The problem with introducing IFF_GSO_HDR is that it needs to set dev->features
(to enable GSO, checksumming, etc), 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 IFF_GSO_HDR.
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 <linux/if_tun.h>
#include <sys/types.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <err.h>
#include <stdio.h>
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" },
{ IFF_GSO_HDR, "GSO_HDR" },
};
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;
}
---
drivers/net/tun.c | 9 +++++++++
include/linux/if_tun.h | 2 ++
2 files changed, 11 insertions(+)
diff -r ba3c0eb8741a drivers/net/tun.c
--- a/drivers/net/tun.c Wed Jan 16 17:35:25 2008 +1100
+++ b/drivers/net/tun.c Wed Jan 16 22:11:11 2008 +1100
@@ -583,6 +779,15 @@ static int tun_chr_ioctl(struct inode *i
if (copy_to_user(argp, &ifr, sizeof(ifr)))
return -EFAULT;
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. This was introduced with IFF_GSO_HDR, so if a
+ * kernel doesn't have this ioctl, it doesn't have GSO header
+ * support. */
+ return put_user(IFF_ALL_FLAGS, (unsigned int __user*)argp);
}
if (!tun)
diff -r ba3c0eb8741a include/linux/if_tun.h
--- a/include/linux/if_tun.h Wed Jan 16 17:35:25 2008 +1100
+++ b/include/linux/if_tun.h Wed Jan 16 22:11:11 2008 +1100
@@ -79,13 +80,15 @@ struct tun_struct {
#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
#define IFF_TAP 0x0002
#define IFF_NO_PI 0x1000
#define IFF_ONE_QUEUE 0x2000
#define IFF_GSO_HDR 0x4000
+#define IFF_ALL_FLAGS (IFF_TUN|IFF_TAP|IFF_NO_PI|IFF_ONE_QUEUE|IFF_GSO_HDR)
struct tun_pi {
unsigned short flags;
--
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