[RFC PATCH v3 13/30] migration/multifd: Add outgoing QIOChannelFile support

[Fabiano Rosas]

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>
---
- open multifd channels with O_WRONLY and no mode
- stop cancelling migration and propagate error via qio_task
---
 migration/file.c      | 47 +++++++++++++++++++++++++++++++++++++++++--
 migration/file.h      |  5 +++++
 migration/multifd.c   | 14 +++++++++++--
 migration/options.c   |  7 +++++++
 migration/options.h   |  1 +
 migration/qemu-file.h |  1 -
 6 files changed, 70 insertions(+), 5 deletions(-)

diff --git a/migration/file.c b/migration/file.c
index 5d4975f43e..67d6f42da7 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -17,6 +17,10 @@
 
 #define OFFSET_OPTION ",offset="
 
+static struct FileOutgoingArgs {
+    char *fname;
+} outgoing_args;
+
 /* Remove the offset option from @filespec and return it in @offsetp. */
 
 int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
@@ -36,6 +40,42 @@ int file_parse_offset(char *filespec, uint64_t *offsetp, 
Error **errp)
     return 0;
 }
 
+static void qio_channel_file_connect_worker(QIOTask *task, gpointer opaque)
+{
+    /* noop */
+}
+
+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 *err = NULL;
+    int flags = O_WRONLY;
+
+    ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, &err);
+
+    task = qio_task_new(OBJECT(ioc), f, (gpointer)data, NULL);
+    if (!ioc) {
+        qio_task_set_error(task, err);
+        return;
+    }
+
+    qio_task_run_in_thread(task, qio_channel_file_connect_worker,
+                           (gpointer)data, NULL, NULL);
+}
+
 void file_start_outgoing_migration(MigrationState *s,
                                    FileMigrationArgs *file_args, Error **errp)
 {
@@ -43,15 +83,18 @@ void file_start_outgoing_migration(MigrationState *s,
     g_autofree char *filename = g_strdup(file_args->filename);
     uint64_t offset = file_args->offset;
     QIOChannel *ioc;
+    int flags = O_CREAT | O_TRUNC | O_WRONLY;
+    mode_t mode = 0660;
 
     trace_migration_file_outgoing(filename);
 
-    fioc = qio_channel_file_new_path(filename, O_CREAT | O_WRONLY | O_TRUNC,
-                                     0600, errp);
+    fioc = qio_channel_file_new_path(filename, flags, mode, errp);
     if (!fioc) {
         return;
     }
 
+    outgoing_args.fname = g_strdup(filename);
+
     ioc = QIO_CHANNEL(fioc);
     if (offset && qio_channel_io_seek(ioc, offset, SEEK_SET, errp) < 0) {
         return;
diff --git a/migration/file.h b/migration/file.h
index 37d6a08bfc..511019b319 100644
--- a/migration/file.h
+++ b/migration/file.h
@@ -9,10 +9,15 @@
 #define QEMU_MIGRATION_FILE_H
 
 #include "qapi/qapi-types-migration.h"
+#include "io/task.h"
+#include "channel.h"
 
 void file_start_incoming_migration(FileMigrationArgs *file_args, Error **errp);
 
 void file_start_outgoing_migration(MigrationState *s,
                                    FileMigrationArgs *file_args, Error **errp);
 int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp);
+
+void file_send_channel_create(QIOTaskFunc f, void *data);
+int file_send_channel_destroy(QIOChannel *ioc);
 #endif
diff --git a/migration/multifd.c b/migration/multifd.c
index 123ff0dec0..427740aab6 100644
--- a/migration/multifd.c
+++ b/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"
 
@@ -511,7 +513,11 @@ static void multifd_send_terminate_threads(Error *err)
 
 static int multifd_send_channel_destroy(QIOChannel *send)
 {
-    return socket_send_channel_destroy(send);
+    if (migrate_to_file()) {
+        return file_send_channel_destroy(send);
+    } else {
+        return socket_send_channel_destroy(send);
+    }
 }
 
 void multifd_save_cleanup(void)
@@ -904,7 +910,11 @@ static void multifd_new_send_channel_async(QIOTask *task, 
gpointer opaque)
 
 static void multifd_new_send_channel_create(gpointer opaque)
 {
-    socket_send_channel_create(multifd_new_send_channel_async, 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)
diff --git a/migration/options.c b/migration/options.c
index 10730b13ba..f671e24758 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -409,6 +409,13 @@ 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,
diff --git a/migration/options.h b/migration/options.h
index 8a19d6939c..84628a76e8 100644
--- a/migration/options.h
+++ b/migration/options.h
@@ -60,6 +60,7 @@ bool migrate_multifd_packets(void);
 bool migrate_postcopy(void);
 bool migrate_rdma(void);
 bool migrate_tls(void);
+bool migrate_to_file(void);
 
 /* capabilities helpers */
 
diff --git a/migration/qemu-file.h b/migration/qemu-file.h
index 32fd4a34fd..78ea21ab98 100644
--- a/migration/qemu-file.h
+++ b/migration/qemu-file.h
@@ -83,5 +83,4 @@ size_t qemu_get_buffer_at(QEMUFile *f, const uint8_t *buf, 
size_t buflen,
                           off_t pos);
 
 QIOChannel *qemu_file_get_ioc(QEMUFile *file);
-
 #endif
-- 
2.35.3