On 2021-04-27 1:22 p.m., Jason Gunthorpe wrote: > On Thu, Apr 08, 2021 at 11:01:12AM -0600, Logan Gunthorpe wrote: >> dma_map_sg() either returns a positive number indicating the number >> of entries mapped or zero indicating that resources were not available >> to create the mapping. When zero is returned, it is always safe to retry >> the mapping later once resources have been freed. >> >> Once P2PDMA pages are mixed into the SGL there may be pages that may >> never be successfully mapped with a given device because that device may >> not actually be able to access those pages. Thus, multiple error >> conditions will need to be distinguished to determine weather a retry >> is safe. >> >> Introduce dma_map_sg_p2pdma[_attrs]() with a different calling >> convention from dma_map_sg(). The function will return a positive >> integer on success or a negative errno on failure. >> >> ENOMEM will be used to indicate a resource failure and EREMOTEIO to >> indicate that a P2PDMA page is not mappable. >> >> The __DMA_ATTR_PCI_P2PDMA attribute is introduced to inform the lower >> level implementations that P2PDMA pages are allowed and to warn if a >> caller introduces them into the regular dma_map_sg() interface. > > So this new API is all about being able to return an error code > because auditing the old API is basically terrifying? > > OK, but why name everything new P2PDMA? It seems nicer to give this > some generic name and have some general program to gradually deprecate > normal non-error-capable dma_map_sg() ? > > I think that will raise less questions when subsystem people see the > changes, as I was wondering why RW was being moved to use what looked > like a p2pdma only API. > > dma_map_sg_or_err() would have been clearer > > The flag is also clearer as to the purpose if it is named > __DMA_ATTR_ERROR_ALLOWED I'm not opposed to these names. I can use them for v2 if there are no other opinions. Logan
