block/write-threshold.c

   1 /*
   2  * QEMU System Emulator block write threshold notification
   3  *
   4  * Copyright Red Hat, Inc. 2014
   5  *
   6  * Authors:
   7  *  Francesco Romani <fromani@redhat.com>
   8  *
   9  * This work is licensed under the terms of the GNU LGPL, version 2 or later.
  10  * See the COPYING.LIB file in the top-level directory.
  11  */
  12
  13 #include "qemu/osdep.h"
  14 #include "block/block_int.h"
  15 #include "qemu/coroutine.h"
  16 #include "block/write-threshold.h"
  17 #include "qemu/notify.h"
  18 #include "qapi/error.h"
  19 #include "qapi/qapi-commands-block-core.h"
  20 #include "qapi/qapi-events-block-core.h"
  21
  22 uint64_t bdrv_write_threshold_get(const BlockDriverState *bs)
  23 {
  24     return bs->write_threshold_offset;
  25 }
  26
  27 bool bdrv_write_threshold_is_set(const BlockDriverState *bs)
  28 {
  29     return bs->write_threshold_offset > 0;
  30 }
  31
  32 static void write_threshold_disable(BlockDriverState *bs)
  33 {
  34     if (bdrv_write_threshold_is_set(bs)) {
  35         notifier_with_return_remove(&bs->write_threshold_notifier);
  36         bs->write_threshold_offset = 0;
  37     }
  38 }
  39
  40 uint64_t bdrv_write_threshold_exceeded(const BlockDriverState *bs,
  41                                        const BdrvTrackedRequest *req)
  42 {
  43     if (bdrv_write_threshold_is_set(bs)) {
  44         if (req->offset > bs->write_threshold_offset) {
  45             return (req->offset - bs->write_threshold_offset) + req->bytes;
  46         }
  47         if ((req->offset + req->bytes) > bs->write_threshold_offset) {
  48             return (req->offset + req->bytes) - bs->write_threshold_offset;
  49         }
  50     }
  51     return 0;
  52 }
  53
  54 static int coroutine_fn before_write_notify(NotifierWithReturn *notifier,
  55                                             void *opaque)
  56 {
  57     BdrvTrackedRequest *req = opaque;
  58     BlockDriverState *bs = req->bs;
  59     uint64_t amount = 0;
  60
  61     amount = bdrv_write_threshold_exceeded(bs, req);
  62     if (amount > 0) {
  63         qapi_event_send_block_write_threshold(
  64             bs->node_name,
  65             amount,
  66             bs->write_threshold_offset);
  67
  68         /* autodisable to avoid flooding the monitor */
  69         write_threshold_disable(bs);
  70     }
  71
  72     return 0; /* should always let other notifiers run */
  73 }
  74
  75 static void write_threshold_register_notifier(BlockDriverState *bs)
  76 {
  77     bs->write_threshold_notifier.notify = before_write_notify;
  78     bdrv_add_before_write_notifier(bs, &bs->write_threshold_notifier);
  79 }
  80
  81 static void write_threshold_update(BlockDriverState *bs,
  82                                    int64_t threshold_bytes)
  83 {
  84     bs->write_threshold_offset = threshold_bytes;
  85 }
  86
  87 void bdrv_write_threshold_set(BlockDriverState *bs, uint64_t threshold_bytes)
  88 {
  89     if (bdrv_write_threshold_is_set(bs)) {
  90         if (threshold_bytes > 0) {
  91             write_threshold_update(bs, threshold_bytes);
  92         } else {
  93             write_threshold_disable(bs);
  94         }
  95     } else {
  96         if (threshold_bytes > 0) {
  97             /* avoid multiple registration */
  98             write_threshold_register_notifier(bs);
  99             write_threshold_update(bs, threshold_bytes);
 100         }
 101         /* discard bogus disable request */
 102     }
 103 }
 104
 105 void qmp_block_set_write_threshold(const char *node_name,
 106                                    uint64_t threshold_bytes,
 107                                    Error **errp)
 108 {
 109     BlockDriverState *bs;
 110     AioContext *aio_context;
 111
 112     bs = bdrv_find_node(node_name);
 113     if (!bs) {
 114         error_setg(errp, "Device '%s' not found", node_name);
 115         return;
 116     }
 117
 118     aio_context = bdrv_get_aio_context(bs);
 119     aio_context_acquire(aio_context);
 120
 121     bdrv_write_threshold_set(bs, threshold_bytes);
 122
 123     aio_context_release(aio_context);
 124 }