mm: merge populate and nopage into fault (fixes nonlinear)

Nonlinear mappings are (AFAIKS) simply a virtual memory concept that encodes
the virtual address -> file offset differently from linear mappings.

->populate is a layering violation because the filesystem/pagecache code
should need to know anything about the virtual memory mapping.  The hitch here
is that the ->nopage handler didn't pass down enough information (ie.  pgoff).
 But it is more logical to pass pgoff rather than have the ->nopage function
calculate it itself anyway (because that's a similar layering violation).

Having the populate handler install the pte itself is likewise a nasty thing
to be doing.

This patch introduces a new fault handler that replaces ->nopage and
->populate and (later) ->nopfn.  Most of the old mechanism is still in place
so there is a lot of duplication and nice cleanups that can be removed if
everyone switches over.

The rationale for doing this in the first place is that nonlinear mappings are
subject to the pagefault vs invalidate/truncate race too, and it seemed stupid
to duplicate the synchronisation logic rather than just consolidate the two.

After this patch, MAP_NONBLOCK no longer sets up ptes for pages present in
pagecache.  Seems like a fringe functionality anyway.

NOPAGE_REFAULT is removed.  This should be implemented with ->fault, and no
users have hit mainline yet.

[akpm@linux-foundation.org: cleanup]
[randy.dunlap@oracle.com: doc. fixes for readahead]
[akpm@linux-foundation.org: build fix]
Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Mark Fasheh <mark.fasheh@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 9 insertions, 10 deletions

diff --git a/fs/ocfs2/aops.c b/fs/ocfs2/aops.c
index 84bf6e79de23..460d440310f2 100644
--- a/fs/ocfs2/aops.c
+++ b/fs/ocfs2/aops.c
@@ -232,7 +232,7 @@ static int ocfs2_readpage(struct file *file, struct page *page)
          * might now be discovering a truncate that hit on another node.
          * block_read_full_page->get_block freaks out if it is asked to read
          * beyond the end of a file, so we check here.  Callers
-         * (generic_file_read, fault->nopage) are clever enough to check i_size
+         * (generic_file_read, vm_ops->fault) are clever enough to check i_size
          * and notice that the page they just read isn't needed.
          *
          * XXX sys_readahead() seems to get that wrong?
diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
index 904f39ff5340..cd75508b1c8a 100644
--- a/fs/ocfs2/mmap.c
+++ b/fs/ocfs2/mmap.c
@@ -60,24 +60,23 @@ static inline int ocfs2_vm_op_unblock_sigs(sigset_t *oldset)
         return sigprocmask(SIG_SETMASK, oldset, NULL);
 }
 
-static struct page *ocfs2_nopage(struct vm_area_struct * area,
-                                 unsigned long address,
-                                 int *type)
+static struct page *ocfs2_fault(struct vm_area_struct *area,
+                                                struct fault_data *fdata)
 {
-        struct page *page = NOPAGE_SIGBUS;
+        struct page *page = NULL;
         sigset_t blocked, oldset;
         int ret;
 
-        mlog_entry("(area=%p, address=%lu, type=%p)\n", area, address,
-                   type);
+        mlog_entry("(area=%p, page offset=%lu)\n", area, fdata->pgoff);
 
         ret = ocfs2_vm_op_block_sigs(&blocked, &oldset);
         if (ret < 0) {
+                fdata->type = VM_FAULT_SIGBUS;
                 mlog_errno(ret);
                 goto out;
         }
 
-        page = filemap_nopage(area, address, type);
+        page = filemap_fault(area, fdata);
 
         ret = ocfs2_vm_op_unblock_sigs(&oldset);
         if (ret < 0)
@@ -209,7 +208,7 @@ out:
 }
 
 static struct vm_operations_struct ocfs2_file_vm_ops = {
-        .nopage         = ocfs2_nopage,
+        .fault          = ocfs2_fault,
         .page_mkwrite   = ocfs2_page_mkwrite,
 };
 
@@ -226,7 +225,7 @@ int ocfs2_mmap(struct file *file, struct vm_area_struct *vma)
         ocfs2_meta_unlock(file->f_dentry->d_inode, lock_level);
 out:
         vma->vm_ops = &ocfs2_file_vm_ops;
-        vma->vm_flags |= VM_CAN_INVALIDATE;
+        vma->vm_flags |= VM_CAN_INVALIDATE | VM_CAN_NONLINEAR;
         return 0;
 }