--- /dev/null
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Fabian Ebner <f.ebner@proxmox.com>
+Date: Tue, 17 May 2022 09:46:02 +0200
+Subject: [PATCH] Revert "block/rbd: implement bdrv_co_block_status"
+
+During backup, bdrv_co_block_status is called for each block copy
+chunk. When RBD is used, the current implementation with
+rbd_diff_iterate2() using whole_object=true takes about linearly more
+time, depending on the image size. Since there are linearly more
+chunks, the slowdown is quadratic, becoming unacceptable for large
+images (starting somewhere between 500-1000 GiB in my testing).
+
+This reverts commit 0347a8fd4c3faaedf119be04c197804be40a384b as a
+stop-gap measure, until it's clear how to make the implemenation
+more efficient.
+
+Upstream bug report:
+https://gitlab.com/qemu-project/qemu/-/issues/1026
+
+Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>
+---
+ block/rbd.c | 112 ----------------------------------------------------
+ 1 file changed, 112 deletions(-)
+
+diff --git a/block/rbd.c b/block/rbd.c
+index a4b8fb482c..3393b06a4e 100644
+--- a/block/rbd.c
++++ b/block/rbd.c
+@@ -97,12 +97,6 @@ typedef struct RBDTask {
+ int64_t ret;
+ } RBDTask;
+
+-typedef struct RBDDiffIterateReq {
+- uint64_t offs;
+- uint64_t bytes;
+- bool exists;
+-} RBDDiffIterateReq;
+-
+ static int qemu_rbd_connect(rados_t *cluster, rados_ioctx_t *io_ctx,
+ BlockdevOptionsRbd *opts, bool cache,
+ const char *keypairs, const char *secretid,
+@@ -1267,111 +1261,6 @@ static ImageInfoSpecific *qemu_rbd_get_specific_info(BlockDriverState *bs,
+ return spec_info;
+ }
+
+-/*
+- * rbd_diff_iterate2 allows to interrupt the exection by returning a negative
+- * value in the callback routine. Choose a value that does not conflict with
+- * an existing exitcode and return it if we want to prematurely stop the
+- * execution because we detected a change in the allocation status.
+- */
+-#define QEMU_RBD_EXIT_DIFF_ITERATE2 -9000
+-
+-static int qemu_rbd_diff_iterate_cb(uint64_t offs, size_t len,
+- int exists, void *opaque)
+-{
+- RBDDiffIterateReq *req = opaque;
+-
+- assert(req->offs + req->bytes <= offs);
+- /*
+- * we do not diff against a snapshot so we should never receive a callback
+- * for a hole.
+- */
+- assert(exists);
+-
+- if (!req->exists && offs > req->offs) {
+- /*
+- * we started in an unallocated area and hit the first allocated
+- * block. req->bytes must be set to the length of the unallocated area
+- * before the allocated area. stop further processing.
+- */
+- req->bytes = offs - req->offs;
+- return QEMU_RBD_EXIT_DIFF_ITERATE2;
+- }
+-
+- if (req->exists && offs > req->offs + req->bytes) {
+- /*
+- * we started in an allocated area and jumped over an unallocated area,
+- * req->bytes contains the length of the allocated area before the
+- * unallocated area. stop further processing.
+- */
+- return QEMU_RBD_EXIT_DIFF_ITERATE2;
+- }
+-
+- req->bytes += len;
+- req->exists = true;
+-
+- return 0;
+-}
+-
+-static int coroutine_fn qemu_rbd_co_block_status(BlockDriverState *bs,
+- bool want_zero, int64_t offset,
+- int64_t bytes, int64_t *pnum,
+- int64_t *map,
+- BlockDriverState **file)
+-{
+- BDRVRBDState *s = bs->opaque;
+- int status, r;
+- RBDDiffIterateReq req = { .offs = offset };
+- uint64_t features, flags;
+-
+- assert(offset + bytes <= s->image_size);
+-
+- /* default to all sectors allocated */
+- status = BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID;
+- *map = offset;
+- *file = bs;
+- *pnum = bytes;
+-
+- /* check if RBD image supports fast-diff */
+- r = rbd_get_features(s->image, &features);
+- if (r < 0) {
+- return status;
+- }
+- if (!(features & RBD_FEATURE_FAST_DIFF)) {
+- return status;
+- }
+-
+- /* check if RBD fast-diff result is valid */
+- r = rbd_get_flags(s->image, &flags);
+- if (r < 0) {
+- return status;
+- }
+- if (flags & RBD_FLAG_FAST_DIFF_INVALID) {
+- return status;
+- }
+-
+- r = rbd_diff_iterate2(s->image, NULL, offset, bytes, true, true,
+- qemu_rbd_diff_iterate_cb, &req);
+- if (r < 0 && r != QEMU_RBD_EXIT_DIFF_ITERATE2) {
+- return status;
+- }
+- assert(req.bytes <= bytes);
+- if (!req.exists) {
+- if (r == 0) {
+- /*
+- * rbd_diff_iterate2 does not invoke callbacks for unallocated
+- * areas. This here catches the case where no callback was
+- * invoked at all (req.bytes == 0).
+- */
+- assert(req.bytes == 0);
+- req.bytes = bytes;
+- }
+- status = BDRV_BLOCK_ZERO | BDRV_BLOCK_OFFSET_VALID;
+- }
+-
+- *pnum = req.bytes;
+- return status;
+-}
+-
+ static int64_t qemu_rbd_getlength(BlockDriverState *bs)
+ {
+ BDRVRBDState *s = bs->opaque;
+@@ -1607,7 +1496,6 @@ static BlockDriver bdrv_rbd = {
+ #ifdef LIBRBD_SUPPORTS_WRITE_ZEROES
+ .bdrv_co_pwrite_zeroes = qemu_rbd_co_pwrite_zeroes,
+ #endif
+- .bdrv_co_block_status = qemu_rbd_co_block_status,
+
+ .bdrv_snapshot_create = qemu_rbd_snap_create,
+ .bdrv_snapshot_delete = qemu_rbd_snap_remove,