Re: [PATCH 10/18] cdev: have devfs_add_partition return existing identical partition, not NULL

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 01.06.23 09:36, Sascha Hauer wrote:
> On Wed, May 31, 2023 at 04:59:19PM +0200, Ahmad Fatoum wrote:
>> Starting with commit 7f9f45b9bfef ("devfs: Do not create overlapping
>> partitions"), any overlapping is disallowed. Overlapping can be useful
>> though to bridge the gap between partition described in DT and via
>> on-disk partition tables. Let's handle the case of identical partitions
>> specially and have it neither be an error or a duplicate partition, but
>> instead just return the existing partition. This existing partition will
>> be given a device tree node and thus enabling schemes like:
>>
>>   &{/state} {
>>   	backend = <&state_part>;
>>   };
>>
>>   &mmc1 {
>>          partitions {
>>                  compatible = "fixed-partitions";
>>                  #address-cells = <2>;
>>                  #size-cells = <2>;
>>
>>                  state_part: partition@5300000 {
>>                          label = "barebox-state";
>> 			 /* will be folded with overlapping GPT partition if found */
>>                          reg = <0x0 0x5300000 0x0 0x100000>;
>>                  };
>>          };
>>   };
> 
> You introduced the DEVFS_PARTITION_FROM_OF earlier this series.
> Depending on the order the code runs you end up with either the
> partition from the partition table or the one created from OF with
> DEVFS_PARTITION_FROM_OF. I am not sure about the implications of
> this inconsistency. Can it lead to problems later?

Order is always the same: parse_partition_table is called before
of_parse_partitions. The latter is called on the cdev populated
by blockdevice_register at all call site.

Nevertheless, I have tested that you can reorder parse_partition_table
and of_parse_partitions, but there's a slight change in behavior: The first
partition that's registered is the namesake. I have adapted the code
to call devfs_create_link(overlap, partinfo->name); in that case. That way
we will always have all partitions in /dev regardless of order. The only
thing that will change, is which is a real cdev and which is a link.

Thanks,
Ahmad

> 
> Sascha
> 

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