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 0913a0af39..1dab254517 100644
--- a/block/rbd.c
+++ b/block/rbd.c
@@ -108,12 +108,6 @@ 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,
@@ -1456,111 +1450,6 @@ 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 coroutine_fn qemu_rbd_co_getlength(BlockDriverState *bs)
 {
     BDRVRBDState *s = bs->opaque;
@@ -1796,7 +1685,6 @@ 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,