linux-kernel - [PATCHv2 1/2] mm: eliminate ifdef of HAVE_IOREMAP

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Message-ID: <SG2PR01MB295111ED8F547B9F99DB9FA99FAD9@SG2PR01MB2951.apcprd01.prod.exchangelabs.com>
Date:   Tue, 14 Jun 2022 22:57:34 -0700
From:   Wang Wenhu <wenhu.wang@...mail.com>
To:     gregkh@...uxfoundation.org, arnd@...db.de, hao.wu@...el.com,
        trix@...hat.com, mdf@...nel.org, yilun.xu@...el.com,
        bhelgaas@...gle.com, akpm@...ux-foundation.org,
        linux-fpga@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org
Cc:     christophe.leroy@...roup.eu, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        wenhu.wang@...mail.com
Subject: [PATCHv2 1/2] mm: eliminate ifdef of HAVE_IOREMAP_PROT in .c files

It is recommended in the "Conditional Compilation" chapter of kernel
coding-style documentation that preprocessor conditionals should not
be used in .c files wherever possible.

As for the macro CONFIG_HAVE_IOREMAP_PROT, now it's a proper chance
to eliminate it in .c files which are referencers. We constrict its usage
only to mm/memory.c.
HAVE_IOREMAP_PROT is supported by part of archectures such as powerpc and
x86, but not supported by some others such as arm. So for some functions,
a no-op version should be available. Currently it's generic_access_phys,
which is referenced by some other modules.

Signed-off-by: Wang Wenhu <wenhu.wang@...mail.com>
---
v2:
 - Added IS_ENABLED(CONFIG_HAVE_IOREMAP_PROT) condition in __access_remote_vm
 - Added generic_access_phys() function with no-op in mm/memory.c instead of the 
 former one of "static inline" in include/linux/mm.h
Former: https://lore.kernel.org/linux-mm/YqMRtWAH5fIWsLQB@kroah.com/T/
---
 drivers/char/mem.c          |  2 --
 drivers/fpga/dfl-afu-main.c |  2 --
 drivers/pci/mmap.c          |  2 --
 drivers/uio/uio.c           |  2 --
 mm/memory.c                 | 13 +++++++++----
 5 files changed, 9 insertions(+), 12 deletions(-)

diff --git a/drivers/char/mem.c b/drivers/char/mem.c
index 84ca98ed1dad..40186a441e38 100644
--- a/drivers/char/mem.c
+++ b/drivers/char/mem.c
@@ -354,9 +354,7 @@ static inline int private_mapping_ok(struct vm_area_struct *vma)
 #endif
 
 static const struct vm_operations_struct mmap_mem_ops = {
-#ifdef CONFIG_HAVE_IOREMAP_PROT
 	.access = generic_access_phys
-#endif
 };
 
 static int mmap_mem(struct file *file, struct vm_area_struct *vma)
diff --git a/drivers/fpga/dfl-afu-main.c b/drivers/fpga/dfl-afu-main.c
index 7f621e96d3b8..833e14806c7a 100644
--- a/drivers/fpga/dfl-afu-main.c
+++ b/drivers/fpga/dfl-afu-main.c
@@ -797,9 +797,7 @@ static long afu_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 }
 
 static const struct vm_operations_struct afu_vma_ops = {
-#ifdef CONFIG_HAVE_IOREMAP_PROT
 	.access = generic_access_phys,
-#endif
 };
 
 static int afu_mmap(struct file *filp, struct vm_area_struct *vma)
diff --git a/drivers/pci/mmap.c b/drivers/pci/mmap.c
index b8c9011987f4..1dcfabf80453 100644
--- a/drivers/pci/mmap.c
+++ b/drivers/pci/mmap.c
@@ -35,9 +35,7 @@ int pci_mmap_page_range(struct pci_dev *pdev, int bar,
 #endif
 
 static const struct vm_operations_struct pci_phys_vm_ops = {
-#ifdef CONFIG_HAVE_IOREMAP_PROT
 	.access = generic_access_phys,
-#endif
 };
 
 int pci_mmap_resource_range(struct pci_dev *pdev, int bar,
diff --git a/drivers/uio/uio.c b/drivers/uio/uio.c
index 43afbb7c5ab9..c9205a121007 100644
--- a/drivers/uio/uio.c
+++ b/drivers/uio/uio.c
@@ -719,9 +719,7 @@ static int uio_mmap_logical(struct vm_area_struct *vma)
 }
 
 static const struct vm_operations_struct uio_physical_vm_ops = {
-#ifdef CONFIG_HAVE_IOREMAP_PROT
 	.access = generic_access_phys,
-#endif
 };
 
 static int uio_mmap_physical(struct vm_area_struct *vma)
diff --git a/mm/memory.c b/mm/memory.c
index 7a089145cad4..7c0e59085456 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -5413,6 +5413,13 @@ int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
 	return ret;
 }
 EXPORT_SYMBOL_GPL(generic_access_phys);
+#else
+int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
+			void *buf, int len, int write)
+{
+	return 0;
+}
+EXPORT_SYMBOL_GPL(generic_access_phys);
 #endif
 
 /*
@@ -5437,9 +5444,8 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 		ret = get_user_pages_remote(mm, addr, 1,
 				gup_flags, &page, &vma, NULL);
 		if (ret <= 0) {
-#ifndef CONFIG_HAVE_IOREMAP_PROT
-			break;
-#else
+			if (!IS_ENABLED(CONFIG_HAVE_IOREMAP_PROT))
+				break;
 			/*
 			 * Check if this is a VM_IO | VM_PFNMAP VMA, which
 			 * we can access using slightly different code.
@@ -5453,7 +5459,6 @@ int __access_remote_vm(struct mm_struct *mm, unsigned long addr, void *buf,
 			if (ret <= 0)
 				break;
 			bytes = ret;
-#endif
 		} else {
 			bytes = len;
 			offset = addr & (PAGE_SIZE-1);
-- 
2.25.1