migration: Teach QEMUFile to be QIOChannel-aware

migration uses QIOChannel typed qemufiles.  In follow up patches, we'll need
the capability to identify this fact, so that we can get the backing QIOChannel
from a QEMUFile.

We can also define types for QEMUFile but so far since we only need to be able
to identify QIOChannel, introduce a boolean which is simpler.

Introduce another helper qemu_file_get_ioc() to return the ioc backend of a
qemufile if has_ioc is set.

No functional change.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20210722175841.938739-5-peterx@redhat.com>
Reviewed-by: Lukas Straub <lukasstraub2@web.de>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

migration/qemu-file-channel.c

@@ -187,11 +187,11 @@ static const QEMUFileOps channel_output_ops = {
 QEMUFile *qemu_fopen_channel_input(QIOChannel *ioc)
 {
     object_ref(OBJECT(ioc));
-    return qemu_fopen_ops(ioc, &channel_input_ops);
+    return qemu_fopen_ops(ioc, &channel_input_ops, true);
 }
 
 QEMUFile *qemu_fopen_channel_output(QIOChannel *ioc)
 {
     object_ref(OBJECT(ioc));
-    return qemu_fopen_ops(ioc, &channel_output_ops);
+    return qemu_fopen_ops(ioc, &channel_output_ops, true);
 }

migration/qemu-file.c

@@ -55,6 +55,8 @@ struct QEMUFile {
     Error *last_error_obj;
     /* has the file has been shutdown */
     bool shutdown;
+    /* Whether opaque points to a QIOChannel */
+    bool has_ioc;
 };
 
 /*
@@ -101,7 +103,7 @@ bool qemu_file_mode_is_not_valid(const char *mode)
     return false;
 }
 
-QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops)
+QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops, bool has_ioc)
 {
     QEMUFile *f;
 
@@ -109,6 +111,7 @@ QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops)
 
     f->opaque = opaque;
     f->ops = ops;
+    f->has_ioc = has_ioc;
     return f;
 }
 
@@ -851,3 +854,15 @@ void qemu_file_set_blocking(QEMUFile *f, bool block)
         f->ops->set_blocking(f->opaque, block, NULL);
     }
 }
+
+/*
+ * Return the ioc object if it's a migration channel.  Note: it can return NULL
+ * for callers passing in a non-migration qemufile.  E.g. see qemu_fopen_bdrv()
+ * and its usage in e.g. load_snapshot().  So we need to check against NULL
+ * before using it.  If without the check, migration_incoming_state_destroy()
+ * could fail for load_snapshot().
+ */
+QIOChannel *qemu_file_get_ioc(QEMUFile *file)
+{
+    return file->has_ioc ? QIO_CHANNEL(file->opaque) : NULL;
+}

migration/qemu-file.h

@@ -27,6 +27,7 @@
 
 #include <zlib.h>
 #include "exec/cpu-common.h"
+#include "io/channel.h"
 
 /* Read a chunk of data from a file at the given position.  The pos argument
  * can be ignored if the file is only be used for streaming.  The number of
@@ -119,7 +120,7 @@ typedef struct QEMUFileHooks {
     QEMURamSaveFunc *save_page;
 } QEMUFileHooks;
 
-QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops);
+QEMUFile *qemu_fopen_ops(void *opaque, const QEMUFileOps *ops, bool has_ioc);
 void qemu_file_set_hooks(QEMUFile *f, const QEMUFileHooks *hooks);
 int qemu_get_fd(QEMUFile *f);
 int qemu_fclose(QEMUFile *f);
@@ -179,5 +180,6 @@ void ram_control_load_hook(QEMUFile *f, uint64_t flags, void *data);
 size_t ram_control_save_page(QEMUFile *f, ram_addr_t block_offset,
                              ram_addr_t offset, size_t size,
                              uint64_t *bytes_sent);
+QIOChannel *qemu_file_get_ioc(QEMUFile *file);
 
 #endif

migration/ram.c

@@ -550,7 +550,7 @@ static int compress_threads_save_setup(void)
         /* comp_param[i].file is just used as a dummy buffer to save data,
          * set its ops to empty.
          */
-        comp_param[i].file = qemu_fopen_ops(NULL, &empty_ops);
+        comp_param[i].file = qemu_fopen_ops(NULL, &empty_ops, false);
         comp_param[i].done = true;
         comp_param[i].quit = false;
         qemu_mutex_init(&comp_param[i].mutex);

migration/savevm.c

@@ -168,9 +168,9 @@ static const QEMUFileOps bdrv_write_ops = {
 static QEMUFile *qemu_fopen_bdrv(BlockDriverState *bs, int is_writable)
 {
     if (is_writable) {
-        return qemu_fopen_ops(bs, &bdrv_write_ops);
+        return qemu_fopen_ops(bs, &bdrv_write_ops, false);
     }
-    return qemu_fopen_ops(bs, &bdrv_read_ops);
+    return qemu_fopen_ops(bs, &bdrv_read_ops, false);
 }