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

[Peter Xu <peterx@redhat.com>]

On Mon, Mar 11, 2024 at 12:03:41PM +0000, Daniel P. Berrangé wrote:
> On Mon, Mar 04, 2024 at 09:26:32AM +0800, 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>
> > ---
> >  migration/fd.h        |  2 ++
> >  migration/fd.c        | 44 +++++++++++++++++++++++++++++++++++++++++++
> >  migration/file.c      | 18 ++++++++++++------
> >  migration/migration.c |  4 ++++
> >  migration/multifd.c   |  2 ++
> >  5 files changed, 64 insertions(+), 6 deletions(-)
> > 
> 
> > @@ -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)));
> > +
> > +            if (QIO_CHANNEL_FILE(ioc)->fd == -1) {
> > +                error_setg(errp, "Failed to duplicate fd %d", fd);
> > +                return;
> > +            }
> 
> I'd suggest that Peter's comment about failure checks be fixed
> by introducing a new constructor that handles the dup + error
> reporting.
> 
>    QIOChannel *qio_channel_file_new_dupfd(int fd, Error **errp;)
> 
> so we're not repeating the error reporting multiple places.

Indeed that looks cleaner.

At the meantime, I just noticed there seems to have an IOC leak on incoming
side..  file_start_incoming_migration():

    do {
        QIOChannel *ioc = QIO_CHANNEL(fioc);

        qio_channel_set_name(ioc, "migration-file-incoming");
        qio_channel_add_watch_full(ioc, G_IO_IN,
                                   file_accept_incoming_migration,
                                   NULL, NULL,
                                   g_main_context_get_thread_default());

        fioc = qio_channel_file_new_fd(dup(fioc->fd)); <-------------------- here

        if (!fioc || fioc->fd == -1) {
            error_setg(errp, "Error creating migration incoming channel");
            break;
        }
    } while (++i < channels);

Fabiano, would you send patches to address these issues (split if both
issues exist)?

Thanks,

-- 
Peter Xu