RUMPCLIENT(3)

NAME
rumpclient - rump client library

LIBRARY
rumpclient

SYNOPSIS
#include <rump/rumpclient.h>
#include <rump/rump_syscalls.h>
int
rumpclient_init();
pid_t
rumpclient_fork();
pid_t
rumpclient_vfork();
struct rumpclient_fork *
rumpclient_prefork();
int
rumpclient_fork_init(struct rumpclient_fork *rfp);
void
rumpclient_fork_cancel(struct rumpclient_fork *rfp);
int
rumpclient_exec(const char *path, char *const argv[], char *const envp[]);
int
rumpclient_daemon(int nochdir, int noclose);
void
rumpclient_setconnretry(time_t retrytime);
int
rumpclient_syscall(int num, const void *sysarg, size_t argsize, register_t *retval);

DESCRIPTION
rumpclient is the clientside implementation of the rump_sp(7) facility. It can be used to connect to a rump kernel server and make system call style requests.

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 rumpclient it is possible to form process trees.

rumpclient_init()
    Initialize rumpclient. The server address is determined from the environment variable RUMP_SERVER according to syntax described in rump_sp(7). The new process is registered to the rump kernel with the command name from getprogname(3).

rumpclient_fork()
    Fork a rump client process. This also causes a host process fork via fork(2). The child will have a copy of the parent's rump kernel file descriptors.

rumpclient_vfork()
    Like above, but the host uses vfork(2).

rumpclient_prefork()
    Low-level routine which instructs the rump kernel that the current process is planning to fork. The routine returns a non-NULL cookie if successful.

rumpclient_fork_init(rfp)
    Low-level routine which works like rumpclient_init(), with the exception that it uses the rfp context created by a call to rumpclient_prefork(). This is typically called from the child of a fork(2) call.

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.

rumpclient_exec(path, argv, envp)
    This call is a rumpclient wrapper around 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 FD_CLOEXEC).

    It should be noted that the newly executed program must call 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.

rumpclient_daemon(noclose, nochdir)
    This function performs the equivalent of daemon(3), but also ensures that the internal call to fork(2) is handled properly. This routine is provided for convenience.

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 sshd(8) gets confused if its sockets go missing.

    If 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 ENOTCONN.

    Additionally, the following special values are accepted:

    RUMPCLIENT_RETRYCONN_INFTIME
        Attempt reconnection indefinitely.

    RUMPCLIENT_RETRYCONN_ONCE
        Attempt reconnect exactly once. What this precisely means depends on the situation: e.g. getting EHOSTUNREACH immediately or the TCP connection request timeouting are considered to be one retry.

    RUMPCLIENT_RETRYCONN_DIE
        In case of a broken connection is detected at runtime, call 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.

rumpclient_syscall(num, sysarg, argsize, retval)
    Execute an "indirect" system call. In the normal case system calls are executed through the interfaces in <rump/rump_syscalls.h> (for example rump_sys_read(fd, buf, nbytes)). This interface allows calling the server with pre-marshalled arguments.

Additionally, all of the supported rump system calls are available through this library. See <rump/rump_syscalls.h> for a list.

RETURN VALUES
rumpclient routines return -1 in case of error and set errno. In case of success a non-negative integer is returned, where applicable.

SEE ALSO
rump_server(1), rump(3), rump_sp(7)

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.