0a88214b72
as we're in a coroutine here too Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
395 lines
13 KiB
Diff
395 lines
13 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Stefan Reiter <s.reiter@proxmox.com>
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Date: Mon, 7 Dec 2020 15:21:03 +0100
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Subject: [PATCH] block: add alloc-track driver
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Add a new filter node 'alloc-track', which seperates reads and writes to
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different children, thus allowing to put a backing image behind any
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blockdev (regardless of driver support). Since we can't detect any
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pre-allocated blocks, we can only track new writes, hence the write
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target ('file') for this node must always be empty.
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Intended use case is for live restoring, i.e. add a backup image as a
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block device into a VM, then put an alloc-track on the restore target
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and set the backup as backing. With this, one can use a regular
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'block-stream' to restore the image, while the VM can already run in the
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background. Copy-on-read will help make progress as the VM reads as
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well.
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This only worked if the target supports backing images, so up until now
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only for qcow2, with alloc-track any driver for the target can be used.
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If 'auto-remove' is set, alloc-track will automatically detach itself
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once the backing image is removed. It will be replaced by 'file'.
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Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
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---
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block/alloc-track.c | 342 ++++++++++++++++++++++++++++++++++++++++++++
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block/meson.build | 1 +
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2 files changed, 343 insertions(+)
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create mode 100644 block/alloc-track.c
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diff --git a/block/alloc-track.c b/block/alloc-track.c
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new file mode 100644
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index 0000000000..b579380279
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--- /dev/null
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+++ b/block/alloc-track.c
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@@ -0,0 +1,345 @@
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+/*
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+ * Node to allow backing images to be applied to any node. Assumes a blank
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+ * image to begin with, only new writes are tracked as allocated, thus this
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+ * must never be put on a node that already contains data.
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+ *
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+ * Copyright (c) 2020 Proxmox Server Solutions GmbH
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+ * Copyright (c) 2020 Stefan Reiter <s.reiter@proxmox.com>
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+ *
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+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
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+ * See the COPYING file in the top-level directory.
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+ */
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+
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+#include "qemu/osdep.h"
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+#include "qapi/error.h"
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+#include "block/block_int.h"
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+#include "qapi/qmp/qdict.h"
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+#include "qapi/qmp/qstring.h"
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+#include "qemu/cutils.h"
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+#include "qemu/option.h"
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+#include "qemu/module.h"
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+#include "sysemu/block-backend.h"
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+
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+#define TRACK_OPT_AUTO_REMOVE "auto-remove"
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+
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+typedef enum DropState {
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+ DropNone,
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+ DropRequested,
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+ DropInProgress,
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+} DropState;
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+
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+typedef struct {
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+ BdrvDirtyBitmap *bitmap;
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+ DropState drop_state;
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+ bool auto_remove;
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+} BDRVAllocTrackState;
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+
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+static QemuOptsList runtime_opts = {
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+ .name = "alloc-track",
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+ .head = QTAILQ_HEAD_INITIALIZER(runtime_opts.head),
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+ .desc = {
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+ {
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+ .name = TRACK_OPT_AUTO_REMOVE,
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+ .type = QEMU_OPT_BOOL,
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+ .help = "automatically replace this node with 'file' when 'backing'"
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+ "is detached",
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+ },
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+ { /* end of list */ }
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+ },
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+};
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+
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+static void track_refresh_limits(BlockDriverState *bs, Error **errp)
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+{
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+ BlockDriverInfo bdi;
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+
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+ if (!bs->file) {
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+ return;
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+ }
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+
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+ /* always use alignment from underlying write device so RMW cycle for
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+ * bdrv_pwritev reads data from our backing via track_co_preadv (no partial
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+ * cluster allocation in 'file') */
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+ bdrv_get_info(bs->file->bs, &bdi);
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+ bs->bl.request_alignment = MAX(bs->file->bs->bl.request_alignment,
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+ MAX(bdi.cluster_size, BDRV_SECTOR_SIZE));
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+}
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+
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+static int track_open(BlockDriverState *bs, QDict *options, int flags,
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+ Error **errp)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+ QemuOpts *opts;
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+ Error *local_err = NULL;
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+ int ret = 0;
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+
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+ opts = qemu_opts_create(&runtime_opts, NULL, 0, &error_abort);
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+ qemu_opts_absorb_qdict(opts, options, &local_err);
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+ if (local_err) {
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+ error_propagate(errp, local_err);
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+ ret = -EINVAL;
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+ goto fail;
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+ }
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+
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+ s->auto_remove = qemu_opt_get_bool(opts, TRACK_OPT_AUTO_REMOVE, false);
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+
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+ /* open the target (write) node, backing will be attached by block layer */
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+ bs->file = bdrv_open_child(NULL, options, "file", bs, &child_of_bds,
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+ BDRV_CHILD_DATA | BDRV_CHILD_METADATA, false,
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+ &local_err);
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+ if (local_err) {
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+ ret = -EINVAL;
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+ error_propagate(errp, local_err);
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+ goto fail;
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+ }
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+
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+ track_refresh_limits(bs, errp);
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+ uint64_t gran = bs->bl.request_alignment;
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+ s->bitmap = bdrv_create_dirty_bitmap(bs->file->bs, gran, NULL, &local_err);
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+ if (local_err) {
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+ ret = -EIO;
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+ error_propagate(errp, local_err);
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+ goto fail;
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+ }
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+
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+ s->drop_state = DropNone;
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+
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+fail:
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+ if (ret < 0) {
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+ bdrv_unref_child(bs, bs->file);
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+ if (s->bitmap) {
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+ bdrv_release_dirty_bitmap(s->bitmap);
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+ }
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+ }
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+ qemu_opts_del(opts);
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+ return ret;
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+}
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+
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+static void track_close(BlockDriverState *bs)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+ if (s->bitmap) {
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+ bdrv_release_dirty_bitmap(s->bitmap);
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+ }
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+}
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+
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+static int64_t track_getlength(BlockDriverState *bs)
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+{
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+ return bdrv_getlength(bs->file->bs);
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+}
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+
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+static int coroutine_fn track_co_preadv(BlockDriverState *bs,
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+ uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+ QEMUIOVector local_qiov;
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+ int ret;
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+
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+ /* 'cur_offset' is relative to 'offset', 'local_offset' to image start */
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+ uint64_t cur_offset, local_offset;
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+ int64_t local_bytes;
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+ bool alloc;
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+
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+ /* a read request can span multiple granularity-sized chunks, and can thus
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+ * contain blocks with different allocation status - we could just iterate
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+ * granularity-wise, but for better performance use bdrv_dirty_bitmap_next_X
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+ * to find the next flip and consider everything up to that in one go */
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+ for (cur_offset = 0; cur_offset < bytes; cur_offset += local_bytes) {
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+ local_offset = offset + cur_offset;
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+ alloc = bdrv_dirty_bitmap_get(s->bitmap, local_offset);
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+ if (alloc) {
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+ local_bytes = bdrv_dirty_bitmap_next_zero(s->bitmap, local_offset,
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+ bytes - cur_offset);
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+ } else {
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+ local_bytes = bdrv_dirty_bitmap_next_dirty(s->bitmap, local_offset,
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+ bytes - cur_offset);
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+ }
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+
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+ /* _bitmap_next_X return is -1 if no end found within limit, otherwise
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+ * offset of next flip (to start of image) */
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+ local_bytes = local_bytes < 0 ?
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+ bytes - cur_offset :
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+ local_bytes - local_offset;
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+
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+ qemu_iovec_init_slice(&local_qiov, qiov, cur_offset, local_bytes);
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+
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+ if (alloc) {
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+ ret = bdrv_co_preadv(bs->file, local_offset, local_bytes,
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+ &local_qiov, flags);
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+ } else if (bs->backing) {
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+ ret = bdrv_co_preadv(bs->backing, local_offset, local_bytes,
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+ &local_qiov, flags);
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+ } else {
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+ ret = qemu_iovec_memset(&local_qiov, cur_offset, 0, local_bytes);
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+ }
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+
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+ if (ret != 0) {
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+ break;
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+ }
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+ }
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+
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+ return ret;
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+}
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+
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+static int coroutine_fn track_co_pwritev(BlockDriverState *bs,
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+ uint64_t offset, uint64_t bytes, QEMUIOVector *qiov, int flags)
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+{
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+ return bdrv_co_pwritev(bs->file, offset, bytes, qiov, flags);
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+}
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+
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+static int coroutine_fn track_co_pwrite_zeroes(BlockDriverState *bs,
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+ int64_t offset, int count, BdrvRequestFlags flags)
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+{
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+ return bdrv_co_pwrite_zeroes(bs->file, offset, count, flags);
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+}
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+
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+static int coroutine_fn track_co_pdiscard(BlockDriverState *bs,
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+ int64_t offset, int count)
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+{
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+ return bdrv_co_pdiscard(bs->file, offset, count);
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+}
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+
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+static coroutine_fn int track_co_flush(BlockDriverState *bs)
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+{
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+ return bdrv_co_flush(bs->file->bs);
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+}
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+
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+static int coroutine_fn track_co_block_status(BlockDriverState *bs,
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+ bool want_zero,
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+ int64_t offset,
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+ int64_t bytes,
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+ int64_t *pnum,
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+ int64_t *map,
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+ BlockDriverState **file)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+
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+ bool alloc = bdrv_dirty_bitmap_get(s->bitmap, offset);
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+ int64_t next_flipped;
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+ if (alloc) {
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+ next_flipped = bdrv_dirty_bitmap_next_zero(s->bitmap, offset, bytes);
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+ } else {
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+ next_flipped = bdrv_dirty_bitmap_next_dirty(s->bitmap, offset, bytes);
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+ }
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+
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+ /* in case not the entire region has the same state, we need to set pnum to
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+ * indicate for how many bytes our result is valid */
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+ *pnum = next_flipped == -1 ? bytes : next_flipped - offset;
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+ *map = offset;
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+
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+ if (alloc) {
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+ *file = bs->file->bs;
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+ return BDRV_BLOCK_RAW | BDRV_BLOCK_OFFSET_VALID;
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+ } else if (bs->backing) {
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+ *file = bs->backing->bs;
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+ }
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+ return 0;
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+}
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+
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+static void track_child_perm(BlockDriverState *bs, BdrvChild *c,
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+ BdrvChildRole role, BlockReopenQueue *reopen_queue,
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+ uint64_t perm, uint64_t shared,
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+ uint64_t *nperm, uint64_t *nshared)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+
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+ *nshared = BLK_PERM_ALL;
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+
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+ /* in case we're currently dropping ourselves, claim to not use any
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+ * permissions at all - which is fine, since from this point on we will
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+ * never issue a read or write anymore */
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+ if (s->drop_state == DropInProgress) {
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+ *nperm = 0;
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+ return;
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+ }
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+
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+ if (role & BDRV_CHILD_DATA) {
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+ *nperm = perm & DEFAULT_PERM_PASSTHROUGH;
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+ } else {
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+ /* 'backing' is also a child of our BDS, but we don't expect it to be
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+ * writeable, so we only forward 'consistent read' */
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+ *nperm = perm & BLK_PERM_CONSISTENT_READ;
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+ }
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+}
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+
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+static void track_drop(void *opaque)
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+{
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+ BlockDriverState *bs = (BlockDriverState*)opaque;
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+ BlockDriverState *file = bs->file->bs;
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+ BDRVAllocTrackState *s = bs->opaque;
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+
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+ assert(file);
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+
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+ /* we rely on the fact that we're not used anywhere else, so let's wait
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+ * until we're only used once - in the drive connected to the guest (and one
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+ * ref is held by bdrv_ref in track_change_backing_file) */
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+ if (bs->refcnt > 2) {
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+ aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, opaque);
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+ return;
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+ }
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+ AioContext *aio_context = bdrv_get_aio_context(bs);
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+ aio_context_acquire(aio_context);
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+
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+ bdrv_drained_begin(bs);
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+
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+ /* now that we're drained, we can safely set 'DropInProgress' */
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+ s->drop_state = DropInProgress;
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+ bdrv_child_refresh_perms(bs, bs->file, &error_abort);
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+
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+ bdrv_replace_node(bs, file, &error_abort);
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+ bdrv_set_backing_hd(bs, NULL, &error_abort);
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+ bdrv_drained_end(bs);
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+ bdrv_unref(bs);
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+ aio_context_release(aio_context);
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+}
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+
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+static int track_change_backing_file(BlockDriverState *bs,
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+ const char *backing_file,
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+ const char *backing_fmt)
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+{
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+ BDRVAllocTrackState *s = bs->opaque;
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+ if (s->auto_remove && s->drop_state == DropNone &&
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+ backing_file == NULL && backing_fmt == NULL)
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+ {
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+ /* backing file has been disconnected, there's no longer any use for
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+ * this node, so let's remove ourselves from the block graph - we need
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+ * to schedule this for later however, since when this function is
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+ * called, the blockjob modifying us is probably not done yet and has a
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+ * blocker on 'bs' */
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+ s->drop_state = DropRequested;
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+ bdrv_ref(bs);
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+ aio_bh_schedule_oneshot(qemu_get_aio_context(), track_drop, (void*)bs);
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+ }
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+
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+ return 0;
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+}
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+
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+static BlockDriver bdrv_alloc_track = {
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+ .format_name = "alloc-track",
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+ .instance_size = sizeof(BDRVAllocTrackState),
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+
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+ .bdrv_file_open = track_open,
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+ .bdrv_close = track_close,
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+ .bdrv_getlength = track_getlength,
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+ .bdrv_child_perm = track_child_perm,
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+ .bdrv_refresh_limits = track_refresh_limits,
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+
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+ .bdrv_co_pwrite_zeroes = track_co_pwrite_zeroes,
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+ .bdrv_co_pwritev = track_co_pwritev,
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+ .bdrv_co_preadv = track_co_preadv,
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+ .bdrv_co_pdiscard = track_co_pdiscard,
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+
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+ .bdrv_co_flush = track_co_flush,
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+ .bdrv_co_flush_to_disk = track_co_flush,
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+
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+ .supports_backing = true,
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+
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+ .bdrv_co_block_status = track_co_block_status,
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+ .bdrv_change_backing_file = track_change_backing_file,
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+};
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+
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+static void bdrv_alloc_track_init(void)
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+{
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+ bdrv_register(&bdrv_alloc_track);
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+}
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+
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+block_init(bdrv_alloc_track_init);
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diff --git a/block/meson.build b/block/meson.build
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index a070060e53..e387990764 100644
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--- a/block/meson.build
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+++ b/block/meson.build
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@@ -2,6 +2,7 @@ block_ss.add(genh)
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block_ss.add(files(
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'accounting.c',
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'aio_task.c',
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+ 'alloc-track.c',
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'amend.c',
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'backup.c',
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'backup-dump.c',
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