Re: [PATCH 19/40] change alloc_pages name in dma_map_ops to avoid name conflicts

[Suren Baghdasaryan <surenb@google.com>]

On Tue, May 2, 2023 at 8:50 AM Petr Tesařík <petr@tesarici.cz> wrote:
>
> On Mon,  1 May 2023 09:54:29 -0700
> Suren Baghdasaryan <surenb@google.com> wrote:
>
> > After redefining alloc_pages, all uses of that name are being replaced.
> > Change the conflicting names to prevent preprocessor from replacing them
> > when it's not intended.
> >
> > Signed-off-by: Suren Baghdasaryan <surenb@google.com>
> > ---
> >  arch/x86/kernel/amd_gart_64.c | 2 +-
> >  drivers/iommu/dma-iommu.c     | 2 +-
> >  drivers/xen/grant-dma-ops.c   | 2 +-
> >  drivers/xen/swiotlb-xen.c     | 2 +-
> >  include/linux/dma-map-ops.h   | 2 +-
> >  kernel/dma/mapping.c          | 4 ++--
> >  6 files changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kernel/amd_gart_64.c b/arch/x86/kernel/amd_gart_64.c
> > index 56a917df410d..842a0ec5eaa9 100644
> > --- a/arch/x86/kernel/amd_gart_64.c
> > +++ b/arch/x86/kernel/amd_gart_64.c
> > @@ -676,7 +676,7 @@ static const struct dma_map_ops gart_dma_ops = {
> >       .get_sgtable                    = dma_common_get_sgtable,
> >       .dma_supported                  = dma_direct_supported,
> >       .get_required_mask              = dma_direct_get_required_mask,
> > -     .alloc_pages                    = dma_direct_alloc_pages,
> > +     .alloc_pages_op                 = dma_direct_alloc_pages,
> >       .free_pages                     = dma_direct_free_pages,
> >  };
> >
> > diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
> > index 7a9f0b0bddbd..76a9d5ca4eee 100644
> > --- a/drivers/iommu/dma-iommu.c
> > +++ b/drivers/iommu/dma-iommu.c
> > @@ -1556,7 +1556,7 @@ static const struct dma_map_ops iommu_dma_ops = {
> >       .flags                  = DMA_F_PCI_P2PDMA_SUPPORTED,
> >       .alloc                  = iommu_dma_alloc,
> >       .free                   = iommu_dma_free,
> > -     .alloc_pages            = dma_common_alloc_pages,
> > +     .alloc_pages_op         = dma_common_alloc_pages,
> >       .free_pages             = dma_common_free_pages,
> >       .alloc_noncontiguous    = iommu_dma_alloc_noncontiguous,
> >       .free_noncontiguous     = iommu_dma_free_noncontiguous,
> > diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> > index 9784a77fa3c9..6c7d984f164d 100644
> > --- a/drivers/xen/grant-dma-ops.c
> > +++ b/drivers/xen/grant-dma-ops.c
> > @@ -282,7 +282,7 @@ static int xen_grant_dma_supported(struct device *dev, u64 mask)
> >  static const struct dma_map_ops xen_grant_dma_ops = {
> >       .alloc = xen_grant_dma_alloc,
> >       .free = xen_grant_dma_free,
> > -     .alloc_pages = xen_grant_dma_alloc_pages,
> > +     .alloc_pages_op = xen_grant_dma_alloc_pages,
> >       .free_pages = xen_grant_dma_free_pages,
> >       .mmap = dma_common_mmap,
> >       .get_sgtable = dma_common_get_sgtable,
> > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> > index 67aa74d20162..5ab2616153f0 100644
> > --- a/drivers/xen/swiotlb-xen.c
> > +++ b/drivers/xen/swiotlb-xen.c
> > @@ -403,6 +403,6 @@ const struct dma_map_ops xen_swiotlb_dma_ops = {
> >       .dma_supported = xen_swiotlb_dma_supported,
> >       .mmap = dma_common_mmap,
> >       .get_sgtable = dma_common_get_sgtable,
> > -     .alloc_pages = dma_common_alloc_pages,
> > +     .alloc_pages_op = dma_common_alloc_pages,
> >       .free_pages = dma_common_free_pages,
> >  };
> > diff --git a/include/linux/dma-map-ops.h b/include/linux/dma-map-ops.h
> > index 31f114f486c4..d741940dcb3b 100644
> > --- a/include/linux/dma-map-ops.h
> > +++ b/include/linux/dma-map-ops.h
> > @@ -27,7 +27,7 @@ struct dma_map_ops {
> >                       unsigned long attrs);
> >       void (*free)(struct device *dev, size_t size, void *vaddr,
> >                       dma_addr_t dma_handle, unsigned long attrs);
> > -     struct page *(*alloc_pages)(struct device *dev, size_t size,
> > +     struct page *(*alloc_pages_op)(struct device *dev, size_t size,
> >                       dma_addr_t *dma_handle, enum dma_data_direction dir,
> >                       gfp_t gfp);
> >       void (*free_pages)(struct device *dev, size_t size, struct page *vaddr,
> > diff --git a/kernel/dma/mapping.c b/kernel/dma/mapping.c
> > index 9a4db5cce600..fc42930af14b 100644
> > --- a/kernel/dma/mapping.c
> > +++ b/kernel/dma/mapping.c
> > @@ -570,9 +570,9 @@ static struct page *__dma_alloc_pages(struct device *dev, size_t size,
> >       size = PAGE_ALIGN(size);
> >       if (dma_alloc_direct(dev, ops))
> >               return dma_direct_alloc_pages(dev, size, dma_handle, dir, gfp);
> > -     if (!ops->alloc_pages)
> > +     if (!ops->alloc_pages_op)
> >               return NULL;
> > -     return ops->alloc_pages(dev, size, dma_handle, dir, gfp);
> > +     return ops->alloc_pages_op(dev, size, dma_handle, dir, gfp);
> >  }
> >
> >  struct page *dma_alloc_pages(struct device *dev, size_t size,
>
> I'm not impressed. This patch increases churn for code which does not
> (directly) benefit from the change, and that for limitations in your
> tooling?
>
> Why not just rename the conflicting uses in your local tree, but then
> remove the rename from the final patch series?

With alloc_pages function becoming a macro, the preprocessor ends up
replacing all instances of that name, even when it's not used as a
function. That what necessitates this change. If there is a way to
work around this issue without changing all alloc_pages() calls in the
source base I would love to learn it but I'm not quite clear about
your suggestion and if it solves the issue. Could you please provide
more details?

>
> Just my two cents,
> Petr T
>
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