Re: [-mm Patch]nbd: check the return value of sysfs_create_file

[Andrew Morton <akpm@linux-foundation.org>]

On Sat, 28 Apr 2007 13:30:23 +0800 WANG Cong <xiyou.wangcong@gmail.com> wrote:

> Since 'sysfs_create_file' is declared with attribute warn_unused_result, we must always check its return value carefully.
> 

Well that's not really the reason for your patch.

warn_unused_result is there to tell us that there are deeper problems in
the code which need addressing: the failure to check the
sysfs_create_file() return value means that bugs in the kernel can remain
undetected, or can be harder to find.

> 
> ---
> 
> --- linux-2.6.21-rc7-mm2/drivers/block/nbd.c.orig	2007-04-27 17:27:47.000000000 +0800
> +++ linux-2.6.21-rc7-mm2/drivers/block/nbd.c	2007-04-27 17:47:32.000000000 +0800
> @@ -373,7 +373,10 @@ static void nbd_do_it(struct nbd_device 
>  	BUG_ON(lo->magic != LO_MAGIC);
>  
>  	lo->pid = current->pid;
> -	sysfs_create_file(&lo->disk->kobj, &pid_attr.attr);
> +	if (sysfs_create_file(&lo->disk->kobj, &pid_attr.attr)) {
> +		printk(KERN_ERR "nbd: sysfs_create_file failed!");
> +		return;
> +	}
>  
>  	while ((req = nbd_read_stat(lo)) != NULL)
>  		nbd_end_request(req);

It would better saner to propagate this error back through callers:

--- a/drivers/block/nbd.c~nbd-check-the-return-value-of-sysfs_create_file-fix
+++ a/drivers/block/nbd.c
@@ -366,23 +366,25 @@ static struct disk_attribute pid_attr = 
 	.show = pid_show,
 };
 
-static void nbd_do_it(struct nbd_device *lo)
+static int nbd_do_it(struct nbd_device *lo)
 {
 	struct request *req;
+	int ret;
 
 	BUG_ON(lo->magic != LO_MAGIC);
 
 	lo->pid = current->pid;
-	if (sysfs_create_file(&lo->disk->kobj, &pid_attr.attr)) {
+	ret = sysfs_create_file(&lo->disk->kobj, &pid_attr.attr);
+	if (ret) {
 		printk(KERN_ERR "nbd: sysfs_create_file failed!");
-		return;
+		return ret;
 	}
 
 	while ((req = nbd_read_stat(lo)) != NULL)
 		nbd_end_request(req);
 
 	sysfs_remove_file(&lo->disk->kobj, &pid_attr.attr);
-	return;
+	return 0;
 }
 
 static void nbd_clear_que(struct nbd_device *lo)
@@ -572,7 +574,9 @@ static int nbd_ioctl(struct inode *inode
 	case NBD_DO_IT:
 		if (!lo->file)
 			return -EINVAL;
-		nbd_do_it(lo);
+		error = nbd_do_it(lo);
+		if (error)
+			return error;
 		/* on return tidy up in case we have a signal */
 		/* Forcibly shutdown the socket causing all listeners
 		 * to error
_