Re: [PATCH hmm 04/15] mm/hmm: define the pre-processor related parts of hmm.h even if disabled

[Jerome Glisse <jglisse@redhat.com>]

On Tue, Oct 15, 2019 at 03:12:31PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@mellanox.com>
> 
> Only the function calls are stubbed out with static inlines that always
> fail. This is the standard way to write a header for an optional component
> and makes it easier for drivers that only optionally need HMM_MIRROR.
> 
> Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> ---
>  include/linux/hmm.h | 59 ++++++++++++++++++++++++++++++++++++---------
>  kernel/fork.c       |  1 -
>  2 files changed, 47 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 8ac1fd6a81af8f..2666eb08a40615 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -62,8 +62,6 @@
>  #include <linux/kconfig.h>
>  #include <asm/pgtable.h>
>  
> -#ifdef CONFIG_HMM_MIRROR
> -
>  #include <linux/device.h>
>  #include <linux/migrate.h>
>  #include <linux/memremap.h>
> @@ -374,6 +372,15 @@ struct hmm_mirror {
>  	struct list_head		list;
>  };
>  
> +/*
> + * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
> + */
> +#define HMM_FAULT_ALLOW_RETRY		(1 << 0)
> +
> +/* Don't fault in missing PTEs, just snapshot the current state. */
> +#define HMM_FAULT_SNAPSHOT		(1 << 1)
> +
> +#ifdef CONFIG_HMM_MIRROR
>  int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm);
>  void hmm_mirror_unregister(struct hmm_mirror *mirror);
>  
> @@ -383,14 +390,6 @@ void hmm_mirror_unregister(struct hmm_mirror *mirror);
>  int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror);
>  void hmm_range_unregister(struct hmm_range *range);
>  
> -/*
> - * Retry fault if non-blocking, drop mmap_sem and return -EAGAIN in that case.
> - */
> -#define HMM_FAULT_ALLOW_RETRY		(1 << 0)
> -
> -/* Don't fault in missing PTEs, just snapshot the current state. */
> -#define HMM_FAULT_SNAPSHOT		(1 << 1)
> -
>  long hmm_range_fault(struct hmm_range *range, unsigned int flags);
>  
>  long hmm_range_dma_map(struct hmm_range *range,
> @@ -401,6 +400,44 @@ long hmm_range_dma_unmap(struct hmm_range *range,
>  			 struct device *device,
>  			 dma_addr_t *daddrs,
>  			 bool dirty);
> +#else
> +int hmm_mirror_register(struct hmm_mirror *mirror, struct mm_struct *mm)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +void hmm_mirror_unregister(struct hmm_mirror *mirror)
> +{
> +}
> +
> +int hmm_range_register(struct hmm_range *range, struct hmm_mirror *mirror)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +void hmm_range_unregister(struct hmm_range *range)
> +{
> +}
> +
> +static inline long hmm_range_fault(struct hmm_range *range, unsigned int flags)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline long hmm_range_dma_map(struct hmm_range *range,
> +				     struct device *device, dma_addr_t *daddrs,
> +				     unsigned int flags)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline long hmm_range_dma_unmap(struct hmm_range *range,
> +				       struct device *device,
> +				       dma_addr_t *daddrs, bool dirty)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif
>  
>  /*
>   * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range
> @@ -411,6 +448,4 @@ long hmm_range_dma_unmap(struct hmm_range *range,
>   */
>  #define HMM_RANGE_DEFAULT_TIMEOUT 1000
>  
> -#endif /* IS_ENABLED(CONFIG_HMM_MIRROR) */
> -
>  #endif /* LINUX_HMM_H */
> diff --git a/kernel/fork.c b/kernel/fork.c
> index f9572f41612628..4561a65d19db88 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -40,7 +40,6 @@
>  #include <linux/binfmts.h>
>  #include <linux/mman.h>
>  #include <linux/mmu_notifier.h>
> -#include <linux/hmm.h>
>  #include <linux/fs.h>
>  #include <linux/mm.h>
>  #include <linux/vmacache.h>
> -- 
> 2.23.0
>