Re: [PATCH v2 2/2] migration/multifd: Ensure we're not given a socket for file migration

[Peter Xu <peterx@redhat.com>]

On Wed, Mar 13, 2024 at 06:28:24PM -0300, Fabiano Rosas wrote:
> When doing migration using the fd: URI, the incoming migration starts
> before the user has passed the file descriptor to QEMU. This means
> that the checks at migration_channels_and_transport_compatible()
> happen too soon and we need to allow a migration channel of type
> SOCKET_ADDRESS_TYPE_FD even though socket migration is not supported
> with multifd.

Hmm, bare with me if this is a stupid one.. why the incoming migration can
start _before_ the user passed in the fd?

IOW, why can't we rely on a single fd_is_socket() check for
SOCKET_ADDRESS_TYPE_FD in transport_supports_multi_channels()?

> 
> The commit decdc76772 ("migration/multifd: Add mapped-ram support to
> fd: URI") was supposed to add a second check prior to starting
> migration to make sure a socket fd is not passed instead of a file fd,
> but failed to do so.
> 
> Add the missing verification.
> 
> Fixes: decdc76772 ("migration/multifd: Add mapped-ram support to fd: URI")
> Signed-off-by: Fabiano Rosas <farosas@suse.de>
> ---
>  migration/fd.c   | 8 ++++++++
>  migration/file.c | 7 +++++++
>  2 files changed, 15 insertions(+)
> 
> diff --git a/migration/fd.c b/migration/fd.c
> index 39a52e5c90..c07030f715 100644
> --- a/migration/fd.c
> +++ b/migration/fd.c
> @@ -22,6 +22,7 @@
>  #include "migration.h"
>  #include "monitor/monitor.h"
>  #include "io/channel-file.h"
> +#include "io/channel-socket.h"
>  #include "io/channel-util.h"
>  #include "options.h"
>  #include "trace.h"
> @@ -95,6 +96,13 @@ void fd_start_incoming_migration(const char *fdname, Error **errp)
>      }
>  
>      if (migrate_multifd()) {
> +        if (fd_is_socket(fd)) {
> +            error_setg(errp,
> +                       "Multifd migration to a socket FD is not supported");
> +            object_unref(ioc);
> +            return;
> +        }
> +
>          file_create_incoming_channels(ioc, errp);
>      } else {
>          qio_channel_set_name(ioc, "migration-fd-incoming");
> diff --git a/migration/file.c b/migration/file.c
> index ddde0ca818..b6e8ba13f2 100644
> --- a/migration/file.c
> +++ b/migration/file.c
> @@ -15,6 +15,7 @@
>  #include "file.h"
>  #include "migration.h"
>  #include "io/channel-file.h"
> +#include "io/channel-socket.h"
>  #include "io/channel-util.h"
>  #include "options.h"
>  #include "trace.h"
> @@ -58,6 +59,12 @@ bool file_send_channel_create(gpointer opaque, Error **errp)
>      int fd = fd_args_get_fd();
>  
>      if (fd && fd != -1) {
> +        if (fd_is_socket(fd)) {
> +            error_setg(errp,
> +                       "Multifd migration to a socket FD is not supported");
> +            goto out;
> +        }
> +
>          ioc = qio_channel_file_new_dupfd(fd, errp);
>      } else {
>          ioc = qio_channel_file_new_path(outgoing_args.fname, flags, 0, errp);
> -- 
> 2.35.3
> 

-- 
Peter Xu