migration/multifd: Add outgoing QIOChannelFile support

Allow multifd to open file-backed channels. This will be used when
enabling the fixed-ram migration stream format which expects a
seekable transport.

The QIOChannel read and write methods will use the preadv/pwritev
versions which don't update the file offset at each call so we can
reuse the fd without re-opening for every channel.

Note that this is just setup code and multifd cannot yet make use of
the file channels.

Signed-off-by: Fabiano Rosas <farosas@suse.de>

include/io/channel-file.h

@@ -22,6 +22,7 @@
 #define QIO_CHANNEL_FILE_H
 
 #include "io/channel.h"
+#include "io/task.h"
 #include "qom/object.h"
 
 #define TYPE_QIO_CHANNEL_FILE "qio-channel-file"

migration/file.c

@@ -1,20 +1,77 @@
 #include "qemu/osdep.h"
-#include "channel.h"
 #include "io/channel-file.h"
 #include "file.h"
 #include "qemu/error-report.h"
 
+static struct FileOutgoingArgs {
+    char *fname;
+    int flags;
+    int mode;
+} outgoing_args;
+
+static void qio_channel_file_connect_worker(QIOTask *task, gpointer opaque)
+{
+    /* noop */
+}
+
+static void file_migration_cancel(Error *errp)
+{
+    MigrationState *s;
+
+    s = migrate_get_current();
+
+    migrate_set_state(&s->state, MIGRATION_STATUS_SETUP,
+                      MIGRATION_STATUS_FAILED);
+    migration_cancel(errp);
+}
+
+int file_send_channel_destroy(QIOChannel *ioc)
+{
+    if (ioc) {
+        qio_channel_close(ioc, NULL);
+        object_unref(OBJECT(ioc));
+    }
+    g_free(outgoing_args.fname);
+    outgoing_args.fname = NULL;
+
+    return 0;
+}
+
+void file_send_channel_create(QIOTaskFunc f, void *data)
+{
+    QIOChannelFile *ioc;
+    QIOTask *task;
+    Error *errp = NULL;
+
+    ioc = qio_channel_file_new_path(outgoing_args.fname,
+                                    outgoing_args.flags,
+                                    outgoing_args.mode, &errp);
+    if (!ioc) {
+        file_migration_cancel(errp);
+        return;
+    }
+
+    task = qio_task_new(OBJECT(ioc), f, (gpointer)data, NULL);
+    qio_task_run_in_thread(task, qio_channel_file_connect_worker,
+                           (gpointer)data, NULL, NULL);
+}
 
 void file_start_outgoing_migration(MigrationState *s, const char *fname, Error **errp)
 {
     QIOChannelFile *ioc;
+    int flags = O_CREAT | O_TRUNC | O_WRONLY;
+    mode_t mode = 0660;
 
-    ioc = qio_channel_file_new_path(fname, O_CREAT | O_TRUNC | O_WRONLY, 0660, errp);
+    ioc = qio_channel_file_new_path(fname, flags, mode, errp);
     if (!ioc) {
-        error_report("Error creating a channel");
+        error_report("Error creating migration outgoing channel");
         return;
     }
 
+    outgoing_args.fname = g_strdup(fname);
+    outgoing_args.flags = flags;
+    outgoing_args.mode = mode;
+
     qio_channel_set_name(QIO_CHANNEL(ioc), "migration-file-outgoing");
     migration_channel_connect(s, QIO_CHANNEL(ioc), NULL, NULL);
     object_unref(OBJECT(ioc));

migration/file.h

@@ -1,10 +1,14 @@
 #ifndef QEMU_MIGRATION_FILE_H
 #define QEMU_MIGRATION_FILE_H
 
+#include "io/task.h"
+#include "channel.h"
+
 void file_start_outgoing_migration(MigrationState *s,
                                    const char *filename,
                                    Error **errp);
 
 void file_start_incoming_migration(const char *fname, Error **errp);
+void file_send_channel_create(QIOTaskFunc f, void *data);
+int file_send_channel_destroy(QIOChannel *ioc);
 #endif
-

migration/migration.c

@@ -106,7 +106,7 @@ static bool migration_needs_multiple_sockets(void)
 static bool uri_supports_multi_channels(const char *uri)
 {
     return strstart(uri, "tcp:", NULL) || strstart(uri, "unix:", NULL) ||
-           strstart(uri, "vsock:", NULL);
+           strstart(uri, "vsock:", NULL) || strstart(uri, "file:", NULL);
 }
 
 static bool

migration/multifd.c

@@ -17,6 +17,7 @@
 #include "exec/ramblock.h"
 #include "qemu/error-report.h"
 #include "qapi/error.h"
+#include "file.h"
 #include "ram.h"
 #include "migration.h"
 #include "migration-stats.h"
@@ -28,6 +29,7 @@
 #include "threadinfo.h"
 #include "options.h"
 #include "qemu/yank.h"
+#include "io/channel-file.h"
 #include "io/channel-socket.h"
 #include "yank_functions.h"
 
@@ -512,7 +514,11 @@ static void multifd_send_terminate_threads(Error *err)
 
 static int multifd_send_channel_destroy(QIOChannel *send)
 {
+    if (migrate_to_file()) {
+        return file_send_channel_destroy(send);
+    } else {
         return socket_send_channel_destroy(send);
+    }
 }
 
 void multifd_save_cleanup(void)
@@ -919,7 +925,11 @@ static void multifd_new_send_channel_async(QIOTask *task, gpointer opaque)
 
 static void multifd_new_send_channel_create(gpointer opaque)
 {
+    if (migrate_to_file()) {
+        file_send_channel_create(multifd_new_send_channel_async, opaque);
+    } else {
         socket_send_channel_create(multifd_new_send_channel_async, opaque);
+    }
 }
 
 int multifd_save_setup(Error **errp)

migration/options.c

@@ -383,6 +383,13 @@ bool migrate_tls(void)
     return s->parameters.tls_creds && *s->parameters.tls_creds;
 }
 
+bool migrate_to_file(void)
+{
+    MigrationState *s = migrate_get_current();
+
+    return qemu_file_is_seekable(s->to_dst_file);
+}
+
 typedef enum WriteTrackingSupport {
     WT_SUPPORT_UNKNOWN = 0,
     WT_SUPPORT_ABSENT,

migration/options.h

@@ -59,6 +59,7 @@ bool migrate_live(void);
 bool migrate_multifd_packets(void);
 bool migrate_postcopy(void);
 bool migrate_tls(void);
+bool migrate_to_file(void);
 
 /* capabilities helpers */