1 files changed, 34 insertions, 0 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 7afc7a7cec6f..b6537211b9cc 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1029,6 +1029,40 @@ unsigned long do_mmap_pgoff(struct file * file, unsigned long addr,
 }
 EXPORT_SYMBOL(do_mmap_pgoff);
 
+/*
+ * Some shared mappigns will want the pages marked read-only
+ * to track write events. If so, we'll downgrade vm_page_prot
+ * to the private version (using protection_map[] without the
+ * VM_SHARED bit).
+ */
+int vma_wants_writenotify(struct vm_area_struct *vma)
+{
+        unsigned int vm_flags = vma->vm_flags;
+
+        /* If it was private or non-writable, the write bit is already clear */
+        if ((vm_flags & (VM_WRITE|VM_SHARED)) != ((VM_WRITE|VM_SHARED)))
+                return 0;
+
+        /* The backer wishes to know when pages are first written to? */
+        if (vma->vm_ops && vma->vm_ops->page_mkwrite)
+                return 1;
+
+        /* The open routine did something to the protections already? */
+        if (pgprot_val(vma->vm_page_prot) !=
+            pgprot_val(protection_map[vm_flags &
+                    (VM_READ|VM_WRITE|VM_EXEC|VM_SHARED)]))
+                return 0;
+
+        /* Specialty mapping? */
+        if (vm_flags & (VM_PFNMAP|VM_INSERTPAGE))
+                return 0;
+
+        /* Can the mapping track the dirty pages? */
+        return vma->vm_file && vma->vm_file->f_mapping &&
+                mapping_cap_account_dirty(vma->vm_file->f_mapping);
+}
+
+
 unsigned long mmap_region(struct file *file, unsigned long addr,
                           unsigned long len, unsigned long flags,
                           unsigned int vm_flags, unsigned long pgoff,