Re: [PATCH 01/22] scatterlist: Introduce sg_map helper functions

[Logan Gunthorpe]

On 14/04/17 02:35 AM, Christoph Hellwig wrote:
>> +
>>  static inline int is_dma_buf_file(struct file *);
>>  
>>  struct dma_buf_list {
> 
> I think the right fix here is to rename the operation to unmap_atomic
> and send out a little patch for that ASAP.

Ok, I can do that next week.

> I'd rather have separate functions for kmap vs kmap_atomic instead of
> the flags parameter.  And while you're at it just always pass the 0
> offset parameter instead of adding a wrapper..
> 
> Otherwise this looks good to me.

I settled on the flags because I thought the interface could be expanded
to do more things like automatically copy iomem to a bounce buffer (with
a flag). It'd also be possible to add things like vmap and
physical_address to the interface which would cover even more sg_page
users. All the implementations would then share the common offset
calculations, and switching between them becomes a matter of changing a
couple flags.

If you're still not convinced by the above arguments  then I'll change
it but I did have reasons for choosing to do it this way.

I am fine with removing the offset versions. I will make that change.

Thanks,

Logan

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Re: [PATCH 01/22] scatterlist: Introduce sg_map helper functions

[Christoph Hellwig]

> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 0007b79..b95934b 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -37,6 +37,9 @@
>  
>  #include 
>  
> +/* Prevent the highmem.h macro from aliasing ops->kunmap_atomic */
> +#undef kunmap_atomic
> +
>  static inline int is_dma_buf_file(struct file *);
>  
>  struct dma_buf_list {

I think the right fix here is to rename the operation to unmap_atomic
and send out a little patch for that ASAP.

> + *   Flags can be any of:
> + *   * SG_KMAP- Use kmap to create the mapping
> + *   * SG_KMAP_ATOMIC - Use kmap_atomic to map the page atommically.
> + *  Thus, the rules of that function apply: the cpu
> + *  may not sleep until it is unmaped.
> + *
> + *   Also, consider carefully whether this function is appropriate. It is
> + *   largely not recommended for new code and if the sgl came from another
> + *   subsystem and you don't know what kind of memory might be in the list
> + *   then you definitely should not call it. Non-mappable memory may be in
> + *   the sgl and thus this function may fail unexpectedly.
> + **/
> +static inline void *sg_map_offset(struct scatterlist *sg, size_t offset,
> +int flags)

I'd rather have separate functions for kmap vs kmap_atomic instead of
the flags parameter.  And while you're at it just always pass the 0
offset parameter instead of adding a wrapper..

Otherwise this looks good to me.
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