[PATCH 2 of 4][SMB3] multichannel: move channel selection above transport layer

[Steve French]

Slightly updated version of Aurelien's multichannel patch 2 of 4
(works around merge conflict with Ronnie's stack size reduction
patch).

    Move the channel (TCP_Server_Info*) selection from the tranport
    layer to higher in the call stack so that:

    - credit handling is done with the server that will actually be used
      to send.
      * ->wait_mtu_credit
      * ->set_credits / set_credits
      * ->add_credits / add_credits
      * add_credits_and_wake_if

    - potential reconnection (smb2_reconnect) done when initializing a
      request is checked and done with the server that will actually be
      used to send.

    To do this:

    - remove the cifs_pick_channel() call out of compound_send_recv()

    - select channel and pass it down by adding a cifs_pick_channel(ses)
      call in:
      - smb311_posix_mkdir
      - SMB2_open
      - SMB2_ioctl
      - __SMB2_close
      - query_info
     - SMB2_change_notify
      - SMB2_flush
      - smb2_async_readv  (if none provided in context param)
      - SMB2_read         (if none provided in context param)
      - smb2_async_writev (if none provided in context param)
      - SMB2_write        (if none provided in context param)
      - SMB2_query_directory
      - send_set_info
      - SMB2_oplock_break
      - SMB311_posix_qfs_info
      - SMB2_QFS_info
      - SMB2_QFS_attr
      - smb2_lockv
      - SMB2_lease_break
        - smb2_compound_op
      - smb2_set_ea
      - smb2_ioctl_query_info
      - smb2_query_dir_first
      - smb2_query_info_comound
      - smb2_query_symlink
      - cifs_writepages
      - cifs_write_from_iter
      - cifs_send_async_read
      - cifs_read
      - cifs_readpages

    - add TCP_Server_Info *server param argument to:
      - cifs_send_recv
      - compound_send_recv
      - SMB2_open_init
      - SMB2_query_info_init
      - SMB2_set_info_init
      - SMB2_close_init
      - SMB2_ioctl_init
      - smb2_iotcl_req_init
      - SMB2_query_directory_init
      - SMB2_notify_init
      - SMB2_flush_init
      - build_qfs_info_req
      - smb2_hdr_assemble
      - smb2_reconnect
      - fill_small_buf
      - smb2_plain_req_init
      - __smb2_plain_req_init

    The read/write codepath is different than the rest as it is using
    pages, io iterators and async calls. To deal with those we add a
    server pointer in the cifs_writedata/cifs_readdata/cifs_io_parms
    context struct and set it in:

    - cifs_writepages      (wdata)
    - cifs_write_from_iter (wdata)
    - cifs_readpages       (rdata)
    - cifs_send_async_read (rdata)

    The [rw]data->server pointer is eventually copied to
    cifs_io_parms->server to pass it down to SMB2_read/SMB2_write.
    If SMB2_read/SMB2_write is called from a different place that doesn't
    set the server field it will pick a channel.

    Some places do not pick a channel and just use ses->server or
    cifs_ses_server(ses). All cifs_ses_server(ses) calls are in codepaths
    involving negprot/sess.setup.

    - SMB2_negotiate         (binding channel)
    - SMB2_sess_alloc_buffer (binding channel)
    - SMB2_echo              (uses provided one)
    - SMB2_logoff            (uses master)
    - SMB2_tdis              (uses master)

    (list not exhaustive)

    Signed-off-by: Aurelien Aptel <aaptel at suse.com>
    Signed-off-by: Steve French <stfrench at microsoft.com>



-- 
Thanks,

Steve
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