libstand
- support library for standalone executables
SYNOPSIS
#include <stand.h>
DESCRIPTION
The
library provides a set of supporting functions for standalone
applications, mimicking where possible the standard
BSD programming
environment.
The following sections group these functions by kind.
Unless specifically described here, see the corresponding section 3
manpages for the given functions.
STRING FUNCTIONS
String functions are available as documented in
string(3)
and
bstring(3).
MEMORY ALLOCATION
void *
malloc (size_t size);
Allocate
Fa size
bytes of memory from the heap using a best-fit algorithm.
void
free (void *ptr);
Free the allocated object at
Fa ptr .
void
setheap (void *start void *limit);
Initialise the heap.
This function must be called before calling
alloc ();
for the first time.
The region between
Fa start
and
Fa limit
will be used for the heap; attempting to allocate beyond this will result
in a panic.
char *
sbrk (int junk);
Provides the behaviour of
sbrk (0 ,);
i.e., returns the highest point that the heap has reached.
This value can
be used during testing to determine the actual heap usage.
The
Fa junk
argument is ignored.
ENVIRONMENT
A set of functions are provided for manipulating a flat variable space similar
to the traditional shell-supported environment.
Major enhancements are support
for set/unset hook functions.
char *
getenv (const char *name);
int
setenv (const char *name const char *value int overwrite);
int
putenv (const char *string);
int
unsetenv (const char *name);
These functions behave similarly to their standard library counterparts.
struct env_var *
env_getenv (const char *name);
Looks up a variable in the environment and returns its entire
data structure.
int
env_setenv (const char *name int flags const void *value ev_sethook_t sethook ev_unsethook_t unsethook);
Creates a new or sets an existing environment variable called
Fa name .
If creating a new variable, the
Fa sethook
and
Fa unsethook
arguments may be specified.
The set hook is invoked whenever an attempt
is made to set the variable, unless the EV_NOHOOK flag is set.
Typically
a set hook will validate the
Fa value
argument, and then call
env_setenv ();
again with EV_NOHOOK set to actually save the value.
The predefined function
env_noset ();
may be specified to refuse all attempts to set a variable.
The unset hook is invoked when an attempt is made to unset a variable.
If it
returns zero, the variable will be unset.
The predefined function
Fa env_nounset
may be used to prevent a variable being unset.
long
strtol (const char *nptr char **endptr int base);
void
srandom (unsigned long seed);
unsigned long
random (void);
char *
strerror (int error);
Returns error messages for the subset of errno values supported by
.
Fn assert expression
Requires
In assert.h .
int
setjmp (jmp_buf env);
void
longjmp (jmp_buf env int val);
Defined as
_setjmp ();
and
_longjmp ();
respectively as there is no signal state to manipulate.
Requires
In setjmp.h .
CHARACTER I/O
void
gets (char *buf);
Read characters from the console into
Fa buf .
All of the standard cautions apply to this function.
void
ngets (char *buf int size);
Read at most
Fa size
- 1 characters from the console into
Fa buf .
If
Fa size
is less than 1, the function's behaviour is as for
gets (.);
int
fgetstr (char *buf int size int fd);
Read a line of at most
Fa size
characters into
Fa buf .
Line terminating characters are stripped, and the buffer is always
NUL
terminated.
Returns the number of characters in
Fa buf
if successful, or -1 if a read error occurs.
The *printf functions implement a subset of the standard
printf ();
family functionality and some extensions.
The following standard conversions
are supported: c,d,n,o,p,s,u,x.
The following modifiers are supported:
+,-,#,*,0,field width,precision,l.
The
b
conversion is provided to decode error registers.
Its usage is:
printf(
Qq reg=%b\n ,
regval,
Qq <base><arg>*
);
where <base> is the output expressed as a control character, e.g. \10 gives
octal, \20 gives hex.
Each <arg> is a sequence of characters, the first of
which gives the bit number to be inspected (origin 1) and the next characters
(up to a character less than 32) give the text to be displayed if the bit is set.
Thus
printf(
Qq %*D ,
len,
ptr,
Qq
); gives
Qq XX XX XX ...
CHARACTER TESTS AND CONVERSIONS
int
isupper (int c);
int
islower (int c);
int
isspace (int c);
int
isdigit (int c);
int
isxdigit (int c);
int
isascii (int c);
int
isalpha (int c);
int
toupper (int c);
int
tolower (int c);
FILE I/O
int
open (const char *path int flags);
Similar to the behaviour as specified in
open(2),
except that file creation is not supported, so the mode parameter is not
required.
The
Fa flags
argument may be one of O_RDONLY, O_WRONLY and O_RDWR (although no file systems
currently support writing).
int
close (int fd);
void
closeall (void);
Close all open files.
ssize_t
read (int fd void *buf size_t len);
ssize_t
write (int fd void *buf size_t len);
(No file systems currently support writing.)
off_t
lseek (int fd off_t offset int whence);
Files being automatically uncompressed during reading cannot seek backwards
from the current point.
int
stat (const char *path struct stat *sb);
int
fstat (int fd struct stat *sb);
The
stat ();
and
fstat ();
functions only fill out the following fields in the
Fa sb
structure: st_mode,st_nlink,st_uid,st_gid,st_size.
The
tftp
file system cannot provide meaningful values for this call, and the
cd9660
file system always reports files having uid/gid of zero.
PAGER
The
library supplies a simple internal pager to ease reading the output of large
commands.
void
pager_open ();
Initialises the pager and tells it that the next line output will be the top of the
display.
The environment variable LINES is consulted to determine the number of
lines to be displayed before pausing.
void
pager_close (void);
Closes the pager.
int
pager_output (const char *lines);
Sends the lines in the
NUL -terminated buffer at
Fa lines
to the pager.
Newline characters are counted in order to determine the number
of lines being output (wrapped lines are not accounted for).
The
pager_output ();
function will return zero when all of the lines have been output, or nonzero
if the display was paused and the user elected to quit.
int
pager_file (const char *fname);
Attempts to open and display the file
Fa fname .
Returns -1 on error, 0 at EOF, or 1 if the user elects to quit while reading.
MISC
void
twiddle (void);
Successive calls emit the characters in the sequence |,/,-,\ followed by a
backspace in order to provide reassurance to the user.
REQUIRED LOW-LEVEL SUPPORT
The following resources are consumed by
- stack, heap, console and devices.
The stack must be established before
functions can be invoked.
Stack requirements vary depending on the functions
and file systems used by the consumer and the support layer functions detailed
below.
The heap must be established before calling
alloc ();
or
open ();
by calling
setheap (.);
Heap usage will vary depending on the number of simultaneously open files,
as well as client behaviour.
Automatic decompression will allocate more
than 64K of data per open file.
Console access is performed via the
getchar (,);
putchar ();
and
ischar ();
functions detailed below.
Device access is initiated via
devopen ();
and is performed through the
dv_strategy (,);
dv_ioctl ();
and
dv_close ();
functions in the device switch structure that
devopen ();
returns.
The consumer must provide the following support functions:
int
getchar (void);
Return a character from the console, used by
gets (,);
ngets ();
and pager functions.
int
ischar (void);
Returns nonzero if a character is waiting from the console.
void
putchar (int);
Write a character to the console, used by
gets (,);
ngets (,);
Fn *printf ,
panic ();
and
twiddle ();
and thus by many other functions for debugging and informational output.
Open the appropriate device for the file named in
Fa name ,
returning in
Fa file
a pointer to the remaining body of
Fa name
which does not refer to the device.
The
f_dev
field in
Fa of
will be set to point to the
Vt devsw
structure for the opened device if successful.
Device identifiers must
always precede the path component, but may otherwise be arbitrarily formatted.
Used by
open ();
and thus for all device-related I/O.
int
devclose (struct open_file *of);
Close the device allocated for
Fa of .
The device driver itself will already have been called for the close; this call
should clean up any allocation made by devopen only.
void
panic (const char *msg ...);
Signal a fatal and unrecoverable error condition.
The
Fa msg ...
arguments are as for
printf (.);
INTERNAL FILE SYSTEMS
Internal file systems are enabled by the consumer exporting the array
Vt struct fs_ops *file_system[] ,
which should be initialised with pointers
to
Vt struct fs_ops
structures.
The following file system handlers are supplied by
,
the consumer may supply other file systems of their own:
ufs_fsops
The
BSD UFS.
ext2fs_fsops
Linux ext2fs file system.
tftp_fsops
File access via TFTP.
nfs_fsops
File access via NFS.
cd9660_fsops
ISO 9660 (CD-ROM) file system.
gzipfs_fsops
Stacked file system supporting gzipped files.
When trying the gzipfs file system,
appends
.gz
to the end of the filename, and then tries to locate the file using the other
file systems.
Placement of this file system in the
file_system[]
array determines whether gzipped files will be opened in preference to non-gzipped
files.
It is only possible to seek a gzipped file forwards, and
stat ();
and
fstat ();
on gzipped files will report an invalid length.
bzipfs_fsops
The same as
gzipfs_fsops
but for
bzip2(1)Ns-compressed
files.
The array of
Vt struct fs_ops
pointers should be terminated with a NULL.
DEVICES
Devices are exported by the supporting code via the array
Vt struct devsw *devsw[]
which is a NULL terminated array of pointers to device switch structures.
HISTORY
The
library contains contributions from many sources, including:
