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diff --git a/static/v10/man2/mpx.2 b/static/v10/man2/mpx.2 new file mode 100644 index 00000000..188a3f30 --- /dev/null +++ b/static/v10/man2/mpx.2 @@ -0,0 +1,503 @@ +.TH MPX 2 +.UC 4 +.SH NAME +mpx \- create and manipulate multiplexed files +.SH SYNOPSIS +.nf +.B mpx(name, access) +.B char *name; +.PP +.B join(fd, xd) +.PP +.B chan(xd) +.PP +.B extract(i, xd) +.PP +.B attach(i, xd) +.PP +.B detach(i, xd) +.PP +.B connect(fd, cd, end) +.PP +.B npgrp(i, xd, pgrp) +.PP +.B ckill(i, xd, signal) +.PP +.B #include <sys/mx.h> +.B mpxcall(cmd, vec) +.B int *vec; +.fi +.SH DESCRIPTION +.PP +.B mpxcall(cmd, vec) +is the system call shared by the +library routines described below. +.I Cmd +selects a command using values +defined in +.IR <sys/mx.h> . +.I Vec +is the address of a +structure containing the arguments +for the command. +.PP +.B mpx(name, access) +.PP +.I Mpx +creates and opens the file +.I name +with access permission +.I access +(see +.IR creat (2)) +and returns a file descriptor available for +reading and writing. +A \-1 is returned if the file cannot be created, +if +.I name +already exists, or +if the file table or other operating system +data structures are full. +The file descriptor is required for use +with other routines. +.PP +If +.I name +is 0, +a file descriptor is returned as described +but no entry is created in the file system. +.PP +Once created an mpx file may be opened +(see +.IR open (2)) +by any process. +This provides a form of interprocess communication +whereby a process B can `call' process A +by opening an mpx file +created by A. +To B, the file is ordinary with one exception: +the +.I connect +primitive could be applied to it. +Otherwise the functions +described below are used only in process A +and descendants that inherit the open mpx file. +.PP +When a process opens an mpx file, the owner of the +file receives a control message when the file is next read. +The method for `answering' +this kind of call involves +using +.I attach +and +.I detach +as described in more detail below. +.PP +Once B has opened A's mpx file +it is said to have a +.I channel +to A. +A channel is a pair of data streams: +in this case, one from B to A and the +other from A to B. +Several processes may open the same mpx file +yielding multiple channels within the one mpx file. +By accessing the appropriate channel, +A can communicate with B and any others. +When A reads (see +.IR read (2)) +from the mpx file +data written to A by the other processes appears +in A's buffer using a record format +described in +.IR mpxio (5). +When A writes (see +.IR write (2)) +on its mpx file the data must be formatted in a similar way. +.PP +The following commands +are used to manipulate mpx files and channels. +.IP +.IR join \- +adds a new channel on an mpx file to an open file F. +I/O on the new channel is I/O on F. +.br +.IR chan \- +creates a new channel. +.br +.IR extract \- +file descriptor maintenance. +.br +.IR connect \- +similar to join except that the open file F is connected +to an existing channel. +.br +.I attach +and +.IR detach \- +used with call protocol. +.br +.IR npgrp \- +manipulates process group numbers so that a channel +can act as a control terminal (see +.IR tty (4)). +.br +.IR ckill \- +send signal (see +.IR signal (2)) +to process group through channel. +.PP +A maximum of 15 channels may be connected to an +mpx file. +They are numbered 0 through 14. +.I Join +may be used to make one mpx file appear as a channel +on another mpx file. +A hierarchy or tree of mpx files may be set up in this way. +In this case +one of the mpx files must be the root of a tree +where the other mpx files are interior nodes. +The maximum depth of such a tree +is 4. +.PP +An +.I index +is a 16-bit value +that denotes a location +in an mpx tree other than the root: +the path through mpx `nodes' from the root +to the location is expressed as a sequence of +4-bit nibbles. +The branch taken at the root is represented by +the low-order 4-bits of an index. +Each succeeding branch is specified by the next +higher-order nibble. +If the length of a path to be expressed +is less than 4, +then the illegal channel number, 15, +must be used to terminate the sequence. +This is not strictly necessary for the +simple case of a tree consisting of +only a root node: its channels +can be expressed by the numbers +0 through 14. +An index +.I i +and file descriptor +.I xd +for the root of an mpx tree are +required as arguments to most +of the commands described below. +Indices also serve as channel identifiers +in the record formats given in +.IR mpxio (5). +Since \-1 is not a valid index, +it can be returned as a error indication +by subroutines that normally return +indices. +.PP +The operating system informs the process managing an mpx file +of changes in the status of channels attached to the file +by generating messages that +are read along with data from the channels. +The form and content of these messages is described +in +.IR mpxio (5). +.PP +.B join(fd, xd) +establishes a connection (channel) between an mpx file +and another object. +.I Fd +is an open file descriptor for a character device +or an mpx file and +.I xd +is the file descriptor of an +mpx file. +.I Join +returns the index for the new channel +if the operation succeeds and \-1 +if it does not. +.PP +Following join, +.I fd +may still be used in any system call that would +have been meaningful before the join operation. +Thus +a process can read and write directly to +.I fd +as well as access it via +.I xd. +If the number of channels +required for a tree of mpx files +exceeds the number of open files +permitted a process by the operating system, +some of the file descriptors can be released using +the standard +.IR close (2) +call. +Following a close on an active file descriptor for a channel +or internal mpx node, +that object may still be accessed through the root of the +tree. +.PP +.B chan(xd) +allocates a channel and connects +one end of it to the mpx file +represented by file descriptor +.I xd. +.I Chan +returns the index of the new channel or +a \-1 indicating failure. +The +.I extract +primitive can be used to get a non-multiplexed +file descriptor for the free end of a channel +created by +.I chan. +.PP +Both +.I chan +and +.I join +operate on the mpx file specified by +.IR xd . +File descriptors for interior nodes of an +mpx tree must be preserved or reconstructed with +.I extract +for use with +.I join +or +.IR chan . +For the remaining commands described here, +.I xd +denotes the file descriptor for the +root of an mpx tree. +.PP +.B extract(i, xd) +returns a file descriptor for the object with +index +.I i +on the mpx tree with root file descriptor +.I xd. +A \-1 is returned by extract if a file descriptor is not available +or if the arguments do not refer to an existing +channel and mpx file. +.PP +.B attach(i, xd) +.br +.BR "detach(i, xd)" . +If a process A has created an mpx file represented +by file descriptor +.I xd, +then a process B +can open (see +.IR open (2)) +the mpx file. +The purpose is to establish a channel between +A and B through the mpx file. +.I Attach +and +.I Detach +are used by A to respond to +such opens. +.PP +An open request by B fails immediately if a +new channel cannot be allocated on the mpx file, +if the mpx file does not exist, +or if it does exist +but there is no process (A) +with a multiplexed file descriptor +for the mpx file +(i.e. +.I xd +as returned by +.IR mpx (2)). +Otherwise a channel +with index number +.I i +is allocated. +The next time A reads on file descriptor +.IR xd , +the WATCH control message +(see +.IR mpxio (5)) +will be delivered on channel +.I i. +A responds to this message with +.I attach +or +.I detach. +The former causes the open to complete and +return a file descriptor to B. +The latter deallocates channel +.I i +and causes the open to fail. +.PP +One mpx file may be placed in `listener' mode. +This is done by writing +.I "ioctl(xd, MXLSTN, 0)" +where +.I xd +is an mpx file descriptor +and MXLSTN is defined in +.IR /usr/include/sgtty.h . +The semantics of listener mode are that +all file names discovered by +.IR open (2) +to have +the syntax +.I "system!pathname" +(see +.IR uucp (1)) +are treated as opens on the mpx file. +The operating system sends the listener process +an OPEN message (see +.IR mpxio (5)) +which includes the file name being opened. +.I Attach +and +.I detach +then apply as described above. +.PP +.I Detach +has two other uses: +it closes and releases the resources +of any active channel it is applied to, +and should be used to respond to +a CLOSE message (see +.IR mpxio (5)) +on a channel so the channel may be reused. +.PP +.BR "connect(fd, cd, end)" . +.I Fd +is a character file descriptor and +.I cd +is a file descriptor for a channel, +such as might be obtained via +.I "extract( chan(xd), xd)" +or by +.IR open (2) +followed by +.I attach. +.I Connect +splices the two streams together. +If +.I end +is negative, only +the output of +.I fd +is spliced to the input of +.I cd. +If +.I end +is positive, the output of +.I cd +is spliced to the input of +.I fd. +If +.I end +is zero, then both splices are made. +.PP +.BR "npgrp(i, xd, pgrp)" . +If +.I xd +is negative +.I npgrp +applies to the process executing it, +otherwise +.I i +and +.I xd +are interpreted as a channel index and +mpx file descriptor +and +.I npgrp +is applied to the process on the +non-multiplexed end of the channel. +If +.I pgrp +is zero, the process group number of the indicated process +is set to the process number of that process, +otherwise the value of +.I pgrp +is used as the process group number. +.PP +.I Npgrp +normally returns the new process group number. +If +.I i +and +.I xd +specify a nonexistent channel, +.I npgrp +returns \-1. +.PP +.B ckill(i, xd, signal) +sends the specified signal (see +.IR signal (2)) +through the channel specified by +.I i +and +.I xd. +If the channel is connected to anything other +than a process, +.I ckill +is a null operation. +If there is a process at the other end of the channel, +the process group will be interrupted (see +.IR signal (2), +.IR kill (2)). +.I Ckill +normally returns +.I signal. +If +.I ch +and +.I xd +specify a nonexistent channel, +.I ckill +returns \-1. +.SH FILES +/usr/include/sys/mx.h +.br +/usr/include/sgtty.h +.SH "SEE ALSO" +mpxio(5) +.SH BUGS +.PP +Mpx files are an experimental part of the operating +system more subject to change and prone to bugs +than other parts. +.PP +Maintenance programs, e.g. +.IR icheck (1), +diagnose mpx files as an illegal mode. +.PP +Channels may only be connected to objects in the operating +system that are accessible through the line discipline +mechanism. +.PP +Higher performance line disciplines are needed. +.PP +The maximum tree depth restriction is not really checked. +.PP +A non-destructive +.I disconnect +primitive (inverse of +.IR connect ) +is not provided. +.PP +A non-blocking flow control strategy +based on messages defined in +.IR mpxio (5) +should not be attempted by novices; +the enabling +.I ioctl +command should be protected. +.PP +The +.I join +operation could be subsumed by +.I connect. +A mechanism is needed for moving a channel from one +location in an mpx tree to another. |