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Dd February 16, 2011
Dt RUMPCLIENT 3
Os
Sh NAME
Nm rumpclient
Nd rump client library
Sh LIBRARY
Lb rumpclient
Sh SYNOPSIS
In rump/rumpclient.h
In rump/rump_syscalls.h
Ft int
Fn rumpclient_init
Ft pid_t
Fn rumpclient_fork
Ft pid_t
Fn rumpclient_vfork
Ft struct rumpclient_fork *
Fn rumpclient_prefork
Ft int
Fn rumpclient_fork_init "struct rumpclient_fork *rfp"
Ft void
Fn rumpclient_fork_cancel "struct rumpclient_fork *rfp"
Ft int
Fn rumpclient_exec "const char *path" "char *const argv[]" "char *const envp[]"
Ft int
Fn rumpclient_daemon "int nochdir" "int noclose"
Ft void
Fn rumpclient_setconnretry "time_t retrytime"
Ft int
Fo rumpclient_syscall
Fa "int num" "const void *sysarg" "size_t argsize" "register_t *retval"
Fc
Sh DESCRIPTION
Nm
is the clientside implementation of the
Xr rump_sp 7
facility.
It can be used to connect to a rump kernel server and make system call
style requests.
Pp
Every connection to a rump kernel server creates a new process
context in the rump kernel.
By default a process is inherited from init, but through existing
connections and the forking facility offered by
Nm
it is possible to form process trees.
Bl -tag -width xxxx
It Fn rumpclient_init
Initialize
Nm .
The server address is determined from the environment variable
Ev RUMP_SERVER
according to syntax described in
Xr rump_sp 7 .
The new process is registered to the rump kernel with the command
name from
Xr getprogname 3 .
It Fn rumpclient_fork
Fork a rump client process.
This also causes a host process fork via
Xr fork 2 .
The child will have a copy of the parent's rump kernel file descriptors.
It Fn rumpclient_vfork
Like above, but the host uses
Xr vfork 2 .
It Fn rumpclient_prefork
Low-level routine which instructs the rump kernel that the current
process is planning to fork.
The routine returns a
Pf non- Dv NULL
cookie if successful.
It Fn rumpclient_fork_init rfp
Low-level routine which works like
Fn rumpclient_init ,
with the exception that it uses the
Ar rfp
context created by a call to
Fn rumpclient_prefork .
This is typically called from the child of a
Xr fork 2
call.
It Fn rumpclient_fork_cancel rfp
Cancel previously initiated prefork context.
This is useful for error handling in case a full fork could not
be carried through.
It Fn rumpclient_exec path argv envp
This call is a
Nm
wrapper around
Xr execve 2 .
The wrapper makes sure that the rump kernel process context stays
the same in the newly executed program.
This means that the rump kernel PID remains the same and the same
rump file descriptors are available (apart from ones which
were marked with
Dv FD_CLOEXEC ) .
Pp
It should be noted that the newly executed program must call
Fn rumpclient_init
before any other rump kernel communication can take place.
The wrapper cannot do it because it no longer has program control.
However, since all rump clients call the init routine,
this should not be a problem.
It Fn rumpclient_daemon noclose nochdir
This function performs the equivalent of
Xr daemon 3 ,
but also ensures that the internal call to
Xr fork 2
is handled properly.
This routine is provided for convenience.
It Fn rumpclient_setconnretry retrytime
Set the timeout for how long the client attempts to reconnect to
the server in case of a broken connection.
After the timeout expires the client will return a failure
for that particular request.
It is critical to note that after a restablished connection the
rump kernel context will be that of a newly connected client.
This means all previous kernel state such as file descriptors
will be lost.
It is largely up to a particular application if this has impact
or not.
For example, web browsers tend to recover fairly smoothly from a
kernel server reconnect, while
Xr sshd 8
gets confused if its sockets go missing.
Pp
If
Ar retrytime
is a positive integer, it means the number of seconds for which
reconnection will be attempted.
The value 0 means that reconnection will not be attempted, and all
subsequent operations will return the errno
Er ENOTCONN .
Pp
Additionally, the following special values are accepted:
Bl -tag -width xxxx
It Dv RUMPCLIENT_RETRYCONN_INFTIME
Attempt reconnection indefinitely.
It Dv RUMPCLIENT_RETRYCONN_ONCE
Attempt reconnect exactly once.
What this precisely means depends on the situation: e.g. getting
Er EHOSTUNREACH
immediately or the TCP connection request timeouting are considered
to be one retry.
It Dv RUMPCLIENT_RETRYCONN_DIE
In case of a broken connection is detected at runtime, call
Xr exit 3 .
This is useful for example in testing.
It ensures that clients are killed immediately when they attempt
to communicate with a halted server.
El
It Fn rumpclient_syscall num sysarg argsize retval
Execute an "indirect" system call.
In the normal case system calls are executed through the interfaces in
In rump/rump_syscalls.h
(for example
Fn rump_sys_read fd buf nbytes ) .
This interface allows calling the server with pre-marshalled arguments.
El
Pp
Additionally, all of the supported rump system calls are available
through this library.
See
In rump/rump_syscalls.h
for a list.
Sh RETURN VALUES
Nm
routines return \-1 in case of error and set errno.
In case of success a non-negative integer is returned, where applicable.
Sh SEE ALSO
Xr rump_server 1 ,
Xr rump 3 ,
Xr rump_sp 7
Sh CAVEATS
Interfaces for a cryptographically authenticated client-server
handshake do not currently exist.
This can be worked around with e.g. host access control and an ssh
tunnel.

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