FreeBSD/Linux Kernel Cross Reference
sys/net/if_media.c

     /*      $NetBSD: if_media.c,v 1.54 2022/09/03 02:47:59 thorpej Exp $    */
     
     /*-
      * Copyright (c) 1998, 2020 The NetBSD Foundation, Inc.
      * All rights reserved.
      *
      * This code is derived from software contributed to The NetBSD Foundation
      * by Jason R. Thorpe of the Numerical Aerospace Simulation Facility,
      * NASA Ames Research Center.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     *
     * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
     * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
     * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
     * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
     * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
     * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
     * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
     * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
     * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
     * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
     * POSSIBILITY OF SUCH DAMAGE.
     */
    
    /*
     * Copyright (c) 1997
     *      Jonathan Stone and Jason R. Thorpe.  All rights reserved.
     *
     * This software is derived from information provided by Matt Thomas.
     *
     * Redistribution and use in source and binary forms, with or without
     * modification, are permitted provided that the following conditions
     * are met:
     * 1. Redistributions of source code must retain the above copyright
     *    notice, this list of conditions and the following disclaimer.
     * 2. Redistributions in binary form must reproduce the above copyright
     *    notice, this list of conditions and the following disclaimer in the
     *    documentation and/or other materials provided with the distribution.
     * 3. All advertising materials mentioning features or use of this software
     *    must display the following acknowledgement:
     *      This product includes software developed by Jonathan Stone
     *      and Jason R. Thorpe for the NetBSD Project.
     * 4. The names of the authors may not be used to endorse or promote products
     *    derived from this software without specific prior written permission.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
     * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
     * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
     * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
     * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
     * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
     * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
     * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
     * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
     * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
     * SUCH DAMAGE.
     */
    
    /*
     * BSD/OS-compatible network interface media selection.
     *
     * Where it is safe to do so, this code strays slightly from the BSD/OS
     * design.  Software which uses the API (device drivers, basically)
     * shouldn't notice any difference.
     *
     * Many thanks to Matt Thomas for providing the information necessary
     * to implement this interface.
     */
    
    #include <sys/cdefs.h>
    __KERNEL_RCSID(0, "$NetBSD: if_media.c,v 1.54 2022/09/03 02:47:59 thorpej Exp $");
    
    #define __IFMEDIA_PRIVATE
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/errno.h>
    #include <sys/ioctl.h>
    #include <sys/socket.h>
    #include <sys/kmem.h>
    
    #include <net/if.h>
    #include <net/if_media.h>
    
    static void     ifmedia_status(struct ifmedia *, struct ifnet *,
                        struct ifmediareq *);
    static struct ifmedia_entry *
                    ifmedia_match_locked(struct ifmedia *, u_int, u_int);
    
    /*
     * Compile-time options:
    * IFMEDIA_DEBUG:
    *      Turn on implementation-level debug printfs.
    *      Useful for debugging newly-ported drivers.
    */
   
   #ifdef IFMEDIA_DEBUG
   int     ifmedia_debug = 0;
   static  void ifmedia_printword(int);
   #endif
   
   /*
    * We need to implement a recursive mutex to handle the un-converted
    * driver case.  For a fully MP-safe driver, the media lock will be
    * held before calling any of the entry points that require it.  However,
    * this is not necessarily the case for a driver that hasn't yet been
    * converted, and the entry point calls may be nested (for example
    * mii_ifmedia_change -> ether_mediachange -> mii_mediachg).  Luckily,
    * the nesting won't be very deep, and 4 nested holds should be plenty.
    */
   #define IFM_L_OWNLOCK           0x01
   #define IFM_L_COUNT_MASK        0x3UL
   #define IFM_L_CPU_MASK          ~(IFM_L_COUNT_MASK)
   
   void
   ifmedia_lock_for_legacy(struct ifmedia *ifm)
   {
           uintptr_t cnt = IFM_L_OWNLOCK;
           uintptr_t ci;
   
           if (mutex_tryenter(ifm->ifm_lock)) {
                   goto gotit;
           }
   
           kpreempt_disable();
           ci = (uintptr_t)curcpu();
           if ((ifm->ifm_legacy & IFM_L_CPU_MASK) == ci) {
                   cnt = ifm->ifm_legacy & IFM_L_COUNT_MASK;
                   KASSERT(cnt < IFM_L_COUNT_MASK);
                   cnt++;
                   kpreempt_enable();
                   goto gotit;
           }
           kpreempt_enable();
   
           mutex_enter(ifm->ifm_lock);
    gotit:
           KASSERT(kpreempt_disabled());
           ci = (uintptr_t)curcpu();
           KASSERT((ci & IFM_L_CPU_MASK) == ci);
           ifm->ifm_legacy = ci | cnt;
   }
   
   void
   ifmedia_unlock_for_legacy(struct ifmedia *ifm)
   {
           uintptr_t cnt;
           uintptr_t ci = (uintptr_t)curcpu();
   
           KASSERT(kpreempt_disabled());
           KASSERT((ifm->ifm_legacy & IFM_L_CPU_MASK) == ci);
           cnt = ifm->ifm_legacy & IFM_L_COUNT_MASK;
           KASSERT(cnt != 0);
           if (cnt == IFM_L_OWNLOCK) {
                   ifm->ifm_legacy = IFM_L_OWNLOCK;
                   mutex_exit(ifm->ifm_lock);
                   return;
           }
           cnt--;
           ifm->ifm_legacy = ci | cnt;
   }
   
   /*
    * Initialize if_media struct for a specific interface instance.
    */
   void
   ifmedia_init_with_lock(struct ifmedia *ifm, int dontcare_mask,
       ifm_change_cb_t change_callback, ifm_stat_cb_t status_callback,
       kmutex_t *lock)
   {
   
           /*
            * XXX Would really like to assert:
            *
            *      !if_is_mpsafe(ifp) || ((if_is_mpsafe(ifp) && lock != NULL)
            *
            * ...but we don't have access to the ifnet here.
            */
   
           TAILQ_INIT(&ifm->ifm_list);
           ifm->ifm_cur = NULL;
           ifm->ifm_media = IFM_NONE;
           ifm->ifm_mask = dontcare_mask;          /* IF don't-care bits */
           ifm->ifm_change = change_callback;
           ifm->ifm_status = status_callback;
           ifm->ifm_legacy = 0;
   
           if (lock == NULL) {
                   /*
                    * This is to support drivers that are not yet MP-safe
                    * with regard to the ifmedia layer.  In these cases,
                    * we supply the lock and we ensure it's taken upon entry
                    * to various routines that expect it to be held.  When
                    * we do this, we expect that the driver is in general a
                    * non-MP-safe driver and has already gone to splnet().
                    */
                   lock = mutex_obj_alloc(MUTEX_DEFAULT, IPL_NET);
                   ifm->ifm_legacy = IFM_L_OWNLOCK;
           }
           ifm->ifm_lock = lock;
   }
   
   void
   ifmedia_init(struct ifmedia *ifm, int dontcare_mask,
       ifm_change_cb_t change_callback, ifm_stat_cb_t status_callback)
   {
           ifmedia_init_with_lock(ifm, dontcare_mask, change_callback,
               status_callback, NULL);
   }
   
   /*
    * Free resources associated with an ifmedia.
    */
   void
   ifmedia_fini(struct ifmedia *ifm)
   {
   
           ifmedia_removeall(ifm);
   
           if (ifm->ifm_legacy) {
                   KASSERT(ifm->ifm_legacy == IFM_L_OWNLOCK);
                   mutex_obj_free(ifm->ifm_lock);
           }
           ifm->ifm_legacy = 0;
           ifm->ifm_lock = NULL;
   }
   
   int
   ifmedia_change(struct ifmedia *ifm, struct ifnet *ifp)
   {
           int rv;
   
           IFMEDIA_LOCK_FOR_LEGACY(ifm);
           KASSERT(ifmedia_locked(ifm));
           if (ifm->ifm_change)
                   rv = (*ifm->ifm_change)(ifp);
           else
                   rv = -1;
           IFMEDIA_UNLOCK_FOR_LEGACY(ifm);
   
           return rv;
   }
   
   static void
   ifmedia_status(struct ifmedia *ifm, struct ifnet *ifp, struct ifmediareq *ifmr)
   {
   
           KASSERT(ifmedia_locked(ifm));
           if (ifm->ifm_status == NULL)
                   return;
           (*ifm->ifm_status)(ifp, ifmr);
   }
   
   /*
    * Add a media configuration to the list of supported media
    * for a specific interface instance.
    */
   static void
   ifmedia_add_entry(struct ifmedia *ifm, int mword, int data, void *aux,
       struct ifmedia_entry *entry)
   {
   
   #ifdef IFMEDIA_DEBUG
           if (ifmedia_debug) {
                   if (ifm == NULL) {
                           printf("ifmedia_add: null ifm\n");
                           return;
                   }
                   printf("Adding entry for ");
                   ifmedia_printword(mword);
           }
   #endif
   
           entry->ifm_media = mword;
           entry->ifm_data = data;
           entry->ifm_aux = aux;
           TAILQ_INSERT_TAIL(&ifm->ifm_list, entry, ifm_list);
   }
   
   void
   ifmedia_add(struct ifmedia *ifm, int mword, int data, void *aux)
   {
           struct ifmedia_entry *entry;
   
           entry = kmem_zalloc(sizeof(*entry), KM_SLEEP);
           ifmedia_lock(ifm);
           ifmedia_add_entry(ifm, mword, data, aux, entry);
           ifmedia_unlock(ifm);
   }
   
   /*
    * Add an array of media configurations to the list of
    * supported media for a specific interface instance.
    */
   void
   ifmedia_list_add(struct ifmedia *ifm, struct ifmedia_entry *lp, int count)
   {
           int i;
   
           for (i = 0; i < count; i++)
                   ifmedia_add(ifm, lp[i].ifm_media, lp[i].ifm_data,
                       lp[i].ifm_aux);
   }
   
   /*
    * Set the default active media.
    *
    * Called by device-specific code which is assumed to have already
    * selected the default media in hardware.  We do _not_ call the
    * media-change callback.
    */
   void
   ifmedia_set(struct ifmedia *ifm, int target)
   {
           struct ifmedia_entry *match, *entry = NULL;
   
           ifmedia_lock(ifm);
           match = ifmedia_match_locked(ifm, target, ifm->ifm_mask);
   
           /*
            * If we didn't find the requested media, then we try to fall
            * back to target-type (IFM_ETHER, e.g.) | IFM_NONE.  If that's
            * not on the list, then we add it and set the media to it.
            *
            * Since ifmedia_set is almost always called with IFM_AUTO or
            * with a known-good media, this really should only occur if we:
            *
            * a) didn't find any PHYs, or
            * b) didn't find an autoselect option on the PHY when the
            *    parent ethernet driver expected to.
            *
            * In either case, it makes sense to select no media.
            */
           if (match == NULL) {
                   printf("ifmedia_set: no match for 0x%x/0x%x\n",
                       target, ~ifm->ifm_mask);
                   target = (target & IFM_NMASK) | IFM_NONE;
                   match = ifmedia_match_locked(ifm, target, ifm->ifm_mask);
                   if (match == NULL) {
                           ifmedia_unlock(ifm);
                           entry = kmem_zalloc(sizeof(*entry), KM_SLEEP);
                           ifmedia_lock(ifm);
                           match = ifmedia_match_locked(ifm, target,
                               ifm->ifm_mask);
                           if (match == NULL) {
                                   ifmedia_add_entry(ifm, target, 0, NULL, entry);
                                   entry = NULL;
                           }
                           match = ifmedia_match_locked(ifm, target,
                               ifm->ifm_mask);
                           if (match == NULL)
                                   panic("ifmedia_set failed");
                   }
           }
           ifm->ifm_cur = match;
           ifmedia_unlock(ifm);
   
           if (entry)
                   kmem_free(entry, sizeof(*entry));
   
   #ifdef IFMEDIA_DEBUG
           if (ifmedia_debug) {
                   printf("ifmedia_set: target ");
                   ifmedia_printword(target);
                   printf("ifmedia_set: setting to ");
                   ifmedia_printword(ifm->ifm_cur->ifm_media);
           }
   #endif
   }
   
   static int
   ifmedia_getwords(struct ifmedia * const ifm, int *words, int maxwords)
   {
           struct ifmedia_entry *ep;
           int nwords = 0;
   
           KASSERT(ifmedia_locked(ifm));
   
           TAILQ_FOREACH(ep, &ifm->ifm_list, ifm_list) {
                   if (words != NULL && nwords < maxwords) {
                           words[nwords] = ep->ifm_media;
                   }
                   nwords++;
           }
   
           return nwords;
   }
   
   #define IFMEDIA_IOCTL_LOCK(ifm)                                         \
   do {                                                                    \
           if (ifmedia_islegacy(ifm))                                      \
                   ifmedia_lock_for_legacy(ifm);                           \
           else                                                            \
                   ifmedia_lock(ifm);                                      \
   } while (/*CONSTCOND*/0)
   
   #define IFMEDIA_IOCTL_UNLOCK(ifm)                                       \
   do {                                                                    \
           if (ifmedia_islegacy(ifm))                                      \
                   ifmedia_unlock_for_legacy(ifm);                         \
           else                                                            \
                   ifmedia_unlock(ifm);                                    \
   } while (/*CONSTCOND*/0)
   
   /*
    * Device-independent media ioctl support function.
    */
   int
   ifmedia_ioctl(struct ifnet *ifp, struct ifreq *ifr, struct ifmedia *ifm,
       u_long cmd)
   {
           struct ifmedia_entry *match;
           struct ifmediareq *ifmr = (struct ifmediareq *)ifr;
           int error = 0;
   
           if (ifp == NULL || ifr == NULL || ifm == NULL)
                   return EINVAL;
   
           KERNEL_LOCK_UNLESS_IFP_MPSAFE(ifp);
   
           switch (cmd) {
           case SIOCSIFMEDIA:      /* Set the current media. */
           {
                   struct ifmedia_entry *oldentry;
                   u_int oldmedia;
                   u_int newmedia = ifr->ifr_media;
   
                   IFMEDIA_IOCTL_LOCK(ifm);
   
                   match = ifmedia_match_locked(ifm, newmedia, ifm->ifm_mask);
                   if (match == NULL) {
   #ifdef IFMEDIA_DEBUG
                           if (ifmedia_debug) {
                                   printf("ifmedia_ioctl: no media found for "
                                       "0x%08x\n", newmedia);
                           }
   #endif
                           IFMEDIA_IOCTL_UNLOCK(ifm);
                           error = EINVAL;
                           break;
                   }
   
                   /*
                    * If no change, we're done.
                    * XXX Automedia may involve software intervention.
                    *     Keep going in case the connected media changed.
                    *     Similarly, if best match changed (kernel debugger?).
                    */
                   if ((IFM_SUBTYPE(newmedia) != IFM_AUTO) &&
                       (newmedia == ifm->ifm_media) && (match == ifm->ifm_cur)) {
                           IFMEDIA_IOCTL_UNLOCK(ifm);
                           break;
                   }
   
                   /*
                    * We found a match, now make the driver switch to it.
                    * Make sure to preserve our old media type in case the
                    * driver can't switch.
                    */
   #ifdef IFMEDIA_DEBUG
                   if (ifmedia_debug) {
                           printf("ifmedia_ioctl: switching %s to ",
                               ifp->if_xname);
                           ifmedia_printword(match->ifm_media);
                   }
   #endif
                   oldentry = ifm->ifm_cur;
                   oldmedia = ifm->ifm_media;
                   ifm->ifm_cur = match;
                   ifm->ifm_media = newmedia;
                   error = ifmedia_change(ifm, ifp);
                   if (error) {
                           ifm->ifm_cur = oldentry;
                           ifm->ifm_media = oldmedia;
                   }
                   IFMEDIA_IOCTL_UNLOCK(ifm);
                   break;
           }
   
           /* Get list of available media and current media on interface. */
           case SIOCGIFMEDIA:
           {
                   int nwords1, nwords2;
   
                   if (ifmr->ifm_count < 0) {
                           error = EINVAL;
                           break;
                   }
   
                   IFMEDIA_IOCTL_LOCK(ifm);
                   ifmr->ifm_active = ifmr->ifm_current = ifm->ifm_cur ?
                       ifm->ifm_cur->ifm_media : IFM_NONE;
                   ifmr->ifm_mask = ifm->ifm_mask;
                   ifmr->ifm_status = 0;
                   ifmedia_status(ifm, ifp, ifmr);
   
                   /*
                    * Count them so we know how much is the max we'll
                    * need.
                    */
                   nwords1 = nwords2 = ifmedia_getwords(ifm, NULL, 0);
                   IFMEDIA_IOCTL_UNLOCK(ifm);
   
                   if (ifmr->ifm_count != 0) {
                           int maxwords = MIN(nwords1, ifmr->ifm_count);
                           int *kptr = kmem_zalloc(maxwords * sizeof(int),
                               KM_SLEEP);
   
                           ifmedia_lock(ifm);
                           nwords2 = ifmedia_getwords(ifm, kptr, maxwords);
                           ifmedia_unlock(ifm);
                           error = copyout(kptr, ifmr->ifm_ulist,
                               maxwords * sizeof(int));
                           if (error == 0 && nwords2 > nwords1)
                                   error = E2BIG;  /* oops! */
                           kmem_free(kptr, maxwords * sizeof(int));
                   }
                   /* Update with the real number */
                   ifmr->ifm_count = nwords2;
                   break;
           }
   
           default:
                   error = EINVAL;
                   break;
           }
   
           KERNEL_UNLOCK_UNLESS_IFP_MPSAFE(ifp);
   
           return error;
   }
   
   /*
    * Find media entry matching a given ifm word.
    */
   static struct ifmedia_entry *
   ifmedia_match_locked(struct ifmedia *ifm, u_int target, u_int mask)
   {
           struct ifmedia_entry *match, *next;
   
           match = NULL;
           mask = ~mask;
   
           TAILQ_FOREACH(next, &ifm->ifm_list, ifm_list) {
                   if ((next->ifm_media & mask) == (target & mask)) {
                           if (match) {
   #if defined(IFMEDIA_DEBUG) || defined(DIAGNOSTIC)
                                   printf("ifmedia_match: multiple match for "
                                       "0x%x/0x%x, selected instance %d\n",
                                       target, mask, IFM_INST(match->ifm_media));
   #endif
                                   break;
                           }
                           match = next;
                   }
           }
   
           return match;
   }
   
   struct ifmedia_entry *
   ifmedia_match(struct ifmedia *ifm, u_int target, u_int mask)
   {
           struct ifmedia_entry *match;
   
           /*
            * N.B. We expect the caller is responsible fot the lifecycle
            * of the media entries.  Use with extreme caution.
            */
   
           ifmedia_lock(ifm);
           match = ifmedia_match_locked(ifm, target, mask);
           ifmedia_unlock(ifm);
           return match;
   }
   
   /*
    * Delete all media for a given instance.
    */
   void
   ifmedia_delete_instance(struct ifmedia *ifm, u_int inst)
   {
           struct ifmedia_entry *ife, *nife;
           TAILQ_HEAD(, ifmedia_entry) dead_entries;
   
           TAILQ_INIT(&dead_entries);
   
           ifmedia_lock(ifm);
           TAILQ_FOREACH_SAFE(ife, &ifm->ifm_list, ifm_list, nife) {
                   if (inst == IFM_INST_ANY ||
                       inst == IFM_INST(ife->ifm_media)) {
                           if (ifm->ifm_cur == ife) {
                                   ifm->ifm_cur = NULL;
                                   ifm->ifm_media = IFM_NONE;
                           }
                           TAILQ_REMOVE(&ifm->ifm_list, ife, ifm_list);
                           TAILQ_INSERT_TAIL(&dead_entries, ife, ifm_list);
                   }
           }
           ifmedia_unlock(ifm);
   
           TAILQ_FOREACH_SAFE(ife, &dead_entries, ifm_list, nife) {
                   TAILQ_REMOVE(&dead_entries, ife, ifm_list);
                   kmem_free(ife, sizeof(*ife));
           }
   }
   
   void
   ifmedia_removeall(struct ifmedia *ifm)
   {
   
           ifmedia_delete_instance(ifm, IFM_INST_ANY);
   }
   
   /*
    * Compute the interface `baudrate' from the media, for the interface
    * metrics (used by routing daemons).
    */
   static const struct ifmedia_baudrate ifmedia_baudrate_descriptions[] =
       IFM_BAUDRATE_DESCRIPTIONS;
   
   uint64_t
   ifmedia_baudrate(int mword)
   {
           int i;
   
           for (i = 0; ifmedia_baudrate_descriptions[i].ifmb_word != 0; i++) {
                   if (IFM_TYPE_SUBTYPE_MATCH(mword,
                       ifmedia_baudrate_descriptions[i].ifmb_word))
                           return ifmedia_baudrate_descriptions[i].ifmb_baudrate;
           }
   
           /* Not known. */
           return 0;
   }
   
   #ifdef IFMEDIA_DEBUG
   
   static const struct ifmedia_description ifm_type_descriptions[] =
       IFM_TYPE_DESCRIPTIONS;
   
   static const struct ifmedia_description ifm_subtype_descriptions[] =
       IFM_SUBTYPE_DESCRIPTIONS;
   
   static const struct ifmedia_description ifm_option_descriptions[] =
       IFM_OPTION_DESCRIPTIONS;
   
   /*
    * print a media word.
    */
   static void
   ifmedia_printword(int ifmw)
   {
           const struct ifmedia_description *desc;
           int seen_option = 0;
   
           /* Print the top-level interface type. */
           for (desc = ifm_type_descriptions; desc->ifmt_string != NULL;
                desc++) {
                   if (IFM_TYPE(ifmw) == desc->ifmt_word)
                           break;
           }
           if (desc->ifmt_string == NULL)
                   printf("<unknown type> ");
           else
                   printf("%s ", desc->ifmt_string);
   
           /* Print the subtype. */
           for (desc = ifm_subtype_descriptions; desc->ifmt_string != NULL;
                desc++) {
                   if (IFM_TYPE_MATCH(desc->ifmt_word, ifmw) &&
                       IFM_SUBTYPE(desc->ifmt_word) == IFM_SUBTYPE(ifmw))
                           break;
           }
           if (desc->ifmt_string == NULL)
                   printf("<unknown subtype>");
           else
                   printf("%s", desc->ifmt_string);
   
           /* Print any options. */
           for (desc = ifm_option_descriptions; desc->ifmt_string != NULL;
                desc++) {
                   if (IFM_TYPE_MATCH(desc->ifmt_word, ifmw) &&
                       (ifmw & desc->ifmt_word) != 0 &&
                       (seen_option & IFM_OPTIONS(desc->ifmt_word)) == 0) {
                           if (seen_option == 0)
                                   printf(" <");
                           printf("%s%s", seen_option ? "," : "",
                               desc->ifmt_string);
                           seen_option |= IFM_OPTIONS(desc->ifmt_word);
                   }
           }
           printf("%s\n", seen_option ? ">" : "");
   }
   
   #endif /* IFMEDIA_DEBUG */

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