[PATCH v2 1/2] block/export: Conditionally ignore set-context error

[Max Reitz <mreitz@redhat.com>]

When invoking block-export-add with some iothread and
fixed-iothread=false, and changing the node's iothread fails, the error
is supposed to be ignored.

However, it is still stored in *errp, which is wrong.  If a second error
occurs, the "*errp must be NULL" assertion in error_setv() fails:

  qemu-system-x86_64: ../util/error.c:59: error_setv: Assertion
  `*errp == NULL' failed.

So if fixed-iothread=false, we should ignore the error by passing NULL
to bdrv_try_set_aio_context().

Fixes: f51d23c80af73c95e0ce703ad06a300f1b3d63ef
       ("block/export: add iothread and fixed-iothread options")
Signed-off-by: Max Reitz <mreitz@redhat.com>
---
 block/export/export.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/block/export/export.c b/block/export/export.c
index fec7d9f738..6d3b9964c8 100644
--- a/block/export/export.c
+++ b/block/export/export.c
@@ -111,6 +111,7 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
     if (export->has_iothread) {
         IOThread *iothread;
         AioContext *new_ctx;
+        Error **set_context_errp;
 
         iothread = iothread_by_id(export->iothread);
         if (!iothread) {
@@ -120,7 +121,9 @@ BlockExport *blk_exp_add(BlockExportOptions *export, Error **errp)
 
         new_ctx = iothread_get_aio_context(iothread);
 
-        ret = bdrv_try_set_aio_context(bs, new_ctx, errp);
+        /* Ignore errors with fixed-iothread=false */
+        set_context_errp = fixed_iothread ? errp : NULL;
+        ret = bdrv_try_set_aio_context(bs, new_ctx, set_context_errp);
         if (ret == 0) {
             aio_context_release(ctx);
             aio_context_acquire(new_ctx);
-- 
2.31.1