INTRO
Section: System Calls (2)
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NAME
intro, errno - introduction to system calls and error numbers
SYNOPSIS
#include <errno.h>
DESCRIPTION
Section 2 of this manual
lists all the entries into the system.
Most of these calls have an error return.
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.
There is a table of messages
associated with each error, and a routine for printing the
message;
See
perror(3).
The possible error numbers
are not recited with each writeup in section 2, since many
errors are possible for most of the calls.
Here is a list of the error numbers,
their names as defined in <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.
-
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 refers to a subdevice that does not
exist,
or beyond the limits of the device.
It may also occur when, for example, a tape drive
is not dialled in or no disk pack is loaded on a drive.
-
7 E2BIG Arg list too long
-
- An argument list longer than 5120 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 (resp. write) request is made to
a file that is open only for writing (resp. 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.
The error may also occur if the arrangement
of text, data, and stack segments
requires too many segmentation registers.
-
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
(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,
mentioning 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 per process.
-
25 ENOTTY Not a typewriter
-
- The file mentioned in
stty
or
gtty
is not a terminal or one of the other
devices to which these calls apply.
-
26 ETXTBSY Text file busy
-
- An attempt to execute a pure-procedure
program that is currently open for writing
(or reading!).
Also an attempt to open for writing a pure-procedure
program that is being executed.
-
27 EFBIG File too large
-
- The size of a file exceeded the maximum (about
1.0E9
bytes).
-
28 ENOSPC No space left on device
-
- During a
write
to an ordinary file,
there is no free space 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)
ASSEMBLER
as /usr/include/sys.s file ...
The PDP11 assembly language interface is given for each
system call.
The assembler symbols are defined in `/usr/include/sys.s'.
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 c-bit of the condition codes.
The error number is returned in r0.
The presence of an error is most easily tested
by the instructions
bes
and
bec
(`branch on error set (or clear)').
These are synonyms for
the
bcs
and
bcc
instructions.
On the Interdata 8/32, the system call arguments
correspond well to the arguments of the C routines.
The sequence is:
-
la %2,errno
l %0,&callno
svc 0,args
Thus register 2 points to a word into which the error number will be
stored as needed; it is cleared if no error occurs.
Register 0 contains the system call number; the nomenclature
is identical to that on the PDP11.
The argument of the
svc
is the address of the arguments, laid out in storage
as in the C calling sequence.
The return value is in register 2 (possibly 3 also, as in
pipe)
and is -1 in case of error.
The overflow bit in the program status word is also
set when errors occur.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- SEE ALSO
-
- ASSEMBLER
-
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