sortix--sortix/share/man/man7/serial-transfer.7

.Dd January 6, 2016
.Dt SERIAL-TRANSFER 7
.Os
.Sh NAME
.Nm serial-transfer
.Nd files over serial device
.Sh DESCRIPTION
You can transfer data using the serial line.
The
.Xr sf 1
program provides simple framing which is useful to conduct advanced transfers by
combining with other tools such as
.Xr tar 1 .
.Pp
The serial device will be available at the appropriate device after boot, such
as
.Pa /dev/com1 .
Data written to it will be available to readers on the other end and likewise
data written on the other end will be available to local readers.
Take care to ensure that the reader is always reading before writing or you may
lose data.
.Pp
You get a byte stream between the guest and host using this interface.
This is powerful but often you want to transfer finite payloads and have the
transfer finish when done rather than needing to manually interrupt it.
.Pp
The
.Xr sf 1
program encodes and decodes frames.
.Li sf -o
will emit a start byte
sequence, then read from stdin and encode a body, and finally emit an end
sequence.
.Li sf -i
will read bytes until it finds a start sequence, then it will decode the body
and emit it to stdout, and finally stop when it receives the end sequence.
We can use this to do transfers over the serial connection.
.Pp
.Xr sf 1
is a Sortix specific program.
Other operating systems don't come with it and you need to build it from the
Sortix source code.
This is automatically done by the
.Sy build-tools
target during
.Xr cross-development 7 .
You can also just transfer its code from
.Pa /src/sf/sf.c
over the serial line.
.Ss Virtual Machines
This method is useful when running inside a virtual machine and you wish to
communicate with the host system.
This is particularly useful if you connect the serial line to a unix socket.
In Qemu, this is done with:
.Bd -literal
   -serial unix:/tmp/serial,server,nowait
.Ed
.Pp
In VirtualBox, in the virtual machine settings, under serial ports, enable one
and put it in mode Host Pipe and mark Create Pipe.
.Ss Conventions
Let
.Pa /dev/receiver
mean the device on the receiving machine and let
.Pa /dev/transmitter
mean the device on the transmitting machine.
This will be devices such as
.Pa /dev/com1 .
If one end is the host of a virtual machine as described above, its device will
be an unix socket such as
.Pa /tmp/serial .
.Ss Simple File Transfer
You can then transfer a file from this system to another.
First run on the receiving machine:
.Bd -literal
    sf -i /dev/receiver > file.txt
.Ed
.Pp
Then run on the transmitting machine:
.Bd -literal
    sf -o /dev/transmitter < file.txt
.Ed
.Pp
The sender will stop when it has transmitted the last byte and the receiver will
end when it has recognized an end sequence.
.Ss Advanced File Transfer
You can transfer multiple files using
.Xr tar 1 .
This also allows you to preserve file meta data such as permissions and modified
time.
First run on the receiving machine:
.Bd -literal
    sf -i /dev/receiver | tar -xv
.Ed
.Pp
Then run on the transmitting machine:
.Bd -literal
    tar -cv *.patch | sf -o /dev/transmitter
.Ed
.Pp
The
.Fl v
option is useful as it displays the names of files as they are transferred.
.Ss Network Connection
It is possible to use the
.Xr sfnc 1
and
.Xr sfncd 1
scripts to create a bidirectional communication channel using two serial ports,
one for each direction.
The scripts use a protocol where
.Xr sfnc 1
sends a hostname, a port, and the body from stdin.
Likewise the
.Xr sfncd 1
script receives the two parameters and invokes
.Xr nc 1
(or another program as specified).
.Pp
For instance, run on the server:
.Bd -literal
    sfncd /dev/receive /dev/transmit
.Ed
.Pp
And then run on the client:
.Bd -literal
    sfnc irc.freenode.net 6667 /dev/transmit /dev/receive
.Ed
.Pp
This will last for the duration of the connection.
.Xr sfncd 1
needs to be run again to start another connection.
This scheme only allows one connection at one given time, but with it is
possible for custom programs on either side to multiplex connections.
.Sh SEE ALSO
.Xr sf 1 ,
.Xr tar 1 ,
.Xr development 7 ,
.Xr user-guide 7