[apple/xnu.git] / osfmk / kern / ledger.c

/*
 * Copyright (c) 2010 Apple Computer, Inc. All rights reserved.
 *
 * @APPLE_OSREFERENCE_LICENSE_HEADER_START@
 * 
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. The rights granted to you under the License
 * may not be used to create, or enable the creation or redistribution of,
 * unlawful or unlicensed copies of an Apple operating system, or to
 * circumvent, violate, or enable the circumvention or violation of, any
 * terms of an Apple operating system software license agreement.
 * 
 * Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this file.
 * 
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 * 
 * @APPLE_OSREFERENCE_LICENSE_HEADER_END@
 */
/*
 * @OSF_COPYRIGHT@
 */

#include <kern/lock.h>
#include <kern/ledger.h>
#include <kern/kalloc.h>
#include <kern/task.h>

#include <kern/processor.h>
#include <kern/machine.h>
#include <kern/queue.h>
#include <sys/errno.h>

#include <libkern/OSAtomic.h>
#include <mach/mach_types.h>

/*
 * Ledger entry flags. Bits in second nibble (masked by 0xF0) are used for
 * ledger actions (LEDGER_ACTION_BLOCK, etc).
 */
#define ENTRY_ACTIVE            0x0001  /* entry is active if set */
#define WAKE_NEEDED             0x0100  /* one or more threads are asleep */
#define WAKE_INPROGRESS         0x0200  /* the wait queue is being processed */
#define REFILL_SCHEDULED        0x0400  /* a refill timer has been set */
#define REFILL_INPROGRESS       0x0800  /* the ledger is being refilled */
#define CALLED_BACK             0x1000  /* callback has already been called */

/* Determine whether a ledger entry exists and has been initialized and active */
#define ENTRY_VALID(l, e)                                       \
        (((l) != NULL) && ((e) >= 0) && ((e) < (l)->l_size) &&  \
        (((l)->l_entries[e].le_flags & ENTRY_ACTIVE) == ENTRY_ACTIVE))

#ifdef LEDGER_DEBUG
int ledger_debug = 0;

#define ASSERT(a) assert(a)
#define lprintf(a) if (ledger_debug) {                                  \
        printf("%lld  ", abstime_to_nsecs(mach_absolute_time() / 1000000)); \
        printf a ;                                                      \
}
#else
#define lprintf(a)
#define ASSERT(a)
#endif

struct ledger_callback {
        ledger_callback_t       lc_func;
        const void              *lc_param0;
        const void              *lc_param1;
};

struct entry_template {
        char                    et_key[LEDGER_NAME_MAX];
        char                    et_group[LEDGER_NAME_MAX];
        char                    et_units[LEDGER_NAME_MAX];
        uint32_t                et_flags;
        struct ledger_callback  *et_callback;
};

lck_grp_t ledger_lck_grp;

/*
 * Modifying the reference count, table size, or table contents requires
 * holding the lt_lock.  Modfying the table address requires both lt_lock
 * and setting the inuse bit.  This means that the lt_entries field can be
 * safely dereferenced if you hold either the lock or the inuse bit.  The
 * inuse bit exists solely to allow us to swap in a new, larger entries
 * table without requiring a full lock to be acquired on each lookup.
 * Accordingly, the inuse bit should never be held for longer than it takes
 * to extract a value from the table - i.e., 2 or 3 memory references.
 */
struct ledger_template {
        const char              *lt_name;
        int                     lt_refs;
        int                     lt_cnt;
        int                     lt_table_size;
        volatile uint32_t       lt_inuse;
        lck_mtx_t               lt_lock;
        struct entry_template   *lt_entries;
};

#define template_lock(template)         lck_mtx_lock(&(template)->lt_lock)
#define template_unlock(template)       lck_mtx_unlock(&(template)->lt_lock)

#define TEMPLATE_INUSE(s, t) {                                  \
        s = splsched();                                         \
        while (OSCompareAndSwap(0, 1, &((t)->lt_inuse)))        \
                ;                                               \
}

#define TEMPLATE_IDLE(s, t) {                                   \
        (t)->lt_inuse = 0;                                      \
        splx(s);                                                \
}

/*
 * The explicit alignment is to ensure that atomic operations don't panic
 * on ARM.
 */
struct ledger_entry {
        volatile uint32_t               le_flags;
        ledger_amount_t                 le_limit;
        volatile ledger_amount_t        le_credit __attribute__((aligned(8)));
        volatile ledger_amount_t        le_debit __attribute__((aligned(8)));
        /*
         * XXX - the following two fields can go away if we move all of
         * the refill logic into process policy
         */
        uint64_t                        le_refill_period;
        uint64_t                        le_last_refill;
} __attribute__((aligned(8)));

struct ledger {
        int                     l_id;
        struct ledger_template  *l_template;
        int                     l_refs;
        int                     l_size;
        struct ledger_entry     *l_entries;
};

static int ledger_cnt = 0;
/* ledger ast helper functions */
static uint32_t ledger_check_needblock(ledger_t l, uint64_t now);
static kern_return_t ledger_perform_blocking(ledger_t l);
static uint32_t flag_set(volatile uint32_t *flags, uint32_t bit);
static uint32_t flag_clear(volatile uint32_t *flags, uint32_t bit);

#if 0
static void
debug_callback(const void *p0, __unused const void *p1)
{
        printf("ledger: resource exhausted [%s] for task %p\n",
            (const char *)p0, p1);
}
#endif

/************************************/

static uint64_t
abstime_to_nsecs(uint64_t abstime)
{
        uint64_t nsecs;

        absolutetime_to_nanoseconds(abstime, &nsecs);
        return (nsecs);
}

static uint64_t
nsecs_to_abstime(uint64_t nsecs)
{
        uint64_t abstime;

        nanoseconds_to_absolutetime(nsecs, &abstime);
        return (abstime);
}

void
ledger_init(void)
{
        lck_grp_init(&ledger_lck_grp, "ledger", LCK_GRP_ATTR_NULL);
}

ledger_template_t
ledger_template_create(const char *name)
{
        ledger_template_t template;

        template = (ledger_template_t)kalloc(sizeof (*template));
        if (template == NULL)
                return (NULL);

        template->lt_name = name;
        template->lt_refs = 1;
        template->lt_cnt = 0;
        template->lt_table_size = 1;
        template->lt_inuse = 0;
        lck_mtx_init(&template->lt_lock, &ledger_lck_grp, LCK_ATTR_NULL);

        template->lt_entries = (struct entry_template *)
            kalloc(sizeof (struct entry_template) * template->lt_table_size);
        if (template->lt_entries == NULL) {
                kfree(template, sizeof (*template));
                template = NULL;
        }

        return (template);
}

void
ledger_template_dereference(ledger_template_t template)
{
        template_lock(template);
        template->lt_refs--;
        template_unlock(template);

        if (template->lt_refs == 0)
                kfree(template, sizeof (*template));
}

/*
 * Add a new entry to the list of entries in a ledger template. There is
 * currently no mechanism to remove an entry.  Implementing such a mechanism
 * would require us to maintain per-entry reference counts, which we would
 * prefer to avoid if possible.
 */
int
ledger_entry_add(ledger_template_t template, const char *key,
    const char *group, const char *units)
{
        int idx;
        struct entry_template *et;

        if ((key == NULL) || (strlen(key) >= LEDGER_NAME_MAX))
                return (-1);

        template_lock(template);

        /* If the table is full, attempt to double its size */
        if (template->lt_cnt == template->lt_table_size) {
                struct entry_template *new_entries, *old_entries;
                int old_cnt, old_sz;
                spl_t s;

                old_cnt = template->lt_table_size;
                old_sz = (int)(old_cnt * sizeof (struct entry_template));
                new_entries = kalloc(old_sz * 2);
                if (new_entries == NULL) {
                        template_unlock(template);
                        return (-1);
                }
                memcpy(new_entries, template->lt_entries, old_sz);
                memset(((char *)new_entries) + old_sz, 0, old_sz);
                template->lt_table_size = old_cnt * 2;

                old_entries = template->lt_entries;

                TEMPLATE_INUSE(s, template);
                template->lt_entries = new_entries;
                TEMPLATE_IDLE(s, template);

                kfree(old_entries, old_sz);
        }

        et = &template->lt_entries[template->lt_cnt];
        strlcpy(et->et_key, key, LEDGER_NAME_MAX);
        strlcpy(et->et_group, group, LEDGER_NAME_MAX);
        strlcpy(et->et_units, units, LEDGER_NAME_MAX);
        et->et_flags = ENTRY_ACTIVE;
        et->et_callback = NULL;

        idx = template->lt_cnt++;
        template_unlock(template);

        return (idx);
}


kern_return_t
ledger_entry_setactive(ledger_t ledger, int entry)
{
        struct ledger_entry *le;

        if ((ledger == NULL)  || (entry < 0) || (entry >= ledger->l_size))
                return (KERN_INVALID_ARGUMENT);

        le = &ledger->l_entries[entry];
        if ((le->le_flags & ENTRY_ACTIVE) == 0) {
                flag_set(&le->le_flags, ENTRY_ACTIVE);
        }
        return (KERN_SUCCESS);
}


int
ledger_key_lookup(ledger_template_t template, const char *key)
{
        int idx;

        template_lock(template);
        for (idx = 0; idx < template->lt_cnt; idx++)
                if (template->lt_entries[idx].et_key &&
                    (strcmp(key, template->lt_entries[idx].et_key) == 0))
                        break;

        if (idx >= template->lt_cnt)
                idx = -1;
        template_unlock(template);

        return (idx);
}

/*
 * Create a new ledger based on the specified template.  As part of the
 * ledger creation we need to allocate space for a table of ledger entries.
 * The size of the table is based on the size of the template at the time
 * the ledger is created.  If additional entries are added to the template
 * after the ledger is created, they will not be tracked in this ledger.
 */
ledger_t
ledger_instantiate(ledger_template_t template, int entry_type)
{
        ledger_t ledger;
        size_t sz;
        int i;

        ledger = (ledger_t)kalloc(sizeof (struct ledger));
        if (ledger == NULL)
                return (LEDGER_NULL);

        ledger->l_template = template;
        ledger->l_id = ledger_cnt++;
        ledger->l_refs = 1;

        template_lock(template);
        template->lt_refs++;
        ledger->l_size = template->lt_cnt;
        template_unlock(template);

        sz = ledger->l_size * sizeof (struct ledger_entry);
        ledger->l_entries = kalloc(sz);
        if (sz && (ledger->l_entries == NULL)) {
                ledger_template_dereference(template);
                kfree(ledger, sizeof(struct ledger));
                return (LEDGER_NULL);
        }

        template_lock(template);
        assert(ledger->l_size <= template->lt_cnt);
        for (i = 0; i < ledger->l_size; i++) {
                struct ledger_entry *le = &ledger->l_entries[i];
                struct entry_template *et = &template->lt_entries[i];

                le->le_flags = et->et_flags;
                /* make entry inactive by removing  active bit */
                if (entry_type == LEDGER_CREATE_INACTIVE_ENTRIES)
                        flag_clear(&le->le_flags, ENTRY_ACTIVE);
                /*
                 * If template has a callback, this entry is opted-in,
                 * by default.
                 */
                if (et->et_callback != NULL)
                        flag_set(&le->le_flags, LEDGER_ACTION_CALLBACK);
                le->le_credit = 0;
                le->le_debit = 0;
                le->le_limit = LEDGER_LIMIT_INFINITY;
                le->le_refill_period = 0;
        }
        template_unlock(template);

        return (ledger);
}

static uint32_t
flag_set(volatile uint32_t *flags, uint32_t bit)
{
        return (OSBitOrAtomic(bit, flags));
}

static uint32_t
flag_clear(volatile uint32_t *flags, uint32_t bit)
{
        return (OSBitAndAtomic(~bit, flags));
}

/*
 * Take a reference on a ledger
 */
kern_return_t
ledger_reference(ledger_t ledger)
{
        if (!LEDGER_VALID(ledger))
                return (KERN_INVALID_ARGUMENT);
        OSIncrementAtomic(&ledger->l_refs);
        return (KERN_SUCCESS);
}

int
ledger_reference_count(ledger_t ledger)
{
        if (!LEDGER_VALID(ledger))
                return (-1);

        return (ledger->l_refs);
}

/*
 * Remove a reference on a ledger.  If this is the last reference,
 * deallocate the unused ledger.
 */
kern_return_t
ledger_dereference(ledger_t ledger)
{
        int v;

        if (!LEDGER_VALID(ledger))
                return (KERN_INVALID_ARGUMENT);

        v = OSDecrementAtomic(&ledger->l_refs);
        ASSERT(v >= 1);

        /* Just released the last reference.  Free it. */
        if (v == 1) {
                kfree(ledger->l_entries,
                    ledger->l_size * sizeof (struct ledger_entry));
                kfree(ledger, sizeof (*ledger));
        }

        return (KERN_SUCCESS);
}

/*
 * Determine whether an entry has exceeded its limit.
 */
static inline int
limit_exceeded(struct ledger_entry *le)
{
        ledger_amount_t balance;

        balance = le->le_credit - le->le_debit;
        if ((le->le_limit <= 0) && (balance < le->le_limit))
                return (1);

        if ((le->le_limit > 0) && (balance > le->le_limit))
                return (1);
        return (0);
}

static inline struct ledger_callback *
entry_get_callback(ledger_t ledger, int entry)
{
        struct ledger_callback *callback;
        spl_t s;

        TEMPLATE_INUSE(s, ledger->l_template);
        callback = ledger->l_template->lt_entries[entry].et_callback;
        TEMPLATE_IDLE(s, ledger->l_template);

        return (callback);
}

/*
 * If the ledger value is positive, wake up anybody waiting on it.
 */
static inline void
ledger_limit_entry_wakeup(struct ledger_entry *le)
{
        uint32_t flags;

        if (!limit_exceeded(le)) {
                flags = flag_clear(&le->le_flags, CALLED_BACK);

                while (le->le_flags & WAKE_NEEDED) {
                        flag_clear(&le->le_flags, WAKE_NEEDED);
                        thread_wakeup((event_t)le);
                }
        }
}

/*
 * Refill the coffers.
 */
static void
ledger_refill(uint64_t now, ledger_t ledger, int entry)
{
        uint64_t elapsed, period, periods;
        struct ledger_entry *le;
        ledger_amount_t balance, due;
        int cnt;

        le = &ledger->l_entries[entry];

        /*
         * If another thread is handling the refill already, we're not
         * needed.  Just sit here for a few cycles while the other thread
         * finishes updating the balance.  If it takes too long, just return
         * and we'll block again.
         */
        if (flag_set(&le->le_flags, REFILL_INPROGRESS) & REFILL_INPROGRESS) {
                cnt = 0;
                while (cnt++ < 100 && (le->le_flags & REFILL_INPROGRESS))
                        ;
                return;
        }

        /*
         * See how many refill periods have passed since we last
         * did a refill.
         */
        period = le->le_refill_period;
        elapsed = now - le->le_last_refill;
        if ((period == 0) || (elapsed < period)) {
                flag_clear(&le->le_flags, REFILL_INPROGRESS);
                return;
        }

        /*
         * Optimize for the most common case of only one or two
         * periods elapsing.
         */
        periods = 0;
        while ((periods < 2) && (elapsed > 0)) {
                periods++;
                elapsed -= period;
        }

        /*
         * OK, it's been a long time.  Do a divide to figure out
         * how long.
         */
        if (elapsed > 0)
                periods = (now - le->le_last_refill) / period;

        balance = le->le_credit - le->le_debit;
        due = periods * le->le_limit;
        if (balance - due < 0)
                due = balance;
        OSAddAtomic64(due, &le->le_debit);

        /*
         * If we've completely refilled the pool, set the refill time to now.
         * Otherwise set it to the time at which it last should have been
         * fully refilled.
         */
        if (balance == due)
                le->le_last_refill = now;
        else
                le->le_last_refill += (le->le_refill_period * periods);

        flag_clear(&le->le_flags, REFILL_INPROGRESS);

        lprintf(("Refill %lld %lld->%lld\n", periods, balance, balance - due));
        if (!limit_exceeded(le))
                ledger_limit_entry_wakeup(le);
}

static void
ledger_check_new_balance(ledger_t ledger, int entry)
{
        struct ledger_entry *le;
        uint64_t now;

        le = &ledger->l_entries[entry];

        /* Check to see whether we're due a refill */
        if (le->le_refill_period) {
                now = mach_absolute_time();
                if ((now - le->le_last_refill) > le->le_refill_period)
                        ledger_refill(now, ledger, entry);
        }

        if (limit_exceeded(le)) {
                /*
                 * We've exceeded the limit for this entry.  There
                 * are several possible ways to handle it.  We can block,
                 * we can execute a callback, or we can ignore it.  In
                 * either of the first two cases, we want to set the AST
                 * flag so we can take the appropriate action just before
                 * leaving the kernel.  The one caveat is that if we have
                 * already called the callback, we don't want to do it
                 * again until it gets rearmed.
                 */
                if ((le->le_flags & LEDGER_ACTION_BLOCK) ||
                    (!(le->le_flags & CALLED_BACK) &&
                    entry_get_callback(ledger, entry))) {
                        set_astledger(current_thread());
                }
        } else {
                /*
                 * The balance on the account is below the limit.  If
                 * there are any threads blocked on this entry, now would
                 * be a good time to wake them up.
                 */
                if (le->le_flags & WAKE_NEEDED)
                        ledger_limit_entry_wakeup(le);
        }
}

/*
 * Add value to an entry in a ledger.
 */
kern_return_t
ledger_credit(ledger_t ledger, int entry, ledger_amount_t amount)
{
        ledger_amount_t old, new;
        struct ledger_entry *le;

        if (!ENTRY_VALID(ledger, entry) || (amount < 0))
                return (KERN_INVALID_VALUE);

        if (amount == 0)
                return (KERN_SUCCESS);

        le = &ledger->l_entries[entry];

        old = OSAddAtomic64(amount, &le->le_credit);
        new = old + amount;
        lprintf(("%p Credit %lld->%lld\n", current_thread(), old, new));
        ledger_check_new_balance(ledger, entry);

        return (KERN_SUCCESS);
}


/*
 * Adjust the limit of a limited resource.  This does not affect the
 * current balance, so the change doesn't affect the thread until the
 * next refill.
 */
kern_return_t
ledger_set_limit(ledger_t ledger, int entry, ledger_amount_t limit)
{
        struct ledger_entry *le;

        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_VALUE);

        lprintf(("ledger_set_limit: %x\n", (uint32_t)limit));
        le = &ledger->l_entries[entry];
        le->le_limit = limit;
        le->le_last_refill = 0;
        flag_clear(&le->le_flags, CALLED_BACK);
        ledger_limit_entry_wakeup(le);

        return (KERN_SUCCESS);
}

/*
 * Add a callback to be executed when the resource goes into deficit
 */
kern_return_t
ledger_set_callback(ledger_template_t template, int entry,
   ledger_callback_t func, const void *param0, const void *param1)
{
        struct entry_template *et;
        struct ledger_callback *old_cb, *new_cb;

        if ((entry < 0) || (entry >= template->lt_cnt))
                return (KERN_INVALID_VALUE);

        if (func) {
                new_cb = (struct ledger_callback *)kalloc(sizeof (*new_cb));
                new_cb->lc_func = func;
                new_cb->lc_param0 = param0;
                new_cb->lc_param1 = param1;
        } else {
                new_cb = NULL;
        }

        template_lock(template);
        et = &template->lt_entries[entry];
        old_cb = et->et_callback;
        et->et_callback = new_cb;
        template_unlock(template);
        if (old_cb)
                kfree(old_cb, sizeof (*old_cb));

        return (KERN_SUCCESS);
}

/*
 * Disable callback notification for a specific ledger entry.
 *
 * Otherwise, if using a ledger template which specified a
 * callback function (ledger_set_callback()), it will be invoked when
 * the resource goes into deficit.
 */
kern_return_t
ledger_disable_callback(ledger_t ledger, int entry)
{
        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_VALUE);

        flag_clear(&ledger->l_entries[entry].le_flags, LEDGER_ACTION_CALLBACK);
        return (KERN_SUCCESS);
}

/*
 * Clear the called_back flag, indicating that we want to be notified
 * again when the limit is next exceeded.
 */
kern_return_t
ledger_reset_callback(ledger_t ledger, int entry)
{
        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_VALUE);

        flag_clear(&ledger->l_entries[entry].le_flags, CALLED_BACK);
        return (KERN_SUCCESS);
}

/*
 * Adjust the automatic refill period.
 */
kern_return_t
ledger_set_period(ledger_t ledger, int entry, uint64_t period)
{
        struct ledger_entry *le;

        lprintf(("ledger_set_period: %llx\n", period));
        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_VALUE);

        le = &ledger->l_entries[entry];
        le->le_refill_period = nsecs_to_abstime(period);

        return (KERN_SUCCESS);
}

kern_return_t
ledger_set_action(ledger_t ledger, int entry, int action)
{
        lprintf(("ledger_set_action: %d\n", action));
        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_VALUE);

        flag_set(&ledger->l_entries[entry].le_flags, action);
        return (KERN_SUCCESS);
}

void
set_astledger(thread_t thread)
{
        spl_t s = splsched();

        if (thread == current_thread()) {
                thread_ast_set(thread, AST_LEDGER);
                ast_propagate(thread->ast);
        } else {
                processor_t p;

                thread_lock(thread);
                thread_ast_set(thread, AST_LEDGER);
                p = thread->last_processor;
                if ((p != PROCESSOR_NULL) && (p->state == PROCESSOR_RUNNING) &&
                   (p->active_thread == thread))
                        cause_ast_check(p);
                thread_unlock(thread);
        }
        
        splx(s);
}

kern_return_t
ledger_debit(ledger_t ledger, int entry, ledger_amount_t amount)
{
        struct ledger_entry *le;
        ledger_amount_t old, new;

        if (!ENTRY_VALID(ledger, entry) || (amount < 0))
                return (KERN_INVALID_ARGUMENT);

        if (amount == 0)
                return (KERN_SUCCESS);

        le = &ledger->l_entries[entry];

        old = OSAddAtomic64(amount, &le->le_debit);
        new = old + amount;

        lprintf(("%p Debit %lld->%lld\n", thread, old, new));
        ledger_check_new_balance(ledger, entry);
        return (KERN_SUCCESS);

}

void
ledger_ast(thread_t thread)
{
        struct ledger *l = thread->t_ledger;
        struct ledger  *thl = thread->t_threadledger;
        uint32_t block;
        uint64_t now;
        kern_return_t ret;
        task_t task = thread->task;

        lprintf(("Ledger AST for %p\n", thread));

        ASSERT(task != NULL);
        ASSERT(thread == current_thread());

top:
        /*
         * Make sure this thread is up to date with regards to any task-wide per-thread
         * CPU limit.
         */
        if ((task->rusage_cpu_flags & TASK_RUSECPU_FLAGS_PERTHR_LIMIT) &&
            ((thread->options & TH_OPT_PROC_CPULIMIT) == 0) ) {
                /*
                 * Task has a per-thread CPU limit on it, and this thread
                 * needs it applied.
                 */
                thread_set_cpulimit(THREAD_CPULIMIT_EXCEPTION, task->rusage_cpu_perthr_percentage,
                        task->rusage_cpu_perthr_interval);
                assert((thread->options & TH_OPT_PROC_CPULIMIT) != 0);
        } else if (((task->rusage_cpu_flags & TASK_RUSECPU_FLAGS_PERTHR_LIMIT) == 0) &&
                    (thread->options & TH_OPT_PROC_CPULIMIT)) {
                /*
                 * Task no longer has a per-thread CPU limit; remove this thread's
                 * corresponding CPU limit.
                 */
                thread_set_cpulimit(THREAD_CPULIMIT_EXCEPTION, 0, 0);
                assert((thread->options & TH_OPT_PROC_CPULIMIT) == 0);
        }

        /*
         * If the task or thread is being terminated, let's just get on with it
         */
        if ((l == NULL) || !task->active || task->halting || !thread->active)
                return;
        
        /*
         * Examine all entries in deficit to see which might be eligble for
         * an automatic refill, which require callbacks to be issued, and
         * which require blocking.
         */
        block = 0;
        now = mach_absolute_time();

        if (LEDGER_VALID(thl)) {
                block |= ledger_check_needblock(thl, now);
        }
        block |= ledger_check_needblock(l, now);

        /*
         * If we are supposed to block on the availability of one or more
         * resources, find the first entry in deficit for which we should wait.
         * Schedule a refill if necessary and then sleep until the resource
         * becomes available.
         */
        if (block) {
                if (LEDGER_VALID(thl)) {
                        ret = ledger_perform_blocking(thl);
                        if (ret != KERN_SUCCESS)
                                goto top;
                }
                ret = ledger_perform_blocking(l);
                if (ret != KERN_SUCCESS)
                        goto top;
        } /* block */
}

static uint32_t
ledger_check_needblock(ledger_t l, uint64_t now)
{
        int i;
        uint32_t flags, block = 0;
        struct ledger_entry *le;
        struct ledger_callback *lc;


        for (i = 0; i < l->l_size; i++) {
                le = &l->l_entries[i];
                if (limit_exceeded(le) == FALSE)
                        continue;

                /* Check for refill eligibility */
                if (le->le_refill_period) {
                        if ((le->le_last_refill + le->le_refill_period) > now) {
                                ledger_refill(now, l, i);
                                if (limit_exceeded(le) == FALSE)
                                        continue;
                        }
                }

                if (le->le_flags & LEDGER_ACTION_BLOCK)
                        block = 1;
                if ((le->le_flags & LEDGER_ACTION_CALLBACK) == 0)
                        continue;
                lc = entry_get_callback(l, i);
                assert(lc != NULL);
                flags = flag_set(&le->le_flags, CALLED_BACK);
                /* Callback has already been called */
                if (flags & CALLED_BACK)
                        continue;
                lc->lc_func(lc->lc_param0, lc->lc_param1);
        }
        return(block);
}


/* return KERN_SUCCESS to continue, KERN_FAILURE to restart */
static kern_return_t
ledger_perform_blocking(ledger_t l)
{
        int i;
        kern_return_t ret;
        struct ledger_entry *le;

        for (i = 0; i < l->l_size; i++) {
                le = &l->l_entries[i];
                if ((!limit_exceeded(le)) ||
                    ((le->le_flags & LEDGER_ACTION_BLOCK) == 0))
                        continue;

                /* Prepare to sleep until the resource is refilled */
                ret = assert_wait_deadline(le, TRUE,
                    le->le_last_refill + le->le_refill_period);
                if (ret != THREAD_WAITING)
                        return(KERN_SUCCESS);

                /* Mark that somebody is waiting on this entry  */
                flag_set(&le->le_flags, WAKE_NEEDED);

                ret = thread_block_reason(THREAD_CONTINUE_NULL, NULL,
                    AST_LEDGER);
                if (ret != THREAD_AWAKENED)
                        return(KERN_SUCCESS);

                /*
                 * The world may have changed while we were asleep.
                 * Some other resource we need may have gone into
                 * deficit.  Or maybe we're supposed to die now.
                 * Go back to the top and reevaluate.
                 */
                return(KERN_FAILURE);
        }
        return(KERN_SUCCESS);
}


kern_return_t
ledger_get_entries(ledger_t ledger, int entry, ledger_amount_t *credit,
    ledger_amount_t *debit)
{
        struct ledger_entry *le;

        if (!ENTRY_VALID(ledger, entry))
                return (KERN_INVALID_ARGUMENT);

        le = &ledger->l_entries[entry];

        *credit = le->le_credit;
        *debit = le->le_debit;

        return (KERN_SUCCESS);
}

int
ledger_template_info(void **buf, int *len)
{
        struct ledger_template_info *lti;
        struct entry_template *et;
        int i;
        ledger_t l;

        /*
         * Since all tasks share a ledger template, we'll just use the
         * caller's as the source.
         */
        l = current_task()->ledger;
        if ((*len < 0) || (l == NULL))
                return (EINVAL);

        if (*len > l->l_size)
                 *len = l->l_size;
        lti = kalloc((*len) * sizeof (struct ledger_template_info));
        if (lti == NULL)
                return (ENOMEM);
        *buf = lti;

        template_lock(l->l_template);
        et = l->l_template->lt_entries;

        for (i = 0; i < *len; i++) {
                memset(lti, 0, sizeof (*lti));
                strlcpy(lti->lti_name, et->et_key, LEDGER_NAME_MAX);
                strlcpy(lti->lti_group, et->et_group, LEDGER_NAME_MAX);
                strlcpy(lti->lti_units, et->et_units, LEDGER_NAME_MAX);
                et++;
                lti++;
        }
        template_unlock(l->l_template);

        return (0);
}

int
ledger_entry_info(task_t task, void **buf, int *len)
{
        struct ledger_entry_info *lei;
        struct ledger_entry *le;
        uint64_t now = mach_absolute_time();
        int i;
        ledger_t l;

        if ((*len < 0) || ((l = task->ledger) == NULL))
                return (EINVAL);

        if (*len > l->l_size)
                 *len = l->l_size;
        lei = kalloc((*len) * sizeof (struct ledger_entry_info));
        if (lei == NULL)
                return (ENOMEM);
        *buf = lei;

        le = l->l_entries;

        for (i = 0; i < *len; i++) {
                memset(lei, 0, sizeof (*lei));
                lei->lei_limit = le->le_limit;
                lei->lei_credit = le->le_credit;
                lei->lei_debit = le->le_debit;
                lei->lei_balance = lei->lei_credit - lei->lei_debit;
                lei->lei_refill_period =
                        abstime_to_nsecs(le->le_refill_period);
                lei->lei_last_refill =
                        abstime_to_nsecs(now - le->le_last_refill);
                le++;
                lei++;
        }

        return (0);
}

int
ledger_info(task_t task, struct ledger_info *info)
{
        ledger_t l;

        if ((l = task->ledger) == NULL)
                return (ENOENT);

        memset(info, 0, sizeof (*info));

        strlcpy(info->li_name, l->l_template->lt_name, LEDGER_NAME_MAX);
        info->li_id = l->l_id;
        info->li_entries = l->l_size;
        return (0);
}

#ifdef LEDGER_DEBUG
int
ledger_limit(task_t task, struct ledger_limit_args *args)
{
        ledger_t l;
        int64_t limit;
        int idx;

        if ((l = task->ledger) == NULL)
                return (EINVAL);

        idx = ledger_key_lookup(l->l_template, args->lla_name);
        if ((idx < 0) || (idx >= l->l_size))
                return (EINVAL);

        /*
         * XXX - this doesn't really seem like the right place to have
         * a context-sensitive conversion of userspace units into kernel
         * units.  For now I'll handwave and say that the ledger() system
         * call isn't meant for civilians to use - they should be using
         * the process policy interfaces.
         */
        if (idx == task_ledgers.cpu_time) {
                int64_t nsecs;

                if (args->lla_refill_period) {
                        /*
                         * If a refill is scheduled, then the limit is 
                         * specified as a percentage of one CPU.  The
                         * syscall specifies the refill period in terms of
                         * milliseconds, so we need to convert to nsecs.
                         */
                        args->lla_refill_period *= 1000000;
                        nsecs = args->lla_limit *
                            (args->lla_refill_period / 100);
                        lprintf(("CPU limited to %lld nsecs per second\n",
                            nsecs));
                } else {
                        /*
                         * If no refill is scheduled, then this is a
                         * fixed amount of CPU time (in nsecs) that can
                         * be consumed.
                         */
                        nsecs = args->lla_limit;
                        lprintf(("CPU limited to %lld nsecs\n", nsecs));
                }
                limit = nsecs_to_abstime(nsecs);
        } else {
                limit = args->lla_limit;
                lprintf(("%s limited to %lld\n", args->lla_name, limit));
        }

        if (args->lla_refill_period > 0)
                ledger_set_period(l, idx, args->lla_refill_period);

        ledger_set_limit(l, idx, limit);
        flag_set(&l->l_entries[idx].le_flags, LEDGER_ACTION_BLOCK);
        return (0);
}
#endif