[Devel] [PATCH vz10 25/32] kernfs: build the KERNFS_GET_NS ioctl only with CONFIG_NET

[Konstantin Khorenko <khorenko@virtuozzo.com>]

From: Eva Kurchatova <eva.kurchatova@virtuozzo.com>

The KERNFS_GET_NS ioctl hands out the network namespace a sysfs directory
is tagged with, so it calls maybe_get_net_ns(), which exists only with the
networking stack:

  fs/kernfs/file.c:1030:50: error: 'maybe_get_net_ns' undeclared (first
                            use in this function)
  fs/kernfs/file.c:1029:21: error: this statement may fall through
                            [-Werror=implicit-fallthrough=]

Compile the whole body under CONFIG_NET and return -ENOTTY otherwise.  The
three local variables move inside the guard along with it: left at function
scope they are unused with CONFIG_NET=n, which is an error once
CONFIG_WERROR=y.

The switch is replaced by an if as part of that, because it reads better
once there is an #ifdef in the picture.  Keeping the switch would mean
either a second #ifdef of its own around the declarations, or a switch
whose only unconditional arm is the default one; an if plus a tail return
says the same thing under a single guard.

Fixes: 38c2983fa828 ("kernfs/sysfs: add ioctl to get fd network namespace tag")
Feature: sysfs: per-CT entries visibility and permissions configuration
https://virtuozzo.atlassian.net/browse/VSTOR-134732
Signed-off-by: Eva Kurchatova <eva.kurchatova@virtuozzo.com>
Signed-off-by: Konstantin Khorenko <khorenko@virtuozzo.com>
---
 fs/kernfs/file.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/kernfs/file.c b/fs/kernfs/file.c
index 092a4dcd2ebf..5c72f05a9e41 100644
--- a/fs/kernfs/file.c
+++ b/fs/kernfs/file.c
@@ -1018,19 +1018,19 @@ EXPORT_SYMBOL_GPL(kernfs_notify);
 long kernfs_ioctl(struct file *file, unsigned int ioctl,
 		  unsigned long arg)
 {
+#ifdef CONFIG_NET
 	struct dentry *dentry = file->f_path.dentry;
 	const void *ns = kernfs_info(dentry->d_sb)->ns;
 	struct net *net;
 
-	switch (ioctl) {
-	case KERNFS_GET_NS:
+	if (ioctl == KERNFS_GET_NS) {
 		if (dentry->d_sb->s_magic != SYSFS_MAGIC || !ns)
 			return -ENOTTY;
 		net = (struct net *)ns;
 		return open_related_ns(&net->ns, maybe_get_net_ns);
-	default:
-		return -ENOTTY;
 	}
+#endif
+	return -ENOTTY;
 }
 
 const struct file_operations kernfs_file_fops = {
-- 
2.47.1