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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Stefan Reiter <s.reiter@proxmox.com>
Date: Mon, 7 Dec 2020 15:21:03 +0100
Subject: [PATCH] block: add alloc-track driver
Add a new filter node 'alloc-track', which seperates reads and writes to
different children, thus allowing to put a backing image behind any
blockdev (regardless of driver support). Since we can't detect any
pre-allocated blocks, we can only track new writes, hence the write
target ('file') for this node must always be empty.
Intended use case is for live restoring, i.e. add a backup image as a
block device into a VM, then put an alloc-track on the restore target
and set the backup as backing. With this, one can use a regular
'block-stream' to restore the image, while the VM can already run in the
background. Copy-on-read will help make progress as the VM reads as
well.
This only worked if the target supports backing images, so up until now
only for qcow2, with alloc-track any driver for the target can be used.
If 'auto-remove' is set, alloc-track will automatically detach itself
once the backing image is removed. It will be replaced by 'file'.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
---
block/alloc-track.c | 345 ++++++++++++++++++++++++++++++++++++++++++++
block/meson.build | 1 +
2 files changed, 346 insertions(+)
create mode 100644 block/alloc-track.c
diff --git a/block/alloc-track.c b/block/alloc-track.c
new file mode 100644
index 0000000000..35f2737c89
--- /dev/null
+++ b/block/alloc-track.c
@@ -0,0 +1,345 @@
+/*
+ * Node to allow backing images to be applied to any node. Assumes a blank
+ * image to begin with, only new writes are tracked as allocated, thus this
+ * must never be put on a node that already contains data.
+ *
+ * Copyright (c) 2020 Proxmox Server Solutions GmbH
+ * Copyright (c) 2020 Stefan Reiter <s.reiter@proxmox.com>
+ *
+ * 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 "qemu/osdep.h"
+#include "qapi/error.h"
+#include "block/block_int.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qstring.h"
+#include "qemu/cutils.h"
+#include "qemu/option.h"
+#include "qemu/module.h"
+#include "sysemu/block-backend.h"
+
+#define TRACK_OPT_AUTO_REMOVE "auto-remove"
+
+typedef enum DropState {
+ DropNone,
+ DropRequested,
+ DropInProgress,
+} DropState;
+
+typedef struct {
+ BdrvDirtyBitmap *bitmap;
+ DropState drop_state;
+ bool auto_remove;
+} BDRVAllocTrackState;
+
+static QemuOptsList runtime_opts = {
+ .name = "alloc-track",
+ .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
+ .desc = {
+ {
+ .name = TRACK_OPT_AUTO_REMOVE,
+ .type = QEMU_OPT_BOOL,
+ .help = "automatically replace this node with 'file' when 'backing'"
+ "is detached",
+ },
+ { /* end of list */ }
+ },
+};
+
+static void track_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+ BlockDriverInfo bdi;
+
+ if (!bs->file) {
+ return;
+ }
+
+ /* always use alignment from underlying write device so RMW cycle for
+ * bdrv_pwritev reads data from our backing via track_co_preadv (no partial
+ * cluster allocation in 'file') */
+ bdrv_get_info(bs->file->bs, &bdi);
+ bs->bl.request_alignment = MAX(bs->file->bs->bl.request_alignment,
+ MAX(bdi.cluster_size, BDRV_SECTOR_SIZE));
+}
+
+static int track_open(BlockDriverState *bs, QDict *options, int flags,
+ Error **errp)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+ QemuOpts *opts;
+ Error *local_err = NULL;
+ int ret = 0;
+
+ opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
+ qemu_opts_absorb_qdict(opts, options, &local_err);
+ if (local_err) {
+ error_propagate(errp, local_err);
+ ret = -EINVAL;
+ goto fail;
+ }
+
+ s->auto_remove = qemu_opt_get_bool(opts, TRACK_OPT_AUTO_REMOVE, false);
+
+ /* open the target (write) node, backing will be attached by block layer */
+ bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+ BDRV_CHILD_DATA | BDRV_CHILD_METADATA, false,
+ &local_err);
+ if (local_err) {
+ ret = -EINVAL;
+ error_propagate(errp, local_err);
+ goto fail;
+ }
+
+ track_refresh_limits(bs, errp);
+ uint64_t gran = bs->bl.request_alignment;
+ s->bitmap = bdrv_create_dirty_bitmap(bs->file->bs, gran, NULL, &local_err);
+ if (local_err) {
+ ret = -EIO;
+ error_propagate(errp, local_err);
+ goto fail;
+ }
+
+ s->drop_state = DropNone;
+
+fail:
+ if (ret < 0) {
+ bdrv_unref_child(bs, bs->file);
+ if (s->bitmap) {
+ bdrv_release_dirty_bitmap(s->bitmap);
+ }
+ }
+ qemu_opts_del(opts);
+ return ret;
+}
+
+static void track_close(BlockDriverState *bs)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+ if (s->bitmap) {
+ bdrv_release_dirty_bitmap(s->bitmap);
+ }
+}
+
+static int64_t track_getlength(BlockDriverState *bs)
+{
+ return bdrv_getlength(bs->file->bs);
+}
+
+static int coroutine_fn track_co_preadv(BlockDriverState *bs,
+ uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+ QEMUIOVector local_qiov;
+ int ret;
+
+ /* 'cur_offset' is relative to 'offset', 'local_offset' to image start */
+ uint64_t cur_offset, local_offset;
+ int64_t local_bytes;
+ bool alloc;
+
+ /* a read request can span multiple granularity-sized chunks, and can thus
+ * contain blocks with different allocation status - we could just iterate
+ * granularity-wise, but for better performance use bdrv_dirty_bitmap_next_X
+ * to find the next flip and consider everything up to that in one go */
+ for (cur_offset = 0; cur_offset < bytes; cur_offset += local_bytes) {
+ local_offset = offset + cur_offset;
+ alloc = bdrv_dirty_bitmap_get(s->bitmap, local_offset);
+ if (alloc) {
+ local_bytes = bdrv_dirty_bitmap_next_zero(s->bitmap, local_offset,
+ bytes - cur_offset);
+ } else {
+ local_bytes = bdrv_dirty_bitmap_next_dirty(s->bitmap, local_offset,
+ bytes - cur_offset);
+ }
+
+ /* _bitmap_next_X return is -1 if no end found within limit, otherwise
+ * offset of next flip (to start of image) */
+ local_bytes = local_bytes < 0 ?
+ bytes - cur_offset :
+ local_bytes - local_offset;
+
+ qemu_iovec_init_slice(&local_qiov, qiov, cur_offset, local_bytes);
+
+ if (alloc) {
+ ret = bdrv_co_preadv(bs->file, local_offset, local_bytes,
+ &local_qiov, flags);
+ } else if (bs->backing) {
+ ret = bdrv_co_preadv(bs->backing, local_offset, local_bytes,
+ &local_qiov, flags);
+ } else {
+ ret = qemu_iovec_memset(&local_qiov, cur_offset, 0, local_bytes);
+ }
+
+ if (ret != 0) {
+ break;
+ }
+ }
+
+ return ret;
+}
+
+static int coroutine_fn track_co_pwritev(BlockDriverState *bs,
+ uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
+{
+ return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
+}
+
+static int coroutine_fn track_co_pwrite_zeroes(BlockDriverState *bs,
+ int64_t offset, int count, BdrvRequestFlags flags)
+{
+ return bdrv_co_pwrite_zeroes(bs->file, offset, count, flags);
+}
+
+static int coroutine_fn track_co_pdiscard(BlockDriverState *bs,
+ int64_t offset, int count)
+{
+ return bdrv_co_pdiscard(bs->file, offset, count);
+}
+
+static coroutine_fn int track_co_flush(BlockDriverState *bs)
+{
+ return bdrv_co_flush(bs->file->bs);
+}
+
+static int coroutine_fn track_co_block_status(BlockDriverState *bs,
+ bool want_zero,
+ int64_t offset,
+ int64_t bytes,
+ int64_t *pnum,
+ int64_t *map,
+ BlockDriverState **file)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+
+ bool alloc = bdrv_dirty_bitmap_get(s->bitmap, offset);
+ int64_t next_flipped;
+ if (alloc) {
+ next_flipped = bdrv_dirty_bitmap_next_zero(s->bitmap, offset, bytes);
+ } else {
+ next_flipped = bdrv_dirty_bitmap_next_dirty(s->bitmap, offset, bytes);
+ }
+
+ /* in case not the entire region has the same state, we need to set pnum to
+ * indicate for how many bytes our result is valid */
+ *pnum = next_flipped == -1 ? bytes : next_flipped - offset;
+ *map = offset;
+
+ if (alloc) {
+ *file = bs->file->bs;
+ return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID;
+ } else if (bs->backing) {
+ *file = bs->backing->bs;
+ }
+ return 0;
+}
+
+static void track_child_perm(BlockDriverState *bs, BdrvChild *c,
+ BdrvChildRole role, BlockReopenQueue *reopen_queue,
+ uint64_t perm, uint64_t shared,
+ uint64_t *nperm, uint64_t *nshared)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+
+ *nshared = BLK_PERM_ALL;
+
+ /* in case we're currently dropping ourselves, claim to not use any
+ * permissions at all - which is fine, since from this point on we will
+ * never issue a read or write anymore */
+ if (s->drop_state == DropInProgress) {
+ *nperm = 0;
+ return;
+ }
+
+ if (role & BDRV_CHILD_DATA) {
+ *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
+ } else {
+ /* 'backing' is also a child of our BDS, but we don't expect it to be
+ * writeable, so we only forward 'consistent read' */
+ *nperm = perm & BLK_PERM_CONSISTENT_READ;
+ }
+}
+
+static void track_drop(void *opaque)
+{
+ BlockDriverState *bs = (BlockDriverState*)opaque;
+ BlockDriverState *file = bs->file->bs;
+ BDRVAllocTrackState *s = bs->opaque;
+
+ assert(file);
+
+ /* we rely on the fact that we're not used anywhere else, so let's wait
+ * until we're only used once - in the drive connected to the guest (and one
+ * ref is held by bdrv_ref in track_change_backing_file) */
+ if (bs->refcnt > 2) {
+ aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, opaque);
+ return;
+ }
+ AioContext *aio_context = bdrv_get_aio_context(bs);
+ aio_context_acquire(aio_context);
+
+ bdrv_drained_begin(bs);
+
+ /* now that we're drained, we can safely set 'DropInProgress' */
+ s->drop_state = DropInProgress;
+ bdrv_child_refresh_perms(bs, bs->file, &error_abort);
+
+ bdrv_replace_node(bs, file, &error_abort);
+ bdrv_set_backing_hd(bs, NULL, &error_abort);
+ bdrv_drained_end(bs);
+ bdrv_unref(bs);
+ aio_context_release(aio_context);
+}
+
+static int track_change_backing_file(BlockDriverState *bs,
+ const char *backing_file,
+ const char *backing_fmt)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+ if (s->auto_remove && s->drop_state == DropNone &&
+ backing_file == NULL && backing_fmt == NULL)
+ {
+ /* backing file has been disconnected, there's no longer any use for
+ * this node, so let's remove ourselves from the block graph - we need
+ * to schedule this for later however, since when this function is
+ * called, the blockjob modifying us is probably not done yet and has a
+ * blocker on 'bs' */
+ s->drop_state = DropRequested;
+ bdrv_ref(bs);
+ aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, (void*)bs);
+ }
+
+ return 0;
+}
+
+static BlockDriver bdrv_alloc_track = {
+ .format_name = "alloc-track",
+ .instance_size = sizeof(BDRVAllocTrackState),
+
+ .bdrv_file_open = track_open,
+ .bdrv_close = track_close,
+ .bdrv_getlength = track_getlength,
+ .bdrv_child_perm = track_child_perm,
+ .bdrv_refresh_limits = track_refresh_limits,
+
+ .bdrv_co_pwrite_zeroes = track_co_pwrite_zeroes,
+ .bdrv_co_pwritev = track_co_pwritev,
+ .bdrv_co_preadv = track_co_preadv,
+ .bdrv_co_pdiscard = track_co_pdiscard,
+
+ .bdrv_co_flush = track_co_flush,
+ .bdrv_co_flush_to_disk = track_co_flush,
+
+ .supports_backing = true,
+
+ .bdrv_co_block_status = track_co_block_status,
+ .bdrv_change_backing_file = track_change_backing_file,
+};
+
+static void bdrv_alloc_track_init(void)
+{
+ bdrv_register(&bdrv_alloc_track);
+}
+
+block_init(bdrv_alloc_track_init);
diff --git a/block/meson.build b/block/meson.build
index 574165e577..f56ec7f6bf 100644
--- a/block/meson.build
+++ b/block/meson.build
@@ -2,6 +2,7 @@ block_ss.add(genh)
block_ss.add(files(
'accounting.c',
'aio_task.c',
+ 'alloc-track.c',
'amend.c',
'backup.c',
'backup-dump.c',
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