[Qemu-devel] [PATCH v3 6/8] Add blkmirror block driver

[Paolo Bonzini <pbonzini@redhat.com>]

From: Marcelo Tosatti <mtosatti@redhat.com>

Mirrored writes are used by live block copy.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 Makefile.objs     |    2 +-
 block/blkmirror.c |  239 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 240 insertions(+), 1 deletions(-)
 create mode 100644 block/blkmirror.c

diff --git a/Makefile.objs b/Makefile.objs
index 808de6a..982f44b 100644
--- a/Makefile.objs
+++ b/Makefile.objs
@@ -74,7 +74,7 @@ fsdev-obj-$(CONFIG_VIRTFS) += $(addprefix fsdev/, $(fsdev-nested-y))
 # suppress *all* target specific code in case of system emulation, i.e. a
 # single QEMU executable should support all CPUs and machines.
 
-common-obj-y = $(block-obj-y) blockdev.o
+common-obj-y = $(block-obj-y) blockdev.o block/blkmirror.o
 common-obj-y += $(net-obj-y)
 common-obj-y += $(qobject-obj-y)
 common-obj-$(CONFIG_LINUX) += $(fsdev-obj-$(CONFIG_LINUX))
diff --git a/block/blkmirror.c b/block/blkmirror.c
new file mode 100644
index 0000000..0ee2ca6
--- /dev/null
+++ b/block/blkmirror.c
@@ -0,0 +1,239 @@
+/*
+ * Block driver for mirrored writes.
+ *
+ * Copyright (C) 2011-2012 Red Hat, Inc.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include <stdarg.h>
+#include "block_int.h"
+
+typedef struct DupAIOCB DupAIOCB;
+
+typedef struct SingleAIOCB {
+    BlockDriverAIOCB *aiocb;
+    DupAIOCB *parent;
+} SingleAIOCB;
+
+struct DupAIOCB {
+    BlockDriverAIOCB common;
+    int count;
+    int canceled;
+
+    BlockDriverCompletionFunc *cb;
+    SingleAIOCB aios[2];
+    int ret;
+};
+
+/* Valid blkmirror filenames look like blkmirror:format:path/to/target.
+ *
+ * The driver is not intended for general usage.  It expects bdrv_append
+ * to tack it onto an existing image, which is used as the primary
+ * source and hardcoded to be the backing file for the target.
+ */
+static int blkmirror_open(BlockDriverState *bs, const char *filename, int flags)
+{
+    int ret, n;
+    const char *filename2;
+    char *format;
+    BlockDriver *drv;
+
+    /* Parse the blkmirror: prefix */
+    if (strncmp(filename, "blkmirror:", strlen("blkmirror:"))) {
+        return -EINVAL;
+    }
+    filename += strlen("blkmirror:");
+
+    /* The source image filename is added by bdrv_append.  We only need
+     * to parse and open the destination image and format.  */
+    n = strcspn(filename, ":");
+    if (filename[n] == 0) {
+        format = NULL;
+        filename2 = filename;
+    } else {
+        format = g_strdup(filename);
+        format[n] = 0;
+        filename2 = format + n + 1;
+    }
+
+    drv = bdrv_find_whitelisted_format(format);
+    if (!drv) {
+        ret = -ENOENT;
+        goto out;
+    }
+
+    bs->file = bdrv_new("");
+    if (bs->file == NULL) {
+        ret = -ENOMEM;
+        goto out;
+    }
+
+    /* If we crash, we cannot assume that the destination is a
+     * valid mirror and we have to start over.  So speed up things
+     * by effectively operating on the destination in cache=unsafe
+     * mode.
+     */
+    ret = bdrv_open(bs->file, filename2,
+                    flags | BDRV_O_NO_BACKING | BDRV_O_NO_FLUSH | BDRV_O_CACHE_WB,
+                    drv);
+    if (ret < 0) {
+        goto out;
+    }
+
+out:
+    g_free(format);
+    return ret;
+}
+
+static void blkmirror_close(BlockDriverState *bs)
+{
+    bs->file->backing_hd = NULL;
+
+    /* backing_hd and file closed by the caller.  */
+}
+
+static coroutine_fn int blkmirror_co_flush(BlockDriverState *bs)
+{
+    return bdrv_co_flush(bs->backing_hd);
+}
+
+static int64_t blkmirror_getlength(BlockDriverState *bs)
+{
+    return bdrv_getlength(bs->file);
+}
+
+static int coroutine_fn blkmirror_co_is_allocated(BlockDriverState *bs,
+                                                  int64_t sector_num,
+                                                  int nb_sectors, int *pnum)
+{
+    return bdrv_is_allocated(bs->file, sector_num, nb_sectors, pnum);
+}
+
+static BlockDriverAIOCB *blkmirror_aio_readv(BlockDriverState *bs,
+                                             int64_t sector_num,
+                                             QEMUIOVector *qiov, int nb_sectors,
+                                             BlockDriverCompletionFunc *cb,
+                                             void *opaque)
+{
+    return bdrv_aio_readv(bs->backing_hd, sector_num, qiov, nb_sectors,
+                          cb, opaque);
+}
+
+static void dup_aio_cancel(BlockDriverAIOCB *acb)
+{
+    DupAIOCB *dcb = container_of(acb, DupAIOCB, common);
+    int i;
+
+    dcb->canceled = true;
+    for (i = 0 ; i < 2; i++) {
+        if (dcb->aios[i].aiocb) {
+            bdrv_aio_cancel(dcb->aios[i].aiocb);
+        }
+    }
+    qemu_aio_release(dcb);
+}
+
+static AIOPool dup_aio_pool = {
+    .aiocb_size         = sizeof(DupAIOCB),
+    .cancel             = dup_aio_cancel,
+};
+
+static void blkmirror_aio_cb(void *opaque, int ret)
+{
+    SingleAIOCB *scb = opaque;
+    DupAIOCB *dcb = scb->parent;
+
+    scb->aiocb = NULL;
+
+    assert(dcb->count > 0);
+    if (ret < 0 && dcb->ret == 0) {
+        dcb->ret = ret;
+    }
+    if (--dcb->count == 0) {
+        dcb->common.cb(dcb->common.opaque, dcb->ret);
+        if (!dcb->canceled) {
+            qemu_aio_release(dcb);
+        }
+    }
+}
+
+static DupAIOCB *dup_aio_get(BlockDriverState *bs,
+                             BlockDriverCompletionFunc *cb,
+                             void *opaque)
+{
+    DupAIOCB *dcb = qemu_aio_get(&dup_aio_pool, bs, cb, opaque);
+
+    dcb->canceled = false;
+    dcb->aios[0].parent = dcb;
+    dcb->aios[1].parent = dcb;
+    dcb->count = 2;
+    dcb->ret = 0;
+    return dcb;
+}
+
+static BlockDriverAIOCB *blkmirror_aio_writev(BlockDriverState *bs,
+                                              int64_t sector_num,
+                                              QEMUIOVector *qiov,
+                                              int nb_sectors,
+                                              BlockDriverCompletionFunc *cb,
+                                              void *opaque)
+{
+    DupAIOCB *dcb = dup_aio_get(bs, cb, opaque);
+
+    /* bs->backing_hd is set after initialization.  */
+    bs->file->backing_hd = bs->backing_hd;
+
+    dcb->aios[0].aiocb = bdrv_aio_writev(bs->backing_hd, sector_num, qiov,
+                                         nb_sectors, blkmirror_aio_cb,
+                                         &dcb->aios[0]);
+    dcb->aios[1].aiocb = bdrv_aio_writev(bs->file, sector_num, qiov,
+                                         nb_sectors, blkmirror_aio_cb,
+                                         &dcb->aios[1]);
+
+    return &dcb->common;
+}
+
+static BlockDriverAIOCB *blkmirror_aio_discard(BlockDriverState *bs,
+                                               int64_t sector_num,
+                                               int nb_sectors,
+                                               BlockDriverCompletionFunc *cb,
+                                               void *opaque)
+{
+    DupAIOCB *dcb = dup_aio_get(bs, cb, opaque);
+
+    dcb->aios[0].aiocb = bdrv_aio_discard(bs->backing_hd, sector_num,
+                                          nb_sectors, blkmirror_aio_cb,
+                                          &dcb->aios[0]);
+    dcb->aios[1].aiocb = bdrv_aio_discard(bs->file, sector_num,
+                                          nb_sectors, blkmirror_aio_cb,
+                                          &dcb->aios[1]);
+
+    return &dcb->common;
+}
+
+
+static BlockDriver bdrv_blkmirror = {
+    .format_name        = "blkmirror",
+    .protocol_name      = "blkmirror",
+    .instance_size      = 0,
+
+    .bdrv_getlength     = blkmirror_getlength,
+
+    .bdrv_file_open     = blkmirror_open,
+    .bdrv_close         = blkmirror_close,
+    .bdrv_co_flush_to_disk = blkmirror_co_flush,
+    .bdrv_co_is_allocated = blkmirror_co_is_allocated,
+
+    .bdrv_aio_readv      = blkmirror_aio_readv,
+    .bdrv_aio_writev     = blkmirror_aio_writev,
+    .bdrv_aio_discard    = blkmirror_aio_discard,
+};
+
+static void bdrv_blkmirror_init(void)
+{
+    bdrv_register(&bdrv_blkmirror);
+}
+
+block_init(bdrv_blkmirror_init);
-- 
1.7.7.6