migration: Add error_desc for file channel errors

Currently, there is no information about error if outgoing migration was failed
because of file channel errors.
Example (QMP session):
-> { "execute": "migrate", "arguments": { "uri": "exec:head -c 1" }}
<- { "return": {} }
...
-> { "execute": "query-migrate" }
<- { "return": { "status": "failed" }} // There is not error's description

And even in the QEMU's output there is nothing.

This patch
1) Adds errp for the most of QEMUFileOps
2) Adds qemu_file_get_error_obj/qemu_file_set_error_obj
3) And finally using of qemu_file_get_error_obj in migration.c

And now, the status for the mentioned fail will be:
-> { "execute": "query-migrate" }
<- { "return": { "status": "failed",
                 "error-desc": "Unable to write to command: Broken pipe" }}

Signed-off-by: Yury Kotov <yury-kotov@yandex-team.ru>
Message-Id: <20190422103420.15686-1-yury-kotov@yandex-team.ru>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 3 insertions, 3 deletions

diff --git a/migration/savevm.c b/migration/savevm.c
index 79ed44d475..a2a5f89b75 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -124,7 +124,7 @@ static struct mig_cmd_args {
 /* savevm/loadvm support */
 
 static ssize_t block_writev_buffer(void *opaque, struct iovec *iov, int iovcnt,
-                                   int64_t pos)
+                                   int64_t pos, Error **errp)
 {
     int ret;
     QEMUIOVector qiov;
@@ -139,12 +139,12 @@ static ssize_t block_writev_buffer(void *opaque, struct iovec *iov, int iovcnt,
 }
 
 static ssize_t block_get_buffer(void *opaque, uint8_t *buf, int64_t pos,
-                                size_t size)
+                                size_t size, Error **errp)
 {
     return bdrv_load_vmstate(opaque, buf, pos, size);
 }
 
-static int bdrv_fclose(void *opaque)
+static int bdrv_fclose(void *opaque, Error **errp)
 {
     return bdrv_flush(opaque);
 }