282 lines
6.2 KiB
Groff
282 lines
6.2 KiB
Groff
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.TH SYSTEM 3ACK "86/03/24"
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.SH NAME
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sys_open, sys_close, sys_read, sys_write, sys_reset, sys_access,
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sys_modtime, sys_remove, sys_filesize, sys_chmode,
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sys_lock, sys_unlock,
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sys_break, sys_stop, sys_time \- system call interface
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.SH SYNOPSIS
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.nf
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.B #include <system.h>
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.PP
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.B File *STDIN, *STDOUT, *STDERR;
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.PP
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.B int sys_open(path, flag, filep)
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.B char *path;
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.B int flag;
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.B File **filep;
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.PP
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.B sys_close(filep)
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.B File *filep;
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.PP
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.B int sys_read(filep, bufptr, bufsiz, pnbytes)
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.B File *filep;
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.B char *bufptr;
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.B int bufsiz, *pnbytes;
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.PP
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.B int sys_write(filep, bufptr, nbytes)
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.B File *filep;
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.B char *bufptr;
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.B int nbytes;
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.PP
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.B int sys_reset(filep)
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.B File *filep
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.PP
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.B int sys_access(path, mode)
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.B char *path;
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.B int mode;
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.PP
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.B int sys_remove(path)
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.B char *path;
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.PP
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.B long sys_filesize(path)
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.B char *path;
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.PP
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.B int sys_chmode(path, mode)
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.B char *path;
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.B int mode;
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.PP
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.B int sys_lock(name)
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.B char *name;
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.PP
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.B int sys_unlock(name)
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.B char *name;
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.PP
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.B char *sys_break(incr)
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.B int incr;
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.PP
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.B sys_stop(how)
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.B int how;
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.PP
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.B long sys_time();
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.PP
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.B long sys_modtime(path)
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.B char *path;
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.fi
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.SH DESCRIPTION
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This package provides a rather system-independent set of "system" calls
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primarily intended for use in compilers.
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The include file contains a defined constant,
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.IR BUFSIZ ,
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which gives the system-dependent block size.
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Another constant,
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.IR SYS_NOPEN ,
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gives the maximum number of open files in a process.
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.PP
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.I Sys_open
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opens a file called
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.I path
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for sequential reading or writing, as specified by
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.I flag
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and returns in
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.I filep
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a decsriptor for the opened file.
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The allowed values for
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.I flag
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are
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.IP OP_READ 15
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open for reading
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.IP OP_WRITE 15
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open for rewriting (create
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.I path
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if it did not exist)
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.IP OP_APPEND 15
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open for writing at the end (create
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.I path
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if it did not exist)
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.LP
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Created files are given read and write permission for its creator and
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read permission for other users.
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.br
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Specifying
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.I path
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as null pointer opens a so-called anonymous file, which has no name and
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disappears when it is closed or when the program exits.
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It is possible to read the contents of an anonymous file by using
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.I reset .
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.br
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There are three normally open files with the following descriptors:
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.IP STDIN 15
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standard input file; opened as OP_READ
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.IP STDOUT 15
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standard output file; opened as OP_APPEND
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.IP STDERR 15
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standard error file; opened as OP_APPEND
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.LP
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.I Sys_close
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causes the open file known by
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.I filep
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to be closed.
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.PP
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.I Sys_read
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causes up to
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.I bufsiz
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contiguous bytes to be read from the open file known by
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.I filep
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into a piece of memory pointed at by
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.IR bufptr .
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The number of bytes actually read is returned in
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.IR *pnbytes .
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If
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.I *pnbytes
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is set to 0 then the end-of-file is reached.
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.PP
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.I Sys_write
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writes
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.I nbytes
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contiguous bytes from the memory pointed at by
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.I bufptr
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onto the open file known by
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.IR filep .
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A non-zero return value indicates that
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.I nbytes
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are actually written.
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.PP
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.I Sys_reset
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causes the open file known by
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.I filep
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to be re-opened for reading (cf. open flag OP_READ).
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This may be useful in reading anonymous files.
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.PP
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.I Sys_access
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checks the given file
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.I path
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for accessibility according to
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.I mode
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which is the result of
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.IR or 'ing
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one or more of the following values:
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.IP AC_READ 15
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file exists and is readable
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.IP AC_WRITE 15
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file exists and is writable
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.IP AC_EXEC 15
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file exists and is executable
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.LP
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Specifying
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.I mode
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as 0 tests whether the directories leading to the file can be searched and the
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file exists.
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The return value is either 0 if the
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file is not reachable, does not exist or if the access is not allowed,
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or 1 if the indicated access is permitted.
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.PP
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.I Sys_modtime
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returns the last-modified time of the file specified in
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.IR path .
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Any failure is indicated by a return value of \-1L.
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.PP
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.I Sys_remove
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removes file
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.I path
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from the system.
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It is supposed that, if the file is still open, the contents of
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the file are available until the last
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.I sys_close
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is performed on it.
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A non-zero return value indicates successful action whereas 0
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indicates that the given file does not exist or cannot be removed.
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.PP
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The function
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.I sys_filesize
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returns the size in bytes of the
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file specified by
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.IR path ,
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if possible.
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The value \-1L is returned if the size cannot be retrieved for some reason.
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.PP
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.I Sys_chmode
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changes the file-protection mode of file
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.I path
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to
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.IR mode .
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.PP
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.I Sys_lock
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and
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.I sys_unlock
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provide a mechanism for setting and clearing symbolic locks for external
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objects.
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This is done by creating and removing file
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.IR name .
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.I Sys_lock
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returns zero if the lock is already set and a non-zero value if the lock
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did not exist and has been created.
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.I Sys_unlock
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returns a non-zero value if the lock did not exist or if the lock has been
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removed succesfully.
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Zero is returned otherwise.
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The actions performed by these routines are atomic:
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race conditions cannot
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occur.
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.PP
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.I Sys_break
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adds
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.I incr
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more bytes to the program's data space and returns a pointer to
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the newly allocated area.
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ILL_BREAK is returned in case of some error, due to a lack of space or
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some interrupt.
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It is equivalent to the UNIX version 7
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.IR sbrk (2).
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.PP
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.I Sys_stop
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should be called when the process is terminated due to
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the end of the program or some error.
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This routine closes all open files and causes the program to
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stop in a way specified by
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.IR how ,
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which parameter has one of the following values:
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.IP S_END 15
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normal termination, indicate successful completion
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.IP S_EXIT 15
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terminate the process with status
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.B 1
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.IP S_ABORT 15
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abort this process and produce a post-mortem dump
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.LP
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.PP
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.I Sys_time
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returns a long value that stands for the system's time.
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Its return value is a long that stands for the time
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since 00:00:00 GMT, Jan. 1, 1970, measured in seconds.
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.SH FILES
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.nf
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~em/modules/h/system.h
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~em/modules/lib/libsystem.a
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.fi
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.SH DIAGNOSTICS
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.PP
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The routines
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.IR sys_open ,
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.IR sys_read ,
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.IR sys_write ,
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.IR sys_reset ,
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.I sys_chmode
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and
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.I sys_remove
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return a value of zero upon any failure and a non-zero
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value if the call succeeds.
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.SH BUGS
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The current implementation does not allow the use of anonymous files.
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.br
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.I Sys_reset
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is not implemented.
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A
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.I sys_close
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followed by a
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.I sys_open
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with the proper mode has the same effect on non-anonymous files.
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.SH "SEE ALSO"
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UNIX version 7 manual volume 1, chapter 2
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.SH AUTHOR
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Erik Baalbergen <erikb@vu44.UUCP>
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