[PATCH v4 20/34] migration/multifd: Add outgoing QIOChannelFile support

[Fabiano Rosas <farosas@suse.de>]

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.

Contrary to the socket migration, the file migration doesn't need an
asynchronous channel creation process, so expose
multifd_channel_connect() and call it directly.

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>
---
 migration/file.c    | 40 ++++++++++++++++++++++++++++++++++++++--
 migration/file.h    |  5 +++++
 migration/multifd.c | 27 ++++++++++++++++++++++-----
 migration/multifd.h |  2 ++
 4 files changed, 67 insertions(+), 7 deletions(-)

diff --git a/migration/file.c b/migration/file.c
index 22d052a71f..ac9f6ae40a 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -12,12 +12,17 @@
 #include "channel.h"
 #include "file.h"
 #include "migration.h"
+#include "multifd.h"
 #include "io/channel-file.h"
 #include "io/channel-util.h"
 #include "trace.h"
 
 #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)
@@ -37,6 +42,34 @@ int file_parse_offset(char *filespec, uint64_t *offsetp, Error **errp)
     return 0;
 }
 
+int file_send_channel_destroy(QIOChannel *ioc)
+{
+    if (ioc) {
+        qio_channel_close(ioc, NULL);
+    }
+    g_free(outgoing_args.fname);
+    outgoing_args.fname = NULL;
+
+    return 0;
+}
+
+bool file_send_channel_create(gpointer opaque, Error **errp)
+{
+    QIOChannelFile *ioc;
+    int flags = O_WRONLY;
+
+    ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
+    if (!ioc) {
+        return false;
+    }
+
+    if (!multifd_channel_connect(opaque, QIO_CHANNEL(ioc), errp)) {
+        return false;
+    }
+
+    return true;
+}
+
 void file_start_outgoing_migration(MigrationState *s,
                                    FileMigrationArgs *file_args, Error **errp)
 {
@@ -44,15 +77,18 @@ 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..90794b494b 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);
+
+bool file_send_channel_create(gpointer opaque, Error **errp);
+int file_send_channel_destroy(QIOChannel *ioc);
 #endif
diff --git a/migration/multifd.c b/migration/multifd.c
index 45a0c7aaa8..507b497d52 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"
 
@@ -680,6 +682,9 @@ static void multifd_send_terminate_threads(void)
 
 static int multifd_send_channel_destroy(QIOChannel *send)
 {
+    if (!multifd_use_packets()) {
+        return file_send_channel_destroy(send);
+    }
     return socket_send_channel_destroy(send);
 }
 
@@ -959,9 +964,8 @@ static bool multifd_tls_channel_connect(MultiFDSendParams *p,
     return true;
 }
 
-static bool multifd_channel_connect(MultiFDSendParams *p,
-                                    QIOChannel *ioc,
-                                    Error **errp)
+bool multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc,
+                             Error **errp)
 {
     qio_channel_set_delay(ioc, false);
 
@@ -1031,9 +1035,14 @@ out:
     error_free(local_err);
 }
 
-static void multifd_new_send_channel_create(gpointer opaque)
+static bool multifd_new_send_channel_create(gpointer opaque, Error **errp)
 {
+    if (!multifd_use_packets()) {
+        return file_send_channel_create(opaque, errp);
+    }
+
     socket_send_channel_create(multifd_new_send_channel_async, opaque);
+    return true;
 }
 
 bool multifd_send_setup(void)
@@ -1082,7 +1091,15 @@ bool multifd_send_setup(void)
         p->page_size = qemu_target_page_size();
         p->page_count = page_count;
         p->write_flags = 0;
-        multifd_new_send_channel_create(p);
+
+        if (!multifd_new_send_channel_create(p, &local_err)) {
+            /*
+             * File channel creation is synchronous, we don't need the
+             * semaphore below, it's safe to return now.
+             */
+            assert(migrate_fixed_ram());
+            return -1;
+        }
     }
 
     if (use_packets) {
diff --git a/migration/multifd.h b/migration/multifd.h
index 19188815a3..135f6ed098 100644
--- a/migration/multifd.h
+++ b/migration/multifd.h
@@ -228,5 +228,7 @@ static inline void multifd_send_prepare_header(MultiFDSendParams *p)
     p->iovs_num++;
 }
 
+bool multifd_channel_connect(MultiFDSendParams *p, QIOChannel *ioc,
+                             Error **errp);
 
 #endif
-- 
2.35.3