Analoguous to follow_phys(), add a helper that looks up the PFN at a
user virtual address in an IO mapping or a raw PFN mapping.
Signed-off-by: Johannes Weiner <hannes@xxxxxxxxxxx>
---
include/linux/mm.h | 2 ++
mm/memory.c | 29 +++++++++++++++++++++++++++++
2 files changed, 31 insertions(+), 0 deletions(-)
On Mon, May 04, 2009 at 07:08:41AM -0400, Christoph Hellwig wrote:
> On Mon, May 04, 2009 at 11:54:34AM +0200, Johannes Weiner wrote:
> > Analoguous to follow_phys(), add a helper that looks up the PFN
> > instead. It also only allows IO mappings or PFN mappings.
>
> A kerneldoc describing what it does and the limitations would be
> extremly helpful.
Agreed. How is this?
diff --git a/include/linux/mm.h b/include/linux/mm.h
index bff1f0d..1cca8b6 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -794,6 +794,8 @@ int copy_page_range(struct mm_struct *dst, struct mm_struct *src,
struct vm_area_struct *vma);
void unmap_mapping_range(struct address_space *mapping,
loff_t const holebegin, loff_t const holelen, int even_cows);
+int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+ unsigned long *pfn);
int follow_phys(struct vm_area_struct *vma, unsigned long address,
unsigned int flags, unsigned long *prot, resource_size_t *phys);
int generic_access_phys(struct vm_area_struct *vma, unsigned long addr,
diff --git a/mm/memory.c b/mm/memory.c
index c047950..f86aee1 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3046,6 +3046,35 @@ out:
return -EINVAL;
}
+/**
+ * follow_pfn - look up PFN at a user virtual address
+ * @vma: memory mapping
+ * @address: user virtual address
+ * @pfn: location to store found PFN
+ *
+ * Only IO mappings and raw PFN mappings are allowed.
+ *
+ * Returns zero and the pfn at @pfn on success, -ve otherwise.
+ */
+int follow_pfn(struct vm_area_struct *vma, unsigned long address,
+ unsigned long *pfn)
+{
+ int ret = -EINVAL;
+ spinlock_t *ptl;
+ pte_t *ptep;
+
+ if (!(vma->vm_flags & (VM_IO | VM_PFNMAP)))
+ return ret;
+
+ ret = follow_pte(vma->vm_mm, address, &ptep, &ptl);
+ if (ret)
+ return ret;
+ *pfn = pte_pfn(*ptep);
+ pte_unmap_unlock(ptep, ptl);
+ return 0;
+}
+EXPORT_SYMBOL(follow_pfn);
+
#ifdef CONFIG_HAVE_IOREMAP_PROT
int follow_phys(struct vm_area_struct *vma,
unsigned long address, unsigned int flags,
--
1.6.2.1.135.gde769
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