Notes on ethtool and underlying kernel hooks/code.

General links:

• ethtool git repo

Kernel source links:

• include/
  • uapi/
    • linux/
      • if.h (for struct ifreq)
      • sockios.h (for SIOCETHTOOL}
      • ethtool.h

From ethtool's internal.h:

/* Context for sub-commands */
struct cmd_context {
        const char *devname;    /* net device name */
        int fd;                 /* socket suitable for ethtool ioctl */
        struct ifreq ifr;       /* ifreq suitable for ethtool ioctl */
        int argc;               /* number of arguments to the sub-command */
        char **argp;            /* arguments to the sub-command */
};

and from ethtool.c, the wrapper for ioctl calls:

#ifndef TEST_ETHTOOL
int send_ioctl(struct cmd_context *ctx, void *cmd)
{
        ctx->ifr.ifr_data = cmd;
        return ioctl(ctx->fd, SIOCETHTOOL, &ctx->ifr);
}
#endif

From if.h:

/* for compatibility with glibc net/if.h */
#if __UAPI_DEF_IF_IFREQ
struct ifreq {
#define IFHWADDRLEN     6
        union
        {
                char    ifrn_name[IFNAMSIZ];            /* if name, e.g. "en0" */
        } ifr_ifrn;

        union {
                struct  sockaddr ifru_addr;
                struct  sockaddr ifru_dstaddr;
                struct  sockaddr ifru_broadaddr;
                struct  sockaddr ifru_netmask;
                struct  sockaddr ifru_hwaddr;
                short   ifru_flags;
                int     ifru_ivalue;
                int     ifru_mtu;
                struct  ifmap ifru_map;
                char    ifru_slave[IFNAMSIZ];   /* Just fits the size */
                char    ifru_newname[IFNAMSIZ];
                void *  ifru_data;
                struct  if_settings ifru_settings;
        } ifr_ifru;
};
#endif /* __UAPI_DEF_IF_IFREQ */

#define ifr_name        ifr_ifrn.ifrn_name      /* interface name       */
#define ifr_hwaddr      ifr_ifru.ifru_hwaddr    /* MAC address          */
#define ifr_addr        ifr_ifru.ifru_addr      /* address              */
#define ifr_dstaddr     ifr_ifru.ifru_dstaddr   /* other end of p-p lnk */
#define ifr_broadaddr   ifr_ifru.ifru_broadaddr /* broadcast address    */
#define ifr_netmask     ifr_ifru.ifru_netmask   /* interface net mask   */
#define ifr_flags       ifr_ifru.ifru_flags     /* flags                */
#define ifr_metric      ifr_ifru.ifru_ivalue    /* metric               */
#define ifr_mtu         ifr_ifru.ifru_mtu       /* mtu                  */
#define ifr_map         ifr_ifru.ifru_map       /* device map           */
#define ifr_slave       ifr_ifru.ifru_slave     /* slave device         */
#define ifr_data        ifr_ifru.ifru_data      /* for use by interface */
#define ifr_ifindex     ifr_ifru.ifru_ivalue    /* interface index      */
#define ifr_bandwidth   ifr_ifru.ifru_ivalue    /* link bandwidth       */
#define ifr_qlen        ifr_ifru.ifru_ivalue    /* Queue length         */
#define ifr_newname     ifr_ifru.ifru_newname   /* New name             */
#define ifr_settings    ifr_ifru.ifru_settings  /* Device/proto settings*/