The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_devstat.c

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    1 /*-
    2  * Copyright (c) 1997, 1998, 1999 Kenneth D. Merry.
    3  * All rights reserved.
    4  *
    5  * Redistribution and use in source and binary forms, with or without
    6  * modification, are permitted provided that the following conditions
    7  * are met:
    8  * 1. Redistributions of source code must retain the above copyright
    9  *    notice, this list of conditions and the following disclaimer.
   10  * 2. Redistributions in binary form must reproduce the above copyright
   11  *    notice, this list of conditions and the following disclaimer in the
   12  *    documentation and/or other materials provided with the distribution.
   13  * 3. The name of the author may not be used to endorse or promote products
   14  *    derived from this software without specific prior written permission.
   15  *
   16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   26  * SUCH DAMAGE.
   27  */
   28 
   29 #include <sys/cdefs.h>
   30 __FBSDID("$FreeBSD$");
   31 
   32 #include <sys/param.h>
   33 #include <sys/kernel.h>
   34 #include <sys/systm.h>
   35 #include <sys/bio.h>
   36 #include <sys/devicestat.h>
   37 #include <sys/sysctl.h>
   38 #include <sys/malloc.h>
   39 #include <sys/lock.h>
   40 #include <sys/mutex.h>
   41 #include <sys/conf.h>
   42 #include <vm/vm.h>
   43 #include <vm/pmap.h>
   44 
   45 #include <machine/atomic.h>
   46 
   47 static int devstat_num_devs;
   48 static long devstat_generation = 1;
   49 static int devstat_version = DEVSTAT_VERSION;
   50 static int devstat_current_devnumber;
   51 static struct mtx devstat_mutex;
   52 
   53 static struct devstatlist device_statq;
   54 static struct devstat *devstat_alloc(void);
   55 static void devstat_free(struct devstat *);
   56 static void devstat_add_entry(struct devstat *ds, const void *dev_name, 
   57                        int unit_number, u_int32_t block_size,
   58                        devstat_support_flags flags,
   59                        devstat_type_flags device_type,
   60                        devstat_priority priority);
   61 
   62 /*
   63  * Allocate a devstat and initialize it
   64  */
   65 struct devstat *
   66 devstat_new_entry(const void *dev_name,
   67                   int unit_number, u_int32_t block_size,
   68                   devstat_support_flags flags,
   69                   devstat_type_flags device_type,
   70                   devstat_priority priority)
   71 {
   72         struct devstat *ds;
   73         static int once;
   74 
   75         if (!once) {
   76                 STAILQ_INIT(&device_statq);
   77                 mtx_init(&devstat_mutex, "devstat", NULL, MTX_DEF);
   78                 once = 1;
   79         }
   80         mtx_assert(&devstat_mutex, MA_NOTOWNED);
   81 
   82         ds = devstat_alloc();
   83         mtx_lock(&devstat_mutex);
   84         if (unit_number == -1) {
   85                 ds->id = dev_name;
   86                 binuptime(&ds->creation_time);
   87                 devstat_generation++;
   88         } else {
   89                 devstat_add_entry(ds, dev_name, unit_number, block_size,
   90                                   flags, device_type, priority);
   91         }
   92         mtx_unlock(&devstat_mutex);
   93         return (ds);
   94 }
   95 
   96 /*
   97  * Take a malloced and zeroed devstat structure given to us, fill it in 
   98  * and add it to the queue of devices.  
   99  */
  100 static void
  101 devstat_add_entry(struct devstat *ds, const void *dev_name, 
  102                   int unit_number, u_int32_t block_size,
  103                   devstat_support_flags flags,
  104                   devstat_type_flags device_type,
  105                   devstat_priority priority)
  106 {
  107         struct devstatlist *devstat_head;
  108         struct devstat *ds_tmp;
  109 
  110         mtx_assert(&devstat_mutex, MA_OWNED);
  111         devstat_num_devs++;
  112 
  113         devstat_head = &device_statq;
  114 
  115         /*
  116          * Priority sort.  Each driver passes in its priority when it adds
  117          * its devstat entry.  Drivers are sorted first by priority, and
  118          * then by probe order.
  119          * 
  120          * For the first device, we just insert it, since the priority
  121          * doesn't really matter yet.  Subsequent devices are inserted into
  122          * the list using the order outlined above.
  123          */
  124         if (devstat_num_devs == 1)
  125                 STAILQ_INSERT_TAIL(devstat_head, ds, dev_links);
  126         else {
  127                 STAILQ_FOREACH(ds_tmp, devstat_head, dev_links) {
  128                         struct devstat *ds_next;
  129 
  130                         ds_next = STAILQ_NEXT(ds_tmp, dev_links);
  131 
  132                         /*
  133                          * If we find a break between higher and lower
  134                          * priority items, and if this item fits in the
  135                          * break, insert it.  This also applies if the
  136                          * "lower priority item" is the end of the list.
  137                          */
  138                         if ((priority <= ds_tmp->priority)
  139                          && ((ds_next == NULL)
  140                            || (priority > ds_next->priority))) {
  141                                 STAILQ_INSERT_AFTER(devstat_head, ds_tmp, ds,
  142                                                     dev_links);
  143                                 break;
  144                         } else if (priority > ds_tmp->priority) {
  145                                 /*
  146                                  * If this is the case, we should be able
  147                                  * to insert ourselves at the head of the
  148                                  * list.  If we can't, something is wrong.
  149                                  */
  150                                 if (ds_tmp == STAILQ_FIRST(devstat_head)) {
  151                                         STAILQ_INSERT_HEAD(devstat_head,
  152                                                            ds, dev_links);
  153                                         break;
  154                                 } else {
  155                                         STAILQ_INSERT_TAIL(devstat_head,
  156                                                            ds, dev_links);
  157                                         printf("devstat_add_entry: HELP! "
  158                                                "sorting problem detected "
  159                                                "for name %p unit %d\n",
  160                                                dev_name, unit_number);
  161                                         break;
  162                                 }
  163                         }
  164                 }
  165         }
  166 
  167         ds->device_number = devstat_current_devnumber++;
  168         ds->unit_number = unit_number;
  169         strlcpy(ds->device_name, dev_name, DEVSTAT_NAME_LEN);
  170         ds->block_size = block_size;
  171         ds->flags = flags;
  172         ds->device_type = device_type;
  173         ds->priority = priority;
  174         binuptime(&ds->creation_time);
  175         devstat_generation++;
  176 }
  177 
  178 /*
  179  * Remove a devstat structure from the list of devices.
  180  */
  181 void
  182 devstat_remove_entry(struct devstat *ds)
  183 {
  184         struct devstatlist *devstat_head;
  185 
  186         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  187         if (ds == NULL)
  188                 return;
  189 
  190         mtx_lock(&devstat_mutex);
  191 
  192         devstat_head = &device_statq;
  193 
  194         /* Remove this entry from the devstat queue */
  195         atomic_add_acq_int(&ds->sequence1, 1);
  196         if (ds->id == NULL) {
  197                 devstat_num_devs--;
  198                 STAILQ_REMOVE(devstat_head, ds, devstat, dev_links);
  199         }
  200         devstat_free(ds);
  201         devstat_generation++;
  202         mtx_unlock(&devstat_mutex);
  203 }
  204 
  205 /*
  206  * Record a transaction start.
  207  *
  208  * See comments for devstat_end_transaction().  Ordering is very important
  209  * here.
  210  */
  211 void
  212 devstat_start_transaction(struct devstat *ds, struct bintime *now)
  213 {
  214 
  215         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  216 
  217         /* sanity check */
  218         if (ds == NULL)
  219                 return;
  220 
  221         atomic_add_acq_int(&ds->sequence1, 1);
  222         /*
  223          * We only want to set the start time when we are going from idle
  224          * to busy.  The start time is really the start of the latest busy
  225          * period.
  226          */
  227         if (ds->start_count == ds->end_count) {
  228                 if (now != NULL)
  229                         ds->busy_from = *now;
  230                 else
  231                         binuptime(&ds->busy_from);
  232         }
  233         ds->start_count++;
  234         atomic_add_rel_int(&ds->sequence0, 1);
  235 }
  236 
  237 void
  238 devstat_start_transaction_bio(struct devstat *ds, struct bio *bp)
  239 {
  240 
  241         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  242 
  243         /* sanity check */
  244         if (ds == NULL)
  245                 return;
  246 
  247         binuptime(&bp->bio_t0);
  248         devstat_start_transaction(ds, &bp->bio_t0);
  249 }
  250 
  251 /*
  252  * Record the ending of a transaction, and incrment the various counters.
  253  *
  254  * Ordering in this function, and in devstat_start_transaction() is VERY
  255  * important.  The idea here is to run without locks, so we are very
  256  * careful to only modify some fields on the way "down" (i.e. at
  257  * transaction start) and some fields on the way "up" (i.e. at transaction
  258  * completion).  One exception is busy_from, which we only modify in
  259  * devstat_start_transaction() when there are no outstanding transactions,
  260  * and thus it can't be modified in devstat_end_transaction()
  261  * simultaneously.
  262  *
  263  * The sequence0 and sequence1 fields are provided to enable an application
  264  * spying on the structures with mmap(2) to tell when a structure is in a
  265  * consistent state or not.
  266  *
  267  * For this to work 100% reliably, it is important that the two fields
  268  * are at opposite ends of the structure and that they are incremented
  269  * in the opposite order of how a memcpy(3) in userland would copy them.
  270  * We assume that the copying happens front to back, but there is actually
  271  * no way short of writing your own memcpy(3) replacement to guarantee
  272  * this will be the case.
  273  *
  274  * In addition to this, being a kind of locks, they must be updated with
  275  * atomic instructions using appropriate memory barriers.
  276  */
  277 void
  278 devstat_end_transaction(struct devstat *ds, u_int32_t bytes, 
  279                         devstat_tag_type tag_type, devstat_trans_flags flags,
  280                         struct bintime *now, struct bintime *then)
  281 {
  282         struct bintime dt, lnow;
  283 
  284         /* sanity check */
  285         if (ds == NULL)
  286                 return;
  287 
  288         if (now == NULL) {
  289                 now = &lnow;
  290                 binuptime(now);
  291         }
  292 
  293         atomic_add_acq_int(&ds->sequence1, 1);
  294         /* Update byte and operations counts */
  295         ds->bytes[flags] += bytes;
  296         ds->operations[flags]++;
  297 
  298         /*
  299          * Keep a count of the various tag types sent.
  300          */
  301         if ((ds->flags & DEVSTAT_NO_ORDERED_TAGS) == 0 &&
  302             tag_type != DEVSTAT_TAG_NONE)
  303                 ds->tag_types[tag_type]++;
  304 
  305         if (then != NULL) {
  306                 /* Update duration of operations */
  307                 dt = *now;
  308                 bintime_sub(&dt, then);
  309                 bintime_add(&ds->duration[flags], &dt);
  310         }
  311 
  312         /* Accumulate busy time */
  313         dt = *now;
  314         bintime_sub(&dt, &ds->busy_from);
  315         bintime_add(&ds->busy_time, &dt);
  316         ds->busy_from = *now;
  317 
  318         ds->end_count++;
  319         atomic_add_rel_int(&ds->sequence0, 1);
  320 }
  321 
  322 void
  323 devstat_end_transaction_bio(struct devstat *ds, struct bio *bp)
  324 {
  325         devstat_trans_flags flg;
  326 
  327         /* sanity check */
  328         if (ds == NULL)
  329                 return;
  330 
  331         if (bp->bio_cmd == BIO_DELETE)
  332                 flg = DEVSTAT_FREE;
  333         else if (bp->bio_cmd == BIO_READ)
  334                 flg = DEVSTAT_READ;
  335         else if (bp->bio_cmd == BIO_WRITE)
  336                 flg = DEVSTAT_WRITE;
  337         else 
  338                 flg = DEVSTAT_NO_DATA;
  339 
  340         devstat_end_transaction(ds, bp->bio_bcount - bp->bio_resid,
  341                                 DEVSTAT_TAG_SIMPLE, flg, NULL, &bp->bio_t0);
  342 }
  343 
  344 /*
  345  * This is the sysctl handler for the devstat package.  The data pushed out
  346  * on the kern.devstat.all sysctl variable consists of the current devstat
  347  * generation number, and then an array of devstat structures, one for each
  348  * device in the system.
  349  *
  350  * This is more cryptic that obvious, but basically we neither can nor
  351  * want to hold the devstat_mutex for any amount of time, so we grab it
  352  * only when we need to and keep an eye on devstat_generation all the time.
  353  */
  354 static int
  355 sysctl_devstat(SYSCTL_HANDLER_ARGS)
  356 {
  357         int error;
  358         long mygen;
  359         struct devstat *nds;
  360 
  361         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  362 
  363         /*
  364          * XXX devstat_generation should really be "volatile" but that
  365          * XXX freaks out the sysctl macro below.  The places where we
  366          * XXX change it and inspect it are bracketed in the mutex which
  367          * XXX guarantees us proper write barriers.  I don't belive the
  368          * XXX compiler is allowed to optimize mygen away across calls
  369          * XXX to other functions, so the following is belived to be safe.
  370          */
  371         mygen = devstat_generation;
  372 
  373         error = SYSCTL_OUT(req, &mygen, sizeof(mygen));
  374 
  375         if (devstat_num_devs == 0)
  376                 return(0);
  377 
  378         if (error != 0)
  379                 return (error);
  380 
  381         mtx_lock(&devstat_mutex);
  382         nds = STAILQ_FIRST(&device_statq); 
  383         if (mygen != devstat_generation)
  384                 error = EBUSY;
  385         mtx_unlock(&devstat_mutex);
  386 
  387         if (error != 0)
  388                 return (error);
  389 
  390         for (;nds != NULL;) {
  391                 error = SYSCTL_OUT(req, nds, sizeof(struct devstat));
  392                 if (error != 0)
  393                         return (error);
  394                 mtx_lock(&devstat_mutex);
  395                 if (mygen != devstat_generation)
  396                         error = EBUSY;
  397                 else
  398                         nds = STAILQ_NEXT(nds, dev_links);
  399                 mtx_unlock(&devstat_mutex);
  400                 if (error != 0)
  401                         return (error);
  402         }
  403         return(error);
  404 }
  405 
  406 /*
  407  * Sysctl entries for devstat.  The first one is a node that all the rest
  408  * hang off of. 
  409  */
  410 SYSCTL_NODE(_kern, OID_AUTO, devstat, CTLFLAG_RD, 0, "Device Statistics");
  411 
  412 SYSCTL_PROC(_kern_devstat, OID_AUTO, all, CTLFLAG_RD|CTLTYPE_OPAQUE,
  413     0, 0, sysctl_devstat, "S,devstat", "All devices in the devstat list");
  414 /*
  415  * Export the number of devices in the system so that userland utilities
  416  * can determine how much memory to allocate to hold all the devices.
  417  */
  418 SYSCTL_INT(_kern_devstat, OID_AUTO, numdevs, CTLFLAG_RD, 
  419     &devstat_num_devs, 0, "Number of devices in the devstat list");
  420 SYSCTL_LONG(_kern_devstat, OID_AUTO, generation, CTLFLAG_RD,
  421     &devstat_generation, 0, "Devstat list generation");
  422 SYSCTL_INT(_kern_devstat, OID_AUTO, version, CTLFLAG_RD, 
  423     &devstat_version, 0, "Devstat list version number");
  424 
  425 /*
  426  * Allocator for struct devstat structures.  We sub-allocate these from pages
  427  * which we get from malloc.  These pages are exported for mmap(2)'ing through
  428  * a miniature device driver
  429  */
  430 
  431 #define statsperpage (PAGE_SIZE / sizeof(struct devstat))
  432 
  433 static d_mmap_t devstat_mmap;
  434 
  435 static struct cdevsw devstat_cdevsw = {
  436         .d_version =    D_VERSION,
  437         .d_flags =      D_NEEDGIANT,
  438         .d_mmap =       devstat_mmap,
  439         .d_name =       "devstat",
  440 };
  441 
  442 struct statspage {
  443         TAILQ_ENTRY(statspage)  list;
  444         struct devstat          *stat;
  445         u_int                   nfree;
  446 };
  447 
  448 static TAILQ_HEAD(, statspage)  pagelist = TAILQ_HEAD_INITIALIZER(pagelist);
  449 static MALLOC_DEFINE(M_DEVSTAT, "devstat", "Device statistics");
  450 
  451 static int
  452 devstat_mmap(struct cdev *dev, vm_offset_t offset, vm_paddr_t *paddr, int nprot)
  453 {
  454         struct statspage *spp;
  455 
  456         if (nprot != VM_PROT_READ)
  457                 return (-1);
  458         TAILQ_FOREACH(spp, &pagelist, list) {
  459                 if (offset == 0) {
  460                         *paddr = vtophys(spp->stat);
  461                         return (0);
  462                 }
  463                 offset -= PAGE_SIZE;
  464         }
  465         return (-1);
  466 }
  467 
  468 static struct devstat *
  469 devstat_alloc(void)
  470 {
  471         struct devstat *dsp;
  472         struct statspage *spp;
  473         u_int u;
  474         static int once;
  475 
  476         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  477         if (!once) {
  478                 make_dev(&devstat_cdevsw, 0,
  479                     UID_ROOT, GID_WHEEL, 0400, DEVSTAT_DEVICE_NAME);
  480                 once = 1;
  481         }
  482         mtx_lock(&devstat_mutex);
  483         for (;;) {
  484                 TAILQ_FOREACH(spp, &pagelist, list) {
  485                         if (spp->nfree > 0)
  486                                 break;
  487                 }
  488                 if (spp != NULL)
  489                         break;
  490                 /*
  491                  * We had no free slot in any of our pages, drop the mutex
  492                  * and get another page.  In theory we could have more than
  493                  * one process doing this at the same time and consequently
  494                  * we may allocate more pages than we will need.  That is
  495                  * Just Too Bad[tm], we can live with that.
  496                  */
  497                 mtx_unlock(&devstat_mutex);
  498                 spp = malloc(sizeof *spp, M_DEVSTAT, M_ZERO | M_WAITOK);
  499                 spp->stat = malloc(PAGE_SIZE, M_DEVSTAT, M_ZERO | M_WAITOK);
  500                 spp->nfree = statsperpage;
  501                 mtx_lock(&devstat_mutex);
  502                 /*
  503                  * It would make more sense to add the new page at the head
  504                  * but the order on the list determine the sequence of the
  505                  * mapping so we can't do that.
  506                  */
  507                 TAILQ_INSERT_TAIL(&pagelist, spp, list);
  508         }
  509         dsp = spp->stat;
  510         for (u = 0; u < statsperpage; u++) {
  511                 if (dsp->allocated == 0)
  512                         break;
  513                 dsp++;
  514         }
  515         spp->nfree--;
  516         dsp->allocated = 1;
  517         mtx_unlock(&devstat_mutex);
  518         return (dsp);
  519 }
  520 
  521 static void
  522 devstat_free(struct devstat *dsp)
  523 {
  524         struct statspage *spp;
  525 
  526         mtx_assert(&devstat_mutex, MA_OWNED);
  527         bzero(dsp, sizeof *dsp);
  528         TAILQ_FOREACH(spp, &pagelist, list) {
  529                 if (dsp >= spp->stat && dsp < (spp->stat + statsperpage)) {
  530                         spp->nfree++;
  531                         return;
  532                 }
  533         }
  534 }
  535 
  536 SYSCTL_INT(_debug_sizeof, OID_AUTO, devstat, CTLFLAG_RD,
  537     0, sizeof(struct devstat), "sizeof(struct devstat)");

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