[dpdk-dev] [PATCH] pci: keep API compatibility with mmap values

[Burakov, Anatoly]

On 10-Jul-20 5:17 PM, Thomas Monjalon wrote:
> 10/07/2020 17:39, Burakov, Anatoly:
>> On 10-Jul-20 12:53 PM, Thomas Monjalon wrote:
>>> The function pci_map_resource() returns MAP_FAILED in case of error.
>>> When replacing the call to mmap() by rte_mem_map(),
>>> the error code became NULL, breaking the API.
>>> This function is probably not used outside of DPDK,
>>> but it is still a problem for two reasons:
>>> 	- the deprecation process was not followed
>>> 	- the Linux function pci_vfio_mmap_bar() is broken for i40e
>>>
>>> The error code is reverted to the Unix value MAP_FAILED.
>>> Windows needs to define this special value (-1 as in Unix).
>>> After proper deprecation process, the API could be changed again
>>> if really needed.
>>>
>>> Because of the switch from mmap() to rte_mem_map(),
>>> another part of the API was changed: "int additional_flags"
>>> are defined as "additional flags for the mapping range"
>>> without mentioning it was directly used in mmap().
>>> Currently it is directly used in rte_mem_map(),
>>> that's why the values rte_map_flags must be mapped (sic) on the mmap ones
>>> in case of Unix OS.
>>>
>>> These are side effects of a badly defined API using Unix values.
> [...]
>>>    /** Additional flags for memory mapping. */
>>>    enum rte_map_flags {
>>> +#ifdef RTE_EXEC_ENV_WINDOWS
>>>    	/** Changes to the mapped memory are visible to other processes. */
>>>    	RTE_MAP_SHARED = 1 << 0,
>>>    	/** Mapping is not backed by a regular file. */
>>> @@ -35,6 +37,12 @@ enum rte_map_flags {
>>>    	 * it is not required to do so, thus mapping with this flag may fail.
>>>    	 */
>>>    	RTE_MAP_FORCE_ADDRESS = 1 << 3
>>> +#else /* map mmap flags because they are exposed in pci_map_resource() API */
>>> +	RTE_MAP_SHARED = MAP_SHARED,
>>> +	RTE_MAP_ANONYMOUS = MAP_ANONYMOUS,
>>> +	RTE_MAP_PRIVATE = MAP_PRIVATE,
>>> +	RTE_MAP_FORCE_ADDRESS = MAP_FIXED,
>>> +#endif
>>
>> I'm probably missing something, but why is this needed? Doesn't
> 
> Yes you missed reading the commit log :)
> Or maybe it is not written clearly enough. Will try to rephrase.
> 
>> rte_mem_map() automatically translate these flags into proper ones?
>> pci_map_resource() will call rte_mem_map(), and that will translate
>> these flags into their Unix equivalents.
> 
> The problem is that we have an API which is taking mmap flags as input.
> "int additional_flags" is a parameter of the function,
> and are supposed to be mmap flags. But it is not stated clearly.
> When Windows will use this function, it won't use mmap flags
> but RTE_MAP_*. So we must accept both.
> That's why the best is to make values the same.
> 
> In 20.11, we could change the API,
> make clear that only RTE_MAP_* is accepted,
> and remove this workaround.
> Or even better, remove pci_map_resource from the PCI lib,
> and implement it in the PCI bus driver.
> 
> pci_map_resource() function is a bad designed API
> 
> 

Right, this makes it clearer :) Thanks!

-- 
Thanks,
Anatoly