fix patch for accepting NULL qiov when padding

[pve-qemu.git] / debian / patches / pve / 0038-block-io-accept-NULL-qiov-in-bdrv_pad_request.patch

From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Stefan Reiter <s.reiter@proxmox.com>
Date: Tue, 2 Mar 2021 16:11:54 +0100
Subject: [PATCH] block/io: accept NULL qiov in bdrv_pad_request

Some operations, e.g. block-stream, perform reads while discarding the
results (only copy-on-read matters). In this case they will pass NULL as
the target QEMUIOVector, which will however trip bdrv_pad_request, since
it wants to extend its passed vector.

If there is no qiov, no operation can be done with it, but the bytes
and offset still need to be updated, so the subsequent aligned read
will actually be aligned and not run into an assertion failure.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
[FE: do update bytes and offset in any case]
Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
---
 block/io.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

diff --git a/block/io.c b/block/io.c
index 83d1b1dfdc..e927881e40 100644
--- a/block/io.c
+++ b/block/io.c
@@ -1723,22 +1723,25 @@ static int bdrv_pad_request(BlockDriverState *bs,
         return 0;
     }
 
-    sliced_iov = qemu_iovec_slice(*qiov, *qiov_offset, *bytes,
-                                  &sliced_head, &sliced_tail,
-                                  &sliced_niov);
-
-    /* Guaranteed by bdrv_check_request32() */
-    assert(*bytes <= SIZE_MAX);
-    ret = bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov,
-                                  sliced_head, *bytes);
-    if (ret < 0) {
-        bdrv_padding_finalize(pad);
-        return ret;
+    if (qiov && *qiov) {
+        sliced_iov = qemu_iovec_slice(*qiov, *qiov_offset, *bytes,
+                                      &sliced_head, &sliced_tail,
+                                      &sliced_niov);
+
+        /* Guaranteed by bdrv_check_request32() */
+        assert(*bytes <= SIZE_MAX);
+        ret = bdrv_create_padded_qiov(bs, pad, sliced_iov, sliced_niov,
+                                      sliced_head, *bytes);
+        if (ret < 0) {
+            bdrv_padding_finalize(pad);
+            return ret;
+        }
+        *qiov = &pad->local_qiov;
+        *qiov_offset = 0;
     }
+
     *bytes += pad->head + pad->tail;
     *offset -= pad->head;
-    *qiov = &pad->local_qiov;
-    *qiov_offset = 0;
     if (padded) {
         *padded = true;
     }