[PATCH 4/9] fbdev: Export helper for implementing page_mkwrite

[Thomas Zimmermann]

Refactor the page-write handler and export it as helper function
fb_deferred_io_page_mkwrite(). Drivers that implement struct
vm_operations_struct.page_mkwrite for deferred I/O should use the
function to let fbdev track written pages of mmap'ed framebuffer
memory.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
---
 drivers/video/fbdev/core/fb_defio.c | 69 ++++++++++++++++++++---------
 include/linux/fb.h                  |  1 +
 2 files changed, 50 insertions(+), 20 deletions(-)

diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
index 20c6eb94a685..8cd40b1714d4 100644
--- a/drivers/video/fbdev/core/fb_defio.c
+++ b/drivers/video/fbdev/core/fb_defio.c
@@ -143,29 +143,18 @@ int fb_deferred_io_fsync(struct file *file, loff_t start, loff_t end, int datasy
 }
 EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);
 
-/* vm_ops->page_mkwrite handler */
-static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
+/*
+ * Adds a page to the dirty list. Requires caller to hold
+ * struct fb_deferred_io.lock. Call this from struct
+ * vm_operations_struct.page_mkwrite.
+ */
+static vm_fault_t __fb_deferred_io_track_page(struct fb_info *info, unsigned long offset,
+					      struct page *page)
 {
-	struct page *page = vmf->page;
-	struct fb_info *info = vmf->vma->vm_private_data;
 	struct fb_deferred_io *fbdefio = info->fbdefio;
 	struct fb_deferred_io_pageref *pageref;
-	unsigned long offset;
 	vm_fault_t ret;
 
-	offset = (vmf->address - vmf->vma->vm_start);
-
-	/* this is a callback we get when userspace first tries to
-	write to the page. we schedule a workqueue. that workqueue
-	will eventually mkclean the touched pages and execute the
-	deferred framebuffer IO. then if userspace touches a page
-	again, we repeat the same scheme */
-
-	file_update_time(vmf->vma->vm_file);
-
-	/* protect against the workqueue changing the page list */
-	mutex_lock(&fbdefio->lock);
-
 	/* first write in this cycle, notify the driver */
 	if (fbdefio->first_io && list_empty(&fbdefio->pagelist))
 		fbdefio->first_io(info);
@@ -186,8 +175,6 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
 	 */
 	lock_page(pageref->page);
 
-	mutex_unlock(&fbdefio->lock);
-
 	/* come back after delay to process the deferred IO */
 	schedule_delayed_work(&info->deferred_work, fbdefio->delay);
 	return VM_FAULT_LOCKED;
@@ -197,6 +184,48 @@ static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
 	return ret;
 }
 
+/**
+ * fb_deferred_io_page_mkwrite - Mark a page as written for deferred I/O
+ * @fb_info: The fbdev info structure
+ * @vmf: The VM fault
+ *
+ * This is a callback we get when userspace first tries to
+ * write to the page. We schedule a workqueue. That workqueue
+ * will eventually mkclean the touched pages and execute the
+ * deferred framebuffer IO. Then if userspace touches a page
+ * again, we repeat the same scheme.
+ *
+ * Returns:
+ * VM_FAULT_LOCKED on success, or a VM_FAULT error otherwise.
+ */
+vm_fault_t fb_deferred_io_page_mkwrite(struct fb_info *info, struct vm_fault *vmf)
+{
+	struct page *page = vmf->page;
+	struct fb_deferred_io *fbdefio = info->fbdefio;
+	unsigned long offset;
+	vm_fault_t ret;
+
+	offset = (vmf->address - vmf->vma->vm_start);
+
+	file_update_time(vmf->vma->vm_file);
+
+	/* protect against the workqueue changing the page list */
+	mutex_lock(&fbdefio->lock);
+	ret = __fb_deferred_io_track_page(info, offset, page);
+	mutex_unlock(&fbdefio->lock);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(fb_deferred_io_page_mkwrite);
+
+/* vm_ops->page_mkwrite handler */
+static vm_fault_t fb_deferred_io_mkwrite(struct vm_fault *vmf)
+{
+	struct fb_info *info = vmf->vma->vm_private_data;
+
+	return fb_deferred_io_page_mkwrite(info, vmf);
+}
+
 static const struct vm_operations_struct fb_deferred_io_vm_ops = {
 	.fault		= fb_deferred_io_fault,
 	.page_mkwrite	= fb_deferred_io_mkwrite,
diff --git a/include/linux/fb.h b/include/linux/fb.h
index 768de6534a82..631a1d0cb193 100644
--- a/include/linux/fb.h
+++ b/include/linux/fb.h
@@ -670,6 +670,7 @@ static inline void __fb_pad_aligned_buffer(u8 *dst, u32 d_pitch,
 }
 
 /* drivers/video/fb_defio.c */
+vm_fault_t fb_deferred_io_page_mkwrite(struct fb_info *info, struct vm_fault *vmf);
 int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma);
 extern int  fb_deferred_io_init(struct fb_info *info);
 extern void fb_deferred_io_open(struct fb_info *info,
-- 
2.35.1