/*-
 * SPDX-License-Identifier: BSD-2-Clause
 *
 * Copyright (c) 2009 Isilon Inc http://www.isilon.com/
 *
 * 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.
 */
/**
 * @file
 *
 * fail(9) Facility.
 *
 * @ingroup failpoint_private
 */
/**
 * @defgroup failpoint fail(9) Facility
 *
 * Failpoints allow for injecting fake errors into running code on the fly,
 * without modifying code or recompiling with flags.  Failpoints are always
 * present, and are very efficient when disabled.  Failpoints are described
 * in man fail(9).
 */
/**
 * @defgroup failpoint_private Private fail(9) Implementation functions
 *
 * Private implementations for the actual failpoint code.
 *
 * @ingroup failpoint
 */
/**
 * @addtogroup failpoint_private
 * @{
 */

#include <sys/cdefs.h>
#include "opt_stack.h"

#include <sys/ctype.h>
#include <sys/errno.h>
#include <sys/fail.h>
#include <sys/kernel.h>
#include <sys/libkern.h>
#include <sys/limits.h>
#include <sys/lock.h>
#include <sys/malloc.h>
#include <sys/mutex.h>
#include <sys/proc.h>
#include <sys/sbuf.h>
#include <sys/sleepqueue.h>
#include <sys/stdarg.h>
#include <sys/sx.h>
#include <sys/sysctl.h>
#include <sys/types.h>

#include <machine/atomic.h>

#ifdef ILOG_DEFINE_FOR_FILE
ILOG_DEFINE_FOR_FILE(L_ISI_FAIL_POINT, L_ILOG, fail_point);
#endif

static MALLOC_DEFINE(M_FAIL_POINT, "Fail Points", "fail points system");
#define fp_free(ptr) free(ptr, M_FAIL_POINT)
#define fp_malloc(size, flags) malloc((size), M_FAIL_POINT, (flags))
#define fs_free(ptr) fp_free(ptr)
#define fs_malloc() fp_malloc(sizeof(struct fail_point_setting), \
    M_WAITOK | M_ZERO)

/**
 * These define the wchans that are used for sleeping, pausing respectively.
 * They are chosen arbitrarily but need to be distinct to the failpoint and
 * the sleep/pause distinction.
 */
#define FP_SLEEP_CHANNEL(fp) (void*)(fp)
#define FP_PAUSE_CHANNEL(fp) __DEVOLATILE(void*, &fp->fp_setting)

/**
 * Don't allow more than this many entries in a fail point set by sysctl.
 * The 99.99...% case is to have 1 entry.  I can't imagine having this many
 * entries, so it should not limit us.  Saves on re-mallocs while holding
 * a non-sleepable lock.
 */
#define FP_MAX_ENTRY_COUNT 20

/* Used to drain sbufs to the sysctl output */
int fail_sysctl_drain_func(void *, const char *, int);

/* Head of tailq of struct fail_point_entry */
TAILQ_HEAD(fail_point_entry_queue, fail_point_entry);

/**
 * fp entries garbage list; outstanding entries are cleaned up in the
 * garbage collector
 */
STAILQ_HEAD(fail_point_setting_garbage, fail_point_setting);
static struct fail_point_setting_garbage fp_setting_garbage =
        STAILQ_HEAD_INITIALIZER(fp_setting_garbage);
static struct mtx mtx_garbage_list;
MTX_SYSINIT(mtx_garbage_list, &mtx_garbage_list, "fail point garbage mtx",
        MTX_SPIN);

static struct sx sx_fp_set;
SX_SYSINIT(sx_fp_set, &sx_fp_set, "fail point set sx");

/**
 * Failpoint types.
 * Don't change these without changing fail_type_strings in fail.c.
 * @ingroup failpoint_private
 */
enum fail_point_t {
        FAIL_POINT_OFF,         /**< don't fail */
        FAIL_POINT_PANIC,       /**< panic */
        FAIL_POINT_RETURN,      /**< return an errorcode */
        FAIL_POINT_BREAK,       /**< break into the debugger */
        FAIL_POINT_PRINT,       /**< print a message */
        FAIL_POINT_SLEEP,       /**< sleep for some msecs */
        FAIL_POINT_PAUSE,       /**< sleep until failpoint is set to off */
        FAIL_POINT_YIELD,       /**< yield the cpu */
        FAIL_POINT_DELAY,       /**< busy wait the cpu */
        FAIL_POINT_NUMTYPES,
        FAIL_POINT_INVALID = -1
};

static struct {
        const char *name;
        int     nmlen;
} fail_type_strings[] = {
#define FP_TYPE_NM_LEN(s)       { s, sizeof(s) - 1 }
        [FAIL_POINT_OFF] =      FP_TYPE_NM_LEN("off"),
        [FAIL_POINT_PANIC] =    FP_TYPE_NM_LEN("panic"),
        [FAIL_POINT_RETURN] =   FP_TYPE_NM_LEN("return"),
        [FAIL_POINT_BREAK] =    FP_TYPE_NM_LEN("break"),
        [FAIL_POINT_PRINT] =    FP_TYPE_NM_LEN("print"),
        [FAIL_POINT_SLEEP] =    FP_TYPE_NM_LEN("sleep"),
        [FAIL_POINT_PAUSE] =    FP_TYPE_NM_LEN("pause"),
        [FAIL_POINT_YIELD] =    FP_TYPE_NM_LEN("yield"),
        [FAIL_POINT_DELAY] =    FP_TYPE_NM_LEN("delay"),
};

#define FE_COUNT_UNTRACKED (INT_MIN)

/**
 * Internal structure tracking a single term of a complete failpoint.
 * @ingroup failpoint_private
 */
struct fail_point_entry {
        volatile bool   fe_stale;
        enum fail_point_t       fe_type;        /**< type of entry */
        int             fe_arg;         /**< argument to type (e.g. return value) */
        int             fe_prob;        /**< likelihood of firing in millionths */
        int32_t         fe_count;       /**< number of times to fire, -1 means infinite */
        pid_t           fe_pid;         /**< only fail for this process */
        struct fail_point       *fe_parent;     /**< backpointer to fp */
        TAILQ_ENTRY(fail_point_entry)   fe_entries; /**< next entry ptr */
};

struct fail_point_setting {
        STAILQ_ENTRY(fail_point_setting) fs_garbage_link;
        struct fail_point_entry_queue fp_entry_queue;
        struct fail_point * fs_parent;
        struct mtx feq_mtx; /* Gives fail_point_pause something to do.  */
};

/**
 * Defines stating the equivalent of probablilty one (100%)
 */
enum {
        PROB_MAX = 1000000,     /* probability between zero and this number */
        PROB_DIGITS = 6         /* number of zero's in above number */
};

/* Get a ref on an fp's fp_setting */
static inline struct fail_point_setting *fail_point_setting_get_ref(
        struct fail_point *fp);
/* Release a ref on an fp_setting */
static inline void fail_point_setting_release_ref(struct fail_point *fp);
/* Allocate and initialize a struct fail_point_setting */
static struct fail_point_setting *fail_point_setting_new(struct
        fail_point *);
/* Free a struct fail_point_setting */
static void fail_point_setting_destroy(struct fail_point_setting *fp_setting);
/* Allocate and initialize a struct fail_point_entry */
static struct fail_point_entry *fail_point_entry_new(struct
        fail_point_setting *);
/* Free a struct fail_point_entry */
static void fail_point_entry_destroy(struct fail_point_entry *fp_entry);
/* Append fp setting to garbage list */
static inline void fail_point_setting_garbage_append(
        struct fail_point_setting *fp_setting);
/* Swap fp's setting with fp_setting_new */
static inline struct fail_point_setting *
        fail_point_swap_settings(struct fail_point *fp,
        struct fail_point_setting *fp_setting_new);
/* Free up any zero-ref setting in the garbage queue */
static void fail_point_garbage_collect(void);
/* If this fail point's setting are empty, then swap it out to NULL. */
static inline void fail_point_eval_swap_out(struct fail_point *fp,
        struct fail_point_setting *fp_setting);

bool
fail_point_is_off(struct fail_point *fp)
{
        bool return_val;
        struct fail_point_setting *fp_setting;
        struct fail_point_entry *ent;

        return_val = true;

        fp_setting = fail_point_setting_get_ref(fp);
        if (fp_setting != NULL) {
                TAILQ_FOREACH(ent, &fp_setting->fp_entry_queue,
                    fe_entries) {
                        if (!ent->fe_stale) {
                                return_val = false;
                                break;
                        }
                }
        }
        fail_point_setting_release_ref(fp);

        return (return_val);
}

/* Allocate and initialize a struct fail_point_setting */
static struct fail_point_setting *
fail_point_setting_new(struct fail_point *fp)
{
        struct fail_point_setting *fs_new;

        fs_new = fs_malloc();
        fs_new->fs_parent = fp;
        TAILQ_INIT(&fs_new->fp_entry_queue);
        mtx_init(&fs_new->feq_mtx, "fail point entries", NULL, MTX_SPIN);

        fail_point_setting_garbage_append(fs_new);

        return (fs_new);
}

/* Free a struct fail_point_setting */
static void
fail_point_setting_destroy(struct fail_point_setting *fp_setting)
{
        struct fail_point_entry *ent;

        while (!TAILQ_EMPTY(&fp_setting->fp_entry_queue)) {
                ent = TAILQ_FIRST(&fp_setting->fp_entry_queue);
                TAILQ_REMOVE(&fp_setting->fp_entry_queue, ent, fe_entries);
                fail_point_entry_destroy(ent);
        }

        fs_free(fp_setting);
}

/* Allocate and initialize a struct fail_point_entry */
static struct fail_point_entry *
fail_point_entry_new(struct fail_point_setting *fp_setting)
{
        struct fail_point_entry *fp_entry;

        fp_entry = fp_malloc(sizeof(struct fail_point_entry),
                M_WAITOK | M_ZERO);
        fp_entry->fe_parent = fp_setting->fs_parent;
        fp_entry->fe_prob = PROB_MAX;
        fp_entry->fe_pid = NO_PID;
        fp_entry->fe_count = FE_COUNT_UNTRACKED;
        TAILQ_INSERT_TAIL(&fp_setting->fp_entry_queue, fp_entry,
                fe_entries);

        return (fp_entry);
}

/* Free a struct fail_point_entry */
static void
fail_point_entry_destroy(struct fail_point_entry *fp_entry)
{

        fp_free(fp_entry);
}

/* Get a ref on an fp's fp_setting */
static inline struct fail_point_setting *
fail_point_setting_get_ref(struct fail_point *fp)
{
        struct fail_point_setting *fp_setting;

        /* Invariant: if we have a ref, our pointer to fp_setting is safe */
        atomic_add_acq_32(&fp->fp_ref_cnt, 1);
        fp_setting = fp->fp_setting;

        return (fp_setting);
}

/* Release a ref on an fp_setting */
static inline void
fail_point_setting_release_ref(struct fail_point *fp)
{

        KASSERT(&fp->fp_ref_cnt > 0, ("Attempting to deref w/no refs"));
        atomic_subtract_rel_32(&fp->fp_ref_cnt, 1);
}

/* Append fp entries to fp garbage list */
static inline void
fail_point_setting_garbage_append(struct fail_point_setting *fp_setting)
{

        mtx_lock_spin(&mtx_garbage_list);
        STAILQ_INSERT_TAIL(&fp_setting_garbage, fp_setting,
                fs_garbage_link);
        mtx_unlock_spin(&mtx_garbage_list);
}

/* Swap fp's entries with fp_setting_new */
static struct fail_point_setting *
fail_point_swap_settings(struct fail_point *fp,
        struct fail_point_setting *fp_setting_new)
{
        struct fail_point_setting *fp_setting_old;

        fp_setting_old = fp->fp_setting;
        fp->fp_setting = fp_setting_new;

        return (fp_setting_old);
}

static inline void
fail_point_eval_swap_out(struct fail_point *fp,
        struct fail_point_setting *fp_setting)
{

        /* We may have already been swapped out and replaced; ignore. */
        if (fp->fp_setting == fp_setting)
                fail_point_swap_settings(fp, NULL);
}

/* Free up any zero-ref entries in the garbage queue */
static void
fail_point_garbage_collect(void)
{
        struct fail_point_setting *fs_current, *fs_next;
        struct fail_point_setting_garbage fp_ents_free_list;

        /**
          * We will transfer the entries to free to fp_ents_free_list while holding
          * the spin mutex, then free it after we drop the lock. This avoids
          * triggering witness due to sleepable mutexes in the memory
          * allocator.
          */
        STAILQ_INIT(&fp_ents_free_list);

        mtx_lock_spin(&mtx_garbage_list);
        STAILQ_FOREACH_SAFE(fs_current, &fp_setting_garbage, fs_garbage_link,
            fs_next) {
                if (fs_current->fs_parent->fp_setting != fs_current &&
                        fs_current->fs_parent->fp_ref_cnt == 0) {
                        STAILQ_REMOVE(&fp_setting_garbage, fs_current,
                                fail_point_setting, fs_garbage_link);
                        STAILQ_INSERT_HEAD(&fp_ents_free_list, fs_current,
                                fs_garbage_link);
                }
        }
        mtx_unlock_spin(&mtx_garbage_list);

        STAILQ_FOREACH_SAFE(fs_current, &fp_ents_free_list, fs_garbage_link,
                fs_next)
                fail_point_setting_destroy(fs_current);
}

/* Drain out all refs from this fail point */
static inline void
fail_point_drain(struct fail_point *fp, int expected_ref)
{
        struct fail_point_setting *entries;

        entries = fail_point_swap_settings(fp, NULL);
        /**
         * We have unpaused all threads; so we will wait no longer
         * than the time taken for the longest remaining sleep, or
         * the length of time of a long-running code block.
         */
        while (fp->fp_ref_cnt > expected_ref) {
                wakeup(FP_PAUSE_CHANNEL(fp));
                tsleep(&fp, PWAIT, "fail_point_drain", hz / 100);
        }
        if (fp->fp_callout)
                callout_drain(fp->fp_callout);
        fail_point_swap_settings(fp, entries);
}

static inline void
fail_point_pause(struct fail_point *fp, enum fail_point_return_code *pret,
        struct mtx *mtx_sleep)
{

        if (fp->fp_pre_sleep_fn)
                fp->fp_pre_sleep_fn(fp->fp_pre_sleep_arg);

        msleep_spin(FP_PAUSE_CHANNEL(fp), mtx_sleep, "failpt", 0);

        if (fp->fp_post_sleep_fn)
                fp->fp_post_sleep_fn(fp->fp_post_sleep_arg);
}

static inline void
fail_point_sleep(struct fail_point *fp, int msecs,
        enum fail_point_return_code *pret)
{
        int timo;

        /* Convert from millisecs to ticks, rounding up */
        timo = howmany((int64_t)msecs * hz, 1000L);

        if (timo > 0) {
                if (!(fp->fp_flags & FAIL_POINT_USE_TIMEOUT_PATH)) {
                        if (fp->fp_pre_sleep_fn)
                                fp->fp_pre_sleep_fn(fp->fp_pre_sleep_arg);

                        tsleep(FP_SLEEP_CHANNEL(fp), PWAIT, "failpt", timo);

                        if (fp->fp_post_sleep_fn)
                                fp->fp_post_sleep_fn(fp->fp_post_sleep_arg);
                } else {
                        if (fp->fp_pre_sleep_fn)
                                fp->fp_pre_sleep_fn(fp->fp_pre_sleep_arg);

                        callout_reset(fp->fp_callout, timo,
                            fp->fp_post_sleep_fn, fp->fp_post_sleep_arg);
                        *pret = FAIL_POINT_RC_QUEUED;
                }
        }
}

static char *parse_fail_point(struct fail_point_setting *, char *);
static char *parse_term(struct fail_point_setting *, char *);
static char *parse_number(int *out_units, int *out_decimal, char *);
static char *parse_type(struct fail_point_entry *, char *);

/**
 * Initialize a fail_point.  The name is formed in a printf-like fashion
 * from "fmt" and subsequent arguments.  This function is generally used
 * for custom failpoints located at odd places in the sysctl tree, and is
 * not explicitly needed for standard in-line-declared failpoints.
 *
 * @ingroup failpoint
 */
void
fail_point_init(struct fail_point *fp, const char *fmt, ...)
{
        va_list ap;
        char *name;
        int n;

        fp->fp_setting = NULL;
        fp->fp_flags = 0;

        /* Figure out the size of the name. */
        va_start(ap, fmt);
        n = vsnprintf(NULL, 0, fmt, ap);
        va_end(ap);

        /* Allocate the name and fill it in. */
        name = fp_malloc(n + 1, M_WAITOK);
        va_start(ap, fmt);
        vsnprintf(name, n + 1, fmt, ap);
        va_end(ap);

        fp->fp_name = name;
        fp->fp_location = "";
        fp->fp_flags |= FAIL_POINT_DYNAMIC_NAME;
        fp->fp_pre_sleep_fn = NULL;
        fp->fp_pre_sleep_arg = NULL;
        fp->fp_post_sleep_fn = NULL;
        fp->fp_post_sleep_arg = NULL;
}

void
fail_point_alloc_callout(struct fail_point *fp)
{

        /**
         * This assumes that calls to fail_point_use_timeout_path()
         * will not race.
         */
        if (fp->fp_callout != NULL)
                return;
        fp->fp_callout = fp_malloc(sizeof(*fp->fp_callout), M_WAITOK);
        callout_init(fp->fp_callout, CALLOUT_MPSAFE);
}

/**
 * Free the resources held by a fail_point, and wake any paused threads.
 * Thou shalt not allow threads to hit this fail point after you enter this
 * function, nor shall you call this multiple times for a given fp.
 * @ingroup failpoint
 */
void
fail_point_destroy(struct fail_point *fp)
{

        fail_point_drain(fp, 0);

        if ((fp->fp_flags & FAIL_POINT_DYNAMIC_NAME) != 0) {
                fp_free(__DECONST(void *, fp->fp_name));
                fp->fp_name = NULL;
        }
        fp->fp_flags = 0;
        if (fp->fp_callout) {
                fp_free(fp->fp_callout);
                fp->fp_callout = NULL;
        }

        sx_xlock(&sx_fp_set);
        fail_point_garbage_collect();
        sx_xunlock(&sx_fp_set);
}

/**
 * This does the real work of evaluating a fail point. If the fail point tells
 * us to return a value, this function returns 1 and fills in 'return_value'
 * (return_value is allowed to be null). If the fail point tells us to panic,
 * we never return. Otherwise we just return 0 after doing some work, which
 * means "keep going".
 */
enum fail_point_return_code
fail_point_eval_nontrivial(struct fail_point *fp, int *return_value)
{
        bool execute = false;
        struct fail_point_entry *ent;
        struct fail_point_setting *fp_setting;
        enum fail_point_return_code ret;
        int cont;
        int count;
        int msecs;
        int usecs;

        ret = FAIL_POINT_RC_CONTINUE;
        cont = 0; /* don't continue by default */

        fp_setting = fail_point_setting_get_ref(fp);
        if (fp_setting == NULL)
                goto abort;

        TAILQ_FOREACH(ent, &fp_setting->fp_entry_queue, fe_entries) {
                if (ent->fe_stale)
                        continue;

                if (ent->fe_prob < PROB_MAX &&
                    ent->fe_prob < random() % PROB_MAX)
                        continue;

                if (ent->fe_pid != NO_PID && ent->fe_pid != curproc->p_pid)
                        continue;

                if (ent->fe_count != FE_COUNT_UNTRACKED) {
                        count = ent->fe_count;
                        while (count > 0) {
                                if (atomic_cmpset_32(&ent->fe_count, count, count - 1)) {
                                        count--;
                                        execute = true;
                                        break;
                                }
                                count = ent->fe_count;
                        }
                        if (execute == false)
                                /* We lost the race; consider the entry stale and bail now */
                                continue;
                        if (count == 0)
                                ent->fe_stale = true;
                }

                switch (ent->fe_type) {
                case FAIL_POINT_PANIC:
                        panic("fail point %s panicking", fp->fp_name);
                        /* NOTREACHED */

                case FAIL_POINT_RETURN:
                        if (return_value != NULL)
                                *return_value = ent->fe_arg;
                        ret = FAIL_POINT_RC_RETURN;
                        break;

                case FAIL_POINT_BREAK:
                        printf("fail point %s breaking to debugger\n",
                                fp->fp_name);
                        breakpoint();
                        break;

                case FAIL_POINT_PRINT:
                        printf("fail point %s executing\n", fp->fp_name);
                        cont = ent->fe_arg;
                        break;

                case FAIL_POINT_SLEEP:
                        msecs = ent->fe_arg;
                        if (msecs)
                                fail_point_sleep(fp, msecs, &ret);
                        break;

                case FAIL_POINT_PAUSE:
                        /**
                         * Pausing is inherently strange with multiple
                         * entries given our design.  That is because some
                         * entries could be unreachable, for instance in cases like:
                         * pause->return. We can never reach the return entry.
                         * The sysctl layer actually truncates all entries after
                         * a pause for this reason.
                         */
                        mtx_lock_spin(&fp_setting->feq_mtx);
                        fail_point_pause(fp, &ret, &fp_setting->feq_mtx);
                        mtx_unlock_spin(&fp_setting->feq_mtx);
                        break;

                case FAIL_POINT_YIELD:
                        kern_yield(PRI_UNCHANGED);
                        break;

                case FAIL_POINT_DELAY:
                        usecs = ent->fe_arg;
                        DELAY(usecs);
                        break;

                default:
                        break;
                }

                if (cont == 0)
                        break;
        }

        if (fail_point_is_off(fp))
                fail_point_eval_swap_out(fp, fp_setting);

abort:
        fail_point_setting_release_ref(fp);

        return (ret);
}

/**
 * Translate internal fail_point structure into human-readable text.
 */
static void
fail_point_get(struct fail_point *fp, struct sbuf *sb,
        bool verbose)
{
        struct fail_point_entry *ent;
        struct fail_point_setting *fp_setting;
        struct fail_point_entry *fp_entry_cpy;
        int cnt_sleeping;
        int idx;
        int printed_entry_count;

        cnt_sleeping = 0;
        idx = 0;
        printed_entry_count = 0;

        fp_entry_cpy = fp_malloc(sizeof(struct fail_point_entry) *
                (FP_MAX_ENTRY_COUNT + 1), M_WAITOK);

        fp_setting = fail_point_setting_get_ref(fp);

        if (fp_setting != NULL) {
                TAILQ_FOREACH(ent, &fp_setting->fp_entry_queue, fe_entries) {
                        if (ent->fe_stale)
                                continue;

                        KASSERT(printed_entry_count < FP_MAX_ENTRY_COUNT,
                                ("FP entry list larger than allowed"));

                        fp_entry_cpy[printed_entry_count] = *ent;
                        ++printed_entry_count;
                }
        }
        fail_point_setting_release_ref(fp);

        /* This is our equivalent of a NULL terminator */
        fp_entry_cpy[printed_entry_count].fe_type = FAIL_POINT_INVALID;

        while (idx < printed_entry_count) {
                ent = &fp_entry_cpy[idx];
                ++idx;
                if (ent->fe_prob < PROB_MAX) {
                        int decimal = ent->fe_prob % (PROB_MAX / 100);
                        int units = ent->fe_prob / (PROB_MAX / 100);
                        sbuf_printf(sb, "%d", units);
                        if (decimal) {
                                int digits = PROB_DIGITS - 2;
                                while (!(decimal % 10)) {
                                        digits--;
                                        decimal /= 10;
                                }
                                sbuf_printf(sb, ".%0*d", digits, decimal);
                        }
                        sbuf_printf(sb, "%%");
                }
                if (ent->fe_count >= 0)
                        sbuf_printf(sb, "%d*", ent->fe_count);
                sbuf_printf(sb, "%s", fail_type_strings[ent->fe_type].name);
                if (ent->fe_arg)
                        sbuf_printf(sb, "(%d)", ent->fe_arg);
                if (ent->fe_pid != NO_PID)
                        sbuf_printf(sb, "[pid %d]", ent->fe_pid);
                if (TAILQ_NEXT(ent, fe_entries))
                        sbuf_cat(sb, "->");
        }
        if (!printed_entry_count)
                sbuf_cat(sb, "off");

        fp_free(fp_entry_cpy);
        if (verbose) {
#ifdef STACK
                /* Print number of sleeping threads. queue=0 is the argument
                 * used by msleep when sending our threads to sleep. */
                sbuf_cat(sb, "\nsleeping_thread_stacks = {\n");
                sleepq_sbuf_print_stacks(sb, FP_SLEEP_CHANNEL(fp), 0,
                        &cnt_sleeping);

                sbuf_cat(sb, "},\n");
#endif
                sbuf_printf(sb, "sleeping_thread_count = %d,\n",
                        cnt_sleeping);

#ifdef STACK
                sbuf_cat(sb, "paused_thread_stacks = {\n");
                sleepq_sbuf_print_stacks(sb, FP_PAUSE_CHANNEL(fp), 0,
                        &cnt_sleeping);

                sbuf_cat(sb, "},\n");
#endif
                sbuf_printf(sb, "paused_thread_count = %d\n",
                        cnt_sleeping);
        }
}

/**
 * Set an internal fail_point structure from a human-readable failpoint string
 * in a lock-safe manner.
 */
static int
fail_point_set(struct fail_point *fp, char *buf)
{
        struct fail_point_entry *ent, *ent_next;
        struct fail_point_setting *entries;
        bool should_wake_paused;
        bool should_truncate;
        int error;

        error = 0;
        should_wake_paused = false;
        should_truncate = false;

        /* Parse new entries. */
        /**
         * ref protects our new malloc'd stuff from being garbage collected
         * before we link it.
         */
        fail_point_setting_get_ref(fp);
        entries = fail_point_setting_new(fp);
        if (parse_fail_point(entries, buf) == NULL) {
                STAILQ_REMOVE(&fp_setting_garbage, entries,
                        fail_point_setting, fs_garbage_link);
                fail_point_setting_destroy(entries);
                error = EINVAL;
                goto end;
        }

        /**
         * Transfer the entries we are going to keep to a new list.
         * Get rid of useless zero probability entries, and entries with hit
         * count 0.
         * If 'off' is present, and it has no hit count set, then all entries
         *       after it are discarded since they are unreachable.
         */
        TAILQ_FOREACH_SAFE(ent, &entries->fp_entry_queue, fe_entries, ent_next) {
                if (ent->fe_prob == 0 || ent->fe_count == 0) {
                        printf("Discarding entry which cannot execute %s\n",
                                fail_type_strings[ent->fe_type].name);
                        TAILQ_REMOVE(&entries->fp_entry_queue, ent,
                                fe_entries);
                        fp_free(ent);
                        continue;
                } else if (should_truncate) {
                        printf("Discarding unreachable entry %s\n",
                                fail_type_strings[ent->fe_type].name);
                        TAILQ_REMOVE(&entries->fp_entry_queue, ent,
                                fe_entries);
                        fp_free(ent);
                        continue;
                }

                if (ent->fe_type == FAIL_POINT_OFF) {
                        should_wake_paused = true;
                        if (ent->fe_count == FE_COUNT_UNTRACKED) {
                                should_truncate = true;
                                TAILQ_REMOVE(&entries->fp_entry_queue, ent,
                                        fe_entries);
                                fp_free(ent);
                        }
                } else if (ent->fe_type == FAIL_POINT_PAUSE) {
                        should_truncate = true;
                } else if (ent->fe_type == FAIL_POINT_SLEEP && (fp->fp_flags &
                        FAIL_POINT_NONSLEEPABLE)) {
                        /**
                         * If this fail point is annotated as being in a
                         * non-sleepable ctx, convert sleep to delay and
                         * convert the msec argument to usecs.
                         */
                        printf("Sleep call request on fail point in "
                                "non-sleepable context; using delay instead "
                                "of sleep\n");
                        ent->fe_type = FAIL_POINT_DELAY;
                        ent->fe_arg *= 1000;
                }
        }

        if (TAILQ_EMPTY(&entries->fp_entry_queue)) {
                entries = fail_point_swap_settings(fp, NULL);
                if (entries != NULL)
                        wakeup(FP_PAUSE_CHANNEL(fp));
        } else {
                if (should_wake_paused)
                        wakeup(FP_PAUSE_CHANNEL(fp));
                fail_point_swap_settings(fp, entries);
        }

end:
#ifdef IWARNING
        if (error)
                IWARNING("Failed to set %s %s to %s",
                    fp->fp_name, fp->fp_location, buf);
        else
                INOTICE("Set %s %s to %s",
                    fp->fp_name, fp->fp_location, buf);
#endif /* IWARNING */

        fail_point_setting_release_ref(fp);
        return (error);
}

#define MAX_FAIL_POINT_BUF      1023

/**
 * Handle kernel failpoint set/get.
 */
int
fail_point_sysctl(SYSCTL_HANDLER_ARGS)
{
        struct fail_point *fp;
        char *buf;
        struct sbuf sb, *sb_check;
        int error;

        buf = NULL;
        error = 0;
        fp = arg1;

        sb_check = sbuf_new(&sb, NULL, 1024, SBUF_AUTOEXTEND);
        if (sb_check != &sb)
                return (ENOMEM);

        sbuf_set_drain(&sb, (sbuf_drain_func *)fail_sysctl_drain_func, req);

        /* Setting */
        /**
         * Lock protects any new entries from being garbage collected before we
         * can link them to the fail point.
         */
        sx_xlock(&sx_fp_set);
        if (req->newptr) {
                if (req->newlen > MAX_FAIL_POINT_BUF) {
                        error = EINVAL;
                        goto out;
                }

                buf = fp_malloc(req->newlen + 1, M_WAITOK);

                error = SYSCTL_IN(req, buf, req->newlen);
                if (error)
                        goto out;
                buf[req->newlen] = '\0';

                error = fail_point_set(fp, buf);
        }

        fail_point_garbage_collect();
        sx_xunlock(&sx_fp_set);

        /* Retrieving. */
        fail_point_get(fp, &sb, false);

out:
        sbuf_finish(&sb);
        sbuf_delete(&sb);

        if (buf)
                fp_free(buf);

        return (error);
}

int
fail_point_sysctl_status(SYSCTL_HANDLER_ARGS)
{
        struct fail_point *fp;
        struct sbuf sb, *sb_check;

        fp = arg1;

        sb_check = sbuf_new(&sb, NULL, 1024, SBUF_AUTOEXTEND);
        if (sb_check != &sb)
                return (ENOMEM);

        sbuf_set_drain(&sb, (sbuf_drain_func *)fail_sysctl_drain_func, req);

        /* Retrieving. */
        fail_point_get(fp, &sb, true);

        sbuf_finish(&sb);
        sbuf_delete(&sb);

        /**
         * Lock protects any new entries from being garbage collected before we
         * can link them to the fail point.
         */
        sx_xlock(&sx_fp_set);
        fail_point_garbage_collect();
        sx_xunlock(&sx_fp_set);

        return (0);
}

int
fail_sysctl_drain_func(void *sysctl_args, const char *buf, int len)
{
        struct sysctl_req *sa;
        int error;

        sa = sysctl_args;

        error = SYSCTL_OUT(sa, buf, len);

        if (error == ENOMEM)
                return (-1);
        else
                return (len);
}

/**
 * Internal helper function to translate a human-readable failpoint string
 * into a internally-parsable fail_point structure.
 */
static char *
parse_fail_point(struct fail_point_setting *ents, char *p)
{
        /*  <fail_point> ::
         *      <term> ( "->" <term> )*
         */
        uint8_t term_count;

        term_count = 1;

        p = parse_term(ents, p);
        if (p == NULL)
                return (NULL);

        while (*p != '\0') {
                term_count++;
                if (p[0] != '-' || p[1] != '>' ||
                        (p = parse_term(ents, p+2)) == NULL ||
                        term_count > FP_MAX_ENTRY_COUNT)
                        return (NULL);
        }
        return (p);
}

/**
 * Internal helper function to parse an individual term from a failpoint.
 */
static char *
parse_term(struct fail_point_setting *ents, char *p)
{
        struct fail_point_entry *ent;

        ent = fail_point_entry_new(ents);

        /*
         * <term> ::
         *     ( (<float> "%") | (<integer> "*" ) )*
         *     <type>
         *     [ "(" <integer> ")" ]
         *     [ "[pid " <integer> "]" ]
         */

        /* ( (<float> "%") | (<integer> "*" ) )* */
        while (isdigit(*p) || *p == '.') {
                int units, decimal;

                p = parse_number(&units, &decimal, p);
                if (p == NULL)
                        return (NULL);

                if (*p == '%') {
                        if (units > 100) /* prevent overflow early */
                                units = 100;
                        ent->fe_prob = units * (PROB_MAX / 100) + decimal;
                        if (ent->fe_prob > PROB_MAX)
                                ent->fe_prob = PROB_MAX;
                } else if (*p == '*') {
                        if (!units || units < 0 || decimal)
                                return (NULL);
                        ent->fe_count = units;
                } else
                        return (NULL);
                p++;
        }

        /* <type> */
        p = parse_type(ent, p);
        if (p == NULL)
                return (NULL);
        if (*p == '\0')
                return (p);

        /* [ "(" <integer> ")" ] */
        if (*p != '(')
                return (p);
        p++;
        if (!isdigit(*p) && *p != '-')
                return (NULL);
        ent->fe_arg = strtol(p, &p, 0);
        if (*p++ != ')')
                return (NULL);

        /* [ "[pid " <integer> "]" ] */
#define PID_STRING "[pid "
        if (strncmp(p, PID_STRING, sizeof(PID_STRING) - 1) != 0)
                return (p);
        p += sizeof(PID_STRING) - 1;
        if (!isdigit(*p))
                return (NULL);
        ent->fe_pid = strtol(p, &p, 0);
        if (*p++ != ']')
                return (NULL);

        return (p);
}

/**
 * Internal helper function to parse a numeric for a failpoint term.
 */
static char *
parse_number(int *out_units, int *out_decimal, char *p)
{
        char *old_p;

        /**
         *  <number> ::
         *      <integer> [ "." <integer> ] |
         *      "." <integer>
         */

        /* whole part */
        old_p = p;
        *out_units = strtol(p, &p, 10);
        if (p == old_p && *p != '.')
                return (NULL);

        /* fractional part */
        *out_decimal = 0;
        if (*p == '.') {
                int digits = 0;
                p++;
                while (isdigit(*p)) {
                        int digit = *p - '0';
                        if (digits < PROB_DIGITS - 2)
                                *out_decimal = *out_decimal * 10 + digit;
                        else if (digits == PROB_DIGITS - 2 && digit >= 5)
                                (*out_decimal)++;
                        digits++;
                        p++;
                }
                if (!digits) /* need at least one digit after '.' */
                        return (NULL);
                while (digits++ < PROB_DIGITS - 2) /* add implicit zeros */
                        *out_decimal *= 10;
        }

        return (p); /* success */
}

/**
 * Internal helper function to parse an individual type for a failpoint term.
 */
static char *
parse_type(struct fail_point_entry *ent, char *beg)
{
        enum fail_point_t type;
        int len;

        for (type = FAIL_POINT_OFF; type < FAIL_POINT_NUMTYPES; type++) {
                len = fail_type_strings[type].nmlen;
                if (strncmp(fail_type_strings[type].name, beg, len) == 0) {
                        ent->fe_type = type;
                        return (beg + len);
                }
        }
        return (NULL);
}

/* The fail point sysctl tree. */
SYSCTL_NODE(_debug, OID_AUTO, fail_point, CTLFLAG_RW | CTLFLAG_MPSAFE, 0,
    "fail points");

/* Debugging/testing stuff for fail point */
static int
sysctl_test_fail_point(SYSCTL_HANDLER_ARGS)
{

        KFAIL_POINT_RETURN(DEBUG_FP, test_fail_point);
        return (0);
}
SYSCTL_OID(_debug_fail_point, OID_AUTO, test_trigger_fail_point,
    CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_NEEDGIANT, NULL, 0,
    sysctl_test_fail_point, "A",
    "Trigger test fail points");