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, 51 insertions, 12 deletions

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 0431585502..c04a7a891b 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -28,6 +28,7 @@
 #include "migration.h"
 #include "qemu-file.h"
 #include "trace.h"
+#include "qapi/error.h"
 
 #define IO_BUF_SIZE 32768
 #define MAX_IOV_SIZE MIN(IOV_MAX, 64)
@@ -51,6 +52,7 @@ struct QEMUFile {
     unsigned int iovcnt;
 
     int last_error;
+    Error *last_error_obj;
 };
 
 /*
@@ -62,7 +64,7 @@ int qemu_file_shutdown(QEMUFile *f)
     if (!f->ops->shut_down) {
         return -ENOSYS;
     }
-    return f->ops->shut_down(f->opaque, true, true);
+    return f->ops->shut_down(f->opaque, true, true, NULL);
 }
 
 /*
@@ -107,24 +109,55 @@ void qemu_file_set_hooks(QEMUFile *f, const QEMUFileHooks *hooks)
 }
 
 /*
- * Get last error for stream f
+ * Get last error for stream f with optional Error*
  *
  * Return negative error value if there has been an error on previous
  * operations, return 0 if no error happened.
+ * Optional, it returns Error* in errp, but it may be NULL even if return value
+ * is not 0.
  *
  */
-int qemu_file_get_error(QEMUFile *f)
+int qemu_file_get_error_obj(QEMUFile *f, Error **errp)
 {
+    if (errp) {
+        *errp = f->last_error_obj ? error_copy(f->last_error_obj) : NULL;
+    }
     return f->last_error;
 }
 
-void qemu_file_set_error(QEMUFile *f, int ret)
+/*
+ * Set the last error for stream f with optional Error*
+ */
+void qemu_file_set_error_obj(QEMUFile *f, int ret, Error *err)
 {
-    if (f->last_error == 0) {
+    if (f->last_error == 0 && ret) {
         f->last_error = ret;
+        error_propagate(&f->last_error_obj, err);
+    } else if (err) {
+        error_report_err(err);
     }
 }
 
+/*
+ * Get last error for stream f
+ *
+ * Return negative error value if there has been an error on previous
+ * operations, return 0 if no error happened.
+ *
+ */
+int qemu_file_get_error(QEMUFile *f)
+{
+    return qemu_file_get_error_obj(f, NULL);
+}
+
+/*
+ * Set the last error for stream f
+ */
+void qemu_file_set_error(QEMUFile *f, int ret)
+{
+    qemu_file_set_error_obj(f, ret, NULL);
+}
+
 bool qemu_file_is_writable(QEMUFile *f)
 {
     return f->ops->writev_buffer;
@@ -176,6 +209,7 @@ void qemu_fflush(QEMUFile *f)
 {
     ssize_t ret = 0;
     ssize_t expect = 0;
+    Error *local_error = NULL;
 
     if (!qemu_file_is_writable(f)) {
         return;
@@ -183,7 +217,8 @@ void qemu_fflush(QEMUFile *f)
 
     if (f->iovcnt > 0) {
         expect = iov_size(f->iov, f->iovcnt);
-        ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos);
+        ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos,
+                                    &local_error);
 
         qemu_iovec_release_ram(f);
     }
@@ -195,7 +230,7 @@ void qemu_fflush(QEMUFile *f)
      * data set we requested, so sanity check that.
      */
     if (ret != expect) {
-        qemu_file_set_error(f, ret < 0 ? ret : -EIO);
+        qemu_file_set_error_obj(f, ret < 0 ? ret : -EIO, local_error);
     }
     f->buf_index = 0;
     f->iovcnt = 0;
@@ -283,6 +318,7 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
 {
     int len;
     int pending;
+    Error *local_error = NULL;
 
     assert(!qemu_file_is_writable(f));
 
@@ -294,14 +330,16 @@ static ssize_t qemu_fill_buffer(QEMUFile *f)
     f->buf_size = pending;
 
     len = f->ops->get_buffer(f->opaque, f->buf + pending, f->pos,
-                        IO_BUF_SIZE - pending);
+                             IO_BUF_SIZE - pending, &local_error);
     if (len > 0) {
         f->buf_size += len;
         f->pos += len;
     } else if (len == 0) {
-        qemu_file_set_error(f, -EIO);
+        qemu_file_set_error_obj(f, -EIO, local_error);
     } else if (len != -EAGAIN) {
-        qemu_file_set_error(f, len);
+        qemu_file_set_error_obj(f, len, local_error);
+    } else {
+        error_free(local_error);
     }
 
     return len;
@@ -327,7 +365,7 @@ int qemu_fclose(QEMUFile *f)
     ret = qemu_file_get_error(f);
 
     if (f->ops->close) {
-        int ret2 = f->ops->close(f->opaque);
+        int ret2 = f->ops->close(f->opaque, NULL);
         if (ret >= 0) {
             ret = ret2;
         }
@@ -338,6 +376,7 @@ int qemu_fclose(QEMUFile *f)
     if (f->last_error) {
         ret = f->last_error;
     }
+    error_free(f->last_error_obj);
     g_free(f);
     trace_qemu_file_fclose();
     return ret;
@@ -783,6 +822,6 @@ void qemu_put_counted_string(QEMUFile *f, const char *str)
 void qemu_file_set_blocking(QEMUFile *f, bool block)
 {
     if (f->ops->set_blocking) {
-        f->ops->set_blocking(f->opaque, block);
+        f->ops->set_blocking(f->opaque, block, NULL);
     }
 }