freebsd-src/stand/libsa/libsa.3

.\" Copyright (c) Michael Smith
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.Dd September 9, 2022
.Dt LIBSA 3
.Os
.Sh NAME
.Nm libsa
.Nd support library for standalone executables
.Sh SYNOPSIS
.In stand.h
.Sh DESCRIPTION
The
.Nm
library provides a set of supporting functions for standalone
applications, mimicking where possible the standard
.Bx
programming
environment.
The following sections group these functions by kind.
Unless specifically described here, see the corresponding section 3
manpages for the given functions.
.Sh STRING FUNCTIONS
String functions are available as documented in
.Xr string 3
and
.Xr bstring 3 .
.Sh MEMORY ALLOCATION
.Bl -hang -width 10n
.It Xo
.Ft "void *"
.Fn malloc "size_t size"
.Xc
.Pp
Allocate
.Fa size
bytes of memory from the heap using a best-fit algorithm.
.It Xo
.Ft void
.Fn free "void *ptr"
.Xc
.Pp
Free the allocated object at
.Fa ptr .
.It Xo
.Ft void
.Fn setheap "void *start" "void *limit"
.Xc
.Pp
Initialise the heap.
This function must be called before calling
.Fn 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.
.It Xo
.Ft "char *"
.Fn sbrk "int junk"
.Xc
.Pp
Provides the behaviour of
.Fn 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.
.El
.Sh 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.
.Bl -hang -width 10n
.It Xo
.Ft "char *"
.Fn getenv "const char *name"
.Xc
.It Xo
.Ft int
.Fn setenv "const char *name" "const char *value" "int overwrite"
.Xc
.It Xo
.Ft int
.Fn putenv "char *string"
.Xc
.It Xo
.Ft int
.Fn unsetenv "const char *name"
.Xc
.Pp
These functions behave similarly to their standard library counterparts.
.It Xo
.Ft "struct env_var *"
.Fn env_getenv "const char *name"
.Xc
.Pp
Looks up a variable in the environment and returns its entire
data structure.
.It Xo
.Ft int
.Fn env_setenv "const char *name" "int flags" "const void *value" "ev_sethook_t sethook" "ev_unsethook_t unsethook"
.Xc
.Pp
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.
.Pp
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
.Fn env_setenv
again with EV_NOHOOK set to actually save the value.
The predefined function
.Fn env_noset
may be specified to refuse all attempts to set a variable.
.Pp
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.
.El
.Sh STANDARD LIBRARY SUPPORT
.Bl -hang -width 10n
.It Xo
.Ft int
.Fn abs "int i"
.Xc
.It Xo
.Ft int
.Fn getopt "int argc" "char * const *argv" "const char *optstring"
.Xc
.It Xo
.Ft long
.Fn strtol "const char *nptr" "char **endptr" "int base"
.Xc
.It Xo
.Ft long long
.Fn strtoll "const char *nptr" "char **endptr" "int base"
.Xc
.It Xo
.Ft long
.Fn strtoul "const char *nptr" "char **endptr" "int base"
.Xc
.It Xo
.Ft long long
.Fn strtoull "const char *nptr" "char **endptr" "int base"
.Xc
.It Xo
.Ft void
.Fn srandom "unsigned int seed"
.Xc
.It Xo
.Ft "long"
.Fn random void
.Xc
.It Xo
.Ft "char *"
.Fn strerror "int error"
.Xc
.Pp
Returns error messages for the subset of errno values supported by
.Nm .
.It Fn assert expression
.Pp
Requires
.In assert.h .
.It Xo
.Ft int
.Fn setjmp "jmp_buf env"
.Xc
.It Xo
.Ft void
.Fn longjmp "jmp_buf env" "int val"
.Xc
.Pp
Defined as
.Fn _setjmp
and
.Fn _longjmp
respectively as there is no signal state to manipulate.
Requires
.In setjmp.h .
.El
.Sh CHARACTER I/O
.Bl -hang -width 10n
.It Xo
.Ft void
.Fn gets "char *buf"
.Xc
.Pp
Read characters from the console into
.Fa buf .
All of the standard cautions apply to this function.
.It Xo
.Ft void
.Fn ngets "char *buf" "int size"
.Xc
.Pp
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
.Fn gets .
.It Xo
.Ft int
.Fn fgetstr "char *buf" "int size" "int fd"
.Xc
.Pp
Read a line of at most
.Fa size
characters into
.Fa buf .
Line terminating characters are stripped, and the buffer is always
.Dv NUL
terminated.
Returns the number of characters in
.Fa buf
if successful, or -1 if a read error occurs.
.It Xo
.Ft int
.Fn printf "const char *fmt" "..."
.Xc
.It Xo
.Ft void
.Fn vprintf "const char *fmt" "va_list ap"
.Xc
.It Xo
.Ft int
.Fn sprintf "char *buf" "const char *fmt" "..."
.Xc
.It Xo
.Ft void
.Fn vsprintf "char *buf" "const char *fmt" "va_list ap"
.Xc
.Pp
The *printf functions implement a subset of the standard
.Fn 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.
.Pp
The
.Li b
conversion is provided to decode error registers.
Its usage is:
.Bd -ragged -offset indent
printf(
.Qq reg=%b\en ,
regval,
.Qq <base><arg>*
);
.Ed
.Pp
where <base> is the output expressed as a control character, e.g.\& \e10 gives
octal, \e20 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
.Bd -ragged -offset indent
printf(
.Qq reg=%b\en ,
3,
.Qq \e10\e2BITTWO\e1BITONE
);
.Ed
.Pp
would give the output
.Bd -ragged -offset indent
reg=3<BITTWO,BITONE>
.Ed
.Pp
The
.Li D
conversion provides a hexdump facility, e.g.
.Bd -ragged -offset indent
printf(
.Qq %6D ,
ptr,
.Qq \&:
); gives
.Qq XX:XX:XX:XX:XX:XX
.Ed
.Bd -ragged -offset indent
printf(
.Qq %*D ,
len,
ptr,
.Qq "\ "
); gives
.Qq XX XX XX ...
.Ed
.El
.Sh CHARACTER TESTS AND CONVERSIONS
.Bl -hang -width 10n
.It Xo
.Ft int
.Fn isupper "int c"
.Xc
.It Xo
.Ft int
.Fn islower "int c"
.Xc
.It Xo
.Ft int
.Fn isspace "int c"
.Xc
.It Xo
.Ft int
.Fn isdigit "int c"
.Xc
.It Xo
.Ft int
.Fn isxdigit "int c"
.Xc
.It Xo
.Ft int
.Fn isascii "int c"
.Xc
.It Xo
.Ft int
.Fn isalpha "int c"
.Xc
.It Xo
.Ft int
.Fn isalnum "int c"
.Xc
.It Xo
.Ft int
.Fn iscntrl "int c"
.Xc
.It Xo
.Ft int
.Fn isgraph "int c"
.Xc
.It Xo
.Ft int
.Fn ispunct "int c"
.Xc
.It Xo
.Ft int
.Fn toupper "int c"
.Xc
.It Xo
.Ft int
.Fn tolower "int c"
.Xc
.El
.Sh FILE I/O
.Bl -hang -width 10n
.It Xo
.Ft int
.Fn open "const char *path" "int flags"
.Xc
.Pp
Similar to the behaviour as specified in
.Xr 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.
Only UFS currently supports writing.
.It Xo
.Ft int
.Fn close "int fd"
.Xc
.It Xo
.Ft void
.Fn closeall void
.Xc
.Pp
Close all open files.
.It Xo
.Ft ssize_t
.Fn read "int fd" "void *buf" "size_t len"
.Xc
.It Xo
.Ft ssize_t
.Fn write "int fd" "void *buf" "size_t len"
.Xc
.Pp
(No file systems currently support writing.)
.It Xo
.Ft off_t
.Fn lseek "int fd" "off_t offset" "int whence"
.Xc
.Pp
Files being automatically uncompressed during reading cannot seek backwards
from the current point.
.It Xo
.Ft int
.Fn stat "const char *path" "struct stat *sb"
.Xc
.It Xo
.Ft int
.Fn fstat "int fd" "struct stat *sb"
.Xc
.Pp
The
.Fn stat
and
.Fn fstat
functions only fill out the following fields in the
.Fa sb
structure: st_mode,st_nlink,st_uid,st_gid,st_size.
The
.Nm tftp
file system cannot provide meaningful values for this call, and the
.Nm cd9660
file system always reports files having uid/gid of zero.
.El
.Sh PAGER
The
.Nm
library supplies a simple internal pager to ease reading the output of large
commands.
.Bl -hang -width 10n
.It Xo
.Ft void
.Fn pager_open
.Xc
.Pp
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.
.It Xo
.Ft void
.Fn pager_close void
.Xc
.Pp
Closes the pager.
.It Xo
.Ft int
.Fn pager_output "const char *lines"
.Xc
.Pp
Sends the lines in the
.Dv NUL Ns
-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
.Fn 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.
.It Xo
.Ft int
.Fn pager_file "const char *fname"
.Xc
.Pp
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.
.El
.Sh FEATURE SUPPORT
A set of functions are provided to communicate support of features from the
loader binary to the interpreter.
These are used to do something sensible if we are still operating with a loader
binary that behaves differently than expected.
.Bl -hang -width 10n
.It Xo
.Ft void
.Fn feature_enable "uint32_t mask"
.Xc
.Pp
Enable the referenced
.Fa mask
feature, which should be one of the
.Li FEATURE_*
macros defined in
.In stand.h .
.It Xo
.Ft bool
.Fn feature_name_is_enabled "const char *name"
.Xc
.Pp
Check if the referenced
.Fa name
feature is enabled.
The
.Fa name
is usually the same name as the
.Li FEATURE_*
macro, but with the FEATURE_ prefix stripped off.
The authoritative source of feature names is the mapping table near the top in
.Pa stand/libsa/features.c .
.It Xo
.Ft void
.Fn "(feature_iter_fn)" "void *cookie" "const char *name" "const char *desc" "bool enabled"
.Xc
.Pp
The
.Fa cookie
argument is passed as-is from the argument of the same name to
.Fn feature_iter .
The
.Fa name
and
.Fa desc
arguments are defined in the mapping table in
.Pa stand/libsa/features.c .
The
.Fa enabled
argument indicates the current status of the feature, though one could
theoretically turn a feature off in later execution.
As such, this should likely not be trusted if it is needed after the iteration
has finished.
.It Xo
.Ft void
.Fn "feature_iter" "feature_iter_fn *iter_fn" "void *cookie"
.Xc
.Pp
Iterate over the current set of features.
.El
.Sh MISC
.Bl -hang -width 10n
.It Xo
.Ft char *
.Fn devformat "struct devdesc *"
.Xc
.Pp
Format the specified device as a string.
.It Xo
.Ft int
.Fn devparse "struct devdesc **dev" "const char *devdesc" "const char **path"
.Xc
.Pp
Parse the
.Dv devdesc
string of the form
.Sq device:[/path/to/file] .
The
.Dv devsw
table is used to match the start of the
.Sq device
string with
.Fa dv_name .
If
.Fa dv_parsedev
is non-NULL, then it will be called to parse the rest of the string and allocate
the
.Dv struct devdesc
for this path.
If NULL, then a default routine will be called that will allocate a simple
.Dv struct devdesc ,
parse a unit number and ensure there's no trailing characters.
If
.Dv path
is non-NULL, then a pointer to the remainder of the
.Dv devdesc
string after the device specification is written.
.It Xo
.Ft int
.Fn devinit void
Calls all the
.Fa dv_init
routines in the
.Dv devsw
array, returning the number of routines that returned an error.
.It Xo
.Ft void
.Fn twiddle void
.Xc
.Pp
Successive calls emit the characters in the sequence |,/,-,\\ followed by a
backspace in order to provide reassurance to the user.
.El
.Sh REQUIRED LOW-LEVEL SUPPORT
The following resources are consumed by
.Nm
- stack, heap, console and devices.
.Pp
The stack must be established before
.Nm
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.
.Pp
The heap must be established before calling
.Fn alloc
or
.Fn open
by calling
.Fn 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.
.Pp
Console access is performed via the
.Fn getchar ,
.Fn putchar
and
.Fn ischar
functions detailed below.
.Pp
Device access is initiated via
.Fn devopen
and is performed through the
.Fn dv_strategy ,
.Fn dv_ioctl
and
.Fn dv_close
functions in the device switch structure that
.Fn devopen
returns.
.Pp
The consumer must provide the following support functions:
.Bl -hang -width 10n
.It Xo
.Ft int
.Fn getchar void
.Xc
.Pp
Return a character from the console, used by
.Fn gets ,
.Fn ngets
and pager functions.
.It Xo
.Ft int
.Fn ischar void
.Xc
.Pp
Returns nonzero if a character is waiting from the console.
.It Xo
.Ft void
.Fn putchar int
.Xc
.Pp
Write a character to the console, used by
.Fn gets ,
.Fn ngets ,
.Fn *printf ,
.Fn panic
and
.Fn twiddle
and thus by many other functions for debugging and informational output.
.It Xo
.Ft int
.Fn devopen "struct open_file *of" "const char *name" "const char **file"
.Xc
.Pp
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
.Va 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
.Fn open
and thus for all device-related I/O.
.It Xo
.Ft int
.Fn devclose "struct open_file *of"
.Xc
.Pp
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.
.It Xo
.Ft void
.Fn __abort
.Xc
.Pp
Calls
.Fn panic
with a fixed string.
.It Xo
.Ft void
.Fn panic "const char *msg" "..."
.Xc
.Pp
Signal a fatal and unrecoverable error condition.
The
.Fa msg ...
arguments are as for
.Fn printf .
.El
.Sh 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
.Nm ,
the consumer may supply other file systems of their own:
.Bl -hang -width ".Va cd9660_fsops"
.It Va ufs_fsops
The
.Bx
UFS.
.It Va ext2fs_fsops
Linux ext2fs file system.
.It Va tftp_fsops
File access via TFTP.
.It Va nfs_fsops
File access via NFS.
.It Va cd9660_fsops
ISO 9660 (CD-ROM) file system.
.It Va gzipfs_fsops
Stacked file system supporting gzipped files.
When trying the gzipfs file system,
.Nm
appends
.Li .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
.Va 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
.Fn stat
and
.Fn fstat
on gzipped files will report an invalid length.
.It Va bzipfs_fsops
The same as
.Va gzipfs_fsops ,
but for
.Xr bzip2 1 Ns -compressed
files.
.El
.Pp
The array of
.Vt struct fs_ops
pointers should be terminated with a NULL.
.Sh 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.
.Sh DRIVER INTERFACE
The driver needs to provide a common set of entry points that are
used by
.Nm libsa
to interface with the device.
.Bd -literal
struct devsw {
    const char	dv_name[DEV_NAMLEN];
    int		dv_type;
    int		(*dv_init)(void);
    int		(*dv_strategy)(void *devdata, int rw, daddr_t blk,
			size_t size, char *buf, size_t *rsize);
    int		(*dv_open)(struct open_file *f, ...);
    int		(*dv_close)(struct open_file *f);
    int		(*dv_ioctl)(struct open_file *f, u_long cmd, void *data);
    int		(*dv_print)(int verbose);
    void	(*dv_cleanup)(void);
    char *	(*dv_fmtdev)(struct devdesc *);
    int		(*dv_parsedev)(struct devdesc **dev, const char *devpart,
    		const char **path);
    bool	(*dv_match)(struct devsw *dv, const char *devspec);
};
.Ed
.Bl -tag -width ".Fn dv_strategy"
.It Fn dv_name
The device's name.
.It Fn dv_type
Type of device.
The supported types are:
.Bl -tag -width "DEVT_NONE"
.It DEVT_NONE
.It DEVT_DISK
.It DEVT_NET
.It DEVT_CD
.It DEVT_ZFS
.It DEVT_FD
.El
Each type may have its own associated (struct type_devdesc),
which has the generic (struct devdesc) as its first member.
.It Fn dv_init
Driver initialization routine.
This routine should probe for available units.
Drivers are responsible for maintaining lists of units for later enumeration.
No other driver routines may be called before
.Fn dv_init
returns.
.It Fn dv_open
The driver open routine.
.It Fn dv_close
The driver close routine.
.It Fn dv_ioctl
The driver ioctl routine.
.It Fn dv_print
Prints information about the available devices.
Information should be presented with
.Fn pager_output .
.It Fn dv_cleanup
Cleans up any memory used by the device before the next stage is run.
.It Fn dv_fmtdev
Converts the specified devdesc to the canonical string representation
for that device.
.It Fn dv_parsedev
Parses the device portion of a file path.
The
.Dv devpart
will point to the
.Sq tail
of device name, possibly followed by a colon and a path within the device.
The
.Sq tail
is, by convention, the part of the device specification that follows the
.Fa dv_name
part of the string.
So when
.Fa devparse
is parsing the string
.Dq disk3p5:/xxx ,
.Dv devpart
will point to the
.Sq 3
in that string.
The parsing routine is expected to allocate a new
.Dv struct devdesc
or subclass and return it in
.Dv dev
when successful.
This routine should set
.Dv path
to point to the portion of the string after device specification, or
.Dq /xxx
in the earlier example.
Generally, code needing to parse a path will use
.Fa devparse
instead of calling this routine directly.
.It Fn dv_match
.Dv NULL
to specify that all device paths starting with
.Fa dv_name
match.
Otherwise, this function returns 0 for a match and a non-zero
.Dv errno
to indicate why it didn't match.
This is helpful when you claim the device path after using it to query
properties on systems that have uniform naming for different types of
devices.
.El
.Sh HISTORY
The
.Nm
library contains contributions from many sources, including:
.Bl -bullet -compact
.It
.Nm libsa
from
.Nx
.It
.Nm libc
and
.Nm libkern
from
.Fx 3.0 .
.It
.Nm zalloc
from
.An Matthew Dillon Aq Mt dillon@backplane.com
.El
.Pp
The reorganisation and port to
.Fx 3.0 ,
the environment functions and this manpage were written by
.An Mike Smith Aq Mt msmith@FreeBSD.org .
.Sh BUGS
The lack of detailed memory usage data is unhelpful.