[PATCH] rmap 3 arches + mapping_mapped

From: Hugh Dickins <hugh@veritas.com>

Some arches refer to page->mapping for their dcache flushing: use
page_mapping(page) for safety, to avoid confusion on anon pages, which will
store a different pointer there - though in most cases flush_dcache_page is
being applied to pagecache pages.

arm has a useful mapping_mapped macro: move that to generic, and add
mapping_writably_mapped, to avoid explicit list_empty checks on i_mmap and
i_mmap_shared in several places.

Very tempted to add page_mapped(page) tests, perhaps along with the
mapping_writably_mapped tests in do_generic_mapping_read and
do_shmem_file_read, to cut down on wasted flush_dcache effort; but the
serialization is not obvious, too unsafe to do in a hurry.

1 files changed, 20 insertions, 0 deletions

diff --git a/include/linux/fs.h b/include/linux/fs.h
index c7f0052b4abd..3d7c320d675e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -374,6 +374,26 @@ struct block_device {
 int mapping_tagged(struct address_space *mapping, int tag);
 
 /*
+ * Might pages of this file be mapped into userspace?
+ */
+static inline int mapping_mapped(struct address_space *mapping)
+{
+	return	!list_empty(&mapping->i_mmap) ||
+		!list_empty(&mapping->i_mmap_shared);
+}
+
+/*
+ * Might pages of this file have been modified in userspace?
+ * Note that i_mmap_shared holds all the VM_SHARED vmas: do_mmap_pgoff
+ * marks vma as VM_SHARED if it is shared, and the file was opened for
+ * writing i.e. vma may be mprotected writable even if now readonly.
+ */
+static inline int mapping_writably_mapped(struct address_space *mapping)
+{
+	return	!list_empty(&mapping->i_mmap_shared);
+}
+
+/*
  * Use sequence counter to get consistent i_size on 32-bit processors.
  */
 #if BITS_PER_LONG==32 && defined(CONFIG_SMP)