migration: unify stdio-based QEMUFile operations

Now that qemu_fseek does not exist anymore, there is no reason to do
an fseek before fread/fwrite when operating on an stdio file.
Thus, unify the get/put_buffer callbacks used by qemu_fopen
with those used for pipes.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: consolidate QEMUFile methods in a single QEMUFileOps struct

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: add qemu_get_fd

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: replace qemu_stdio_fd with qemu_get_fd

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: clean up server sockets and handlers before invoking process_incoming_migration

A first step towards making a common "suffix" for all migration protocols,
and moving it to process_incoming_migration.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: use migrate_fd_close in migrate_fd_cleanup

migrate_fd_cleanup will usually close the file descriptor via
buffered_file_close's call to migrate_fd_close.  However, in the case
of s->file == NULL it is "inlining" migrate_fd_close (almost: there is a
direct close() instead of using s->close(s)).  To fix the inconsistency
and clean up the code, allow multiple calls to migrate_fd_close and use
the function in migrate_fd_cleanup.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: use closesocket, not close

Windows requires this.  Migration does not quite work under Windows
but let's be uniform across QEMU.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: xxx_close will only be called once

No need to test s->fd again, it is tested in the caller.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: close socket QEMUFile from socket_close

The common suffix now is process_incoming_migration+qemu_fclose.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: move qemu_fclose to process_incoming_migration

The common suffix is now just process_incoming_migration.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: handle EAGAIN while reading QEMUFile

This will never happen right now (the assertion would fail).  The
next patch will set the socket or pipe in non-blocking mode, thus
enabling this part of the code.

Coroutines can just stop whenever they want with qemu_coroutine_yield.
As soon as select tells the main loop that the migration stream is
readable, the coroutine is re-entered directly in qemu_get_buffer,
where it will read more data and pass it to the loading routines.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
migration: move process_incoming_migration to a coroutine

The final part of incoming migration, which now consists of
process_incoming_migration for all protocols, is thus made non-blocking.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>