Access to POSIX

This chapter describes Scheme 48’s interface to the POSIX C calls [1]. Scheme versions of most of the functions in POSIX are provided. Both the interface and implementation are new and are likely to change in future releases. Section 9.12 lists which Scheme functions call which C functions.

Scheme 48’s POSIX interface will likely change significantly in the future. The implementation is new and may have significant bugs.

The POSIX bindings are available in several structures:

posix-processes fork, exec, and friends
posix-process-data information about processes
posix-files files and directories
posix-i/o operations on ports
posix-time time functions
posix-users users and groups
posix-regexps regular expression matching
posix-syslog POSIX logging facility
posix-errnos POSIX error codes
posix all of the above

Scheme 48’s POSIX interface differs from Scsh’s [1112] in several ways. The interface here lacks Scsh’s high-level constructs and utilities, such as the process notation, awk procedure, and parsing utilities. Scheme 48 uses distinct types for some values that Scsh leaves as symbols or unboxed integers; these include file types, file modes, and user and group ids. Many of the names and other interface details are different, as well.

9.1  Process primitives

The procedures described in this section control the creation of processes and the execution of programs. They are in the structures posix-process and posix.

9.1.1  Process creation and termination

Fork creates a new child process and returns the child’s process-id in the parent and #f in the child. Fork-and-forget calls thunk in a new process; no process-id is returned. Fork-and-forget uses an intermediate process to avoid creating a zombie process.

Process-id? is a predicate for process-ids, process-id=? compares two to see if they are the same, and process-id-uid returns the actual Unix id. Process-id->integer and integer->process-id convert process ids to and from integers.

If a process terminates normally process-id-exit-status will return its exit status. If the process is still running or was terminated by a signal then process-id-exit-status will return #f. Similarly, if a child process was terminated by a signal process-id-terminating-signal will return that signal and will return #f if the process is still running or terminated normally. Wait-for-child-process blocks until the child process terminates. Scheme 48 may reap child processes before the user requests their exit status, but it does not always do so.

Terminates the current process with the integer status as its exit status.

9.1.2  Exec

All of these replace the current program with a new one. They differ in how the new program is found, what its environment is, and what arguments it is passed. Exec and exec-with-environment look up the new program in the search path, while exec-file and exec-file-with-environment execute a particular file. The environment is either inherited from the current process (exec and exec-file) or given as an argument (...-with-environment). Program-name and filename and any argi should be os-string-thing arguments (see section 5.15. Env should be a list of os-string-thing arguments of the form "name=value". The first four procedures add their first argument, program-name or filename, before the arg0 ... arguments.

Exec-with-alias is an omnibus procedure that subsumes the other four. Name is looked up in the search path if lookup? is true and is used as a filename otherwise. Maybe-env is either a list of os-string-things for the environment of the new program or #f in which case the new program inherits its environment from the current one. Arguments should be a list of os-string-things; unlike with the other four procedures, name is not added to this list (hence -with-alias).

9.2  Signals

There are two varieties of signals available, named and anonymous. A named signal is one for which we have a symbolic name, such as kill or pipe. Anonymous signals, for which we only have the current operating system’s signal number, have no meaning in other operating systems. Named signals preserve their meaning in image files. Not all named signals are available from all OS’s and there may be multiple names for a single OS signal number.

The syntax signal returns a (named) signal associated with signal-name. Name->signal returns a (named) signal or #f if the the signal name is not supported by the operating system. The signal returned by integer->signal is a named signal if integer corresponds to a named signal in the current operating system; otherwise it returns an anonymous signal. Signal-name returns a symbol if signal is named and #f if it is anonymous. Signal=? returns #t if signal0 and signal1 have the same operating system number and #f if they do not.

9.2.1  POSIX signals

The following lists the names of the POSIX signals.

abrt abort - abnormal termination (as by abort())
alrm alarm - timeout signal (as by alarm())
fpe floating point exception
hup hangup - hangup on controlling terminal or death of controlling process
ill illegal instruction
int interrupt - interaction attention
kill kill - termination signal, cannot be caught or ignored
pipe pipe - write on a pipe with no readers
quit quit - interaction termination
segv segmentation violation - invalid memory reference
term termination - termination signal
usr1 user1 - for use by applications
usr2 user2 - for use by applications
chld child - child process stopped or terminated
cont continue - continue if stopped
stop stop - cannot be caught or ignored
tstp interactive stop
ttin read from control terminal attempted by background process
ttou write to control terminal attempted by background process
bus bus error - access to undefined portion of memory

9.2.2  Other signals

The following lists the names of the non-POSIX signals that the system is currently aware of.

trap trace or breakpoint trap
iot IOT trap - a synonym for ABRT
emt
sys bad argument to routine (SVID)
stkflt stack fault on coprocessor
urg urgent condition on socket (4.2 BSD)
io I/O now possible (4.2 BSD)
poll A synonym for SIGIO (System V)
cld A synonym for SIGCHLD
xcpu CPU time limit exceeded (4.2 BSD)
xfsz File size limit exceeded (4.2 BSD)
vtalrm Virtual alarm clock (4.2 BSD)
prof Profile alarm clock
pwr Power failure (System V)
info A synonym for SIGPWR
lost File lock lost
winch Window resize signal (4.3 BSD, Sun)
unused Unused signal

9.2.3  Sending signals

Send signal to the process corresponding to process-id.

9.2.4  Receiving signals

Signals received by the Scheme process can be obtained via one or more signal-queues. Each signal queue has a list of monitored signals and a queue of received signals that have yet to be read from the signal-queue. When the Scheme process receives a signal that signal is added to the received-signal queues of all signal-queues which are currently monitoring that particular signal.

Make-signal-queue returns a new signal-queue that will monitor the signals in the list signals. Signal-queue? is a predicate for signal queues. Signal-queue-monitored-signals returns a list of the signals currently monitored by signal-queue. Dequeue-signal! and maybe-dequeue-signal both return the next received-but-unread signal from signal-queue. If signal-queue’s queue of signals is empty dequeue-signal! blocks until an appropriate signal is received. Maybe-dequeue-signal! does not block; it returns #f instead.

There is a bug in the current system that causes an erroneous deadlock error if threads are blocked waiting for signals and no other threads are available to run. A work around is to create a thread that sleeps for a long time, which prevents any deadlock errors (including real ones):

> ,open threads
> (spawn (lambda ()
           ; Sleep for a year
           (sleep (* 1000 60 60 24 365))))

These two procedures can be used to add or remove signals from a signal-queue’s list of monitored signals. When a signal is removed from a signal-queue’s list of monitored signals any occurances of the signal are removed from that signal-queue’s pending signals. In other words, dequeue-signal! and maybe-dequeue-signal! will only return signals that are currently on the signal-queue’s list of signals.

9.3  Process environment

These are in structures posix-process-data and posix.

9.3.1  Process identification

These return the process ids of the current process and its parent. See section 9.1.1 for operations on process ids.

Every process has both the original and effective user id and group id. The effective values may be set, but the original ones can only be set if the process has appropriate privelages.

Get-groups returns a list of the supplementary groups of the current process. Get-login-name returns a user name for the current process.

9.3.2  Environment variables

Lookup-environment-variable looks up its argument in the environment list and returns the corresponding value or #f if there is none. Set-environment-variable! sets the value of name in the environment list to value. If name is not already an environment variable, it’s created. If it already exists, its value is overwritten with value. Both arguments must be os-string-things. Environment-alist returns the entire environment as a list of (name-os-string . value-os-string) pairs.

9.4  Users and groups

User-ids and group-ids are boxed integers representing Unix users and groups. The procedures in this section are in structures posix-users and posix.

User-ids and group-ids have their own own predicates and comparison, boxing, and unboxing functions.

These return the user info for a user identified by user-id or name.

A user-info contains information about a user. Available are the user’s name, id, group, home directory, and shell.

These return the group info for a group identified by group-id or name.

A group-info contains information about a group. Available are the group’s name, id, and a list of members.

9.5  OS and machine identification

These procedures return strings that are supposed to identify the current OS and machine. The POSIX standard does not indicate the format of the strings. The procedures are in structures posix-platform-names and posix.

9.6  Files and directories

These procedures are in structures posix-files and posix.

9.6.1  Directory streams

Directory streams are like input ports, with each read operation returning the next name in the directory.

Open-directory-stream opens a new directory stream. Directory-stream? is a predicate that recognizes directory streams. Read-directory-stream returns the next name in the directory or #f if all names have been read. Close-directory-stream closes a directory stream.

This is the obvious utility; it returns a list of the names in directory name.

9.6.2  Working directory

These return and set the working directory.

9.6.3  File creation and removal

Open-file opens a port to the file named by path, which must be a os-string-thing argument. The file-options argument determines various aspects of the returned port. The optional file-mode argument is used only if the file to be opened does not already exist. The returned port is an input port if file-options includes read-only; otherwise it returns an output port. Dup-switching-mode can be used to open an input port for output ports opened with the read/write option.

The syntax file-options returns a file-option with the indicated options set. File-options-on? returns true if its first argument includes all of the options listed in the second argument. File-options-union returns a file-options argument containing exactly all of the options listed in either argument. The following file options may be used with open-file.

create create file if it does not already exist; a file-mode argument is required with this option
exclusive an error will be raised if this option and create are both set and the file already exists
no-controlling-tty if path is a terminal device this option causes the terminal to not become the controlling terminal of the process
truncate file is truncated
append writes are appended to existing contents
nonblocking read and write operations do not block
read-only port may not be written
read-write file descriptor may be read or written
write-only port may not be read

Only one of the last three options may be used. If read-write is specified, an output port is returned.

For example

(open-file "some-file.txt"
           (file-options create write-only)
           (file-mode read owner-write))

returns an output port that writes to a newly-created file that can be read by anyone and written only by the owner. Once the file exists,

(open-file "some-file.txt"
           (file-options append write-only))

will open an output port that appends to the file.

The append and nonblocking options and the read/write nature of the port can be read using i/o-flags. The append and nonblocking options can be set using set-i/o-flags!.

To keep port operations from blocking the Scheme 48 process, output ports are set to be nonblocking at the time of creation (input ports are managed using select()). You can use set-i/o-flags! to make an output port blocking, for example just before a fork, but care should be exercised. The Scheme 48 runtime code may get confused if an I/O operation blocks.

Sets the file creation mask to be file-mode. Bits set in file-mode are cleared in the modes of any files or directories created by the current process.

Both existing and new must be os-string-thing arguments. Link makes path new be a new link to the file pointed to by path existing. The two paths must be in the same file system.

These two procedures make new directories and fifo files. In both cases, path must be a os-string-thing argument.

Path, old-path and new-path must all be os-string-thing arguments. Unlink removes the link indicated by path. Remove-directory removes the indicated (empty) directory. Rename moves the file pointed to by old-path to the location pointed to by new-path (the two paths must be in the same file system). Any other links to the file remain unchanged.

Accessible? returns true if path (which must be a os-string-thing argument) is a file that can be accessed in the listed mode. If more than one mode is specified accessible? returns true if all of the specified modes are permitted. The mode-names are: read, write, execute, exists.

9.6.4  File information

Get-file-info and get-file/link-info both return a file info record for the file named by path, which must be a os-string-thing argument. Get-file-info follows symbolic links while get-file/link-info does not. Get-port-info returns a file info record for the file which port reads from or writes to. An error is raised if fd-port does not read from or write to a file descriptor.

File-info? is a predicate for file-info records. File-info-name is the name which was used to get file-info, either as passed to get-file-info or get-file/link-info, or used to open the port passed to get-port-info.

File-info-type returns the type of the file, as a file-type object File types may be compared using eq?. The valid file types are:

regular
directory
character-device
block-device
fifo
symbolic-link
socket
other

Symbolic-link and socket are not required by POSIX.

The device and inode numbers uniquely determine a file.

These return the number of links to a file and the file size in bytes. The size is only meaningful for regular files.

These return the owner, group, and access mode of a file.

These return the time the file was last read, modified, or had its status modified.

9.6.5  File modes

A file mode is a boxed integer representing a file protection mask.

File-mode is syntax for creating file modes. The mode-names are listed below. File-mode? is a predicate for file modes. File-mode+ returns a mode that contains all of permissions of its arguments. File-mode- returns a mode that has all of the permissions of file-mode0 that are not in file-mode1.

File-mode=? returns true if the two modes are exactly the same. File-mode<=? returns true if file-mode0 has a subset of the permissions of file-mode1. File-mode>=? is file-mode<=? with the arguments reversed.

Integer->file-mode and file-mode->integer translate file modes to and from the classic Unix file mode masks. These may not be the masks used by the underlying OS.

Permission name Bit mask
set-uid #o4000 set user id when executing
set-gid #o2000 set group id when executing
owner-read #o0400 read by owner
owner-write #o0200 write by owner
owner-exec #o0100 execute (or search) by owner
group-read #o0040 read by group
group-write #o0020 write by group
group-exec #o0010 execute (or search) by group
other-read #o0004 read by others
other-write #o0002 write by others
other-exec #o0001 execute (or search) by others

Names for sets of permissions
owner #o0700 read, write, and execute by owner
group #o0070 read, write, and execute by group
other #o0007 read, write, and execute by others
read #o0444 read by anyone
write #o0222 write by anyone
exec #o0111 execute by anyone
all #o0777 anything by anyone

9.6.6  Symbolic links

This creates a symbolic link at path2 that contains path1. Path1 and path2 must be os-string-thing arguments.

This returns contents of the symbolic link at path. Path must be an os-string-thing argument.

9.7  Time and Date

These procedures are in structures posix-time and posix.

9.7.1  Time

A time record contains an integer that represents time as the number of second since the Unix epoch (00:00:00 GMT, January 1, 1970). Make-time and current-time return times, with make-time’s using its argument while current-time’s has the current time. Time? is a predicate that recognizes times and time-seconds returns the number of seconds time represents.

These perform various comparison operations on the times.

Time->string returns a string representation of time in the locale’s version of the following form.

"Wed Jun 30 21:49:08 1993
"

9.7.2  Date

A date is a time specification relative to a specific but implicit time zone, broken out into the familar year-month-day-hour-minute-second format.

These are the constructor, predicate and corresponding accessors for date objects. The meaning of the various field types are as follows:

seconds seconds (0--60)
minutes minutes (0--59)
hour hours (0--23)
month-day day of month (1--31)
mon month of year (0--11)
year year since 1900
week-day day of week (Sunday = 0)
year-day day of year (0--365)
dst is summer time in effect? #t, #f or unspecific

returns a string representation of date in the locale’s version of the following form:

"Wed Jun 30 21:49:08 1993
"

These convert a time object into a date object; the first does this relative to the UTC time zone, the second relative to the current timezone setting.

This converts a date object into a time object relative to the current timezone setting.

This formats a date into a string, according to the format specification in the first argument. The format specification is according to the specification of the C strftime function:

lp0.9 %a & is replaced by the locale’s abbreviated weekday name.
%A & is replaced by the locale’s full weekday name.
%b & is replaced by the locale’s abbreviated month name.
%B & is replaced by the locale’s full month name.
%c & is replaced by the locale’s appropriate date and time representation.
%C & is replaced by the year divided by 100 and truncated to an integer, as a decimal number (00--99).
%d & is replaced by the day of the month as a decimal number (01--31).
%D & is equivalent to ‘‘%m/%d/%y’’.
%e & is replaced by the day of the month as a decimal number (1--31); a single digit is preceded by a space.
%F & is equivalent to ‘‘%Y‑%m‑%d’’ (the ISO 8601 date format).
%g & is replaced by the last 2 digits of the week-based year (see below) as a decimal number (00--99).
%G & is replaced by the week-based year (see below) as a decimal number (e.g., 1997).
%h & is equivalent to ‘‘%b’’.
%H & is replaced by the hour (24-hour clock) as a decimal number (00--23).
%I & is replaced by the hour (12-hour clock) as a decimal number (01--12).
%j & is replaced by the day of the year as a decimal number (001--366).
%m & is replaced by the month as a decimal number (01--12).
%M & is replaced by the minute as a decimal number (00--59).
%n & is replaced by a new-line character.
%p & is replaced by the locale’s equivalent of the AM/PM designations associated with a 12-hour clock.
%r & is replaced by the locale’s 12-hour clock time.
%R & is equivalent to ‘‘%H:%M’’.
%S & is replaced by the second as a decimal number (00--60).
%t & is replaced by a horizontal-tab character.
%T & is equivalent to ‘‘%H:%M:%S’’ (the ISO 8601 time format).
%u & is replaced by the ISO 8601 weekday as a decimal number (1--7), where Monday is 1.
%U & is replaced by the week number of the year (the first Sunday as the first day of week 1) as a decimal number (00--53).
%V & is replaced by the ISO 8601 week number (see below) as a decimal number (01--53).
%w & is replaced by the weekday as a decimal number (0--6), where Sunday is 0.
%W & is replaced by the week number of the year (the first Monday as the first day of week 1) as a decimal number (00--53).
%x & is replaced by the locale’s appropriate date representation.
%X & is replaced by the locale’s appropriate time representation.
%y & is replaced by the last 2 digits of the year as a decimal number (00--99).
%Y & is replaced by the year as a decimal number (e.g., 1997).
%z & is replaced by the offset from UTC in the ISO 8601 format ‘‘‑0430’’ (meaning 4 hours 30 minutes behind UTC, west of Greenwich), or by no characters if no time zone is determinable.
%Z & is replaced by the locale’s time zone name or abbreviation, or by no characters if no time zone is determinable.
%% & is replaced by %.

9.8  I/O

These procedures are in structures posix-i/o and posix.

Open-pipe creates a new pipe and returns the two ends as an input port and an output port.

A file descriptor port (or fd-port) is a port that reads to or writes from an OS file descriptor. Fd-ports are returned by open-input-file, open-output-file, open-file, open-pipe, and other procedures.

Fd-port? returns true if its argument is an fd-port. Port->fd returns the file descriptor associated with or #f if port is not an fd-port.

Remap-file-descriptors reassigns file descriptors to ports. The fd-specs indicate which port is to be mapped to each file descriptor: the first gets file descriptor 0, the second gets 1, and so forth. A fd-spec is either a port that reads from or writes to a file descriptor, or #f, with #f indicating that the corresponding file descriptor is not used. Any open ports not listed are marked ‘close-on-exec’. The same port may be moved to multiple new file descriptors.

For example,

(remap-file-descriptors (current-output-port)
                        #f
                        (current-input-port))

moves the current output port to file descriptor 0 and the current input port to file descriptor 2.

These change fd-port’s file descriptor and return a new port that uses ports’s old file descriptor. Dup uses the lowest unused file descriptor and dup2 uses the one provided. Dup-switching-mode is the same as dup except that the returned port is an input port if the argument was an output port and vice versa. If any existing port uses the file descriptor passed to dup2, that port is closed.

Close-all-but closes all file descriptors whose associated ports are not passed to it as arguments.

Close-on-exec? returns true if port will be closed when a new program is exec’ed. Set-close-on-exec?! sets port’s close-on-exec flag.

These two procedures read and write various options for port. The options that can be read are append, nonblocking, read-only, write-only, and read/write. Only the append and nonblocking can be written.

Port-is-a-terminal? returns true if port has an underlying file descriptor that is associated with a terminal. For such ports port-terminal-name returns the name of the terminal, for all others it returns #f.

9.9  Regular expressions

The procedures in this section provide access to POSIX regular expression matching. The regular expression syntax and semantics are far too complex to be described here. Due to limitations in the underlying facility, only Latin-1 strings are guaranteed to work here---on some platforms, only ASCII may function correctly. Moreover, because the C interface uses zero bytes for marking the ends of strings, patterns and strings that contain zero bytes will not work correctly.

These procedures are in structures posix-regexps and posix.

An abstract data type for creating POSIX regular expressions is described in section 5.21.

Make-regexp makes a new regular expression, using string as the pattern. The possible option names are:

extended use the extended patterns
ignore-case ignore case when matching
submatches report submatches
newline treat newlines specially

The regular expression is not compiled until it matched against a string, so any errors in the pattern string will not be reported until that point.

This is a predicate for regular expressions.

Regexp-match matches the regular expression against the characters in string, starting at position start. If the string does not match the regular expression, regexp-match returns #f. If the string does match, then a list of match records is returned if submatches? is true, or #t is returned if it is not. Each match record contains the index of the character at the beginning of the match and one more than the index of the character at the end. The first match record gives the location of the substring that matched regexp. If the pattern in regexp contained submatches, then the results of these are returned in order, with a match records reporting submatches that succeeded and #f in place of those that did not.

Starts-line? should be true if string starts at the beginning of a line and ends-line? should be true if it ends one.

9.10  Syslog facility

The procedures in this section provide access to the POSIX syslog facility. The functionality is in a structure called posix-syslog. The Scheme 48 interface to the syslog facility differs significantly from that of the Unix library functionality in order to support multiple simultaneous connections to the syslog facility.

Log messages carry a variety of parameters beside the text of the message itself, namely a set of options controlling the output format and destination, the facility identifying the class of programs the message is coming from, an identifier specifying the concrete program, and the level identifying the importance of the message. Moreover, a log mask can prevent messages at certain levels to be actually sent to the syslog daemon.

Log options

A log option specifies details of the I/O behavior of the syslog facility. A syslog option is an element of a finite type (see Section 5.10) constructed by the syslog-option macro. The syslog facility works with sets of options which are represented as enum sets (see Section 5.11).

Syslog-option constructs a log option from the name of an option. (The possible names are listed below.) Syslog-option? is a predicate for log options. Options are comparable using eq?. Make-syslog-options constructs a set of options from a list of options. Syslog-options is a macro which expands into an expression returning a set of options from names. Syslog-options? is a predicate for sets of options.

Here is a list of possible names of syslog options:

console
If syslog cannot pass the message to syslogd it will attempt to write the message to the console.

delay
Delay opening the connection to syslogd immediately until the first message is logged.

no-delay
Open the connection to syslogd immediately. Normally the open is delayed until the first message is logged. Useful for programs that need to manage the order in which file descriptors are allocated.

NOTA BENE: The delay and no-delay options are included for completeness, but do not have the expected effect in the present Scheme interface: Because the Scheme interface has to multiplex multiple simultaneous connections to the syslog facility over a single one, open and close operations on that facility happen at unpredictable times.

log-pid
Log the process id with each message: useful for identifying instantiations of daemons.

no-wait
Do not wait for child processes.

Log facilities

A log facility identifies the originator of a log message from a finite set known to the system. Each originator is identified by a name:

Syslog-facility is macro that expands into an expression returning a facility for a given name. Syslog-facility? is a predicate for facilities. Facilities are comparable via eq?.

Here is a list of possible names of syslog facilities:

authorization
The authorization system: login, su, getty, etc.

cron
The cron daemon.

daemon
System daemons, such as routed, that are not provided for explicitly by other facilities.

kernel
Messages generated by the kernel.

lpr
The line printer spooling system: lpr, lpc, lpd, etc.

mail
The mail system.

news
The network news system.

user
Messages generated by random user processes.

uucp
The uucp system.

local0 local1 local2 local3 local4 local5 local6 local7
Reserved for local use.

Log levels

A log level identifies the importance of a message from a fixed set of possible levels.

Syslog-level is macro that expands into an expression returning a facility for a given name. Syslog-level? is a predicate for facilities. Levels are comparable via eq?.

Here is a list of possible names of syslog levels:

emergency
A panic condition. This is normally broadcast to all users.

alert
A condition that should be corrected immediately, such as a corrupted system database.

critical
Critical conditions, e.g., hard device errors.

error
Errors.

warning
Warning messages.

notice
Conditions that are not error conditions, but should possibly be handled specially.

info
Informational messages.

debug
Messages that contain information normally of use only when debugging a program.

Log masks

A log masks can mask out log messages at a set of levels. A log mask is an enum set of log levels.

Make-syslog-mask constructs a mask from a list of levels. Syslog-mask is a macro which constructs a mask from names of levels. Syslog-mask-all is a predefined log mask containing all levels. Syslog-mask-upto returns a mask consisting of all levels up to and including a certain level, starting with emergency.

Logging

Scheme 48 dynamically maintains implicit connections to the syslog facility specifying a current identifier, current options, a current facility and a current log mask. Every thread maintains it own implicit connection to syslog. Note that the connection is not implicitly preserved across a spawn.

With-syslog-destination dynamically binds parameters of the implicit connection to the syslog facility and runs thunk within those parameter bindings, returning what thunk returns. Each of the parameters may be #f in which case the previous values will be used.

Syslog actually logs a message. Each of the parameters of the implicit connection (except for the log mask) can be explicitly specified as well for the current call to syslog, overriding the parameters of the channel. The parameters revert to their original values after the call.

The final form specifies the destination of the log message as a channel; see the next section.

Syslog channels

These procedures allow direct manipulation of syslog channels, the objects that represent connections to the syslog facility. Note that it is not necessary to explicitly open a syslog channel to do logging.

Open-syslog-channel and close-syslog-channel create and destroy a connection to the syslog facility, respectively. The specified form of calling syslog logs to the specified channel.

With-syslog-channel dynamically binds parameters of the implicit connection to the syslog facility to those specified in channel and runs thunk within those parameter bindings, returning what thunk returns.

9.11  Error codes

POSIX functions report the nature of an error via system error numbers---OS-specific integers that encode a variety of different error situations. At the Scheme level, error numbers are represented as errnos, objects that specify a name for the error sitation. Errnos are definted in the structures posix-errnos and posix.

Currently, the system reports such error situations by raising exceptions with condition type &os-error. The &os-error condition type has a field code that contains the system error number.

There are two varieties of errnos available, named and anonymous. A named errno is one for which we have a symbolic name, such as fault or intr. Anonymous errnos, for which we only have the current operating system’s errno number, have no meaning in other operating systems. Named errnos preserve their meaning in image files. Not all named errnos are available from all OS’s and there may be multiple names for a single OS errno number.

The syntax errno returns a (named) errno associated with errno-name. Name->errno returns a (named) errno or #f if the the errno name is not supported by the operating system. The errno returned by integer->errno is a named errno if integer corresponds to a named errno in the current operating system; otherwise it returns an anonymous errno. Errno-name returns a symbol if errno is named and #f if it is anonymous. Errno=? returns #t if errno0 and errno1 have the same operating system number and #f if they do not.

9.11.1  POSIX errnos

The following lists the names of the POSIX errnos.

@lp0.6 toobig                         Argument list too long.
acces                                 Permission denied.
addrinuse                                 Address in use.
addrnotavail                         Address not available.
afnosupport                 Address family not supported.
again Resource unavailable, try again.
already                         Connection already in progress.
badf                                 Bad file descriptor.
badmsg                                 Bad message.
busy                                 Device or resource busy.
canceled                                 Operation canceled.
child                                 No child processes.
connaborted                         Connection aborted.
connrefused                         Connection refused.
connreset                                 Connection reset.
deadlk                         Resource deadlock would occur.
destaddrreq                 Destination address required.
dom         Mathematics argument out of domain of function.
dquot                                 Reserved.
exist                                 File exists.
fault                                 Bad address.
fbig                                 File too large.
hostunreach                         Host is unreachable.
idrm                                 Identifier removed.
ilseq                                 Illegal byte sequence.
inprogress                                 Operation in progress.
intr                                 Interrupted function.
inval                                 Invalid argument.
io                                         I/O error.
isconn                                 Socket is connected.
isdir                                 Is a directory.
loop                         Too many levels of symbolic links.
mfile                                 Too many open files.
mlink                                 Too many links.
msgsize                                 Message too large.
multihop                                 Reserved.
nametoolong                         Filename too long.
netdown                                 Network is down.
netreset                         Connection aborted by network.
netunreach                                 Network unreachable.
nfile                         Too many files open in system.
nobufs                                 No buffer space available.
nodata No message is available on the STREAM head read queue.
nodev                                 No such device.
noent                                 No such file or directory.
noexec                         Executable file format error.
nolck                                 No locks available.
nolink                                 Reserved.
nomem                                 Not enough space.
nomsg                         No message of the desired type.
noprotoopt                                 Protocol not available.
nospc                                 No space left on device.
nosr                                 No STREAM resources.
nostr                                 Not a STREAM.
nosys                                 Function not supported.
notconn                                 The socket is not connected.
notdir                                 Not a directory.
notempty                                 Directory not empty.
notsock                                 Not a socket.
notsup                                 Not supported.
notty                         Inappropriate I/O control operation.
nxio                                 No such device or address.
opnotsupp                         Operation not supported on socket.
overflow                 Value too large to be stored in data type.
perm                                 Operation not permitted.
pipe                                 Broken pipe.
proto                                 Protocol error.
protonosupport                         Protocol not supported.
prototype                         Protocol wrong type for socket.
range                                 Result too large.
rofs                                 Read-only file system.
spipe                                 Invalid seek.
srch                                 No such process.
stale                                 Reserved.
time                         Stream ioctl() timeout.
timedout                                 Connection timed out.
txtbsy                                 Text file busy.
wouldblock         Operation would block.
xdev                                 Cross-device link.

9.12  C to Scheme correspondence

The following table lists the Scheme procedures that correspond to particular C procedures. Not all of the Scheme procedures listed are part of the POSIX interface.

C procedure Scheme procedure(s)
C procedure Scheme procedure(s)
accessaccessible?
asctimedate->string
chdirset-working-directory!
closeclose-input-port, close-output-port,
close-channel, close-socket
closedirclose-directory-stream
creatopen-file
ctimetime->string
dupdup, dup-switching-mode
dup2dup2
exec[l|v][e|p|ε] exec, exec-with-environment,
exec-file, exec-file-with-environment,
exec-with-alias
_exitexit
fcntlio-flags, set-io-flags!,
close-on-exec, set-close-on-exec!
forkfork, fork-and-forget
fstatget-port-info
getcwdworking-directory
getegidget-effective-group-id
getenvlookup-environment-variable,
environment-alist
geteuidget-effective-user-id
getgidget-group-id
getgroupsget-groups
getloginget-login-name
getpidget-process-id
getppidget-parent-process-id
getuidget-user-id
gmtimetime->local-date
isattyport-is-a-terminal?
linklink
localtimetime->utc-date
lstatget-file/link-info
mkdirmake-directory
mkfifomake-fifo
mktimedate->time
openopen-file
opendiropen-directory-stream
pipeopen-pipe
readread-char, read-block
readdirread-directory-stream
readlinkread-symbolic-link
renamerename
rmdirremove-directory
setgidset-group-id!
setegidset-effective-group-id!
setuidset-user-id!
seteuidset-effective-user-id!
statget-file-info
strftimeformat-date
symlinkcreate-symbolic-link
syslogsyslog
timecurrent-time
ttynameport-terminal-name
umaskset-file-creation-mask!
unameos-name, os-node-name,
os-release-name, os-version-name,
machine-name
unlinkunlink
waitpidwait-for-child-process
writewrite-char, write-block