tun: Report "persist" flag to userspace

The TUN_PERSIST flag is not reported at all -- both TUNGETIFF, and sysfs
"flags" attribute skip one. Knowing whether a device is persistent or not
is critical for checkpoint-restore, thus I propose to add the read-only
IFF_PERSIST one for this.

Setting this new IFF_PERSIST is hardly possible, as TUNSETIFF doesn't check
for unknown flags being zero and thus there can be trash.

Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 0 deletions

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 89776c592151..b90a73165d30 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -1530,6 +1530,9 @@ static int tun_flags(struct tun_struct *tun)
         if (tun->flags & TUN_TAP_MQ)
                 flags |= IFF_MULTI_QUEUE;
 
+        if (tun->flags & TUN_PERSIST)
+                flags |= IFF_PERSIST;
+
         return flags;
 }