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1.1 root 1: .th INTRO II 11/5/73
2: .de pg
3: .sp
4: ..
5: .de en
6: .pg
7: .in 3
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9: \\$1\t\\$2\t\\$3
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11: ..
12: .sp 2
13: .in 0
14: .if t .ta 3 10
15: .ce
16: INTRODUCTION TO SYSTEM CALLS
17: .sp
18: Section II of this manual
19: lists all the entries into the system.
20: In most cases two calling sequences are specified,
21: one of which is usable from assembly language, and the other from C.
22: Most of these calls have an error return.
23: From assembly language an erroneous call is always
24: indicated by turning on the c-bit of the condition codes.
25: The presence of an error is most easily tested
26: by the instructions
27: .it bes
28: and
29: .it bec
30: (``branch on error set (or clear)'').
31: These are synonyms for
32: the
33: .it bcs
34: and
35: .it bcc
36: instructions.
37: .pg
38: From C, an error condition is indicated by an otherwise
39: impossible returned value.
40: Almost always this is \(mi1;
41: the individual sections specify the details.
42: .pg
43: In both cases an error number is also available.
44: In assembly language,
45: this number is returned in r0 on erroneous calls.
46: From C,
47: the external variable
48: .it errno
49: is set to the error number.
50: .it Errno
51: is not cleared on succesful calls, so it should be tested only
52: after an error has occurred.
53: There is a table of messages
54: associated with each error, and a routine for printing the
55: message.
56: See
57: .it "perror (III)."
58: .pg
59: The possible error numbers
60: are not recited with each writeup in section II, since many
61: errors are possible for most of the calls.
62: Here is a list of the error numbers,
63: their names inside the system (for the benefit of
64: system-readers),
65: and the messages available using
66: .it perror.
67: A short explanation is also provided.
68: .en 0 \(mi (unused)
69: .en 1 EPERM "Not owner and not super-user"
70: Typically this error indicates
71: an attempt to modify a file in some way forbidden
72: except to its owner.
73: It is also returned for attempts
74: by ordinary users to do things
75: allowed only to the super-user.
76: .en 2 ENOENT "No such file or directory"
77: This error occurs when a file name is specified
78: and the file should exist but doesn't, or when one
79: of the directories in a path name does not exist.
80: .en 3 ESRCH "No such process"
81: The process whose number was given to
82: .it signal
83: does not exist, or is already dead.
84: .en 4 \(mi (unused)
85: .en 5 EIO "I/O error"
86: Some physical I/O error occurred during a
87: .it read
88: or
89: .it write.
90: This error may in some cases occur
91: on a call following the one to which it actually applies.
92: .en 6 ENXIO "No such device or address"
93: I/O on a special file refers to a subdevice which does not
94: exist,
95: or beyond the limits of the device.
96: It may also occur when, for example, a tape drive
97: is not dialled in or no disk pack is loaded on a drive.
98: .en 7 E2BIG "Arg list too long"
99: An argument list longer than 512 bytes
100: (counting the null at the end of each argument)
101: is presented to
102: .it exec.
103: .en 8 ENOEXEC "Exec format error"
104: A request is made to execute a file
105: which, although it has the appropriate permissions,
106: does not start with one of the magic numbers
107: 407 or 410.
108: .en 9 EBADF "Bad file number"
109: Either a file descriptor refers to no
110: open file,
111: or a read (resp. write) request is made to
112: a file which is open only for writing (resp. reading).
113: .en 10 ECHILD "No children"
114: .it Wait
115: and the process has no
116: living or unwaited-for children.
117: .en 11 EAGAIN "No more processes"
118: In a
119: .it fork,
120: the system's process table is full and no
121: more processes can for the moment be created.
122: .en 12 ENOMEM "Not enough core"
123: During an
124: .it exec
125: or
126: .it break,
127: a program asks for more core than the system is able to supply.
128: This is not a temporary condition; the maximum core size
129: is a system parameter.
130: The error may also occur if the arrangement
131: of text, data, and stack segments is such as to
132: require more than the existing 8 segmentation registers.
133: .en 13 EACCES "Permission denied"
134: An attempt was made to access a file in a way forbidden
135: by the protection system.
136: .en 14 \(mi (unused)
137: .en 15 ENOTBLK "Block device required"
138: A plain file was mentioned where a block device was required,
139: e.g. in
140: .it mount.
141: .en 16 EBUSY "Mount device busy"
142: An attempt was made to dismount a device
143: on which there is an open file or some process's current
144: directory.
145: .en 17 EEXIST "File exists"
146: In existing file was mentioned in a context in which
147: it should not have,
148: e.g.
149: .it link.
150: .en 18 EXDEV "Cross-device link"
151: A link to a file on another device
152: was attempted.
153: .en 19 ENODEV "No such device"
154: An attempt was made to apply an inappropriate
155: system call to a device;
156: e.g. read a write-only device.
157: .en 20 ENOTDIR "Not a directory"
158: A non-directory was specified where a directory
159: is required,
160: for example in a path name or
161: as an argument to
162: .it chdir.
163: .en 21 EISDIR "Is a directory"
164: An attempt to write on a directory.
165: .en 22 EINVAL "Invalid argument"
166: Some invalid argument:
167: currently, dismounting a non-mounted
168: device,
169: mentioning an unknown signal in
170: .it signal,
171: and giving an unknown request in
172: .it stty
173: to the TIU special file.
174: .en 23 ENFILE "File table overflow"
175: The system's table of open files is full,
176: and temporarily no more
177: .it opens
178: can be accepted.
179: .en 24 EMFILE "Too many open files"
180: Only 10 files can be open per process;
181: this error occurs when the eleventh is opened.
182: .en 25 ENOTTY "Not a typewriter"
183: The file mentioned in
184: .it stty
185: or
186: .it gtty
187: is not a typewriter or one of the other
188: devices to which these calls apply.
189: .en 26 ETXTBSY "Text file busy"
190: An attempt to execute a pure-procedure
191: program which is currently open for writing
192: (or reading!).
193: .en 27 EFBIG "File too large"
194: An attempt to make a file larger than the maximum of 2048 blocks.
195: .en 28 ENOSPC "No space left on device"
196: During a
197: .it write
198: to an ordinary file,
199: there is no free space left on the device.
200: .en 29 ESPIPE "Seek on pipe"
201: A
202: .it seek
203: was issued to a pipe.
204: This error should also be issued for
205: other non-seekable devices.
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