can't print a target pointer string field

[Jeff Haran <Jeff dot Haran at citrix dot com>]

Hi,

First off, if this is the wrong place to be posting dumb newbie user questions like this, please let me know if there is a more appropriate venue.

I am trying to displayt the name of the device associated with a struct sk_buff, but am getting an error when stap parses my script:

[root@s01b06 jharan]# cat neigh_event_send.stp
global hit
probe kernel.statement("*@net/core/neighbour.c:934")
{
        printf("__neigh_event_send() hit %d, skb %x, dev %x, name %s\n", hit++, $skb, $skb->dev, $skb->dev->name)
}

[root@s01b06 jharan]# stap -v -r 2.6.32-220.el6.x86_64 neigh_event_send.stp -m neigh_event_send -p 4
Pass 1: parsed user script and 77 library script(s) using 97288virt/22844res/2920shr kb, in 130usr/10sys/143real ms.
semantic error: type mismatch ( long vs. string ): identifier '$skb' at neigh_event_send.stp:4:98
        source:         printf("__neigh_event_send() hit %d, skb %x, dev %x, name %s\n", hit++, $skb, $skb->dev, $skb->dev->name)
                                                                                                                 ^
Pass 2: analyzed script: 1 probe(s), 3 function(s), 0 embed(s), 1 global(s) using 271644virt/81032res/19500shr kb, in 190usr/80sys/267real ms.
Pass 2: analysis failed.  Try again with another '--vp 01' option.
[root@s01b06 jharan]#

On a fixed font, the '^' pointing out the error shows up under the last parameter to printf (the '$' at the beginning of $skb->dev->name).

skb is a pointer to one of these (omitting most fields for brevity):

struct sk_buff {
        ...
        struct net_device       *dev;
        ...
};

struct net_device looks like:

struct net_device
{
        ...
        char                    name[IFNAMSIZ];
        ...
};

So skb->dev->name looks like a string to me.

Why the reported type mismatch? And how can I display the name field, if that's possible?

Thanks,

Jeff Haran