X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=blobdiff_plain;f=mm%2Fmmap.c;h=b6537211b9ccfdfcf1f7d9d63c5891ba89e483e7;hb=75ecb1a4d148b274aa9acd1d6ccaca0a4654784e;hp=7afc7a7cec6f681001817ad6656d3a20d9ed53a7;hpb=d638d4990bfb99998420e78e8fd4607bca5cf8d0;p=linux-2.6

diff --git a/mm/mmap.c b/mm/mmap.c
index 7afc7a7cec..b6537211b9 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,