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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.
Replacing the node cannot be done in the
track_co_change_backing_file() callback, because replacing a node
cannot happen in a coroutine and requires the block graph lock
exclusively. Could either become a special option for the stream job,
or maybe the upcoming blockdev-replace QMP command can be used in the
future.
Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
[FE: adapt to changed function signatures
make error return value consistent with QEMU
avoid premature break during read
adhere to block graph lock requirements]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
block/alloc-track.c | 366 ++++++++++++++++++++++++++++++++++++++++++++
block/meson.build | 1 +
block/stream.c | 34 ++++
3 files changed, 401 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..b9f8ea9137
--- /dev/null
+++ b/block/alloc-track.c
@@ -0,0 +1,366 @@
+/*
+ * 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 "block/dirty-bitmap.h"
+#include "block/graph-lock.h"
+#include "qapi/qmp/qdict.h"
+#include "qapi/qmp/qstring.h"
+#include "qemu/cutils.h"
+#include "qemu/error-report.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,
+ DropInProgress,
+} DropState;
+
+typedef struct {
+ BdrvDirtyBitmap *bitmap;
+ uint64_t granularity;
+ 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 GRAPH_RDLOCK
+track_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+
+ 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. Also use at
+ * least the bitmap granularity.
+ */
+ bs->bl.request_alignment = MAX(bs->file->bs->bl.request_alignment,
+ s->granularity);
+}
+
+static int track_open(BlockDriverState *bs, QDict *options, int flags,
+ Error **errp)
+{
+ BDRVAllocTrackState *s = bs->opaque;
+ BdrvChild *file = NULL;
+ 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 */
+ file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
+ BDRV_CHILD_DATA | BDRV_CHILD_METADATA, false,
+ &local_err);
+ bdrv_graph_wrlock();
+ bs->file = file;
+ bdrv_graph_wrunlock();
+ if (local_err) {
+ ret = -EINVAL;
+ error_propagate(errp, local_err);
+ goto fail;
+ }
+
+ bdrv_graph_rdlock_main_loop();
+ BlockDriverInfo bdi = {0};
+ ret = bdrv_get_info(bs->file->bs, &bdi);
+ if (ret < 0) {
+ /*
+ * Not a hard failure. Worst that can happen is partial cluster
+ * allocation in the write target. However, the driver here returns its
+ * allocation status based on the dirty bitmap, so any other data that
+ * maps to such a cluster will still be copied later by a stream job (or
+ * during writes to that cluster).
+ */
+ warn_report("alloc-track: unable to query cluster size for write target: %s",
+ strerror(ret));
+ }
+ ret = 0;
+ /*
+ * Always consider alignment from underlying write device so RMW cycle for
+ * bdrv_pwritev reads data from our backing via track_co_preadv. Also try to
+ * avoid partial cluster allocation in the write target by considering the
+ * cluster size.
+ */
+ s->granularity = MAX(bs->file->bs->bl.request_alignment,
+ MAX(bdi.cluster_size, BDRV_SECTOR_SIZE));
+ track_refresh_limits(bs, errp);
+ s->bitmap = bdrv_create_dirty_bitmap(bs->file->bs, s->granularity, NULL,
+ &local_err);
+ bdrv_graph_rdunlock_main_loop();
+ if (local_err) {
+ ret = -EIO;
+ error_propagate(errp, local_err);
+ goto fail;
+ }
+
+ s->drop_state = DropNone;
+
+fail:
+ if (ret < 0) {
+ bdrv_graph_wrlock();
+ bdrv_unref_child(bs, bs->file);
+ bdrv_graph_wrunlock();
+ 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 coroutine_fn int64_t GRAPH_RDLOCK
+track_co_getlength(BlockDriverState *bs)
+{
+ return bdrv_co_getlength(bs->file->bs);
+}
+
+static int coroutine_fn GRAPH_RDLOCK
+track_co_preadv(BlockDriverState *bs, int64_t offset, int64_t bytes,
+ QEMUIOVector *qiov, BdrvRequestFlags 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;
+
+ if (offset < 0 || bytes < 0) {
+ fprintf(stderr, "unexpected negative 'offset' or 'bytes' value!\n");
+ return -EIO;
+ }
+
+ /* 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 {
+ qemu_iovec_memset(&local_qiov, cur_offset, 0, local_bytes);
+ ret = 0;
+ }
+
+ if (ret != 0) {
+ break;
+ }
+ }
+
+ return ret;
+}
+
+static int coroutine_fn GRAPH_RDLOCK
+track_co_pwritev(BlockDriverState *bs, int64_t offset, int64_t bytes,
+ QEMUIOVector *qiov, BdrvRequestFlags flags)
+{
+ return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
+}
+
+static int coroutine_fn GRAPH_RDLOCK
+track_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int64_t bytes,
+ BdrvRequestFlags flags)
+{
+ return bdrv_co_pwrite_zeroes(bs->file, offset, bytes, flags);
+}
+
+static int coroutine_fn GRAPH_RDLOCK
+track_co_pdiscard(BlockDriverState *bs, int64_t offset, int64_t bytes)
+{
+ return bdrv_co_pdiscard(bs->file, offset, bytes);
+}
+
+static coroutine_fn int GRAPH_RDLOCK
+track_co_flush(BlockDriverState *bs)
+{
+ return bdrv_co_flush(bs->file->bs);
+}
+
+static int coroutine_fn GRAPH_RDLOCK
+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 GRAPH_RDLOCK
+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 int coroutine_fn GRAPH_RDLOCK
+track_co_change_backing_file(BlockDriverState *bs, const char *backing_file,
+ const char *backing_fmt)
+{
+ /*
+ * Note that the actual backing file graph change is already done in the
+ * stream job itself with bdrv_set_backing_hd_drained(), so no need to
+ * actually do anything here. But still needs to be implemented, to make
+ * our caller (i.e. bdrv_co_change_backing_file() do the right thing).
+ *
+ * FIXME
+ * We'd like to auto-remove ourselves from the block graph, but it cannot
+ * be done from a coroutine. Currently done in the stream job, where it
+ * kinda fits better, but in the long-term, a special parameter would be
+ * nice (or done via qemu-server via upcoming blockdev-replace QMP command).
+ */
+ if (backing_file == NULL) {
+ BDRVAllocTrackState *s = bs->opaque;
+ bdrv_drained_begin(bs);
+ s->drop_state = DropInProgress;
+ bdrv_child_refresh_perms(bs, bs->file, &error_abort);
+ bdrv_drained_end(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_co_getlength = track_co_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_co_change_backing_file = track_co_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 1945e04eeb..2873f3a25a 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',
diff --git a/block/stream.c b/block/stream.c
index d2da83ae7c..f941cba14e 100644
--- a/block/stream.c
+++ b/block/stream.c
@@ -120,6 +120,40 @@ static int stream_prepare(Job *job)
ret = -EPERM;
goto out;
}
+
+ /*
+ * This cannot be done in the co_change_backing_file callback, because
+ * bdrv_replace_node() cannot be done in a coroutine. The latter also
+ * requires the graph lock exclusively. Only required for the
+ * alloc-track driver.
+ *
+ * The long-term plan is to either have an explicit parameter for the
+ * stream job or use the upcoming blockdev-replace QMP command.
+ */
+ if (base_id == NULL && strcmp(unfiltered_bs->drv->format_name, "alloc-track") == 0) {
+ BlockDriverState *file_bs;
+
+ bdrv_graph_rdlock_main_loop();
+ file_bs = unfiltered_bs->file->bs;
+ bdrv_graph_rdunlock_main_loop();
+
+ bdrv_ref(unfiltered_bs); // unrefed by bdrv_replace_node()
+ bdrv_drained_begin(file_bs);
+ bdrv_graph_wrlock();
+
+ bdrv_replace_node(unfiltered_bs, file_bs, &local_err);
+
+ bdrv_graph_wrunlock();
+ bdrv_drained_end(file_bs);
+ bdrv_unref(unfiltered_bs);
+
+ if (local_err) {
+ error_prepend(&local_err, "failed to replace alloc-track node: ");
+ error_report_err(local_err);
+ ret = -EPERM;
+ goto out;
+ }
+ }
}
out:
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