-on-it", so
> > 
> > 	devm_gen_pool_named_create
> > 	dev_gen_pool_named_get
> > 	of_named_gen_pool_get
> > 
> > ie: it's big-endian.  The name starts out with the most significant
> > thing (subsystem identification) and fields in order of decreasing
> > significance.
> > 
> > Anyway, please have a think about it ;)
> 
> What would be your opinion on the following naming proposal:
> 
>   devm_gen_pool_create()  --> devm_gen_pool_create(),
>                               devm_gen_pool_create_named()
> 
> No changes, and "named" flavour of a new gen_pool create interface goes
> to the suffix position.
> 
>   dev_get_gen_pool()      --> dev_gen_pool_get(),
>                               dev_gen_pool_get_named()
> 
> And the last one
> 
>   of_get_named_gen_pool() --> of_gen_pool_get()
> 
> Here "named" reminds of need to provide a phandle name, not gen_pool
> name as above, to avoid confusion I would propose to drop it.
> 
> If it is okay from your point of view, I'll send another non-functional
> patch against linux-next to rename existing interfaces.

Sounds good.

> >> +/**
> >> + * dev_get_gen_pool_named - Obtain the gen_pool (if any) for a device
> >> + * @dev: device to retrieve the gen_pool from
> >> + * @name: name of a gen_pool, addresses a particular gen_pool from device
> >> + *
> >> + * Returns the gen_pool for the device if one is present, or NULL.
> >> + */
> >> +struct gen_pool *dev_get_gen_pool_named(struct device *dev, const char *name)
> >> +{
> >> +	struct gen_pool **p = devres_find(dev, devm_gen_pool_release,
> >> +					  dev_gen_pool_match, (void *)name);
> >> +
> >> +	if (!p)
> >> +		return NULL;
> >> +	return *p;
> >> +}
> >> +EXPORT_SYMBOL_GPL(dev_get_gen_pool_named);
> > 
> > But we didn't do anything to prevent duplicated names.
> 
> Like with MTD OF partitions used as a template technically it is
> possible to register several gen_pools under the same name, when
> requested the first found one is returned to a client, correctness of
> one to one mapping is offloaded to the register party, for instance if
> of_get_named_gen_pool() is supposed to be used, then DTS description is
> expected to be consistent.

Well, if we go this way then your "first found one" becomes part of
the dev_get_gen_pool_named() interface definition and should be
documented and maintained.  Most-recently-registered or
least-recently-registered?

But either way, does the interface make sense?  Or it is an error
condition?  If it's an error condition then we should check for it
rather than silently ignoring it.

> Is it good enough or better to add a name uniqueness check? In my
> opinion the latter case may require to change error return value of
> devm_gen_pool_create() from NULL to ERR_PTR().

It sounds that way.


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