On Tue, Jul 22, 2014 at 03:47:58PM -0400, Matthew Wilcox wrote:

Instead of calling aops->get_xip_mem from the fault handler, the
filesystem passes a get_block_t that is used to find the appropriate
blocks.

Signed-off-by: Matthew Wilcox <redacted>
Reviewed-by: Jan Kara <jack@suse.cz>
---
 fs/dax.c           | 221 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 fs/ext2/file.c     |  35 ++++++++-
 include/linux/fs.h |   4 +-
 mm/filemap_xip.c   | 206 -------------------------------------------------
 4 files changed, 257 insertions(+), 209 deletions(-)

...

+/**
+ * dax_fault - handle a page fault on a DAX file
+ * @vma: The virtual memory area where the fault occurred
+ * @vmf: The description of the fault
+ * @get_block: The filesystem method used to translate file offsets to blocks
+ *
+ * When a page fault occurs, filesystems may call this helper in their
+ * fault handler for DAX files.
+ */
+int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
+			get_block_t get_block)
+{
+	int result;
+	struct super_block *sb = file_inode(vma->vm_file)->i_sb;
+
+	if (vmf->flags & FAULT_FLAG_WRITE) {

Nobody seems calls sb_start_pagefault() in fault handler.
Do you mean FAULT_FLAG_MKWRITE?

+		sb_start_pagefault(sb);
+		file_update_time(vma->vm_file);
+	}
+	result = do_dax_fault(vma, vmf, get_block);
+	if (vmf->flags & FAULT_FLAG_WRITE)
+		sb_end_pagefault(sb);
+
+	return result;
+}
+EXPORT_SYMBOL_GPL(dax_fault);
+
+/**
+ * dax_mkwrite - convert a read-only page to read-write in a DAX file
+ * @vma: The virtual memory area where the fault occurred
+ * @vmf: The description of the fault
+ * @get_block: The filesystem method used to translate file offsets to blocks
+ *
+ * DAX handles reads of holes by adding pages full of zeroes into the
+ * mapping.  If the page is subsequenty written to, we have to allocate
+ * the page on media and free the page that was in the cache.
+ */
+int dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
+			get_block_t get_block)
+{
+	return dax_fault(vma, vmf, get_block);
+}
+EXPORT_SYMBOL_GPL(dax_mkwrite);

I don't think we want to introduce new exported symbol just for dummy
wrapper. Just use ".page_mkwrite = foo_fault,". perf and selinux do
this.
Or add #define into header file if you want better readability.

-- 
 Kirill A. Shutemov

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