Block patches

- Fix for file-posix's zoning code crashing on I/O errors
 - Throttling refactoring
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Merge tag 'pull-block-2023-09-01' of https://gitlab.com/hreitz/qemu into staging

Block patches

- Fix for file-posix's zoning code crashing on I/O errors
- Throttling refactoring

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# gpg: Signature made Fri 01 Sep 2023 04:11:46 EDT
# gpg:                using RSA key CB62D7A0EE3829E45F004D34A1FA40D098019CDF
# gpg:                issuer "hreitz@redhat.com"
# gpg: Good signature from "Hanna Reitz <hreitz@redhat.com>" [unknown]
# gpg: WARNING: The key's User ID is not certified with a trusted signature!
# gpg:          There is no indication that the signature belongs to the owner.
# Primary key fingerprint: CB62 D7A0 EE38 29E4 5F00  4D34 A1FA 40D0 9801 9CDF

* tag 'pull-block-2023-09-01' of https://gitlab.com/hreitz/qemu:
  tests/file-io-error: New test
  file-posix: Simplify raw_co_prw's 'out' zone code
  file-posix: Fix zone update in I/O error path
  file-posix: Check bs->bl.zoned for zone info
  file-posix: Clear bs->bl.zoned on error
  block/throttle-groups: Use ThrottleDirection instread of bool is_write
  fsdev: Use ThrottleDirection instread of bool is_write
  throttle: use THROTTLE_MAX/ARRAY_SIZE for hard code
  throttle: use enum ThrottleDirection instead of bool is_write
  cryptodev: use NULL throttle timer cb for read direction
  test-throttle: test read only and write only
  throttle: support read-only and write-only
  test-throttle: use enum ThrottleDirection
  throttle: introduce enum ThrottleDirection

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

backends/cryptodev.c

@@ -252,10 +252,11 @@ static void cryptodev_backend_throttle_timer_cb(void *opaque)
             continue;
         }
 
-        throttle_account(&backend->ts, true, ret);
+        throttle_account(&backend->ts, THROTTLE_WRITE, ret);
         cryptodev_backend_operation(backend, op_info);
         if (throttle_enabled(&backend->tc) &&
-            throttle_schedule_timer(&backend->ts, &backend->tt, true)) {
+            throttle_schedule_timer(&backend->ts, &backend->tt,
+                                    THROTTLE_WRITE)) {
             break;
         }
     }
@@ -271,7 +272,7 @@ int cryptodev_backend_crypto_operation(
         goto do_account;
     }
 
-    if (throttle_schedule_timer(&backend->ts, &backend->tt, true) ||
+    if (throttle_schedule_timer(&backend->ts, &backend->tt, THROTTLE_WRITE) ||
         !QTAILQ_EMPTY(&backend->opinfos)) {
         QTAILQ_INSERT_TAIL(&backend->opinfos, op_info, next);
         return 0;
@@ -283,7 +284,7 @@ do_account:
         return ret;
     }
 
-    throttle_account(&backend->ts, true, ret);
+    throttle_account(&backend->ts, THROTTLE_WRITE, ret);
 
     return cryptodev_backend_operation(backend, op_info);
 }
@@ -341,8 +342,7 @@ static void cryptodev_backend_set_throttle(CryptoDevBackend *backend, int field,
     if (!enabled) {
         throttle_init(&backend->ts);
         throttle_timers_init(&backend->tt, qemu_get_aio_context(),
-                             QEMU_CLOCK_REALTIME,
+                             QEMU_CLOCK_REALTIME, NULL,
-                             cryptodev_backend_throttle_timer_cb, /* FIXME */
                              cryptodev_backend_throttle_timer_cb, backend);
     }
 

block/block-backend.c

@@ -1341,7 +1341,7 @@ blk_co_do_preadv_part(BlockBackend *blk, int64_t offset, int64_t bytes,
     /* throttling disk I/O */
     if (blk->public.throttle_group_member.throttle_state) {
         throttle_group_co_io_limits_intercept(&blk->public.throttle_group_member,
-                bytes, false);
+                bytes, THROTTLE_READ);
     }
 
     ret = bdrv_co_preadv_part(blk->root, offset, bytes, qiov, qiov_offset,
@@ -1415,7 +1415,7 @@ blk_co_do_pwritev_part(BlockBackend *blk, int64_t offset, int64_t bytes,
     /* throttling disk I/O */
     if (blk->public.throttle_group_member.throttle_state) {
         throttle_group_co_io_limits_intercept(&blk->public.throttle_group_member,
-                bytes, true);
+                bytes, THROTTLE_WRITE);
     }
 
     if (!blk->enable_write_cache) {

block/file-posix.c

@@ -1412,11 +1412,9 @@ static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
     BlockZoneModel zoned;
     int ret;
 
-    bs->bl.zoned = BLK_Z_NONE;
-
     ret = get_sysfs_zoned_model(st, &zoned);
     if (ret < 0 || zoned == BLK_Z_NONE) {
-        return;
+        goto no_zoned;
     }
     bs->bl.zoned = zoned;
 
@@ -1437,10 +1435,10 @@ static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Unable to read chunk_sectors "
                                      "sysfs attribute");
-        return;
+        goto no_zoned;
     } else if (!ret) {
         error_setg(errp, "Read 0 from chunk_sectors sysfs attribute");
-        return;
+        goto no_zoned;
     }
     bs->bl.zone_size = ret << BDRV_SECTOR_BITS;
 
@@ -1448,10 +1446,10 @@ static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
     if (ret < 0) {
         error_setg_errno(errp, -ret, "Unable to read nr_zones "
                                      "sysfs attribute");
-        return;
+        goto no_zoned;
     } else if (!ret) {
         error_setg(errp, "Read 0 from nr_zones sysfs attribute");
-        return;
+        goto no_zoned;
     }
     bs->bl.nr_zones = ret;
 
@@ -1472,10 +1470,15 @@ static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
     ret = get_zones_wp(bs, s->fd, 0, bs->bl.nr_zones, 0);
     if (ret < 0) {
         error_setg_errno(errp, -ret, "report wps failed");
-        bs->wps = NULL;
+        goto no_zoned;
-        return;
     }
     qemu_co_mutex_init(&bs->wps->colock);
+    return;
+
+no_zoned:
+    bs->bl.zoned = BLK_Z_NONE;
+    g_free(bs->wps);
+    bs->wps = NULL;
 }
 #else /* !defined(CONFIG_BLKZONED) */
 static void raw_refresh_zoned_limits(BlockDriverState *bs, struct stat *st,
@@ -2452,9 +2455,10 @@ static int coroutine_fn raw_co_prw(BlockDriverState *bs, uint64_t offset,
     if (fd_open(bs) < 0)
         return -EIO;
 #if defined(CONFIG_BLKZONED)
-    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) && bs->wps) {
+    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) &&
+        bs->bl.zoned != BLK_Z_NONE) {
         qemu_co_mutex_lock(&bs->wps->colock);
-        if (type & QEMU_AIO_ZONE_APPEND && bs->bl.zone_size) {
+        if (type & QEMU_AIO_ZONE_APPEND) {
             int index = offset / bs->bl.zone_size;
             offset = bs->wps->wp[index];
         }
@@ -2502,11 +2506,10 @@ static int coroutine_fn raw_co_prw(BlockDriverState *bs, uint64_t offset,
 
 out:
 #if defined(CONFIG_BLKZONED)
-{
+    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) &&
+        bs->bl.zoned != BLK_Z_NONE) {
         BlockZoneWps *wps = bs->wps;
         if (ret == 0) {
-        if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND))
-            && wps && bs->bl.zone_size) {
             uint64_t *wp = &wps->wp[offset / bs->bl.zone_size];
             if (!BDRV_ZT_IS_CONV(*wp)) {
                 if (type & QEMU_AIO_ZONE_APPEND) {
@@ -2519,17 +2522,12 @@ out:
                     *wp = offset + bytes;
                 }
             }
-        }
         } else {
-        if (type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) {
             update_zones_wp(bs, s->fd, 0, 1);
         }
-    }
 
-    if ((type & (QEMU_AIO_WRITE | QEMU_AIO_ZONE_APPEND)) && wps) {
         qemu_co_mutex_unlock(&wps->colock);
     }
-}
 #endif
     return ret;
 }

block/throttle-groups.c

@@ -37,7 +37,7 @@
 
 static void throttle_group_obj_init(Object *obj);
 static void throttle_group_obj_complete(UserCreatable *obj, Error **errp);
-static void timer_cb(ThrottleGroupMember *tgm, bool is_write);
+static void timer_cb(ThrottleGroupMember *tgm, ThrottleDirection direction);
 
 /* The ThrottleGroup structure (with its ThrottleState) is shared
  * among different ThrottleGroupMembers and it's independent from
@@ -73,8 +73,8 @@ struct ThrottleGroup {
     QemuMutex lock; /* This lock protects the following four fields */
     ThrottleState ts;
     QLIST_HEAD(, ThrottleGroupMember) head;
-    ThrottleGroupMember *tokens[2];
+    ThrottleGroupMember *tokens[THROTTLE_MAX];
-    bool any_timer_armed[2];
+    bool any_timer_armed[THROTTLE_MAX];
     QEMUClockType clock_type;
 
     /* This field is protected by the global QEMU mutex */
@@ -197,13 +197,13 @@ static ThrottleGroupMember *throttle_group_next_tgm(ThrottleGroupMember *tgm)
  * This assumes that tg->lock is held.
  *
  * @tgm:        the ThrottleGroupMember
- * @is_write:   the type of operation (read/write)
+ * @direction:  the ThrottleDirection
  * @ret:        whether the ThrottleGroupMember has pending requests.
  */
 static inline bool tgm_has_pending_reqs(ThrottleGroupMember *tgm,
-                                        bool is_write)
+                                        ThrottleDirection direction)
 {
-    return tgm->pending_reqs[is_write];
+    return tgm->pending_reqs[direction];
 }
 
 /* Return the next ThrottleGroupMember in the round-robin sequence with pending
@@ -212,12 +212,12 @@ static inline bool tgm_has_pending_reqs(ThrottleGroupMember *tgm,
  * This assumes that tg->lock is held.
  *
  * @tgm:       the current ThrottleGroupMember
- * @is_write:  the type of operation (read/write)
+ * @direction: the ThrottleDirection
  * @ret:       the next ThrottleGroupMember with pending requests, or tgm if
  *             there is none.
  */
 static ThrottleGroupMember *next_throttle_token(ThrottleGroupMember *tgm,
-                                                bool is_write)
+                                                ThrottleDirection direction)
 {
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
@@ -227,16 +227,16 @@ static ThrottleGroupMember *next_throttle_token(ThrottleGroupMember *tgm,
      * it's being drained. Skip the round-robin search and return tgm
      * immediately if it has pending requests. Otherwise we could be
      * forcing it to wait for other member's throttled requests. */
-    if (tgm_has_pending_reqs(tgm, is_write) &&
+    if (tgm_has_pending_reqs(tgm, direction) &&
         qatomic_read(&tgm->io_limits_disabled)) {
         return tgm;
     }
 
-    start = token = tg->tokens[is_write];
+    start = token = tg->tokens[direction];
 
     /* get next bs round in round robin style */
     token = throttle_group_next_tgm(token);
-    while (token != start && !tgm_has_pending_reqs(token, is_write)) {
+    while (token != start && !tgm_has_pending_reqs(token, direction)) {
         token = throttle_group_next_tgm(token);
     }
 
@@ -244,12 +244,12 @@ static ThrottleGroupMember *next_throttle_token(ThrottleGroupMember *tgm,
      * then decide the token is the current tgm because chances are
      * the current tgm got the current request queued.
      */
-    if (token == start && !tgm_has_pending_reqs(token, is_write)) {
+    if (token == start && !tgm_has_pending_reqs(token, direction)) {
         token = tgm;
     }
 
     /* Either we return the original TGM, or one with pending requests */
-    assert(token == tgm || tgm_has_pending_reqs(token, is_write));
+    assert(token == tgm || tgm_has_pending_reqs(token, direction));
 
     return token;
 }
@@ -261,11 +261,11 @@ static ThrottleGroupMember *next_throttle_token(ThrottleGroupMember *tgm,
  * This assumes that tg->lock is held.
  *
  * @tgm:        the current ThrottleGroupMember
- * @is_write:   the type of operation (read/write)
+ * @direction:  the ThrottleDirection
  * @ret:        whether the I/O request needs to be throttled or not
  */
 static bool throttle_group_schedule_timer(ThrottleGroupMember *tgm,
-                                          bool is_write)
+                                          ThrottleDirection direction)
 {
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
@@ -277,16 +277,16 @@ static bool throttle_group_schedule_timer(ThrottleGroupMember *tgm,
     }
 
     /* Check if any of the timers in this group is already armed */
-    if (tg->any_timer_armed[is_write]) {
+    if (tg->any_timer_armed[direction]) {
         return true;
     }
 
-    must_wait = throttle_schedule_timer(ts, tt, is_write);
+    must_wait = throttle_schedule_timer(ts, tt, direction);
 
     /* If a timer just got armed, set tgm as the current token */
     if (must_wait) {
-        tg->tokens[is_write] = tgm;
+        tg->tokens[direction] = tgm;
-        tg->any_timer_armed[is_write] = true;
+        tg->any_timer_armed[direction] = true;
     }
 
     return must_wait;
@@ -296,15 +296,15 @@ static bool throttle_group_schedule_timer(ThrottleGroupMember *tgm,
  * any request was actually pending.
  *
  * @tgm:       the current ThrottleGroupMember
- * @is_write:  the type of operation (read/write)
+ * @direction: the ThrottleDirection
  */
 static bool coroutine_fn throttle_group_co_restart_queue(ThrottleGroupMember *tgm,
-                                                         bool is_write)
+                                                         ThrottleDirection direction)
 {
     bool ret;
 
     qemu_co_mutex_lock(&tgm->throttled_reqs_lock);
-    ret = qemu_co_queue_next(&tgm->throttled_reqs[is_write]);
+    ret = qemu_co_queue_next(&tgm->throttled_reqs[direction]);
     qemu_co_mutex_unlock(&tgm->throttled_reqs_lock);
 
     return ret;
@@ -315,9 +315,10 @@ static bool coroutine_fn throttle_group_co_restart_queue(ThrottleGroupMember *tg
  * This assumes that tg->lock is held.
  *
  * @tgm:       the current ThrottleGroupMember
- * @is_write:  the type of operation (read/write)
+ * @direction: the ThrottleDirection
  */
-static void schedule_next_request(ThrottleGroupMember *tgm, bool is_write)
+static void schedule_next_request(ThrottleGroupMember *tgm,
+                                  ThrottleDirection direction)
 {
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
@@ -325,27 +326,27 @@ static void schedule_next_request(ThrottleGroupMember *tgm, bool is_write)
     ThrottleGroupMember *token;
 
     /* Check if there's any pending request to schedule next */
-    token = next_throttle_token(tgm, is_write);
+    token = next_throttle_token(tgm, direction);
-    if (!tgm_has_pending_reqs(token, is_write)) {
+    if (!tgm_has_pending_reqs(token, direction)) {
         return;
     }
 
     /* Set a timer for the request if it needs to be throttled */
-    must_wait = throttle_group_schedule_timer(token, is_write);
+    must_wait = throttle_group_schedule_timer(token, direction);
 
     /* If it doesn't have to wait, queue it for immediate execution */
     if (!must_wait) {
         /* Give preference to requests from the current tgm */
         if (qemu_in_coroutine() &&
-            throttle_group_co_restart_queue(tgm, is_write)) {
+            throttle_group_co_restart_queue(tgm, direction)) {
             token = tgm;
         } else {
             ThrottleTimers *tt = &token->throttle_timers;
             int64_t now = qemu_clock_get_ns(tg->clock_type);
-            timer_mod(tt->timers[is_write], now);
+            timer_mod(tt->timers[direction], now);
-            tg->any_timer_armed[is_write] = true;
+            tg->any_timer_armed[direction] = true;
         }
-        tg->tokens[is_write] = token;
+        tg->tokens[direction] = token;
     }
 }
 
@@ -355,48 +356,49 @@ static void schedule_next_request(ThrottleGroupMember *tgm, bool is_write)
  *
  * @tgm:       the current ThrottleGroupMember
  * @bytes:     the number of bytes for this I/O
- * @is_write:  the type of operation (read/write)
+ * @direction: the ThrottleDirection
  */
 void coroutine_fn throttle_group_co_io_limits_intercept(ThrottleGroupMember *tgm,
                                                         int64_t bytes,
-                                                        bool is_write)
+                                                        ThrottleDirection direction)
 {
     bool must_wait;
     ThrottleGroupMember *token;
     ThrottleGroup *tg = container_of(tgm->throttle_state, ThrottleGroup, ts);
 
     assert(bytes >= 0);
+    assert(direction < THROTTLE_MAX);
 
     qemu_mutex_lock(&tg->lock);
 
     /* First we check if this I/O has to be throttled. */
-    token = next_throttle_token(tgm, is_write);
+    token = next_throttle_token(tgm, direction);
-    must_wait = throttle_group_schedule_timer(token, is_write);
+    must_wait = throttle_group_schedule_timer(token, direction);
 
     /* Wait if there's a timer set or queued requests of this type */
-    if (must_wait || tgm->pending_reqs[is_write]) {
+    if (must_wait || tgm->pending_reqs[direction]) {
-        tgm->pending_reqs[is_write]++;
+        tgm->pending_reqs[direction]++;
         qemu_mutex_unlock(&tg->lock);
         qemu_co_mutex_lock(&tgm->throttled_reqs_lock);
-        qemu_co_queue_wait(&tgm->throttled_reqs[is_write],
+        qemu_co_queue_wait(&tgm->throttled_reqs[direction],
                            &tgm->throttled_reqs_lock);
         qemu_co_mutex_unlock(&tgm->throttled_reqs_lock);
         qemu_mutex_lock(&tg->lock);
-        tgm->pending_reqs[is_write]--;
+        tgm->pending_reqs[direction]--;
     }
 
     /* The I/O will be executed, so do the accounting */
-    throttle_account(tgm->throttle_state, is_write, bytes);
+    throttle_account(tgm->throttle_state, direction, bytes);
 
     /* Schedule the next request */
-    schedule_next_request(tgm, is_write);
+    schedule_next_request(tgm, direction);
 
     qemu_mutex_unlock(&tg->lock);
 }
 
 typedef struct {
     ThrottleGroupMember *tgm;
-    bool is_write;
+    ThrottleDirection direction;
 } RestartData;
 
 static void coroutine_fn throttle_group_restart_queue_entry(void *opaque)
@@ -405,16 +407,16 @@ static void coroutine_fn throttle_group_restart_queue_entry(void *opaque)
     ThrottleGroupMember *tgm = data->tgm;
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
-    bool is_write = data->is_write;
+    ThrottleDirection direction = data->direction;
     bool empty_queue;
 
-    empty_queue = !throttle_group_co_restart_queue(tgm, is_write);
+    empty_queue = !throttle_group_co_restart_queue(tgm, direction);
 
     /* If the request queue was empty then we have to take care of
      * scheduling the next one */
     if (empty_queue) {
         qemu_mutex_lock(&tg->lock);
-        schedule_next_request(tgm, is_write);
+        schedule_next_request(tgm, direction);
         qemu_mutex_unlock(&tg->lock);
     }
 
@@ -424,18 +426,19 @@ static void coroutine_fn throttle_group_restart_queue_entry(void *opaque)
     aio_wait_kick();
 }
 
-static void throttle_group_restart_queue(ThrottleGroupMember *tgm, bool is_write)
+static void throttle_group_restart_queue(ThrottleGroupMember *tgm,
+                                        ThrottleDirection direction)
 {
     Coroutine *co;
     RestartData *rd = g_new0(RestartData, 1);
 
     rd->tgm = tgm;
-    rd->is_write = is_write;
+    rd->direction = direction;
 
     /* This function is called when a timer is fired or when
      * throttle_group_restart_tgm() is called. Either way, there can
      * be no timer pending on this tgm at this point */
-    assert(!timer_pending(tgm->throttle_timers.timers[is_write]));
+    assert(!timer_pending(tgm->throttle_timers.timers[direction]));
 
     qatomic_inc(&tgm->restart_pending);
 
@@ -445,18 +448,18 @@ static void throttle_group_restart_queue(ThrottleGroupMember *tgm, bool is_write
 
 void throttle_group_restart_tgm(ThrottleGroupMember *tgm)
 {
-    int i;
+    ThrottleDirection dir;
 
     if (tgm->throttle_state) {
-        for (i = 0; i < 2; i++) {
+        for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-            QEMUTimer *t = tgm->throttle_timers.timers[i];
+            QEMUTimer *t = tgm->throttle_timers.timers[dir];
             if (timer_pending(t)) {
                 /* If there's a pending timer on this tgm, fire it now */
                 timer_del(t);
-                timer_cb(tgm, i);
+                timer_cb(tgm, dir);
             } else {
                 /* Else run the next request from the queue manually */
-                throttle_group_restart_queue(tgm, i);
+                throttle_group_restart_queue(tgm, dir);
             }
         }
     }
@@ -500,30 +503,30 @@ void throttle_group_get_config(ThrottleGroupMember *tgm, ThrottleConfig *cfg)
  * because it had been throttled.
  *
  * @tgm:       the ThrottleGroupMember whose request had been throttled
- * @is_write:  the type of operation (read/write)
+ * @direction: the ThrottleDirection
  */
-static void timer_cb(ThrottleGroupMember *tgm, bool is_write)
+static void timer_cb(ThrottleGroupMember *tgm, ThrottleDirection direction)
 {
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 
     /* The timer has just been fired, so we can update the flag */
     qemu_mutex_lock(&tg->lock);
-    tg->any_timer_armed[is_write] = false;
+    tg->any_timer_armed[direction] = false;
     qemu_mutex_unlock(&tg->lock);
 
     /* Run the request that was waiting for this timer */
-    throttle_group_restart_queue(tgm, is_write);
+    throttle_group_restart_queue(tgm, direction);
 }
 
 static void read_timer_cb(void *opaque)
 {
-    timer_cb(opaque, false);
+    timer_cb(opaque, THROTTLE_READ);
 }
 
 static void write_timer_cb(void *opaque)
 {
-    timer_cb(opaque, true);
+    timer_cb(opaque, THROTTLE_WRITE);
 }
 
 /* Register a ThrottleGroupMember from the throttling group, also initializing
@@ -541,7 +544,7 @@ void throttle_group_register_tgm(ThrottleGroupMember *tgm,
                                  const char *groupname,
                                  AioContext *ctx)
 {
-    int i;
+    ThrottleDirection dir;
     ThrottleState *ts = throttle_group_incref(groupname);
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
 
@@ -551,10 +554,11 @@ void throttle_group_register_tgm(ThrottleGroupMember *tgm,
 
     QEMU_LOCK_GUARD(&tg->lock);
     /* If the ThrottleGroup is new set this ThrottleGroupMember as the token */
-    for (i = 0; i < 2; i++) {
+    for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-        if (!tg->tokens[i]) {
+        if (!tg->tokens[dir]) {
-            tg->tokens[i] = tgm;
+            tg->tokens[dir] = tgm;
         }
+        qemu_co_queue_init(&tgm->throttled_reqs[dir]);
     }
 
     QLIST_INSERT_HEAD(&tg->head, tgm, round_robin);
@@ -566,8 +570,6 @@ void throttle_group_register_tgm(ThrottleGroupMember *tgm,
                          write_timer_cb,
                          tgm);
     qemu_co_mutex_init(&tgm->throttled_reqs_lock);
-    qemu_co_queue_init(&tgm->throttled_reqs[0]);
-    qemu_co_queue_init(&tgm->throttled_reqs[1]);
 }
 
 /* Unregister a ThrottleGroupMember from its group, removing it from the list,
@@ -585,7 +587,7 @@ void throttle_group_unregister_tgm(ThrottleGroupMember *tgm)
     ThrottleState *ts = tgm->throttle_state;
     ThrottleGroup *tg = container_of(ts, ThrottleGroup, ts);
     ThrottleGroupMember *token;
-    int i;
+    ThrottleDirection dir;
 
     if (!ts) {
         /* Discard already unregistered tgm */
@@ -596,17 +598,17 @@ void throttle_group_unregister_tgm(ThrottleGroupMember *tgm)
     AIO_WAIT_WHILE(tgm->aio_context, qatomic_read(&tgm->restart_pending) > 0);
 
     WITH_QEMU_LOCK_GUARD(&tg->lock) {
-        for (i = 0; i < 2; i++) {
+        for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-            assert(tgm->pending_reqs[i] == 0);
+            assert(tgm->pending_reqs[dir] == 0);
-            assert(qemu_co_queue_empty(&tgm->throttled_reqs[i]));
+            assert(qemu_co_queue_empty(&tgm->throttled_reqs[dir]));
-            assert(!timer_pending(tgm->throttle_timers.timers[i]));
+            assert(!timer_pending(tgm->throttle_timers.timers[dir]));
-            if (tg->tokens[i] == tgm) {
+            if (tg->tokens[dir] == tgm) {
                 token = throttle_group_next_tgm(tgm);
                 /* Take care of the case where this is the last tgm in the group */
                 if (token == tgm) {
                     token = NULL;
                 }
-                tg->tokens[i] = token;
+                tg->tokens[dir] = token;
             }
         }
 
@@ -631,19 +633,20 @@ void throttle_group_detach_aio_context(ThrottleGroupMember *tgm)
 {
     ThrottleGroup *tg = container_of(tgm->throttle_state, ThrottleGroup, ts);
     ThrottleTimers *tt = &tgm->throttle_timers;
-    int i;
+    ThrottleDirection dir;
 
     /* Requests must have been drained */
-    assert(tgm->pending_reqs[0] == 0 && tgm->pending_reqs[1] == 0);
+    for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-    assert(qemu_co_queue_empty(&tgm->throttled_reqs[0]));
+        assert(tgm->pending_reqs[dir] == 0);
-    assert(qemu_co_queue_empty(&tgm->throttled_reqs[1]));
+        assert(qemu_co_queue_empty(&tgm->throttled_reqs[dir]));
+    }
 
     /* Kick off next ThrottleGroupMember, if necessary */
     WITH_QEMU_LOCK_GUARD(&tg->lock) {
-        for (i = 0; i < 2; i++) {
+        for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-            if (timer_pending(tt->timers[i])) {
+            if (timer_pending(tt->timers[dir])) {
-                tg->any_timer_armed[i] = false;
+                tg->any_timer_armed[dir] = false;
-                schedule_next_request(tgm, i);
+                schedule_next_request(tgm, dir);
             }
         }
     }

block/throttle.c

@@ -118,7 +118,7 @@ throttle_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
 {
 
     ThrottleGroupMember *tgm = bs->opaque;
-    throttle_group_co_io_limits_intercept(tgm, bytes, false);
+    throttle_group_co_io_limits_intercept(tgm, bytes, THROTTLE_READ);
 
     return bdrv_co_preadv(bs->file, offset, bytes, qiov, flags);
 }
@@ -128,7 +128,7 @@ throttle_co_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
                     QEMUIOVector *qiov, BdrvRequestFlags flags)
 {
     ThrottleGroupMember *tgm = bs->opaque;
-    throttle_group_co_io_limits_intercept(tgm, bytes, true);
+    throttle_group_co_io_limits_intercept(tgm, bytes, THROTTLE_WRITE);
 
     return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
 }
@@ -138,7 +138,7 @@ throttle_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
                           BdrvRequestFlags flags)
 {
     ThrottleGroupMember *tgm = bs->opaque;
-    throttle_group_co_io_limits_intercept(tgm, bytes, true);
+    throttle_group_co_io_limits_intercept(tgm, bytes, THROTTLE_WRITE);
 
     return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
 }
@@ -147,7 +147,7 @@ static int coroutine_fn GRAPH_RDLOCK
 throttle_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
 {
     ThrottleGroupMember *tgm = bs->opaque;
-    throttle_group_co_io_limits_intercept(tgm, bytes, true);
+    throttle_group_co_io_limits_intercept(tgm, bytes, THROTTLE_WRITE);
 
     return bdrv_co_pdiscard(bs->file, offset, bytes);
 }

fsdev/qemu-fsdev-throttle.c

@@ -94,20 +94,22 @@ void fsdev_throttle_init(FsThrottle *fst)
     }
 }
 
-void coroutine_fn fsdev_co_throttle_request(FsThrottle *fst, bool is_write,
+void coroutine_fn fsdev_co_throttle_request(FsThrottle *fst,
+                                            ThrottleDirection direction,
                                             struct iovec *iov, int iovcnt)
 {
+    assert(direction < THROTTLE_MAX);
     if (throttle_enabled(&fst->cfg)) {
-        if (throttle_schedule_timer(&fst->ts, &fst->tt, is_write) ||
+        if (throttle_schedule_timer(&fst->ts, &fst->tt, direction) ||
-            !qemu_co_queue_empty(&fst->throttled_reqs[is_write])) {
+            !qemu_co_queue_empty(&fst->throttled_reqs[direction])) {
-            qemu_co_queue_wait(&fst->throttled_reqs[is_write], NULL);
+            qemu_co_queue_wait(&fst->throttled_reqs[direction], NULL);
         }
 
-        throttle_account(&fst->ts, is_write, iov_size(iov, iovcnt));
+        throttle_account(&fst->ts, direction, iov_size(iov, iovcnt));
 
-        if (!qemu_co_queue_empty(&fst->throttled_reqs[is_write]) &&
+        if (!qemu_co_queue_empty(&fst->throttled_reqs[direction]) &&
-            !throttle_schedule_timer(&fst->ts, &fst->tt, is_write)) {
+            !throttle_schedule_timer(&fst->ts, &fst->tt, direction)) {
-            qemu_co_queue_next(&fst->throttled_reqs[is_write]);
+            qemu_co_queue_next(&fst->throttled_reqs[direction]);
         }
     }
 }

fsdev/qemu-fsdev-throttle.h

@@ -23,14 +23,14 @@ typedef struct FsThrottle {
     ThrottleState ts;
     ThrottleTimers tt;
     ThrottleConfig cfg;
-    CoQueue      throttled_reqs[2];
+    CoQueue      throttled_reqs[THROTTLE_MAX];
 } FsThrottle;
 
 int fsdev_throttle_parse_opts(QemuOpts *, FsThrottle *, Error **);
 
 void fsdev_throttle_init(FsThrottle *);
 
-void coroutine_fn fsdev_co_throttle_request(FsThrottle *, bool ,
+void coroutine_fn fsdev_co_throttle_request(FsThrottle *, ThrottleDirection ,
                                             struct iovec *, int);
 
 void fsdev_throttle_cleanup(FsThrottle *);

hw/9pfs/cofile.c

@@ -252,7 +252,7 @@ int coroutine_fn v9fs_co_pwritev(V9fsPDU *pdu, V9fsFidState *fidp,
     if (v9fs_request_cancelled(pdu)) {
         return -EINTR;
     }
-    fsdev_co_throttle_request(s->ctx.fst, true, iov, iovcnt);
+    fsdev_co_throttle_request(s->ctx.fst, THROTTLE_WRITE, iov, iovcnt);
     v9fs_co_run_in_worker(
         {
             err = s->ops->pwritev(&s->ctx, &fidp->fs, iov, iovcnt, offset);
@@ -272,7 +272,7 @@ int coroutine_fn v9fs_co_preadv(V9fsPDU *pdu, V9fsFidState *fidp,
     if (v9fs_request_cancelled(pdu)) {
         return -EINTR;
     }
-    fsdev_co_throttle_request(s->ctx.fst, false, iov, iovcnt);
+    fsdev_co_throttle_request(s->ctx.fst, THROTTLE_READ, iov, iovcnt);
     v9fs_co_run_in_worker(
         {
             err = s->ops->preadv(&s->ctx, &fidp->fs, iov, iovcnt, offset);

include/block/throttle-groups.h

@@ -37,7 +37,7 @@ typedef struct ThrottleGroupMember {
     AioContext   *aio_context;
     /* throttled_reqs_lock protects the CoQueues for throttled requests.  */
     CoMutex      throttled_reqs_lock;
-    CoQueue      throttled_reqs[2];
+    CoQueue      throttled_reqs[THROTTLE_MAX];
 
     /* Nonzero if the I/O limits are currently being ignored; generally
      * it is zero.  Accessed with atomic operations.
@@ -54,7 +54,7 @@ typedef struct ThrottleGroupMember {
      * throttle_state tells us if I/O limits are configured. */
     ThrottleState *throttle_state;
     ThrottleTimers throttle_timers;
-    unsigned       pending_reqs[2];
+    unsigned       pending_reqs[THROTTLE_MAX];
     QLIST_ENTRY(ThrottleGroupMember) round_robin;
 
 } ThrottleGroupMember;
@@ -78,7 +78,7 @@ void throttle_group_restart_tgm(ThrottleGroupMember *tgm);
 
 void coroutine_fn throttle_group_co_io_limits_intercept(ThrottleGroupMember *tgm,
                                                         int64_t bytes,
-                                                        bool is_write);
+                                                        ThrottleDirection direction);
 void throttle_group_attach_aio_context(ThrottleGroupMember *tgm,
                                        AioContext *new_context);
 void throttle_group_detach_aio_context(ThrottleGroupMember *tgm);

include/qemu/throttle.h

@@ -99,13 +99,18 @@ typedef struct ThrottleState {
     int64_t previous_leak;    /* timestamp of the last leak done */
 } ThrottleState;
 
+typedef enum {
+    THROTTLE_READ = 0,
+    THROTTLE_WRITE,
+    THROTTLE_MAX
+} ThrottleDirection;
+
 typedef struct ThrottleTimers {
-    QEMUTimer *timers[2];     /* timers used to do the throttling */
+    QEMUTimer *timers[THROTTLE_MAX];    /* timers used to do the throttling */
     QEMUClockType clock_type; /* the clock used */
 
     /* Callbacks */
-    QEMUTimerCB *read_timer_cb;
+    QEMUTimerCB *timer_cb[THROTTLE_MAX];
-    QEMUTimerCB *write_timer_cb;
     void *timer_opaque;
 } ThrottleTimers;
 
@@ -149,9 +154,10 @@ void throttle_config_init(ThrottleConfig *cfg);
 /* usage */
 bool throttle_schedule_timer(ThrottleState *ts,
                              ThrottleTimers *tt,
-                             bool is_write);
+                             ThrottleDirection direction);
 
-void throttle_account(ThrottleState *ts, bool is_write, uint64_t size);
+void throttle_account(ThrottleState *ts, ThrottleDirection direction,
+                      uint64_t size);
 void throttle_limits_to_config(ThrottleLimits *arg, ThrottleConfig *cfg,
                                Error **errp);
 void throttle_config_to_limits(ThrottleConfig *cfg, ThrottleLimits *var);

tests/qemu-iotests/tests/file-io-error

@@ -0,0 +1,119 @@
+#!/usr/bin/env bash
+# group: rw
+#
+# Produce an I/O error in file-posix, and hope that it is not catastrophic.
+# Regression test for: https://bugzilla.redhat.com/show_bug.cgi?id=2234374
+#
+# Copyright (C) 2023 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+seq=$(basename "$0")
+echo "QA output created by $seq"
+
+status=1	# failure is the default!
+
+_cleanup()
+{
+    _cleanup_qemu
+    rm -f "$TEST_DIR/fuse-export"
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ../common.rc
+. ../common.filter
+. ../common.qemu
+
+# Format-agnostic (we do not use any), but we do test the file protocol
+_supported_proto file
+_require_drivers blkdebug null-co
+
+if [ "$IMGOPTSSYNTAX" = "true" ]; then
+    # We need `$QEMU_IO -f file` to work; IMGOPTSSYNTAX uses --image-opts,
+    # breaking -f.
+    _unsupported_fmt $IMGFMT
+fi
+
+# This is a regression test of a bug in which flie-posix would access zone
+# information in case of an I/O error even when there is no zone information,
+# resulting in a division by zero.
+# To reproduce the problem, we need to trigger an I/O error inside of
+# file-posix, which can be done (rootless) by providing a FUSE export that
+# presents only errors when accessed.
+
+_launch_qemu
+_send_qemu_cmd $QEMU_HANDLE \
+    "{'execute': 'qmp_capabilities'}" \
+    'return'
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{'execute': 'blockdev-add',
+      'arguments': {
+          'driver': 'blkdebug',
+          'node-name': 'node0',
+          'inject-error': [{'event': 'none'}],
+          'image': {
+              'driver': 'null-co'
+          }
+      }}" \
+    'return'
+
+# FUSE mountpoint must exist and be a regular file
+touch "$TEST_DIR/fuse-export"
+
+# The grep -v to filter fusermount's (benign) error when /etc/fuse.conf does
+# not contain user_allow_other and the subsequent check for missing FUSE support
+# have both been taken from iotest 308.
+output=$(_send_qemu_cmd $QEMU_HANDLE \
+    "{'execute': 'block-export-add',
+      'arguments': {
+          'id': 'exp0',
+          'type': 'fuse',
+          'node-name': 'node0',
+          'mountpoint': '$TEST_DIR/fuse-export',
+          'writable': true
+      }}" \
+    'return' \
+    | grep -v 'option allow_other only allowed if')
+
+if echo "$output" | grep -q "Parameter 'type' does not accept value 'fuse'"; then
+    _notrun 'No FUSE support'
+fi
+echo "$output"
+
+echo
+# This should fail, but gracefully, i.e. just print an I/O error, not crash.
+$QEMU_IO -f file -c 'write 0 64M' "$TEST_DIR/fuse-export" | _filter_qemu_io
+echo
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{'execute': 'block-export-del',
+      'arguments': {'id': 'exp0'}}" \
+    'return'
+
+_send_qemu_cmd $QEMU_HANDLE \
+    '' \
+    'BLOCK_EXPORT_DELETED'
+
+_send_qemu_cmd $QEMU_HANDLE \
+    "{'execute': 'blockdev-del',
+      'arguments': {'node-name': 'node0'}}" \
+    'return'
+
+# success, all done
+echo "*** done"
+rm -f $seq.full
+status=0

tests/qemu-iotests/tests/file-io-error.out

@@ -0,0 +1,33 @@
+QA output created by file-io-error
+{'execute': 'qmp_capabilities'}
+{"return": {}}
+{'execute': 'blockdev-add',
+      'arguments': {
+          'driver': 'blkdebug',
+          'node-name': 'node0',
+          'inject-error': [{'event': 'none'}],
+          'image': {
+              'driver': 'null-co'
+          }
+      }}
+{"return": {}}
+{'execute': 'block-export-add',
+      'arguments': {
+          'id': 'exp0',
+          'type': 'fuse',
+          'node-name': 'node0',
+          'mountpoint': 'TEST_DIR/fuse-export',
+          'writable': true
+      }}
+{"return": {}}
+
+write failed: Input/output error
+
+{'execute': 'block-export-del',
+      'arguments': {'id': 'exp0'}}
+{"return": {}}
+{"timestamp": {"seconds":  TIMESTAMP, "microseconds":  TIMESTAMP}, "event": "BLOCK_EXPORT_DELETED", "data": {"id": "exp0"}}
+{'execute': 'blockdev-del',
+      'arguments': {'node-name': 'node0'}}
+{"return": {}}
+*** done

tests/unit/test-throttle.c

@@ -169,8 +169,72 @@ static void test_init(void)
 
     /* check initialized fields */
     g_assert(tt->clock_type == QEMU_CLOCK_VIRTUAL);
-    g_assert(tt->timers[0]);
+    g_assert(tt->timers[THROTTLE_READ]);
-    g_assert(tt->timers[1]);
+    g_assert(tt->timers[THROTTLE_WRITE]);
+
+    /* check other fields where cleared */
+    g_assert(!ts.previous_leak);
+    g_assert(!ts.cfg.op_size);
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        g_assert(!ts.cfg.buckets[i].avg);
+        g_assert(!ts.cfg.buckets[i].max);
+        g_assert(!ts.cfg.buckets[i].level);
+    }
+
+    throttle_timers_destroy(tt);
+}
+
+static void test_init_readonly(void)
+{
+    int i;
+
+    tt = &tgm.throttle_timers;
+
+    /* fill the structures with crap */
+    memset(&ts, 1, sizeof(ts));
+    memset(tt, 1, sizeof(*tt));
+
+    /* init structures */
+    throttle_init(&ts);
+    throttle_timers_init(tt, ctx, QEMU_CLOCK_VIRTUAL,
+                         read_timer_cb, NULL, &ts);
+
+    /* check initialized fields */
+    g_assert(tt->clock_type == QEMU_CLOCK_VIRTUAL);
+    g_assert(tt->timers[THROTTLE_READ]);
+    g_assert(!tt->timers[THROTTLE_WRITE]);
+
+    /* check other fields where cleared */
+    g_assert(!ts.previous_leak);
+    g_assert(!ts.cfg.op_size);
+    for (i = 0; i < BUCKETS_COUNT; i++) {
+        g_assert(!ts.cfg.buckets[i].avg);
+        g_assert(!ts.cfg.buckets[i].max);
+        g_assert(!ts.cfg.buckets[i].level);
+    }
+
+    throttle_timers_destroy(tt);
+}
+
+static void test_init_writeonly(void)
+{
+    int i;
+
+    tt = &tgm.throttle_timers;
+
+    /* fill the structures with crap */
+    memset(&ts, 1, sizeof(ts));
+    memset(tt, 1, sizeof(*tt));
+
+    /* init structures */
+    throttle_init(&ts);
+    throttle_timers_init(tt, ctx, QEMU_CLOCK_VIRTUAL,
+                         NULL, write_timer_cb, &ts);
+
+    /* check initialized fields */
+    g_assert(tt->clock_type == QEMU_CLOCK_VIRTUAL);
+    g_assert(!tt->timers[THROTTLE_READ]);
+    g_assert(tt->timers[THROTTLE_WRITE]);
 
     /* check other fields where cleared */
     g_assert(!ts.previous_leak);
@@ -191,7 +255,7 @@ static void test_destroy(void)
     throttle_timers_init(tt, ctx, QEMU_CLOCK_VIRTUAL,
                          read_timer_cb, write_timer_cb, &ts);
     throttle_timers_destroy(tt);
-    for (i = 0; i < 2; i++) {
+    for (i = 0; i < THROTTLE_MAX; i++) {
         g_assert(!tt->timers[i]);
     }
 }
@@ -573,9 +637,9 @@ static bool do_test_accounting(bool is_ops, /* are we testing bps or ops */
     throttle_config(&ts, QEMU_CLOCK_VIRTUAL, &cfg);
 
     /* account a read */
-    throttle_account(&ts, false, size);
+    throttle_account(&ts, THROTTLE_READ, size);
     /* account a write */
-    throttle_account(&ts, true, size);
+    throttle_account(&ts, THROTTLE_WRITE, size);
 
     /* check total result */
     index = to_test[is_ops][0];
@@ -752,6 +816,8 @@ int main(int argc, char **argv)
     g_test_add_func("/throttle/leak_bucket",        test_leak_bucket);
     g_test_add_func("/throttle/compute_wait",       test_compute_wait);
     g_test_add_func("/throttle/init",               test_init);
+    g_test_add_func("/throttle/init_readonly",      test_init_readonly);
+    g_test_add_func("/throttle/init_writeonly",     test_init_writeonly);
     g_test_add_func("/throttle/destroy",            test_destroy);
     g_test_add_func("/throttle/have_timer",         test_have_timer);
     g_test_add_func("/throttle/detach_attach",      test_detach_attach);

util/throttle.c

@@ -136,13 +136,14 @@ int64_t throttle_compute_wait(LeakyBucket *bkt)
 
 /* This function compute the time that must be waited while this IO
  *
- * @is_write:   true if the current IO is a write, false if it's a read
+ * @direction:  throttle direction
  * @ret:        time to wait
  */
 static int64_t throttle_compute_wait_for(ThrottleState *ts,
-                                         bool is_write)
+                                         ThrottleDirection direction)
 {
-    BucketType to_check[2][4] = { {THROTTLE_BPS_TOTAL,
+    static const BucketType to_check[THROTTLE_MAX][4] = {
+                                  {THROTTLE_BPS_TOTAL,
                                    THROTTLE_OPS_TOTAL,
                                    THROTTLE_BPS_READ,
                                    THROTTLE_OPS_READ},
@@ -153,8 +154,8 @@ static int64_t throttle_compute_wait_for(ThrottleState *ts,
     int64_t wait, max_wait = 0;
     int i;
 
-    for (i = 0; i < 4; i++) {
+    for (i = 0; i < ARRAY_SIZE(to_check[THROTTLE_READ]); i++) {
-        BucketType index = to_check[is_write][i];
+        BucketType index = to_check[direction][i];
         wait = throttle_compute_wait(&ts->cfg.buckets[index]);
         if (wait > max_wait) {
             max_wait = wait;
@@ -166,13 +167,13 @@ static int64_t throttle_compute_wait_for(ThrottleState *ts,
 
 /* compute the timer for this type of operation
  *
- * @is_write:   the type of operation
+ * @direction:  throttle direction
  * @now:        the current clock timestamp
  * @next_timestamp: the resulting timer
  * @ret:        true if a timer must be set
  */
 static bool throttle_compute_timer(ThrottleState *ts,
-                                   bool is_write,
+                                   ThrottleDirection direction,
                                    int64_t now,
                                    int64_t *next_timestamp)
 {
@@ -182,7 +183,7 @@ static bool throttle_compute_timer(ThrottleState *ts,
     throttle_do_leak(ts, now);
 
     /* compute the wait time if any */
-    wait = throttle_compute_wait_for(ts, is_write);
+    wait = throttle_compute_wait_for(ts, direction);
 
     /* if the code must wait compute when the next timer should fire */
     if (wait) {
@@ -199,10 +200,15 @@ static bool throttle_compute_timer(ThrottleState *ts,
 void throttle_timers_attach_aio_context(ThrottleTimers *tt,
                                         AioContext *new_context)
 {
-    tt->timers[0] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
+    ThrottleDirection dir;
-                                  tt->read_timer_cb, tt->timer_opaque);
+
-    tt->timers[1] = aio_timer_new(new_context, tt->clock_type, SCALE_NS,
+    for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-                                  tt->write_timer_cb, tt->timer_opaque);
+        if (tt->timer_cb[dir]) {
+            tt->timers[dir] =
+                aio_timer_new(new_context, tt->clock_type, SCALE_NS,
+                              tt->timer_cb[dir], tt->timer_opaque);
+        }
+    }
 }
 
 /*
@@ -233,11 +239,12 @@ void throttle_timers_init(ThrottleTimers *tt,
                           QEMUTimerCB *write_timer_cb,
                           void *timer_opaque)
 {
+    assert(read_timer_cb || write_timer_cb);
     memset(tt, 0, sizeof(ThrottleTimers));
 
     tt->clock_type = clock_type;
-    tt->read_timer_cb = read_timer_cb;
+    tt->timer_cb[THROTTLE_READ] = read_timer_cb;
-    tt->write_timer_cb = write_timer_cb;
+    tt->timer_cb[THROTTLE_WRITE] = write_timer_cb;
     tt->timer_opaque = timer_opaque;
     throttle_timers_attach_aio_context(tt, aio_context);
 }
@@ -245,7 +252,9 @@ void throttle_timers_init(ThrottleTimers *tt,
 /* destroy a timer */
 static void throttle_timer_destroy(QEMUTimer **timer)
 {
-    assert(*timer != NULL);
+    if (*timer == NULL) {
+        return;
+    }
 
     timer_free(*timer);
     *timer = NULL;
@@ -254,10 +263,10 @@ static void throttle_timer_destroy(QEMUTimer **timer)
 /* Remove timers from event loop */
 void throttle_timers_detach_aio_context(ThrottleTimers *tt)
 {
-    int i;
+    ThrottleDirection dir;
 
-    for (i = 0; i < 2; i++) {
+    for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
-        throttle_timer_destroy(&tt->timers[i]);
+        throttle_timer_destroy(&tt->timers[dir]);
     }
 }
 
@@ -270,9 +279,13 @@ void throttle_timers_destroy(ThrottleTimers *tt)
 /* is any throttling timer configured */
 bool throttle_timers_are_initialized(ThrottleTimers *tt)
 {
-    if (tt->timers[0]) {
+    ThrottleDirection dir;
+
+    for (dir = THROTTLE_READ; dir < THROTTLE_MAX; dir++) {
+        if (tt->timers[dir]) {
             return true;
         }
+    }
 
     return false;
 }
@@ -413,19 +426,24 @@ void throttle_get_config(ThrottleState *ts, ThrottleConfig *cfg)
  * NOTE: this function is not unit tested due to it's usage of timer_mod
  *
  * @tt:       the timers structure
- * @is_write: the type of operation (read/write)
+ * @direction: throttle direction
  * @ret:      true if the timer has been scheduled else false
  */
 bool throttle_schedule_timer(ThrottleState *ts,
                              ThrottleTimers *tt,
-                             bool is_write)
+                             ThrottleDirection direction)
 {
     int64_t now = qemu_clock_get_ns(tt->clock_type);
     int64_t next_timestamp;
+    QEMUTimer *timer;
     bool must_wait;
 
+    assert(direction < THROTTLE_MAX);
+    timer = tt->timers[direction];
+    assert(timer);
+
     must_wait = throttle_compute_timer(ts,
-                                       is_write,
+                                       direction,
                                        now,
                                        &next_timestamp);
 
@@ -435,48 +453,50 @@ bool throttle_schedule_timer(ThrottleState *ts,
     }
 
     /* request throttled and timer pending -> do nothing */
-    if (timer_pending(tt->timers[is_write])) {
+    if (timer_pending(timer)) {
         return true;
     }
 
     /* request throttled and timer not pending -> arm timer */
-    timer_mod(tt->timers[is_write], next_timestamp);
+    timer_mod(timer, next_timestamp);
     return true;
 }
 
 /* do the accounting for this operation
  *
- * @is_write: the type of operation (read/write)
+ * @direction: throttle direction
  * @size:     the size of the operation
  */
-void throttle_account(ThrottleState *ts, bool is_write, uint64_t size)
+void throttle_account(ThrottleState *ts, ThrottleDirection direction,
+                      uint64_t size)
 {
-    const BucketType bucket_types_size[2][2] = {
+    static const BucketType bucket_types_size[THROTTLE_MAX][2] = {
         { THROTTLE_BPS_TOTAL, THROTTLE_BPS_READ },
         { THROTTLE_BPS_TOTAL, THROTTLE_BPS_WRITE }
     };
-    const BucketType bucket_types_units[2][2] = {
+    static const BucketType bucket_types_units[THROTTLE_MAX][2] = {
         { THROTTLE_OPS_TOTAL, THROTTLE_OPS_READ },
         { THROTTLE_OPS_TOTAL, THROTTLE_OPS_WRITE }
     };
     double units = 1.0;
     unsigned i;
 
+    assert(direction < THROTTLE_MAX);
     /* if cfg.op_size is defined and smaller than size we compute unit count */
     if (ts->cfg.op_size && size > ts->cfg.op_size) {
         units = (double) size / ts->cfg.op_size;
     }
 
-    for (i = 0; i < 2; i++) {
+    for (i = 0; i < ARRAY_SIZE(bucket_types_size[THROTTLE_READ]); i++) {
         LeakyBucket *bkt;
 
-        bkt = &ts->cfg.buckets[bucket_types_size[is_write][i]];
+        bkt = &ts->cfg.buckets[bucket_types_size[direction][i]];
         bkt->level += size;
         if (bkt->burst_length > 1) {
             bkt->burst_level += size;
         }
 
-        bkt = &ts->cfg.buckets[bucket_types_units[is_write][i]];
+        bkt = &ts->cfg.buckets[bucket_types_units[direction][i]];
         bkt->level += units;
         if (bkt->burst_length > 1) {
             bkt->burst_level += units;