[PATCH] NOMMU: Make mremap() partially work for NOMMU kernels

Make mremap() partially work for NOMMU kernels.  It may resize a VMA provided
that it doesn't exceed the size of the slab object in which the storage is
allocated that the VMA refers to.  Shareable VMAs may not be resized.

Moving VMAs (as permitted by MREMAP_MAYMOVE) is not currently supported.

This patch also makes use of the fact that the VMA list is now ordered to cut
it short when possible.

Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 24 insertions, 0 deletions

diff --git a/Documentation/nommu-mmap.txt b/Documentation/nommu-mmap.txt
index 83f4b083d57e..3ce890664936 100644
--- a/Documentation/nommu-mmap.txt
+++ b/Documentation/nommu-mmap.txt
@@ -128,6 +128,30 @@ FURTHER NOTES ON NO-MMU MMAP
      error will result if they don't. This is most likely to be encountered
      with character device files, pipes, fifos and sockets.
 
+
+=============
+NO-MMU MREMAP
+=============
+
+The mremap() function is partially supported.  It may change the size of a
+mapping, and may move it[*] if MREMAP_MAYMOVE is specified and if the new size
+of the mapping exceeds the size of the slab object currently occupied by the
+memory to which the mapping refers, or if a smaller slab object could be used.
+
+MREMAP_FIXED is not supported, though it is ignored if there's no change of
+address and the object does not need to be moved.
+
+Shared mappings may not be moved.  Shareable mappings may not be moved either,
+even if they are not currently shared.
+
+The mremap() function must be given an exact match for base address and size of
+a previously mapped object.  It may not be used to create holes in existing
+mappings, move parts of existing mappings or resize parts of mappings.  It must
+act on a complete mapping.
+
+[*] Not currently supported.
+
+
 ============================================
 PROVIDING SHAREABLE CHARACTER DEVICE SUPPORT
 ============================================