Message-ID: <5570E0C2.5030105@mentor.com>
Date:	Fri, 5 Jun 2015 02:35:30 +0300
From:	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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

Hello Andrew,

thank you for review.

On 05.06.2015 01:35, Andrew Morton wrote:
> On Thu, 4 Jun 2015 14:55:52 +0300 Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com> wrote:
> 
>> This change adds two more exported interfaces to genalloc:
>>
>> * devm_gen_pool_create_named() -- same as devm_gen_pool_create(), but
>>   the created gen_pool object can be referenced by a given name,
>> * dev_get_gen_pool_named() -- same as dev_get_gen_pool(), but allows
>>   to get a previously registered particular gen_pool instance by name
> 
> The naming is inconsistent.  Either
> 
> 	devm_gen_pool_create_named, dev_gen_pool_get_named
> 
> or
> 
> 	devm_create_gen_pool_create, dev_get_gen_pool_named
> 
>> Also the change extends the logic of of_get_named_gen_pool(), if
> 
> and "of_get_named_gen_pool" is inconsistent with all the above!
> 

This naming is based on the naming of existing interfaces found in
lib/genalloc.c:

  devm_gen_pool_create()  --> devm_gen_pool_create_named()
  dev_get_gen_pool()      --> dev_get_gen_pool_named()
  of_get_named_gen_pool() --- this is untouched.

Just "_named" suffix has been added as you can see.

> Can we fix all this up please?

Sure, but since the inconsistent naming is already present in the
kernel, I suppose another preceding cross domain patch is needed,
relatively small though.

> 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.

>> there is no associated platform device with a given device node, it
>> attempts to get a label property or device node name (= repeats MTD
>> OF partition standard) and seeks for a named gen_pool registered by
>> parent device node device.
>>
>> The main idea of the change is to allow registration of independent
>> gen_pools under the same umbrella device, say "partitions" on "storage
>> device", the original functionality of one "partition" per "storage
>> device" is untouched.
>>
>> ...
>>
>>  /**
>> + * devm_gen_pool_create_named - managed gen_pool_create
>> + * @dev: device that provides the gen_pool
>> + * @min_alloc_order: log base 2 of number of bytes each bitmap bit represents
>> + * @nid: node id of the node the pool structure should be allocated on, or -1
> 
> Let's use "NUMA_NO_NODE" instead of a bare "-1".

Makes sense, thank you.

>> + * @name: name of a gen_pool within all gen_pool associated with the device
>> + *
>> + * Create a new special memory pool that can be used to manage special purpose
>> + * memory not managed by the regular kmalloc/kfree interface. The pool will be
>> + * automatically destroyed by the device management code.
>> + */
>> +struct gen_pool *devm_gen_pool_create_named(struct device *dev,
>> +		int min_alloc_order, int nid, const char *name)
>> +{
>> +	struct gen_pool *pool;
>> +
>> +	pool = devm_gen_pool_create(dev, min_alloc_order, nid);
>> +	if (pool)
>> +		pool->name = name;
> 
> This requires that the caller perform management of the memory at
> *name, which is a bit klunky.  It's more work for the caller to do and
> it creates a dependency in the other direction: genpool requires that
> the caller keep the storage alive.
> 
> So maybe it would be better to kstrdup() this string and make genpool
> kfree() it when appropriate.
> 

I agree, will fix it.

>> +	return pool;
>> +}
>> +EXPORT_SYMBOL(devm_gen_pool_create_named);
>> +
>>
>> ...
>>
>> +/**
>> + * 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.

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().

>>  #ifdef CONFIG_OF
>>  /**
>>   * of_get_named_gen_pool - find a pool by phandle property
>> @@ -633,16 +689,30 @@ struct gen_pool *of_get_named_gen_pool(struct device_node *np,
>>  	const char *propname, int index)
>>  {
>>  	struct platform_device *pdev;
>> -	struct device_node *np_pool;
>> +	struct device_node *np_pool, *parent;
>> +	const char *name = NULL;
>>  
>>  	np_pool = of_parse_phandle(np, propname, index);
>>  	if (!np_pool)
>>  		return NULL;
>> +
>>  	pdev = of_find_device_by_node(np_pool);
>> +	if (!pdev) {
>> +		/* Check if named gen_pool is created by parent node device */
>> +		parent = of_get_parent(np_pool);
>> +		pdev = of_find_device_by_node(parent);
>> +		of_node_put(parent);
>> +
>> +		of_property_read_string(np_pool, "label", &name);
>> +		if (!name)
>> +			name = np_pool->name;
>> +	}
>>  	of_node_put(np_pool);
>> +
>>  	if (!pdev)
>>  		return NULL;
>> -	return dev_get_gen_pool(&pdev->dev);
>> +
>> +	return dev_get_gen_pool_named(&pdev->dev, name);
>>  }
>>  EXPORT_SYMBOL_GPL(of_get_named_gen_pool);
>>  #endif /* CONFIG_OF */
> 

--
With best wishes,
Vladimir
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