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: stable/10/sys/kern/subr_devstat.c 302234 2016-06-27 21:50:30Z bdrewery $");
   31 
   32 #include "opt_kdtrace.h"
   33 
   34 #include <sys/param.h>
   35 #include <sys/kernel.h>
   36 #include <sys/systm.h>
   37 #include <sys/bio.h>
   38 #include <sys/devicestat.h>
   39 #include <sys/sdt.h>
   40 #include <sys/sysctl.h>
   41 #include <sys/malloc.h>
   42 #include <sys/lock.h>
   43 #include <sys/mutex.h>
   44 #include <sys/conf.h>
   45 #include <vm/vm.h>
   46 #include <vm/pmap.h>
   47 
   48 #include <machine/atomic.h>
   49 
   50 SDT_PROVIDER_DEFINE(io);
   51 
   52 SDT_PROBE_DEFINE2(io, , , start, "struct bio *", "struct devstat *");
   53 SDT_PROBE_DEFINE2(io, , , done, "struct bio *", "struct devstat *");
   54 SDT_PROBE_DEFINE2(io, , , wait__start, "struct bio *",
   55     "struct devstat *");
   56 SDT_PROBE_DEFINE2(io, , , wait__done, "struct bio *",
   57     "struct devstat *");
   58 
   59 #define DTRACE_DEVSTAT_START()          SDT_PROBE2(io, , , start, NULL, ds)
   60 #define DTRACE_DEVSTAT_BIO_START()      SDT_PROBE2(io, , , start, bp, ds)
   61 #define DTRACE_DEVSTAT_DONE()           SDT_PROBE2(io, , , done, NULL, ds)
   62 #define DTRACE_DEVSTAT_BIO_DONE()       SDT_PROBE2(io, , , done, bp, ds)
   63 #define DTRACE_DEVSTAT_WAIT_START()     SDT_PROBE2(io, , , wait__start, NULL, ds)
   64 #define DTRACE_DEVSTAT_WAIT_DONE()      SDT_PROBE2(io, , , wait__done, NULL, ds)
   65 
   66 static int devstat_num_devs;
   67 static long devstat_generation = 1;
   68 static int devstat_version = DEVSTAT_VERSION;
   69 static int devstat_current_devnumber;
   70 static struct mtx devstat_mutex;
   71 MTX_SYSINIT(devstat_mutex, &devstat_mutex, "devstat", MTX_DEF);
   72 
   73 static struct devstatlist device_statq = STAILQ_HEAD_INITIALIZER(device_statq);
   74 static struct devstat *devstat_alloc(void);
   75 static void devstat_free(struct devstat *);
   76 static void devstat_add_entry(struct devstat *ds, const void *dev_name, 
   77                        int unit_number, uint32_t block_size,
   78                        devstat_support_flags flags,
   79                        devstat_type_flags device_type,
   80                        devstat_priority priority);
   81 
   82 /*
   83  * Allocate a devstat and initialize it
   84  */
   85 struct devstat *
   86 devstat_new_entry(const void *dev_name,
   87                   int unit_number, uint32_t block_size,
   88                   devstat_support_flags flags,
   89                   devstat_type_flags device_type,
   90                   devstat_priority priority)
   91 {
   92         struct devstat *ds;
   93 
   94         mtx_assert(&devstat_mutex, MA_NOTOWNED);
   95 
   96         ds = devstat_alloc();
   97         mtx_lock(&devstat_mutex);
   98         if (unit_number == -1) {
   99                 ds->unit_number = unit_number;
  100                 ds->id = dev_name;
  101                 binuptime(&ds->creation_time);
  102                 devstat_generation++;
  103         } else {
  104                 devstat_add_entry(ds, dev_name, unit_number, block_size,
  105                                   flags, device_type, priority);
  106         }
  107         mtx_unlock(&devstat_mutex);
  108         return (ds);
  109 }
  110 
  111 /*
  112  * Take a malloced and zeroed devstat structure given to us, fill it in 
  113  * and add it to the queue of devices.  
  114  */
  115 static void
  116 devstat_add_entry(struct devstat *ds, const void *dev_name, 
  117                   int unit_number, uint32_t block_size,
  118                   devstat_support_flags flags,
  119                   devstat_type_flags device_type,
  120                   devstat_priority priority)
  121 {
  122         struct devstatlist *devstat_head;
  123         struct devstat *ds_tmp;
  124 
  125         mtx_assert(&devstat_mutex, MA_OWNED);
  126         devstat_num_devs++;
  127 
  128         devstat_head = &device_statq;
  129 
  130         /*
  131          * Priority sort.  Each driver passes in its priority when it adds
  132          * its devstat entry.  Drivers are sorted first by priority, and
  133          * then by probe order.
  134          * 
  135          * For the first device, we just insert it, since the priority
  136          * doesn't really matter yet.  Subsequent devices are inserted into
  137          * the list using the order outlined above.
  138          */
  139         if (devstat_num_devs == 1)
  140                 STAILQ_INSERT_TAIL(devstat_head, ds, dev_links);
  141         else {
  142                 STAILQ_FOREACH(ds_tmp, devstat_head, dev_links) {
  143                         struct devstat *ds_next;
  144 
  145                         ds_next = STAILQ_NEXT(ds_tmp, dev_links);
  146 
  147                         /*
  148                          * If we find a break between higher and lower
  149                          * priority items, and if this item fits in the
  150                          * break, insert it.  This also applies if the
  151                          * "lower priority item" is the end of the list.
  152                          */
  153                         if ((priority <= ds_tmp->priority)
  154                          && ((ds_next == NULL)
  155                            || (priority > ds_next->priority))) {
  156                                 STAILQ_INSERT_AFTER(devstat_head, ds_tmp, ds,
  157                                                     dev_links);
  158                                 break;
  159                         } else if (priority > ds_tmp->priority) {
  160                                 /*
  161                                  * If this is the case, we should be able
  162                                  * to insert ourselves at the head of the
  163                                  * list.  If we can't, something is wrong.
  164                                  */
  165                                 if (ds_tmp == STAILQ_FIRST(devstat_head)) {
  166                                         STAILQ_INSERT_HEAD(devstat_head,
  167                                                            ds, dev_links);
  168                                         break;
  169                                 } else {
  170                                         STAILQ_INSERT_TAIL(devstat_head,
  171                                                            ds, dev_links);
  172                                         printf("devstat_add_entry: HELP! "
  173                                                "sorting problem detected "
  174                                                "for name %p unit %d\n",
  175                                                dev_name, unit_number);
  176                                         break;
  177                                 }
  178                         }
  179                 }
  180         }
  181 
  182         ds->device_number = devstat_current_devnumber++;
  183         ds->unit_number = unit_number;
  184         strlcpy(ds->device_name, dev_name, DEVSTAT_NAME_LEN);
  185         ds->block_size = block_size;
  186         ds->flags = flags;
  187         ds->device_type = device_type;
  188         ds->priority = priority;
  189         binuptime(&ds->creation_time);
  190         devstat_generation++;
  191 }
  192 
  193 /*
  194  * Remove a devstat structure from the list of devices.
  195  */
  196 void
  197 devstat_remove_entry(struct devstat *ds)
  198 {
  199         struct devstatlist *devstat_head;
  200 
  201         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  202         if (ds == NULL)
  203                 return;
  204 
  205         mtx_lock(&devstat_mutex);
  206 
  207         devstat_head = &device_statq;
  208 
  209         /* Remove this entry from the devstat queue */
  210         atomic_add_acq_int(&ds->sequence1, 1);
  211         if (ds->unit_number != -1) {
  212                 devstat_num_devs--;
  213                 STAILQ_REMOVE(devstat_head, ds, devstat, dev_links);
  214         }
  215         devstat_free(ds);
  216         devstat_generation++;
  217         mtx_unlock(&devstat_mutex);
  218 }
  219 
  220 /*
  221  * Record a transaction start.
  222  *
  223  * See comments for devstat_end_transaction().  Ordering is very important
  224  * here.
  225  */
  226 void
  227 devstat_start_transaction(struct devstat *ds, struct bintime *now)
  228 {
  229 
  230         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  231 
  232         /* sanity check */
  233         if (ds == NULL)
  234                 return;
  235 
  236         atomic_add_acq_int(&ds->sequence1, 1);
  237         /*
  238          * We only want to set the start time when we are going from idle
  239          * to busy.  The start time is really the start of the latest busy
  240          * period.
  241          */
  242         if (ds->start_count == ds->end_count) {
  243                 if (now != NULL)
  244                         ds->busy_from = *now;
  245                 else
  246                         binuptime(&ds->busy_from);
  247         }
  248         ds->start_count++;
  249         atomic_add_rel_int(&ds->sequence0, 1);
  250         DTRACE_DEVSTAT_START();
  251 }
  252 
  253 void
  254 devstat_start_transaction_bio(struct devstat *ds, struct bio *bp)
  255 {
  256 
  257         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  258 
  259         /* sanity check */
  260         if (ds == NULL)
  261                 return;
  262 
  263         binuptime(&bp->bio_t0);
  264         devstat_start_transaction(ds, &bp->bio_t0);
  265         DTRACE_DEVSTAT_BIO_START();
  266 }
  267 
  268 /*
  269  * Record the ending of a transaction, and incrment the various counters.
  270  *
  271  * Ordering in this function, and in devstat_start_transaction() is VERY
  272  * important.  The idea here is to run without locks, so we are very
  273  * careful to only modify some fields on the way "down" (i.e. at
  274  * transaction start) and some fields on the way "up" (i.e. at transaction
  275  * completion).  One exception is busy_from, which we only modify in
  276  * devstat_start_transaction() when there are no outstanding transactions,
  277  * and thus it can't be modified in devstat_end_transaction()
  278  * simultaneously.
  279  *
  280  * The sequence0 and sequence1 fields are provided to enable an application
  281  * spying on the structures with mmap(2) to tell when a structure is in a
  282  * consistent state or not.
  283  *
  284  * For this to work 100% reliably, it is important that the two fields
  285  * are at opposite ends of the structure and that they are incremented
  286  * in the opposite order of how a memcpy(3) in userland would copy them.
  287  * We assume that the copying happens front to back, but there is actually
  288  * no way short of writing your own memcpy(3) replacement to guarantee
  289  * this will be the case.
  290  *
  291  * In addition to this, being a kind of locks, they must be updated with
  292  * atomic instructions using appropriate memory barriers.
  293  */
  294 void
  295 devstat_end_transaction(struct devstat *ds, uint32_t bytes, 
  296                         devstat_tag_type tag_type, devstat_trans_flags flags,
  297                         struct bintime *now, struct bintime *then)
  298 {
  299         struct bintime dt, lnow;
  300 
  301         /* sanity check */
  302         if (ds == NULL)
  303                 return;
  304 
  305         if (now == NULL) {
  306                 now = &lnow;
  307                 binuptime(now);
  308         }
  309 
  310         atomic_add_acq_int(&ds->sequence1, 1);
  311         /* Update byte and operations counts */
  312         ds->bytes[flags] += bytes;
  313         ds->operations[flags]++;
  314 
  315         /*
  316          * Keep a count of the various tag types sent.
  317          */
  318         if ((ds->flags & DEVSTAT_NO_ORDERED_TAGS) == 0 &&
  319             tag_type != DEVSTAT_TAG_NONE)
  320                 ds->tag_types[tag_type]++;
  321 
  322         if (then != NULL) {
  323                 /* Update duration of operations */
  324                 dt = *now;
  325                 bintime_sub(&dt, then);
  326                 bintime_add(&ds->duration[flags], &dt);
  327         }
  328 
  329         /* Accumulate busy time */
  330         dt = *now;
  331         bintime_sub(&dt, &ds->busy_from);
  332         bintime_add(&ds->busy_time, &dt);
  333         ds->busy_from = *now;
  334 
  335         ds->end_count++;
  336         atomic_add_rel_int(&ds->sequence0, 1);
  337         DTRACE_DEVSTAT_DONE();
  338 }
  339 
  340 void
  341 devstat_end_transaction_bio(struct devstat *ds, struct bio *bp)
  342 {
  343 
  344         devstat_end_transaction_bio_bt(ds, bp, NULL);
  345 }
  346 
  347 void
  348 devstat_end_transaction_bio_bt(struct devstat *ds, struct bio *bp,
  349     struct bintime *now)
  350 {
  351         devstat_trans_flags flg;
  352 
  353         /* sanity check */
  354         if (ds == NULL)
  355                 return;
  356 
  357         if (bp->bio_cmd == BIO_DELETE)
  358                 flg = DEVSTAT_FREE;
  359         else if (bp->bio_cmd == BIO_READ)
  360                 flg = DEVSTAT_READ;
  361         else if (bp->bio_cmd == BIO_WRITE)
  362                 flg = DEVSTAT_WRITE;
  363         else 
  364                 flg = DEVSTAT_NO_DATA;
  365 
  366         devstat_end_transaction(ds, bp->bio_bcount - bp->bio_resid,
  367                                 DEVSTAT_TAG_SIMPLE, flg, now, &bp->bio_t0);
  368         DTRACE_DEVSTAT_BIO_DONE();
  369 }
  370 
  371 /*
  372  * This is the sysctl handler for the devstat package.  The data pushed out
  373  * on the kern.devstat.all sysctl variable consists of the current devstat
  374  * generation number, and then an array of devstat structures, one for each
  375  * device in the system.
  376  *
  377  * This is more cryptic that obvious, but basically we neither can nor
  378  * want to hold the devstat_mutex for any amount of time, so we grab it
  379  * only when we need to and keep an eye on devstat_generation all the time.
  380  */
  381 static int
  382 sysctl_devstat(SYSCTL_HANDLER_ARGS)
  383 {
  384         int error;
  385         long mygen;
  386         struct devstat *nds;
  387 
  388         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  389 
  390         /*
  391          * XXX devstat_generation should really be "volatile" but that
  392          * XXX freaks out the sysctl macro below.  The places where we
  393          * XXX change it and inspect it are bracketed in the mutex which
  394          * XXX guarantees us proper write barriers.  I don't believe the
  395          * XXX compiler is allowed to optimize mygen away across calls
  396          * XXX to other functions, so the following is belived to be safe.
  397          */
  398         mygen = devstat_generation;
  399 
  400         error = SYSCTL_OUT(req, &mygen, sizeof(mygen));
  401 
  402         if (devstat_num_devs == 0)
  403                 return(0);
  404 
  405         if (error != 0)
  406                 return (error);
  407 
  408         mtx_lock(&devstat_mutex);
  409         nds = STAILQ_FIRST(&device_statq); 
  410         if (mygen != devstat_generation)
  411                 error = EBUSY;
  412         mtx_unlock(&devstat_mutex);
  413 
  414         if (error != 0)
  415                 return (error);
  416 
  417         for (;nds != NULL;) {
  418                 error = SYSCTL_OUT(req, nds, sizeof(struct devstat));
  419                 if (error != 0)
  420                         return (error);
  421                 mtx_lock(&devstat_mutex);
  422                 if (mygen != devstat_generation)
  423                         error = EBUSY;
  424                 else
  425                         nds = STAILQ_NEXT(nds, dev_links);
  426                 mtx_unlock(&devstat_mutex);
  427                 if (error != 0)
  428                         return (error);
  429         }
  430         return(error);
  431 }
  432 
  433 /*
  434  * Sysctl entries for devstat.  The first one is a node that all the rest
  435  * hang off of. 
  436  */
  437 static SYSCTL_NODE(_kern, OID_AUTO, devstat, CTLFLAG_RD, NULL,
  438     "Device Statistics");
  439 
  440 SYSCTL_PROC(_kern_devstat, OID_AUTO, all, CTLFLAG_RD|CTLTYPE_OPAQUE,
  441     NULL, 0, sysctl_devstat, "S,devstat", "All devices in the devstat list");
  442 /*
  443  * Export the number of devices in the system so that userland utilities
  444  * can determine how much memory to allocate to hold all the devices.
  445  */
  446 SYSCTL_INT(_kern_devstat, OID_AUTO, numdevs, CTLFLAG_RD, 
  447     &devstat_num_devs, 0, "Number of devices in the devstat list");
  448 SYSCTL_LONG(_kern_devstat, OID_AUTO, generation, CTLFLAG_RD,
  449     &devstat_generation, 0, "Devstat list generation");
  450 SYSCTL_INT(_kern_devstat, OID_AUTO, version, CTLFLAG_RD, 
  451     &devstat_version, 0, "Devstat list version number");
  452 
  453 /*
  454  * Allocator for struct devstat structures.  We sub-allocate these from pages
  455  * which we get from malloc.  These pages are exported for mmap(2)'ing through
  456  * a miniature device driver
  457  */
  458 
  459 #define statsperpage (PAGE_SIZE / sizeof(struct devstat))
  460 
  461 static d_mmap_t devstat_mmap;
  462 
  463 static struct cdevsw devstat_cdevsw = {
  464         .d_version =    D_VERSION,
  465         .d_mmap =       devstat_mmap,
  466         .d_name =       "devstat",
  467 };
  468 
  469 struct statspage {
  470         TAILQ_ENTRY(statspage)  list;
  471         struct devstat          *stat;
  472         u_int                   nfree;
  473 };
  474 
  475 static TAILQ_HEAD(, statspage)  pagelist = TAILQ_HEAD_INITIALIZER(pagelist);
  476 static MALLOC_DEFINE(M_DEVSTAT, "devstat", "Device statistics");
  477 
  478 static int
  479 devstat_mmap(struct cdev *dev, vm_ooffset_t offset, vm_paddr_t *paddr,
  480     int nprot, vm_memattr_t *memattr)
  481 {
  482         struct statspage *spp;
  483 
  484         if (nprot != VM_PROT_READ)
  485                 return (-1);
  486         mtx_lock(&devstat_mutex);
  487         TAILQ_FOREACH(spp, &pagelist, list) {
  488                 if (offset == 0) {
  489                         *paddr = vtophys(spp->stat);
  490                         mtx_unlock(&devstat_mutex);
  491                         return (0);
  492                 }
  493                 offset -= PAGE_SIZE;
  494         }
  495         mtx_unlock(&devstat_mutex);
  496         return (-1);
  497 }
  498 
  499 static struct devstat *
  500 devstat_alloc(void)
  501 {
  502         struct devstat *dsp;
  503         struct statspage *spp, *spp2;
  504         u_int u;
  505         static int once;
  506 
  507         mtx_assert(&devstat_mutex, MA_NOTOWNED);
  508         if (!once) {
  509                 make_dev_credf(MAKEDEV_ETERNAL | MAKEDEV_CHECKNAME,
  510                     &devstat_cdevsw, 0, NULL, UID_ROOT, GID_WHEEL, 0444,
  511                     DEVSTAT_DEVICE_NAME);
  512                 once = 1;
  513         }
  514         spp2 = NULL;
  515         mtx_lock(&devstat_mutex);
  516         for (;;) {
  517                 TAILQ_FOREACH(spp, &pagelist, list) {
  518                         if (spp->nfree > 0)
  519                                 break;
  520                 }
  521                 if (spp != NULL)
  522                         break;
  523                 mtx_unlock(&devstat_mutex);
  524                 spp2 = malloc(sizeof *spp, M_DEVSTAT, M_ZERO | M_WAITOK);
  525                 spp2->stat = malloc(PAGE_SIZE, M_DEVSTAT, M_ZERO | M_WAITOK);
  526                 spp2->nfree = statsperpage;
  527 
  528                 /*
  529                  * If free statspages were added while the lock was released
  530                  * just reuse them.
  531                  */
  532                 mtx_lock(&devstat_mutex);
  533                 TAILQ_FOREACH(spp, &pagelist, list)
  534                         if (spp->nfree > 0)
  535                                 break;
  536                 if (spp == NULL) {
  537                         spp = spp2;
  538 
  539                         /*
  540                          * It would make more sense to add the new page at the
  541                          * head but the order on the list determine the
  542                          * sequence of the mapping so we can't do that.
  543                          */
  544                         TAILQ_INSERT_TAIL(&pagelist, spp, list);
  545                 } else
  546                         break;
  547         }
  548         dsp = spp->stat;
  549         for (u = 0; u < statsperpage; u++) {
  550                 if (dsp->allocated == 0)
  551                         break;
  552                 dsp++;
  553         }
  554         spp->nfree--;
  555         dsp->allocated = 1;
  556         mtx_unlock(&devstat_mutex);
  557         if (spp2 != NULL && spp2 != spp) {
  558                 free(spp2->stat, M_DEVSTAT);
  559                 free(spp2, M_DEVSTAT);
  560         }
  561         return (dsp);
  562 }
  563 
  564 static void
  565 devstat_free(struct devstat *dsp)
  566 {
  567         struct statspage *spp;
  568 
  569         mtx_assert(&devstat_mutex, MA_OWNED);
  570         bzero(dsp, sizeof *dsp);
  571         TAILQ_FOREACH(spp, &pagelist, list) {
  572                 if (dsp >= spp->stat && dsp < (spp->stat + statsperpage)) {
  573                         spp->nfree++;
  574                         return;
  575                 }
  576         }
  577 }
  578 
  579 SYSCTL_INT(_debug_sizeof, OID_AUTO, devstat, CTLFLAG_RD,
  580     SYSCTL_NULL_INT_PTR, sizeof(struct devstat), "sizeof(struct devstat)");

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