Re: [PATCH V2 for-6.2 2/2] block/rbd: workaround for ceph issue #53784

[Stefano Garzarella <sgarzare@redhat.com>]

On Thu, Jan 13, 2022 at 03:44:26PM +0100, Peter Lieven wrote:
>librbd had a bug until early 2022 that affected all versions of ceph that
>supported fast-diff. This bug results in reporting of incorrect offsets
>if the offset parameter to rbd_diff_iterate2 is not object aligned.
>
>This patch works around this bug for pre Quincy versions of librbd.
>

I'm not sure, but maybe we could add the fixes tag also to this patch, 
since without this workaround we can have issues with buggy librbd.

Fixes: 0347a8fd4c3faaedf119be04c197804be40a384b

>Cc: qemu-stable@nongnu.org
>Signed-off-by: Peter Lieven <pl@kamp.de>
>---
> block/rbd.c | 42 ++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 40 insertions(+), 2 deletions(-)

Tested-by: Stefano Garzarella <sgarzare@redhat.com>


>
>diff --git a/block/rbd.c b/block/rbd.c
>index 20bb896c4a..d174d51659 100644
>--- a/block/rbd.c
>+++ b/block/rbd.c
>@@ -1320,6 +1320,7 @@ static int coroutine_fn qemu_rbd_co_block_status(BlockDriverState *bs,
>     int status, r;
>     RBDDiffIterateReq req = { .offs = offset };
>     uint64_t features, flags;
>+    uint64_t head = 0;
>
>     assert(offset + bytes <= s->image_size);
>
>@@ -1347,7 +1348,43 @@ static int coroutine_fn qemu_rbd_co_block_status(BlockDriverState *bs,
>         return status;
>     }
>
>-    r = rbd_diff_iterate2(s->image, NULL, offset, bytes, true, true,
>+#if LIBRBD_VERSION_CODE < LIBRBD_VERSION(1, 17, 0)
>+    /*
>+     * librbd had a bug until early 2022 that affected all versions of ceph that
>+     * supported fast-diff. This bug results in reporting of incorrect offsets
>+     * if the offset parameter to rbd_diff_iterate2 is not object aligned.
>+     * Work around this bug by rounding down the offset to object boundaries.
>+     * This is OK because we call rbd_diff_iterate2 with whole_object = true.
>+     * However, this workaround only works for non cloned images with default
>+     * striping.
>+     *
>+     * See: https://tracker.ceph.com/issues/53784
>+     */
>+
>+    /*  check if RBD image has non-default striping enabled */
>+    if (features & RBD_FEATURE_STRIPINGV2) {
>+        return status;
>+    }
>+
>+#pragma GCC diagnostic push
>+#pragma GCC diagnostic ignored "-Wdeprecated-declarations"
>+    /*
>+     * check if RBD image is a clone (= has a parent).
>+     *
>+     * rbd_get_parent_info is deprecated from Nautilus onwards, but the
>+     * replacement rbd_get_parent is not present in Luminous and Mimic.
>+     */
>+    if (rbd_get_parent_info(s->image, NULL, 0, NULL, 0, NULL, 0) != -ENOENT) {
>+        return status;
>+    }
>+#pragma GCC diagnostic pop
>+
>+    head = req.offs & (s->object_size - 1);
>+    req.offs -= head;
>+    bytes += head;
>+#endif
>+
>+    r = rbd_diff_iterate2(s->image, NULL, req.offs, bytes, true, true,
>                           qemu_rbd_diff_iterate_cb, &req);
>     if (r < 0 && r != QEMU_RBD_EXIT_DIFF_ITERATE2) {
>         return status;
>@@ -1366,7 +1403,8 @@ static int coroutine_fn qemu_rbd_co_block_status(BlockDriverState *bs,
>         status = BDRV_BLOCK_ZERO | BDRV_BLOCK_OFFSET_VALID;
>     }
>
>-    *pnum = req.bytes;
>+    assert(req.bytes > head);
>+    *pnum = req.bytes - head;
>     return status;
> }
>
>-- 
>2.25.1
>
>
>