Re: Behaviour change of /dev/fb0?

["Antonino A. Daplas" <adaplas@gmail.com>]

Richard Purdie wrote:
> Ignoring whether this is a good idea or not, under 2.6.15 you could run
> 
> dd if=/dev/zero of=/dev/fb0
> 
> which would clear the framebuffer. It would end up saying "dd: /dev/fb0:
> No space left on device".
> 
> Under 2.6.16 (and a recent git kernel), the same command clears the
> screen but then hangs. Was the change in behaviour intentional? 
> 
> I've noticed this on a couple of ARM based Zaurus handhelds under both
> w100fb and pxafb.
> 

After reading 'man 2 read' more thoroughly, I've adjusted fb_write()'s
return codes  appropriately.  Can you try this patch and let me know if it
fixes your problem.

Tony

fbdev: Fix return error of fb_write()

- return -EFBIG if file offset is past the maximum allowable offset
- return -EFBIG and write to end of framebuffer if size is bigger than the
  framebuffer length
- return -ENOSPC and write to end of framebuffer if size is bigger than the
  framebuffer length - file offset

Signed-off-by: Antonino Daplas <adaplas@pol.net>
---

 drivers/video/fbmem.c |   12 +++++++++---
 1 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/video/fbmem.c b/drivers/video/fbmem.c
index 944855b..8a643bf 100644
--- a/drivers/video/fbmem.c
+++ b/drivers/video/fbmem.c
@@ -669,13 +669,19 @@ fb_write(struct file *file, const char _
 		total_size = info->fix.smem_len;
 
 	if (p > total_size)
-		return 0;
+		return -EFBIG;
 
-	if (count >= total_size)
+	if (count >= total_size) {
+		err = -EFBIG;
 		count = total_size;
+	}
+
+	if (count + p > total_size) {
+		if (!err)
+			err = -ENOSPC;
 
-	if (count + p > total_size)
 		count = total_size - p;
+	}
 
 	buffer = kmalloc((count > PAGE_SIZE) ? PAGE_SIZE : count,
 			 GFP_KERNEL);


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