223 lines
5.5 KiB
Text
223 lines
5.5 KiB
Text
.TH CMD 3
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.SH NAME
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cmd \- interface to host operating system commands
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.SH SYNOPSIS
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.B bind -a '#C' /
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.PP
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.B /cmd/clone
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.br
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.BI /cmd/ n /ctl
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.br
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.BI /cmd/ n /data
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.br
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.BI /cmd/ n /stderr
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.br
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.BI /cmd/ n /status
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.br
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.BI /cmd/ n /wait
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.SH DESCRIPTION
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.I Cmd
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provides a way to run commands in the underlying operating system's
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command interpreter of drawterm or when Inferno is running hosted.
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It serves a three-level directory that is conventionally bound
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behind the root directory.
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The top of the hierarchy is a directory
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.BR cmd ,
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that contains a
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.B clone
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file and zero or more numbered directories.
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Each directory represents a distinct connection to the host's command interpreter.
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The directory contains five files:
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.BR ctl ,
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.BR data ,
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.BR stderr ,
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.B status
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and
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.BR wait ,
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used as described below.
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Opening the
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.B clone
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file reserves a connection: it is equivalent to opening the
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.B ctl
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file of an unused connection directory, creating a new one if necessary.
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.PP
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The file
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.B ctl
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controls a connection.
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When read, it returns the decimal number
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.I n
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of its connection directory.
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Thus, opening and reading
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.B clone
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allocates a connection directory and reveals the number of the allocated directory,
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allowing the other files to be named (eg,
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.BI /cmd/ n /data\fR).
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.PP
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.B Ctl
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accepts the following textual commands, allowing quoting as interpreted by
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.IR parsecmd (2):
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.TP
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.BI "dir " wdir
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Run the host command in directory
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.IR wdir ,
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which is a directory
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.IR "on the host system" .
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Issue this request before starting the command.
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By default, commands are run in the Inferno root directory on the host system.
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.TP
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.BI "exec " "command args ..."
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Spawn a host process to run the
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.I command
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with arguments as given.
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The write returns with an error, setting the error string, if anything prevents
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starting the command.
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If write returns successfully, the command has started, and its standard input and
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output may be accessed through
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.BR data ,
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and its error output accessed through
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.B stderr
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(see below).
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If arguments containing white space are quoted (following the conventions of
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.IR rc (1)
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or
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.IR parsecmd (2)),
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they are requoted by
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.I cmd
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using the host command interpreter's conventions so that
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.I command
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sees exactly the same arguments as were written to
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.BR ctl .
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.TP
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.B kill
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Kill the host command immediately.
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.TP
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.B killonclose
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Set the device to kill the host command when the
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.B ctl
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file is closed (normally all files must be closed, see below).
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.TP
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.BI nice " \fR[\fPn\fR]\fP"
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Run the host command at less than normal scheduling priority.
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Issue this request before starting the command.
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The optional value
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.IR n ,
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in the range 1 to 3,
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indicates the degree of `niceness' (default: 1).
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.PP
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The
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.B data
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file provides a connection to the input and output of a previously-started
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host command.
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It must be opened separately for reading and for writing.
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When opened for reading, it returns data that the command writes to its standard output; when closed, further writes by the command will receive the host
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equivalent of `write to closed pipe'.
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When opened for writing, data written to the file
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can be read by the command on its standard input; when closed, further reads by
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the command will see the host equivalent of `end of file'.
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(Unfortunately there is no way to know when the command needs input.)
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.PP
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The
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.B stderr
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file provides a similar read-only connection to the error output from the command.
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If the
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.B stderr
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file is not opened, the error output will be discarded.
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.PP
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Once started, a host command runs until it terminates or until it is killed,
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by using the
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.B kill
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or
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.B killonclose
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requests above, or by closing all
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.BR ctl ,
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.B data
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and
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.B wait
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files for a connection.
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.PP
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The read-only
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.B status
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file provides a single line giving the status of the connection (not the command), of the form:
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.IP
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.BI cmd/ "n opens state wdir arg0"
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.PP
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where the fields are separated by white space. The meaning of each field is:
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.TP
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.I n
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The
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.B cmd
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directory number.
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.TP
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.I opens
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The decimal number of open file descriptors for
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.BR ctl ,
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.B data
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and
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.BR wait .
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.TP
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.I state
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The status of the interface in directory
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.IR n :
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.RS
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.TF Execute
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.TP
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.B Open
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Allocated for use but not yet running a command.
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.TP
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.B Execute
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Running a command.
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.TP
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.B Done
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Command terminated: status available in the
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.B status
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file (or via
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.BR wait ).
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.TP
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.B Closed
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Command completed. Available for reallocation via
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.BR clone .
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.RE
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.PD
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.TP
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.I wdir
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The command's initial working directory on the host.
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.TP
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.I arg0
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The host command name (without arguments).
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.PP
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The read-only
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.B wait
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file must be opened before starting a command via
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.BR ctl .
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When read, it blocks until the command terminates.
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The read then returns with a single status line, to be
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parsed using
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.B tokenize
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(see
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.IR getfields (2)).
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There are five fields:
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host process ID (or 0 if unknown);
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time the command spent in user code in milliseconds (or 0);
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time spent in system code in milliseconds (or 0);
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real time in milliseconds (or 0);
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and a string giving the exit status of the command.
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The exit status is host-dependent, except that an empty string
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means success, and a non-empty string contains a diagnostic.
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.PP
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.SS "Command execution"
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In all cases, the command runs in the host operating system's
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own file name space.
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All file names will be interpreted in that space, not Plan 9's.
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For example, on Unix
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.B /
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refers to the host's file system root, not Plan 9's;
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the effects of mounts and binds will not be visible.
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.SH "SEE ALSO"
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.IR os (1)
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.SH DIAGNOSTICS
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A
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.B write
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to
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.B ctl
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returns with an error and sets the error string if
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a command cannot be started or killed successfully.
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