Re: [PATCH] adjust /dev/{kmem,mem,port} write handlers

[Andrew Morton <akpm@osdl.org>]

"Jan Beulich" <JBeulich@novell.com> wrote:
>
> The /dev/mem and /dev/kmem write handlers weren't fully POSIX compliant in
> that they wouldn't always force the file pointer to be updated when returning
> success status.
> The /dev/port write handler was inconsistent with the /dev/mem and /dev/kmem
> handlers in that when encountering a -EFAULT condition after already having
> written a number of items it would return -EFAULT rather than the number of
> bytes written.
> 
> ...
>
> @@ -514,11 +510,10 @@ static ssize_t write_kmem(struct file * 
>  			if (len) {
>  				written = copy_from_user(kbuf, buf, len);
>  				if (written) {
> -					ssize_t ret;
> -
> +					if (wrote + virtr)
> +						break;
>  					free_page((unsigned long)kbuf);
> -					ret = wrote + virtr + (len - written);
> -					return ret ? ret : -EFAULT;
> +					return -EFAULT;
>  				}
>  			}
>  			len = vwrite(kbuf, (char *)p, len);


I think write_kmem() still isn't quie right - it needs to update `p' (and
hence *ppos) to account for a partial copy_from_user().  (Please double-check)


--- devel/drivers/char/mem.c~adjust-dev-kmemmemport-write-handlers-fix	2006-03-04 22:10:55.000000000 -0800
+++ devel-akpm/drivers/char/mem.c	2006-03-04 22:15:19.000000000 -0800
@@ -504,8 +504,11 @@ static ssize_t write_kmem(struct file * 
 			if (len) {
 				written = copy_from_user(kbuf, buf, len);
 				if (written) {
-					if (wrote + virtr)
+					if (wrote + virtr) {
+						p += len - written;
+						virtr += len - written;
 						break;
+					}
 					free_page((unsigned long)kbuf);
 					return -EFAULT;
 				}
_