Aio context switch should just work because the requests will be
drained, so the scheduled timer(s) on the old context will be freed.
Signed-off-by: Fam Zheng <f...@redhat.com>
---
v3: latency_ns -> latency-ns; Add documentation in qapi json. [Eric]
v2: Check for negative value; add sleep in null-co://. [Kevin]
---
block/null.c | 55 +++++++++++++++++++++++++++++++++++++++++++++++-----
qapi/block-core.json | 5 ++++-
2 files changed, 54 insertions(+), 6 deletions(-)
diff --git a/block/null.c b/block/null.c
index ec2bd27..602f93c 100644
--- a/block/null.c
+++ b/block/null.c
@@ -12,8 +12,11 @@
#include "block/block_int.h"
+#define NULL_OPT_LATENCY "latency-ns"
+
typedef struct {
int64_t length;
+ int64_t latency_ns;
} BDRVNullState;
static QemuOptsList runtime_opts = {
@@ -30,6 +33,12 @@ static QemuOptsList runtime_opts = {
.type = QEMU_OPT_SIZE,
.help = "size of the null block",
},
+ {
+ .name = NULL_OPT_LATENCY,
+ .type = QEMU_OPT_NUMBER,
+ .help = "nanoseconds (approximated) to wait "
+ "before completing request",
+ },
{ /* end of list */ }
},
};
@@ -44,6 +53,11 @@ static int null_file_open(BlockDriverState *bs, QDict
*options, int flags,
qemu_opts_absorb_qdict(opts, options, &error_abort);
s->length =
qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 1 << 30);
+ s->latency_ns =
+ qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
+ if (s->latency_ns < 0) {
+ error_setg(errp, "latency-ns is invalid");
+ }
qemu_opts_del(opts);
return 0;
}
@@ -58,28 +72,41 @@ static int64_t null_getlength(BlockDriverState *bs)
return s->length;
}
+static coroutine_fn int null_co_common(BlockDriverState *bs)
+{
+ BDRVNullState *s = bs->opaque;
+
+ /* Only emulate latency after vcpu is running. */
+ if (s->latency_ns && qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) > 0) {
+ co_aio_sleep_ns(bdrv_get_aio_context(bs), QEMU_CLOCK_VIRTUAL,
+ s->latency_ns);
+ }
+ return 0;
+}
+
static coroutine_fn int null_co_readv(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
{
- return 0;
+ return null_co_common(bs);
}
static coroutine_fn int null_co_writev(BlockDriverState *bs,
int64_t sector_num, int nb_sectors,
QEMUIOVector *qiov)
{
- return 0;
+ return null_co_common(bs);
}
static coroutine_fn int null_co_flush(BlockDriverState *bs)
{
- return 0;
+ return null_co_common(bs);
}
typedef struct {
BlockAIOCB common;
QEMUBH *bh;
+ QEMUTimer timer;
} NullAIOCB;
static const AIOCBInfo null_aiocb_info = {
@@ -94,15 +121,33 @@ static void null_bh_cb(void *opaque)
qemu_aio_unref(acb);
}
+static void null_timer_cb(void *opaque)
+{
+ NullAIOCB *acb = opaque;
+ acb->common.cb(acb->common.opaque, 0);
+ timer_deinit(&acb->timer);
+ qemu_aio_unref(acb);
+}
+
static inline BlockAIOCB *null_aio_common(BlockDriverState *bs,
BlockCompletionFunc *cb,
void *opaque)
{
NullAIOCB *acb;
+ BDRVNullState *s = bs->opaque;
acb = qemu_aio_get(&null_aiocb_info, bs, cb, opaque);
- acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
- qemu_bh_schedule(acb->bh);
+ /* Only emulate latency after vcpu is running. */
+ if (s->latency_ns && qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) > 0) {
+ aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
+ QEMU_CLOCK_VIRTUAL, SCALE_NS,
+ null_timer_cb, acb);
+ timer_mod_ns(&acb->timer,
+ qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + s->latency_ns);
+ } else {
+ acb->bh = aio_bh_new(bdrv_get_aio_context(bs), null_bh_cb, acb);
+ qemu_bh_schedule(acb->bh);
+ }
return &acb->common;
}
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 90586a5..bdd5198 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1311,11 +1311,14 @@
# Driver specific block device options for the null backend.
#
# @size: #optional size of the device in bytes.
+# @latency-ns: #optional emulated latency (in nanoseconds) in processing
+# requests. Default to zero which completes requests immediately.
+# (Since 2.4)
#
# Since: 2.2
##
{ 'type': 'BlockdevOptionsNull',
- 'data': { '*size': 'int' } }
+ 'data': { '*size': 'int', '*latency-ns': 'uint64' } }
##
# @BlockdevOptionsVVFAT
--
1.9.3
