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

On Tue, 2 May 2023 11:38:49 -0700
Suren Baghdasaryan [off-list ref] wrote:

On Tue, May 2, 2023 at 8:50 AM Petr Tesařík [off-list ref] wrote:

quoted

On Mon,  1 May 2023 09:54:29 -0700
Suren Baghdasaryan [off-list ref] wrote:
 

quoted

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?

Ah, right, I admit I did not quite understand why this change is
needed. However, this is exactly what I don't like about preprocessor
macros. Each macro effectively adds a new keyword to the language.

I believe everything can be solved with inline functions. What exactly
does not work if you rename alloc_pages() to e.g. alloc_pages_caller()
and then add an alloc_pages() inline function which calls
alloc_pages_caller() with _RET_IP_ as a parameter?

Petr T