Re: [PULL 25/27] migration/multifd: Add mapped-ram support to fd: URI

[Peter Maydell]

On Mon, 4 Mar 2024 at 01:28, <peterx@redhat.com> wrote:
>
> From: Fabiano Rosas <farosas@suse.de>
>
> 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>

Hi; Coverity points out some issues with this commit (CID 1539961, 1539965):


> @@ -73,4 +98,23 @@ void fd_start_incoming_migration(const char *fdname, Error 
> **errp)
>                                 fd_accept_incoming_migration,
>                                 NULL, NULL,
>                                 g_main_context_get_thread_default());
> +
> +    if (migrate_multifd()) {
> +        int channels = migrate_multifd_channels();
> +
> +        while (channels--) {
> +            ioc = QIO_CHANNEL(qio_channel_file_new_fd(dup(fd)));

dup() can fail and return -1, but we don't check for failure
and pass the return value directly to qio_channel_file_new_fd(),
which will call lseek() on it, which isn't valid.

> +
> +            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> +                error_setg(errp, "Failed to duplicate fd %d", fd);
> +                return;
> +            }
> +
> +            qio_channel_set_name(ioc, "migration-fd-incoming");
> +            qio_channel_add_watch_full(ioc, G_IO_IN,
> +                                       fd_accept_incoming_migration,
> +                                       NULL, NULL,
> +                                       g_main_context_get_thread_default());
> +        }
> +    }

> @@ -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));

Similarly here.

> +    } 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:
>      /*

thanks
-- PMM