FreeBSD/Linux Kernel Cross Reference
sys/fs/devfs/devfs_rule.c

     /*-
      * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
      *
      * Copyright (c) 2002 Dima Dorfman.
      * All rights reserved.
      *
      * 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 AUTHOR 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 AUTHOR 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.
     *
     * $FreeBSD$
     */
    
    /*
     * DEVFS ruleset implementation.
     *
     * A note on terminology: To "run" a rule on a dirent is to take the
     * prescribed action; to "apply" a rule is to check whether it matches
     * a dirent and run if if it does.
     *
     * A note on locking: Only foreign entry points (non-static functions)
     * should deal with locking.  Everything else assumes we already hold
     * the required kind of lock.
     *
     * A note on namespace: devfs_rules_* are the non-static functions for
     * the entire "ruleset" subsystem, devfs_rule_* are the static
     * functions that operate on rules, and devfs_ruleset_* are the static
     * functions that operate on rulesets.  The line between the last two
     * isn't always clear, but the guideline is still useful.
     *
     * A note on "special" identifiers: Ruleset 0 is the NULL, or empty,
     * ruleset; it cannot be deleted or changed in any way.  This may be
     * assumed inside the code; e.g., a ruleset of 0 may be interpeted to
     * mean "no ruleset".  The interpretation of rule 0 is
     * command-dependent, but in no case is there a real rule with number
     * 0.
     *
     * A note on errno codes: To make it easier for the userland to tell
     * what went wrong, we sometimes use errno codes that are not entirely
     * appropriate for the error but that would be less ambiguous than the
     * appropriate "generic" code.  For example, when we can't find a
     * ruleset, we return ESRCH instead of ENOENT (except in
     * DEVFSIO_{R,S}GETNEXT, where a nonexistent ruleset means "end of
     * list", and the userland expects ENOENT to be this indicator); this
     * way, when an operation fails, it's clear that what couldn't be
     * found is a ruleset and not a rule (well, it's clear to those who
     * know the convention).
     */
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/conf.h>
    #include <sys/kernel.h>
    #include <sys/malloc.h>
    #include <sys/priv.h>
    #include <sys/dirent.h>
    #include <sys/ioccom.h>
    #include <sys/lock.h>
    #include <sys/sx.h>
    
    #include <fs/devfs/devfs.h>
    #include <fs/devfs/devfs_int.h>
    
    /*
     * Kernel version of devfs_rule.
     */
    struct devfs_krule {
            TAILQ_ENTRY(devfs_krule)        dk_list;
            struct devfs_ruleset            *dk_ruleset;
            struct devfs_rule               dk_rule;
    };
    
    TAILQ_HEAD(rulehead, devfs_krule);
    static MALLOC_DEFINE(M_DEVFSRULE, "DEVFS_RULE", "DEVFS rule storage");
    
    /*
     * Structure to describe a ruleset.
     */
    struct devfs_ruleset {
            TAILQ_ENTRY(devfs_ruleset)      ds_list;
            struct rulehead                 ds_rules;
            devfs_rsnum                     ds_number;
           int                             ds_refcount;
   };
   
   static devfs_rid devfs_rid_input(devfs_rid rid, struct devfs_mount *dm);
   
   static void devfs_rule_applyde_recursive(struct devfs_krule *dk,
                   struct devfs_mount *dm, struct devfs_dirent *de);
   static void devfs_rule_applydm(struct devfs_krule *dk, struct devfs_mount *dm);
   static int  devfs_rule_autonumber(struct devfs_ruleset *ds, devfs_rnum *rnp);
   static struct devfs_krule *devfs_rule_byid(devfs_rid rid);
   static int  devfs_rule_delete(struct devfs_krule *dkp);
   static struct cdev *devfs_rule_getdev(struct devfs_dirent *de);
   static int  devfs_rule_input(struct devfs_rule *dr, struct devfs_mount *dm);
   static int  devfs_rule_insert(struct devfs_rule *dr);
   static int  devfs_rule_match(struct devfs_krule *dk, struct devfs_mount *dm,
                   struct devfs_dirent *de);
   static int  devfs_rule_matchpath(struct devfs_krule *dk, struct devfs_mount *dm,
                   struct devfs_dirent *de);
   static void devfs_rule_run(struct devfs_krule *dk, struct devfs_mount *dm,
                   struct devfs_dirent *de, unsigned depth);
   
   static void devfs_ruleset_applyde(struct devfs_ruleset *ds,
                   struct devfs_mount *dm, struct devfs_dirent *de,
                   unsigned depth);
   static void devfs_ruleset_applydm(struct devfs_ruleset *ds,
                   struct devfs_mount *dm);
   static struct devfs_ruleset *devfs_ruleset_bynum(devfs_rsnum rsnum);
   static struct devfs_ruleset *devfs_ruleset_create(devfs_rsnum rsnum);
   static void devfs_ruleset_reap(struct devfs_ruleset *dsp);
   static int  devfs_ruleset_use(devfs_rsnum rsnum, struct devfs_mount *dm);
   
   static struct sx sx_rules;
   SX_SYSINIT(sx_rules, &sx_rules, "DEVFS ruleset lock");
   
   static TAILQ_HEAD(, devfs_ruleset) devfs_rulesets =
       TAILQ_HEAD_INITIALIZER(devfs_rulesets);
   
   /*
    * Called to apply the proper rules for 'de' before it can be
    * exposed to the userland.  This should be called with an exclusive
    * lock on dm in case we need to run anything.
    */
   void
   devfs_rules_apply(struct devfs_mount *dm, struct devfs_dirent *de)
   {
           struct devfs_ruleset *ds;
   
           sx_assert(&dm->dm_lock, SX_XLOCKED);
   
           if (dm->dm_ruleset == 0)
                   return;
           sx_slock(&sx_rules);
           ds = devfs_ruleset_bynum(dm->dm_ruleset);
           KASSERT(ds != NULL, ("mount-point has NULL ruleset"));
           devfs_ruleset_applyde(ds, dm, de, devfs_rule_depth);
           sx_sunlock(&sx_rules);
   }
   
   /*
    * Rule subsystem ioctl hook.
    */
   int
   devfs_rules_ioctl(struct devfs_mount *dm, u_long cmd, caddr_t data, struct thread *td)
   {
           struct devfs_ruleset *ds;
           struct devfs_krule *dk;
           struct devfs_rule *dr;
           devfs_rsnum rsnum;
           devfs_rnum rnum;
           devfs_rid rid;
           int error;
   
           sx_assert(&dm->dm_lock, SX_XLOCKED);
   
           /*
            * XXX: This returns an error regardless of whether we actually
            * support the cmd or not.
            *
            * We could make this privileges finer grained if desired.
            */
           error = priv_check(td, PRIV_DEVFS_RULE);
           if (error)
                   return (error);
   
           sx_xlock(&sx_rules);
   
           switch (cmd) {
           case DEVFSIO_RADD:
                   dr = (struct devfs_rule *)data;
                   error = devfs_rule_input(dr, dm);
                   if (error != 0)
                           break;
                   dk = devfs_rule_byid(dr->dr_id);
                   if (dk != NULL) {
                           error = EEXIST;
                           break;
                   }
                   if (rid2rsn(dr->dr_id) == 0) {
                           error = EIO;
                           break;
                   }
                   error = devfs_rule_insert(dr);
                   break;
           case DEVFSIO_RAPPLY:
                   dr = (struct devfs_rule *)data;
                   error = devfs_rule_input(dr, dm);
                   if (error != 0)
                           break;
   
                   /*
                    * This is one of many possible hackish
                    * implementations.  The primary contender is an
                    * implementation where the rule we read in is
                    * temporarily inserted into some ruleset, perhaps
                    * with a hypothetical DRO_NOAUTO flag so that it
                    * doesn't get used where it isn't intended, and
                    * applied in the normal way.  This can be done in the
                    * userland (DEVFSIO_ADD, DEVFSIO_APPLYID,
                    * DEVFSIO_DEL) or in the kernel; either way it breaks
                    * some corner case assumptions in other parts of the
                    * code (not that this implementation doesn't do
                    * that).
                    */
                   if (dr->dr_iacts & DRA_INCSET &&
                       devfs_ruleset_bynum(dr->dr_incset) == NULL) {
                           error = ESRCH;
                           break;
                   }
                   dk = malloc(sizeof(*dk), M_TEMP, M_WAITOK | M_ZERO);
                   memcpy(&dk->dk_rule, dr, sizeof(*dr));
                   devfs_rule_applydm(dk, dm);
                   free(dk, M_TEMP);
                   break;
           case DEVFSIO_RAPPLYID:
                   rid = *(devfs_rid *)data;
                   rid = devfs_rid_input(rid, dm);
                   dk = devfs_rule_byid(rid);
                   if (dk == NULL) {
                           error = ENOENT;
                           break;
                   }
                   devfs_rule_applydm(dk, dm);
                   break;
           case DEVFSIO_RDEL:
                   rid = *(devfs_rid *)data;
                   rid = devfs_rid_input(rid, dm);
                   dk = devfs_rule_byid(rid);
                   if (dk == NULL) {
                           error = ENOENT;
                           break;
                   }
                   ds = dk->dk_ruleset;
                   error = devfs_rule_delete(dk);
                   break;
           case DEVFSIO_RGETNEXT:
                   dr = (struct devfs_rule *)data;
                   error = devfs_rule_input(dr, dm);
                   if (error != 0)
                           break;
                   /*
                    * We can't use devfs_rule_byid() here since that
                    * requires the rule specified to exist, but we want
                    * getnext(N) to work whether there is a rule N or not
                    * (specifically, getnext(0) must work, but we should
                    * never have a rule 0 since the add command
                    * interprets 0 to mean "auto-number").
                    */
                   ds = devfs_ruleset_bynum(rid2rsn(dr->dr_id));
                   if (ds == NULL) {
                           error = ENOENT;
                           break;
                   }
                   rnum = rid2rn(dr->dr_id);
                   TAILQ_FOREACH(dk, &ds->ds_rules, dk_list) {
                           if (rid2rn(dk->dk_rule.dr_id) > rnum)
                                   break;
                   }
                   if (dk == NULL) {
                           error = ENOENT;
                           break;
                   }
                   memcpy(dr, &dk->dk_rule, sizeof(*dr));
                   break;
           case DEVFSIO_SUSE:
                   rsnum = *(devfs_rsnum *)data;
                   error = devfs_ruleset_use(rsnum, dm);
                   break;
           case DEVFSIO_SAPPLY:
                   rsnum = *(devfs_rsnum *)data;
                   rsnum = rid2rsn(devfs_rid_input(mkrid(rsnum, 0), dm));
                   ds = devfs_ruleset_bynum(rsnum);
                   if (ds == NULL) {
                           error = ESRCH;
                           break;
                   }
                   devfs_ruleset_applydm(ds, dm);
                   break;
           case DEVFSIO_SGETNEXT:
                   rsnum = *(devfs_rsnum *)data;
                   TAILQ_FOREACH(ds, &devfs_rulesets, ds_list) {
                           if (ds->ds_number > rsnum)
                                   break;
                   }
                   if (ds == NULL) {
                           error = ENOENT;
                           break;
                   }
                   *(devfs_rsnum *)data = ds->ds_number;
                   break;
           default:
                   error = ENOIOCTL;
                   break;
           }
   
           sx_xunlock(&sx_rules);
           return (error);
   }
   
   /*
    * Adjust the rule identifier to use the ruleset of dm if one isn't
    * explicitly specified.
    *
    * Note that after this operation, rid2rsn(rid) might still be 0, and
    * that's okay; ruleset 0 is a valid ruleset, but when it's read in
    * from the userland, it means "current ruleset for this mount-point".
    */
   static devfs_rid
   devfs_rid_input(devfs_rid rid, struct devfs_mount *dm)
   {
   
           if (rid2rsn(rid) == 0)
                   return (mkrid(dm->dm_ruleset, rid2rn(rid)));
           else
                   return (rid);
   }
   
   /*
    * Apply dk to de and everything under de.
    *
    * XXX: This method needs a function call for every nested
    * subdirectory in a devfs mount.  If we plan to have many of these,
    * we might eventually run out of kernel stack space.
    * XXX: a linear search could be done through the cdev list instead.
    */
   static void
   devfs_rule_applyde_recursive(struct devfs_krule *dk, struct devfs_mount *dm,
       struct devfs_dirent *de)
   {
           struct devfs_dirent *de2;
   
           TAILQ_FOREACH(de2, &de->de_dlist, de_list)
                   devfs_rule_applyde_recursive(dk, dm, de2);
           devfs_rule_run(dk, dm, de, devfs_rule_depth);
   }
   
   /*
    * Apply dk to all entires in dm.
    */
   static void
   devfs_rule_applydm(struct devfs_krule *dk, struct devfs_mount *dm)
   {
   
           devfs_rule_applyde_recursive(dk, dm, dm->dm_rootdir);
   }
   
   /*
    * Automatically select a number for a new rule in ds, and write the
    * result into rnump.
    */
   static int
   devfs_rule_autonumber(struct devfs_ruleset *ds, devfs_rnum *rnump)
   {
           struct devfs_krule *dk;
   
           /* Find the last rule. */
           dk = TAILQ_LAST(&ds->ds_rules, rulehead);
           if (dk == NULL)
                   *rnump = 100;
           else {
                   *rnump = rid2rn(dk->dk_rule.dr_id) + 100;
                   /* Detect overflow. */
                   if (*rnump < rid2rn(dk->dk_rule.dr_id))
                           return (ERANGE);
           }
           KASSERT(devfs_rule_byid(mkrid(ds->ds_number, *rnump)) == NULL,
               ("autonumbering resulted in an already existing rule"));
           return (0);
   }
   
   /*
    * Find a krule by id.
    */
   static struct devfs_krule *
   devfs_rule_byid(devfs_rid rid)
   {
           struct devfs_ruleset *ds;
           struct devfs_krule *dk;
           devfs_rnum rn;
   
           rn = rid2rn(rid);
           ds = devfs_ruleset_bynum(rid2rsn(rid));
           if (ds == NULL)
                   return (NULL);
           TAILQ_FOREACH(dk, &ds->ds_rules, dk_list) {
                   if (rid2rn(dk->dk_rule.dr_id) == rn)
                           return (dk);
                   else if (rid2rn(dk->dk_rule.dr_id) > rn)
                           break;
           }
           return (NULL);
   }
   
   /*
    * Remove dkp from any lists it may be on and remove memory associated
    * with it.
    */
   static int
   devfs_rule_delete(struct devfs_krule *dk)
   {
           struct devfs_ruleset *ds;
   
           if (dk->dk_rule.dr_iacts & DRA_INCSET) {
                   ds = devfs_ruleset_bynum(dk->dk_rule.dr_incset);
                   KASSERT(ds != NULL, ("DRA_INCSET but bad dr_incset"));
                   --ds->ds_refcount;
                   devfs_ruleset_reap(ds);
           }
           ds = dk->dk_ruleset;
           TAILQ_REMOVE(&ds->ds_rules, dk, dk_list);
           devfs_ruleset_reap(ds);
           free(dk, M_DEVFSRULE);
           return (0);
   }
   
   /*
    * Get a struct cdev *corresponding to de so we can try to match rules based
    * on it.  If this routine returns NULL, there is no struct cdev *associated
    * with the dirent (symlinks and directories don't have dev_ts), and
    * the caller should assume that any critera dependent on a dev_t
    * don't match.
    */
   static struct cdev *
   devfs_rule_getdev(struct devfs_dirent *de)
   {
   
           if (de->de_cdp == NULL)
                   return (NULL);
           if (de->de_cdp->cdp_flags & CDP_ACTIVE)
                   return (&de->de_cdp->cdp_c);
           else
                   return (NULL);
   }
   
   /*
    * Do what we need to do to a rule that we just loaded from the
    * userland.  In particular, we need to check the magic, and adjust
    * the ruleset appropriate if desired.
    */
   static int
   devfs_rule_input(struct devfs_rule *dr, struct devfs_mount *dm)
   {
   
           if (dr->dr_magic != DEVFS_MAGIC)
                   return (ERPCMISMATCH);
           dr->dr_id = devfs_rid_input(dr->dr_id, dm);
           return (0);
   }
   
   /*
    * Import dr into the appropriate place in the kernel (i.e., make a
    * krule).  The value of dr is copied, so the pointer may be destroyed
    * after this call completes.
    */
   static int
   devfs_rule_insert(struct devfs_rule *dr)
   {
           struct devfs_ruleset *ds, *dsi;
           struct devfs_krule *k1;
           struct devfs_krule *dk;
           devfs_rsnum rsnum;
           devfs_rnum dkrn;
           int error;
   
           /*
            * This stuff seems out of place here, but we want to do it as
            * soon as possible so that if it fails, we don't have to roll
            * back any changes we already made (e.g., ruleset creation).
            */
           if (dr->dr_iacts & DRA_INCSET) {
                   dsi = devfs_ruleset_bynum(dr->dr_incset);
                   if (dsi == NULL)
                           return (ESRCH);
           } else
                   dsi = NULL;
   
           rsnum = rid2rsn(dr->dr_id);
           KASSERT(rsnum != 0, ("Inserting into ruleset zero"));
   
           ds = devfs_ruleset_bynum(rsnum);
           if (ds == NULL)
                   ds = devfs_ruleset_create(rsnum);
           dkrn = rid2rn(dr->dr_id);
           if (dkrn == 0) {
                   error = devfs_rule_autonumber(ds, &dkrn);
                   if (error != 0) {
                           devfs_ruleset_reap(ds);
                           return (error);
                   }
           }
   
           dk = malloc(sizeof(*dk), M_DEVFSRULE, M_WAITOK | M_ZERO);
           dk->dk_ruleset = ds;
           if (dsi != NULL)
                   ++dsi->ds_refcount;
           /* XXX: Inspect dr? */
           memcpy(&dk->dk_rule, dr, sizeof(*dr));
           dk->dk_rule.dr_id = mkrid(rid2rsn(dk->dk_rule.dr_id), dkrn);
   
           TAILQ_FOREACH(k1, &ds->ds_rules, dk_list) {
                   if (rid2rn(k1->dk_rule.dr_id) > dkrn) {
                           TAILQ_INSERT_BEFORE(k1, dk, dk_list);
                           break;
                   }
           }
           if (k1 == NULL)
                   TAILQ_INSERT_TAIL(&ds->ds_rules, dk, dk_list);
           return (0);
   }
   
   /*
    * Determine whether dk matches de.  Returns 1 if dk should be run on
    * de; 0, otherwise.
    */
   static int
   devfs_rule_match(struct devfs_krule *dk, struct devfs_mount *dm,
       struct devfs_dirent *de)
   {
           struct devfs_rule *dr = &dk->dk_rule;
           struct cdev *dev;
           struct cdevsw *dsw;
           int ref;
   
           dev = devfs_rule_getdev(de);
           /*
            * At this point, if dev is NULL, we should assume that any
            * criteria that depend on it don't match.  We should *not*
            * just ignore them (i.e., act like they weren't specified),
            * since that makes a rule that only has criteria dependent on
            * the struct cdev *match all symlinks and directories.
            *
            * Note also that the following tests are somewhat reversed:
            * They're actually testing to see whether the condition does
            * *not* match, since the default is to assume the rule should
            * be run (such as if there are no conditions).
            */
           if (dr->dr_icond & DRC_DSWFLAGS) {
                   if (dev == NULL)
                           return (0);
                   dsw = dev_refthread(dev, &ref);
                   if (dsw == NULL)
                           return (0);
                   if ((dsw->d_flags & dr->dr_dswflags) == 0) {
                           dev_relthread(dev, ref);
                           return (0);
                   }
                   dev_relthread(dev, ref);
           }
           if (dr->dr_icond & DRC_PATHPTRN)
                   if (!devfs_rule_matchpath(dk, dm, de))
                           return (0);
   
           return (1);
   }
   
   /*
    * Determine whether dk matches de on account of dr_pathptrn.
    */
   static int
   devfs_rule_matchpath(struct devfs_krule *dk, struct devfs_mount *dm,
       struct devfs_dirent *de)
   {
           struct devfs_rule *dr = &dk->dk_rule;
           struct cdev *dev;
           int match;
           char *pname, *specname;
   
           specname = NULL;
           dev = devfs_rule_getdev(de);
           if (dev != NULL)
                   pname = dev->si_name;
           else if (de->de_dirent->d_type == DT_LNK ||
               (de->de_dirent->d_type == DT_DIR && de != dm->dm_rootdir &&
               (de->de_flags & (DE_DOT | DE_DOTDOT)) == 0)) {
                   specname = malloc(SPECNAMELEN + 1, M_TEMP, M_WAITOK);
                   pname = devfs_fqpn(specname, dm, de, NULL);
           } else
                   return (0);
   
           KASSERT(pname != NULL, ("devfs_rule_matchpath: NULL pname"));
           match = fnmatch(dr->dr_pathptrn, pname, FNM_PATHNAME) == 0;
           free(specname, M_TEMP);
           return (match);
   }
   
   /*
    * Run dk on de.
    */
   static void
   devfs_rule_run(struct devfs_krule *dk,  struct devfs_mount *dm,
       struct devfs_dirent *de, unsigned depth)
   {
           struct devfs_rule *dr = &dk->dk_rule;
           struct devfs_ruleset *ds;
   
           if (!devfs_rule_match(dk, dm, de))
                   return;
           if (dr->dr_iacts & DRA_BACTS) {
                   if (dr->dr_bacts & DRB_HIDE)
                           de->de_flags |= DE_WHITEOUT;
                   if (dr->dr_bacts & DRB_UNHIDE)
                           de->de_flags &= ~DE_WHITEOUT;
           }
           if (dr->dr_iacts & DRA_UID)
                   de->de_uid = dr->dr_uid;
           if (dr->dr_iacts & DRA_GID)
                   de->de_gid = dr->dr_gid;
           if (dr->dr_iacts & DRA_MODE)
                   de->de_mode = dr->dr_mode;
           if (dr->dr_iacts & DRA_INCSET) {
                   /*
                    * XXX: we should tell the user if the depth is exceeded here
                    * XXX: but it is not obvious how to.  A return value will
                    * XXX: not work as this is called when devices are created
                    * XXX: long time after the rules were instantiated.
                    * XXX: a printf() would probably give too much noise, or
                    * XXX: DoS the machine.  I guess a rate-limited message
                    * XXX: might work.
                    */
                   if (depth > 0) {
                           ds = devfs_ruleset_bynum(dk->dk_rule.dr_incset);
                           KASSERT(ds != NULL, ("DRA_INCSET but bad dr_incset"));
                           devfs_ruleset_applyde(ds, dm, de, depth - 1);
                   }
           }
   }
   
   /*
    * Apply all the rules in ds to de.
    */
   static void
   devfs_ruleset_applyde(struct devfs_ruleset *ds, struct devfs_mount *dm,
       struct devfs_dirent *de, unsigned depth)
   {
           struct devfs_krule *dk;
   
           TAILQ_FOREACH(dk, &ds->ds_rules, dk_list)
                   devfs_rule_run(dk, dm, de, depth);
   }
   
   /*
    * Apply all the rules in ds to all the entires in dm.
    */
   static void
   devfs_ruleset_applydm(struct devfs_ruleset *ds, struct devfs_mount *dm)
   {
           struct devfs_krule *dk;
   
           /*
            * XXX: Does it matter whether we do
            *
            *      foreach(dk in ds)
            *              foreach(de in dm)
            *                      apply(dk to de)
            *
            * as opposed to
            *
            *      foreach(de in dm)
            *              foreach(dk in ds)
            *                      apply(dk to de)
            *
            * The end result is obviously the same, but does the order
            * matter?
            */
           TAILQ_FOREACH(dk, &ds->ds_rules, dk_list)
                   devfs_rule_applydm(dk, dm);
   }
   
   /*
    * Find a ruleset by number.
    */
   static struct devfs_ruleset *
   devfs_ruleset_bynum(devfs_rsnum rsnum)
   {
           struct devfs_ruleset *ds;
   
           TAILQ_FOREACH(ds, &devfs_rulesets, ds_list) {
                   if (ds->ds_number == rsnum)
                           return (ds);
           }
           return (NULL);
   }
   
   /*
    * Create a new ruleset.
    */
   static struct devfs_ruleset *
   devfs_ruleset_create(devfs_rsnum rsnum)
   {
           struct devfs_ruleset *s1;
           struct devfs_ruleset *ds;
   
           KASSERT(rsnum != 0, ("creating ruleset zero"));
   
           KASSERT(devfs_ruleset_bynum(rsnum) == NULL,
               ("creating already existent ruleset %d", rsnum));
   
           ds = malloc(sizeof(*ds), M_DEVFSRULE, M_WAITOK | M_ZERO);
           ds->ds_number = rsnum;
           TAILQ_INIT(&ds->ds_rules);
   
           TAILQ_FOREACH(s1, &devfs_rulesets, ds_list) {
                   if (s1->ds_number > rsnum) {
                           TAILQ_INSERT_BEFORE(s1, ds, ds_list);
                           break;
                   }
           }
           if (s1 == NULL)
                   TAILQ_INSERT_TAIL(&devfs_rulesets, ds, ds_list);
           return (ds);
   }
   
   /*
    * Remove a ruleset from the system if it's empty and not used
    * anywhere.  This should be called after every time a rule is deleted
    * from this ruleset or the reference count is decremented.
    */
   static void
   devfs_ruleset_reap(struct devfs_ruleset *ds)
   {
   
           KASSERT(ds->ds_number != 0, ("reaping ruleset zero "));
   
           if (!TAILQ_EMPTY(&ds->ds_rules) || ds->ds_refcount != 0) 
                   return;
   
           TAILQ_REMOVE(&devfs_rulesets, ds, ds_list);
           free(ds, M_DEVFSRULE);
   }
   
   /*
    * Make rsnum the active ruleset for dm.
    */
   static int
   devfs_ruleset_use(devfs_rsnum rsnum, struct devfs_mount *dm)
   {
           struct devfs_ruleset *cds, *ds;
   
           if (dm->dm_ruleset != 0) {
                   cds = devfs_ruleset_bynum(dm->dm_ruleset);
                   --cds->ds_refcount;
                   devfs_ruleset_reap(cds);
           }
   
           if (rsnum == 0) {
                   dm->dm_ruleset = 0;
                   return (0);
           }
   
           ds = devfs_ruleset_bynum(rsnum);
           if (ds == NULL)
                   ds = devfs_ruleset_create(rsnum);
           /* These should probably be made atomic somehow. */
           ++ds->ds_refcount;
           dm->dm_ruleset = rsnum;
   
           return (0);
   }
   
   void
   devfs_rules_cleanup(struct devfs_mount *dm)
   {
           struct devfs_ruleset *ds;
   
           sx_assert(&dm->dm_lock, SX_XLOCKED);
           if (dm->dm_ruleset != 0) {
                   ds = devfs_ruleset_bynum(dm->dm_ruleset);
                   --ds->ds_refcount;
                   devfs_ruleset_reap(ds);
           }
   }
   
   /*
    * Make rsnum the active ruleset for dm (locked)
    */
   void
   devfs_ruleset_set(devfs_rsnum rsnum, struct devfs_mount *dm)
   {
   
           sx_assert(&dm->dm_lock, SX_XLOCKED);
   
           sx_xlock(&sx_rules);
           devfs_ruleset_use(rsnum, dm);
           sx_xunlock(&sx_rules);
   }
   
   /*
    * Apply the current active ruleset on a mount
    */
   void
   devfs_ruleset_apply(struct devfs_mount *dm)
   {
           struct devfs_ruleset *ds;
   
           sx_assert(&dm->dm_lock, SX_XLOCKED);
   
           sx_xlock(&sx_rules);
           if (dm->dm_ruleset == 0) {
                   sx_xunlock(&sx_rules);
                   return;
           }
           ds = devfs_ruleset_bynum(dm->dm_ruleset);
           if (ds != NULL)
                   devfs_ruleset_applydm(ds, dm);
           sx_xunlock(&sx_rules);
   }

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