INTRO(2) GENIX Programmer's Manual INTRO(2)
NAME
intro, errno - introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
Section 2 of this manual describes all of the system calls. To aid
portability, the calls have been identified in accordance with the
following categories, as indicated by the page heading:
(2) System calls that are standard in Version 7 UNIX systems.
(2J) System calls added in support of the job control mechanisms of
csh(1). These system calls are not available in standard Ver-
sion 7 UNIX systems, and should be used only when necessary; to
prevent inexplicit use they are contained in the jobs library
which must be specifically requested with the -ljobs loader
option. The use of conditional compilation is recommended when
possible so that programs that use these features will grace-
fully degrade on systems that lack job control.
(2V) System calls added for the Virtual Memory version of 4.1bsd
UNIX distributed by Berkeley. These calls are also available
in the GENIX operating system. Some of these calls are likely
to be replaced by new facilities in future versions; in cases
where this is imminent, this is indicated in the individual
manual pages. Certain (2V) calls are specific to GENIX: vspy,
vlock, and vmap.
An error condition is indicated by an otherwise impossible returned
value. Almost always this is -1; the individual sections specify
the details. An error number is also made available in the external
variable errno. Errno is not cleared on successful calls, so it
should be tested only after an error has occurred.
A table of messages is associated with each error; see perror(3) for
the routine to print the error message. The possible error numbers
are not recited with each writeup in section 2, because many errors
are possible for most of the calls. Here is a list of the error
numbers, their names as defined in /usr/include/errno.h, and the
messages available using perror.
0 Error 0
Unused.
1 EPERM Not owner
Typically this error indicates an attempt to modify a file in
some way forbidden except to its owner or super-user. It is
also returned for attempts by ordinary users to do things
allowed only to the super-user.
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2 ENOENT No such file or directory
This error occurs when a file name is specified and the file
should exist but doesn't, or when one of the directories in a
path name does not exist.
3 ESRCH No such process
The process whose number was given to signal and ptrace does
not exist, or is already dead.
4 EINTR Interrupted system call
An asynchronous signal (such as interrupt or quit), which the
user has elected to catch, occurred during a system call. If
execution is resumed after processing the signal, it will
appear as if the interrupted system call returned this error
condition.
5 EIO I/O error
Some physical I/O error occurred during a read or write. This
error may in some cases occur on a call following the one to
which it actually applies.
6 ENXIO No such device or address
I/O on a special file referencing a subdevice that does not
exist, or attempted beyond the limits of the device. It may
also occur when, for example, a tape drive is not dialed in or
no disk pack is loaded on a drive.
7 E2BIG Arg list too long
An argument list longer than 10240 bytes is presented to exec.
8 ENOEXEC Exec format error
A request is made to execute a file which, although it has the
appropriate permissions, does not start with a valid magic
number. See a.out(5).
9 EBADF Bad file number
Either a file descriptor refers to no open file, or a read
(respectively write) request is made to a file which is open
only for writing (respectively reading).
10 ECHILD No children
Wait and the process has no living or unwaited-for children.
11 EAGAIN No more processes
In a fork, the system's process table is full or the user is
not allowed to create any more processes.
12 ENOMEM Not enough core
During an exec or break, a program asks for more core than the
system is able to supply. This is not a temporary condition;
the maximum core size is a system parameter.
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INTRO(2) GENIX Programmer's Manual INTRO(2)
13 EACCES Permission denied
An attempt was made to access a file in a way forbidden by the
protection system.
14 EFAULT Bad address
The system encountered a hardware fault in attempting to access
the arguments of a system call.
15 ENOTBLK Block device required
A plain file was mentioned where a block device was required,
e.g. in mount.
16 EBUSY Mount device busy
An attempt to mount a device that was already mounted or an
attempt was made to dismount a device on which there is an
active file directory. (open file, current directory,
mounted-on file, active text segment).
17 EEXIST File exists
An existing file was mentioned in an inappropriate context,
e.g. link.
18 EXDEV Cross-device link
A link to a file on another device was attempted.
19 ENODEV No such device
An attempt was made to apply an inappropriate system call to a
device; e.g. read a write-only device.
20 ENOTDIR Not a directory
A non-directory was specified where a directory is required,
for example in a path name or as an argument to chdir.
21 EISDIR Is a directory
An attempt to write on a directory.
22 EINVAL Invalid argument
Some invalid argument: dismounting a non-mounted device, men-
tioning an unknown signal in signal, reading or writing a file
for which seek has generated a negative pointer. Also set by
math functions. See intro(3).
23 ENFILE File table overflow
The system's table of open files is full, and temporarily no
more opens can be accepted.
24 EMFILE Too many open files
Customary configuration limit is 20 open file descriptors per
process.
25 ENOTTY Not a typewriter
The file mentioned in stty or gtty is not a terminal or one of
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INTRO(2) GENIX Programmer's Manual INTRO(2)
the other devices to which these calls apply.
26 ETXTBSY Text file busy
An attempt to execute a pure-procedure program which is
currently open for writing (or reading). Also an attempt to
open for writing a pure-procedure program that is being exe-
cuted.
27 EFBIG File too large
The size of a file exceeded the maximum (approximately 1.0E9
bytes).
28 ENOSPC No space left on device
During a write to an ordinary file, no free space is left on
the device.
29 ESPIPE Illegal seek
An lseek was issued to a pipe. This error should also be
issued for other non-seekable devices.
30 EROFS Read-only file system
An attempt to modify a file or directory was made on a device
mounted read-only.
31 EMLINK Too many links
An attempt to make more than 32767 links to a file.
32 EPIPE Broken pipe
A write on a pipe for which there is no process to read the
data. This condition normally generates a signal; the error is
returned if the signal is ignored.
33 EDOM Math argument
The argument of a function in the math package (3M) is out of
the domain of the function.
34 ERANGE Result too large
The value of a function in the math package (3M) is
unrepresentable within machine precision.
SEE ALSO
intro(3), Chapter 8 of The C Programming Language by Kernighan and
Ritchie.
ASSEMBLER (NS16000)
as file ...
The NS16000 assembly language interface for a system call is
oriented towards a C calling convention. The general form is
described here.
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INTRO(2) GENIX Programmer's Manual INTRO(2)
Arguments for system calls are stacked in a right to left first
order, with each argument taking four bytes. An argument pointer
indicating the base of arguments is placed in r1, and the index of
the desired system call is placed in r0. An svc instruction is then
executed.
Return values appear in registers r0 and r1; it is unwise to count
on these registers being preserved when no value is expected. An
erroneous call is always indicated by turning on the F bit of the
condition codes. The error number is returned in r0. The presence
of an error is most easily tested by the instructions bfs and bfc
(branch on flag set or clear).
BUGS
The message "Mount device busy" is reported when a terminal is inac-
cessible because the "exclusive use" bit is set; this is confusing.
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