[PATCH 1/3] block: Introduce the 'zeroes-co' driver

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

The 'zeroes-co' block driver is almost a copy of the 'null-co'
block driver designed for performance testing, but targets
security needs, by always zero-initializing read accesses.
Write accesses are discarded.

Suggested-by: Fam Zheng <fam@euphon.net>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 block/zeroes.c    | 306 ++++++++++++++++++++++++++++++++++++++++++++++
 block/meson.build |   1 +
 2 files changed, 307 insertions(+)
 create mode 100644 block/zeroes.c

diff --git a/block/zeroes.c b/block/zeroes.c
new file mode 100644
index 00000000000..7256b6d02ee
--- /dev/null
+++ b/block/zeroes.c
@@ -0,0 +1,306 @@
+/*
+ * Zeroes block driver
+ *
+ * Based on block/null.c
+ *
+ * Copyright (C) 2021 Red Hat, Inc.
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qstring.h"
+#include "qemu/module.h"
+#include "qemu/option.h"
+#include "block/block_int.h"
+#include "sysemu/replay.h"
+
+#define NULL_OPT_LATENCY "latency-ns"
+
+typedef struct {
+    int64_t length;
+    int64_t latency_ns;
+} BDRVZeroesState;
+
+static QemuOptsList runtime_opts = {
+    .name = "zeroes",
+    .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
+    .desc = {
+        {
+            .name = BLOCK_OPT_SIZE,
+            .type = QEMU_OPT_SIZE,
+            .help = "size of the zeroes block",
+        },
+        {
+            .name = NULL_OPT_LATENCY,
+            .type = QEMU_OPT_NUMBER,
+            .help = "nanoseconds (approximated) to wait "
+                    "before completing request",
+        },
+        { /* end of list */ }
+    },
+};
+
+static void zeroes_co_parse_filename(const char *filename, QDict *options,
+                                     Error **errp)
+{
+    /*
+     * This functions only exists so that a zeroes-co:// filename
+     * is accepted with the zeroes-co driver.
+     */
+    if (strcmp(filename, "zeroes-co://")) {
+        error_setg(errp, "The only allowed filename for this driver is "
+                         "'zeroes-co://'");
+        return;
+    }
+}
+
+static void zeroes_aio_parse_filename(const char *filename, QDict *options,
+                                      Error **errp)
+{
+    /*
+     * This functions only exists so that a zeroes-aio:// filename
+     * is accepted with the zeroes-aio driver.
+     */
+    if (strcmp(filename, "zeroes-aio://")) {
+        error_setg(errp, "The only allowed filename for this driver is "
+                         "'zeroes-aio://'");
+        return;
+    }
+}
+
+static int zeroes_file_open(BlockDriverState *bs, QDict *options,
+                            int flags, Error **errp)
+{
+    QemuOpts *opts;
+    BDRVZeroesState *s = bs->opaque;
+    int ret = 0;
+
+    opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+    qemu_opts_absorb_qdict(opts, options, &error_abort);
+    s->length = qemu_opt_get_size(opts, BLOCK_OPT_SIZE, 0);
+    if (s->length < 0) {
+        error_setg(errp, "%s is invalid", BLOCK_OPT_SIZE);
+        ret = -EINVAL;
+    }
+    s->latency_ns = qemu_opt_get_number(opts, NULL_OPT_LATENCY, 0);
+    if (s->latency_ns < 0) {
+        error_setg(errp, "%s is invalid", NULL_OPT_LATENCY);
+        ret = -EINVAL;
+    }
+    qemu_opts_del(opts);
+    bs->supported_write_flags = BDRV_REQ_FUA;
+    return ret;
+}
+
+static int64_t zeroes_getlength(BlockDriverState *bs)
+{
+    BDRVZeroesState *s = bs->opaque;
+    return s->length;
+}
+
+static coroutine_fn int zeroes_co_common(BlockDriverState *bs)
+{
+    BDRVZeroesState *s = bs->opaque;
+
+    if (s->latency_ns) {
+        qemu_co_sleep_ns(QEMU_CLOCK_REALTIME, s->latency_ns);
+    }
+    return 0;
+}
+
+static coroutine_fn int zeroes_co_preadv(BlockDriverState *bs,
+                                         uint64_t offset, uint64_t bytes,
+                                         QEMUIOVector *qiov, int flags)
+{
+    qemu_iovec_memset(qiov, 0, 0, bytes);
+
+    return zeroes_co_common(bs);
+}
+
+static coroutine_fn int zeroes_co_pwritev(BlockDriverState *bs,
+                                          uint64_t offset, uint64_t bytes,
+                                          QEMUIOVector *qiov, int flags)
+{
+    return zeroes_co_common(bs);
+}
+
+static coroutine_fn int zeroes_co_flush(BlockDriverState *bs)
+{
+    return zeroes_co_common(bs);
+}
+
+typedef struct {
+    BlockAIOCB common;
+    QEMUTimer timer;
+} ZeroesAIOCB;
+
+static const AIOCBInfo zeroes_aiocb_info = {
+    .aiocb_size = sizeof(ZeroesAIOCB),
+};
+
+static void zeroes_bh_cb(void *opaque)
+{
+    ZeroesAIOCB *acb = opaque;
+    acb->common.cb(acb->common.opaque, 0);
+    qemu_aio_unref(acb);
+}
+
+static void zeroes_timer_cb(void *opaque)
+{
+    ZeroesAIOCB *acb = opaque;
+    acb->common.cb(acb->common.opaque, 0);
+    timer_deinit(&acb->timer);
+    qemu_aio_unref(acb);
+}
+
+static inline BlockAIOCB *zeroes_aio_common(BlockDriverState *bs,
+                                            BlockCompletionFunc *cb,
+                                            void *opaque)
+{
+    ZeroesAIOCB *acb;
+    BDRVZeroesState *s = bs->opaque;
+
+    acb = qemu_aio_get(&zeroes_aiocb_info, bs, cb, opaque);
+    /* Only emulate latency after vcpu is running. */
+    if (s->latency_ns) {
+        aio_timer_init(bdrv_get_aio_context(bs), &acb->timer,
+                       QEMU_CLOCK_REALTIME, SCALE_NS,
+                       zeroes_timer_cb, acb);
+        timer_mod_ns(&acb->timer,
+                     qemu_clock_get_ns(QEMU_CLOCK_REALTIME) + s->latency_ns);
+    } else {
+        replay_bh_schedule_oneshot_event(bdrv_get_aio_context(bs),
+                                         zeroes_bh_cb, acb);
+    }
+    return &acb->common;
+}
+
+static BlockAIOCB *zeroes_aio_preadv(BlockDriverState *bs,
+                                   uint64_t offset, uint64_t bytes,
+                                   QEMUIOVector *qiov, int flags,
+                                   BlockCompletionFunc *cb,
+                                   void *opaque)
+{
+    qemu_iovec_memset(qiov, 0, 0, bytes);
+
+    return zeroes_aio_common(bs, cb, opaque);
+}
+
+static BlockAIOCB *zeroes_aio_pwritev(BlockDriverState *bs,
+                                      uint64_t offset, uint64_t bytes,
+                                      QEMUIOVector *qiov, int flags,
+                                      BlockCompletionFunc *cb,
+                                      void *opaque)
+{
+    return zeroes_aio_common(bs, cb, opaque);
+}
+
+static BlockAIOCB *zeroes_aio_flush(BlockDriverState *bs,
+                                    BlockCompletionFunc *cb,
+                                    void *opaque)
+{
+    return zeroes_aio_common(bs, cb, opaque);
+}
+
+static int zeroes_reopen_prepare(BDRVReopenState *reopen_state,
+                                 BlockReopenQueue *queue, Error **errp)
+{
+    return 0;
+}
+
+static int coroutine_fn zeroes_co_block_status(BlockDriverState *bs,
+                                               bool want_zero, int64_t offset,
+                                               int64_t bytes, int64_t *pnum,
+                                               int64_t *map,
+                                               BlockDriverState **file)
+{
+    *pnum = bytes;
+    *map = offset;
+    *file = bs;
+
+    return BDRV_BLOCK_OFFSET_VALID | BDRV_BLOCK_ZERO;
+}
+
+static void zeroes_refresh_filename(BlockDriverState *bs)
+{
+    const QDictEntry *e;
+
+    for (e = qdict_first(bs->full_open_options); e;
+         e = qdict_next(bs->full_open_options, e))
+    {
+        /* These options can be ignored */
+        if (strcmp(qdict_entry_key(e), "filename") &&
+            strcmp(qdict_entry_key(e), "driver") &&
+            strcmp(qdict_entry_key(e), NULL_OPT_LATENCY))
+        {
+            return;
+        }
+    }
+
+    snprintf(bs->exact_filename, sizeof(bs->exact_filename),
+             "%s://", bs->drv->format_name);
+}
+
+static int64_t zeroes_allocated_file_size(BlockDriverState *bs)
+{
+    return 0;
+}
+
+static const char *const zeroes_strong_runtime_opts[] = {
+    BLOCK_OPT_SIZE,
+
+    NULL
+};
+
+static BlockDriver bdrv_zeroes_co = {
+    .format_name            = "zeroes-co",
+    .protocol_name          = "zeroes-co",
+    .instance_size          = sizeof(BDRVZeroesState),
+
+    .bdrv_file_open         = zeroes_file_open,
+    .bdrv_parse_filename    = zeroes_co_parse_filename,
+    .bdrv_getlength         = zeroes_getlength,
+    .bdrv_get_allocated_file_size = zeroes_allocated_file_size,
+
+    .bdrv_co_preadv         = zeroes_co_preadv,
+    .bdrv_co_pwritev        = zeroes_co_pwritev,
+    .bdrv_co_flush_to_disk  = zeroes_co_flush,
+    .bdrv_reopen_prepare    = zeroes_reopen_prepare,
+
+    .bdrv_co_block_status   = zeroes_co_block_status,
+
+    .bdrv_refresh_filename  = zeroes_refresh_filename,
+    .strong_runtime_opts    = zeroes_strong_runtime_opts,
+};
+
+static BlockDriver bdrv_zeroes_aio = {
+    .format_name            = "zeroes-aio",
+    .protocol_name          = "zeroes-aio",
+    .instance_size          = sizeof(BDRVZeroesState),
+
+    .bdrv_file_open         = zeroes_file_open,
+    .bdrv_parse_filename    = zeroes_aio_parse_filename,
+    .bdrv_getlength         = zeroes_getlength,
+    .bdrv_get_allocated_file_size = zeroes_allocated_file_size,
+
+    .bdrv_aio_preadv        = zeroes_aio_preadv,
+    .bdrv_aio_pwritev       = zeroes_aio_pwritev,
+    .bdrv_aio_flush         = zeroes_aio_flush,
+    .bdrv_reopen_prepare    = zeroes_reopen_prepare,
+
+    .bdrv_co_block_status   = zeroes_co_block_status,
+
+    .bdrv_refresh_filename  = zeroes_refresh_filename,
+    .strong_runtime_opts    = zeroes_strong_runtime_opts,
+};
+
+static void bdrv_zeroes_init(void)
+{
+    bdrv_register(&bdrv_zeroes_co);
+    bdrv_register(&bdrv_zeroes_aio);
+}
+
+block_init(bdrv_zeroes_init);
diff --git a/block/meson.build b/block/meson.build
index d21990ec95a..661d84118fb 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -40,6 +40,7 @@
   'vmdk.c',
   'vpc.c',
   'write-threshold.c',
+  'zeroes.c',
 ), zstd, zlib, gnutls)
 
 softmmu_ss.add(when: 'CONFIG_TCG', if_true: files('blkreplay.c'))
-- 
2.26.2