migration/multifd: Add mapped-ram support to fd: URI

If we receive a file descriptor that points to a regular file, there's
nothing stopping us from doing multifd migration with mapped-ram to
that file.

Enable the fd: URI to work with multifd + mapped-ram.

Note that the fds passed into multifd are duplicated because we want
to avoid cross-thread effects when doing cleanup (i.e. close(fd)). The
original fd doesn't need to be duplicated because monitor_get_fd()
transfers ownership to the caller.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Peter Xu <peterx@redhat.com>
Link: https://lore.kernel.org/r/20240229153017.2221-23-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>

1 files changed, 12 insertions, 6 deletions

diff --git a/migration/file.c b/migration/file.c
index 499d2782fe..164b079966 100644
--- a/migration/file.c
+++ b/migration/file.c
@@ -11,6 +11,7 @@
 #include "qemu/error-report.h"
 #include "qapi/error.h"
 #include "channel.h"
+#include "fd.h"
 #include "file.h"
 #include "migration.h"
 #include "io/channel-file.h"
@@ -53,15 +54,20 @@ bool file_send_channel_create(gpointer opaque, Error **errp)
 {
     QIOChannelFile *ioc;
     int flags = O_WRONLY;
-    bool ret = true;
-
-    ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
-    if (!ioc) {
-        ret = false;
-        goto out;
+    bool ret = false;
+    int fd = fd_args_get_fd();
+
+    if (fd && fd != -1) {
+        ioc = qio_channel_file_new_fd(dup(fd));
+    } else {
+        ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
+        if (!ioc) {
+            goto out;
+        }
     }
 
     multifd_channel_connect(opaque, QIO_CHANNEL(ioc));
+    ret = true;
 
 out:
     /*