man(1) Manual page archive

     INTRO(2)                                                 INTRO(2)

          intro - introduction to library functions

          #include <u.h>

          #include <libc.h>

          #include <stdio.h>

          #include <bio.h>

          #include <libg.h>

          #include <gnot.h>

          #include <frame.h>

          #include <layer.h>

          #include <regexp.h>

          This section describes functions in various libraries.  For
          the most part, each library is defined by a single C include
          file, listed above, and a single archive file containing the
          library proper.  The name of the archive is
          /$objtype/lib/libx.a, where x is the base of the include
          file name, stripped of a leading lib if present.  For exam-
          ple, <libg.h> defines the contents of library
          /$objtype/lib/libg.a which may be abbreviated when named to
          the loader as -lg . In practice, each include file contains
          a #pragma that directs the loader to pick up the associated
          archive automatically, so it is rarely necessary to tell the
          loader which libraries a program needs.

          The library to which a function belongs is identified by the
          section number at the top of the manual page:

          (2)  These functions constitute the `C library', libc, con-
               taining most of the basic non-system call subroutines
               such as strlen . Declarations for all of these func-
               tions are in <libc.h>, which must be preceded by
               (needs) an include of <u.h>.

          (2G) These functions constitute the library libg, the graph-
               ics library.  Declarations for these functions are in
               <libg.h>, which needs <libc.h> and <u.h>.

          (2S) These functions constitute the library libstdio, the

     INTRO(2)                                                 INTRO(2)

               `standard I/O package' (see fgetc(2)). Declarations for
               these functions are in <stdio.h>.

          (2X) Various specialized libraries have not been given dis-
               tinctive captions.  Files in which such libraries are
               found are named on appropriate pages.

          The include file <u.h>, a prerequisite of several other
          include files, declares the architecture-dependent and
          -independent types, including: ushort, uchar, and ulong, the
          unsigned integer types; schar, the signed char type; vlong,
          a very long integral type; jmp_buf, the type of the argument
          to setjmp and longjmp, plus macros that define the layout of
          jmp_buf (see setjmp(2)); definitions of the bits in the
          floating-point control register as used by getfcr(2);
          Length, a union giving different views of the 64-bit length
          of a file, declared as

               typedef union
                     char   clength[8];
                     vlong  vlength;
                            long hlength;   /* high order */
                            long length;    /* low order */
               } Length;

        Name space
          Files are collected into a hierarchical organization called
          a file tree starting in a directory called the root. File
          names, also called paths, consist of a number of /-separated
          path elements with the slashes corresponding to directories.
          A path element must contain only printable characters that
          occupy no more than NAMELEN-1 bytes.  A path element cannot
          contain a space or slash.

          When a process presents a file name to Plan 9, it is
          evaluated by the following algorithm.  Start with a direc-
          tory that depends on the first character of the path: `/'
          means the root of the main hierarchy, `#' means the separate
          root of a kernel device's file tree (see Section 3), and
          anything else means the process's current working directory.
          Then for each path element, look up the element in the
          directory, advance to that directory, do a possible transla-
          tion (see below) and repeat.  The last step may yield a
          directory or regular file.  The collection of files reach-
          able from the root is called the name space of a process.

          A program can use bind or mount (see bind(2)) to say that
          whenever a specified file is reached during evaluation,

     INTRO(2)                                                 INTRO(2)

          evaluation instead continues from a second specified file.
          Also, the same system calls create union directories, which
          are concatenations of ordinary directories that are searched
          sequentially until the desired element is found.  Using bind
          and mount to do name space adjustment affects only the cur-
          rent process group (see below).  Certain conventions about
          the layout of the name space should be preserved; see

        File I/O
          Files are opened for input or output by open or create (see
          open(2)). These calls return an integer called a file
          descriptor which identifies the file to subsequent I/O
          calls, notably read(2) and write. File descriptors range
          from 0 to 99 in the current system.  The system allocates
          the numbers by selecting the lowest unused descriptor.  They
          may be reassigned using dup(2). File descriptors are indices
          into a kernel resident file descriptor table. Each process
          has an associated file descriptor table.  In some cases (see
          rfork in fork(2)) a file descriptor table may be shared by
          several processes.

          By convention, file descriptor 0 is the standard input, 1 is
          the standard output, and 2 is the standard error output.
          With one exception, the operating system is unaware of these
          conventions; it is permissible to close file 0, or even to
          replace it by a file open only for writing, but many pro-
          grams will be confused by such chicanery.  The exception is
          that the system prints messages about broken processes to
          file descriptor 2.

          Files are normally read or written in sequential order.  The
          I/O position in the file is called the file offset and may
          be set arbitrarily using the seek(2) system call.

          Directories may be opened and read much like regular files.
          They contain an integral number of records, called directory
          entries, of length DIRLEN (defined in <libc.h>).  Each entry
          is a machine-independent representation of the information
          about an existing file in the directory, including the name,
          ownership, permission, access dates, and so on.  The entry
          corresponding to an arbitrary file can be retrieved by
          stat(2) or fstat; wstat and fwstat write back entries, thus
          changing the properties of a file.  An entry may be trans-
          lated into a more convenient, addressable form called a Dir
          structure; dirstat, dirfstat, dirwstat, and dirfwstat exe-
          cute the appropriate translations (see stat(2)).

          New files are made with create (in open(2)) and deleted with
          remove(2). Directories may not directly be written; create,
          remove, wstat, and fwstat alter them.

     INTRO(2)                                                 INTRO(2)

          Pipe(2) creates a connected pair of file descriptors, useful
          for local communication.

        Process execution and control
          A new process is created when an existing one calls rfork
          with the RFPROC bit set, usually just by calling fork(2).
          The new (child) process starts out with copies of the
          address space and most other attributes of the old (parent)
          process.  In particular, the child starts out running the
          same program as the parent; exec(2) will bring in a differ-
          ent one.

          Each process has a unique integer process id; a set of open
          files, indexed by file descriptor; and a current working
          directory (changed by chdir(2)).

          Each process has a set of attributes - memory, open files,
          name space, etc. - that may be shared or unique.  Flags to
          rfork control the sharing of these attributes.

          A process terminates by calling exits(2). A parent process
          may call wait (in exits(2)) to wait for some child to termi-
          nate.  A string of status information may be passed from
          exits to wait. A process can go to sleep for a specified
          time by calling sleep(2).

          There is a notification mechanism for telling a process
          about events such as address faults, floating point faults,
          and messages from other processes.  A process uses notify(2)
          to register the function to be called (the notification
          handler) when such events occur.

          nm(1), 2l(1), 2c(1)

          Math functions in libc will return special values when the
          function is undefined for the given arguments or when the
          value is not representable (see nan(2)).

          Some of the functions in libc are system calls and many oth-
          ers employ system calls in their implementation.  All system
          calls return integers, with -1 indicating that an error
          occurred; errstr(2) recovers a string describing the error.
          Functions that may affect the value of the error string are
          said to ``set errstr''; it is understood that the error
          string is altered only if an error occurs.