From 07240fd0902c872f044f523893364a1a24c9f278 Mon Sep 17 00:00:00 2001 From: Rusty Russell Date: Thu, 3 Jul 2008 03:45:32 -0700 Subject: [PATCH] tun: Interface to query tun/tap features. The problem with introducing checksum offload and gso to tun is they need to set dev->features to enable GSO and/or checksumming, which is supposed to be done before register_netdevice(), ie. as part of TUNSETIFF. Unfortunately, TUNSETIFF has always just ignored flags it doesn't understand, so there's no good way of detecting whether the kernel supports new IFF_ flags. This patch implements a TUNGETFEATURES ioctl which returns all the valid IFF flags. It could be extended later to include other features. Here's an example program which uses it: #include #include #include #include #include #include #include static struct { unsigned int flag; const char *name; } known_flags[] = { { IFF_TUN, "TUN" }, { IFF_TAP, "TAP" }, { IFF_NO_PI, "NO_PI" }, { IFF_ONE_QUEUE, "ONE_QUEUE" }, }; int main() { unsigned int features, i; int netfd = open("/dev/net/tun", O_RDWR); if (netfd < 0) err(1, "Opening /dev/net/tun"); if (ioctl(netfd, TUNGETFEATURES, &features) != 0) { printf("Kernel does not support TUNGETFEATURES, guessing\n"); features = (IFF_TUN|IFF_TAP|IFF_NO_PI|IFF_ONE_QUEUE); } printf("Available features are: "); for (i = 0; i < sizeof(known_flags)/sizeof(known_flags[0]); i++) { if (features & known_flags[i].flag) { features &= ~known_flags[i].flag; printf("%s ", known_flags[i].name); } } if (features) printf("(UNKNOWN %#x)", features); printf("\n"); return 0; } Signed-off-by: Rusty Russell Acked-by: Max Krasnyansky Signed-off-by: David S. Miller --- drivers/net/tun.c | 8 ++++++++ include/linux/if_tun.h | 1 + 2 files changed, 9 insertions(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 7ab94c825b57..3bb991fd2b51 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -640,6 +640,14 @@ static int tun_chr_ioctl(struct inode *inode, struct file *file, return 0; } + if (cmd == TUNGETFEATURES) { + /* Currently this just means: "what IFF flags are valid?". + * This is needed because we never checked for invalid flags on + * TUNSETIFF. */ + return put_user(IFF_TUN | IFF_TAP | IFF_NO_PI | IFF_ONE_QUEUE, + (unsigned int __user*)argp); + } + if (!tun) return -EBADFD; diff --git a/include/linux/if_tun.h b/include/linux/if_tun.h index 18f31b6187a3..94f76a112303 100644 --- a/include/linux/if_tun.h +++ b/include/linux/if_tun.h @@ -40,6 +40,7 @@ #define TUNSETOWNER _IOW('T', 204, int) #define TUNSETLINK _IOW('T', 205, int) #define TUNSETGROUP _IOW('T', 206, int) +#define TUNGETFEATURES _IOR('T', 207, unsigned int) /* TUNSETIFF ifr flags */ #define IFF_TUN 0x0001 -- 2.30.2