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1.1 root 1: .\" Copyright (c) 1980 Regents of the University of California.
2: .\" All rights reserved. The Berkeley software License Agreement
3: .\" specifies the terms and conditions for redistribution.
4: .\"
5: .\" @(#)write.2 6.5 (Berkeley) 5/14/86
6: .\"
7: .TH WRITE 2 "May 14, 1986"
8: .UC 4
9: .SH NAME
10: write, writev \- write output
11: .SH SYNOPSIS
12: .nf
13: .ft B
14: cc = write(d, buf, nbytes)
15: int cc, d;
16: char *buf;
17: int nbytes;
18: .PP
19: .ft B
20: #include <sys/types.h>
21: #include <sys/uio.h>
22: .PP
23: .ft B
24: cc = writev(d, iov, iovcnt)
25: int cc, d;
26: struct iovec *iov;
27: int iovcnt;
28: .fi
29: .SH DESCRIPTION
30: .I Write
31: attempts to write
32: .I nbytes
33: of data to the object referenced by the descriptor
34: .I d
35: from the buffer pointed to by
36: .IR buf .
37: .I Writev
38: performs the same action, but gathers the output data
39: from the
40: .I iovcnt
41: buffers specified by the members of the
42: .I iov
43: array: iov[0], iov[1], ..., iov[iovcnt\|\-\|1].
44: .PP
45: For
46: .IR writev ,
47: the
48: .I iovec
49: structure is defined as
50: .PP
51: .nf
52: .RS
53: .DT
54: struct iovec {
55: caddr_t iov_base;
56: int iov_len;
57: };
58: .RE
59: .fi
60: .PP
61: Each
62: .I iovec
63: entry specifies the base address and length of an area
64: in memory from which data should be written.
65: .I Writev
66: will always write a complete area before proceeding
67: to the next.
68: .PP
69: On objects capable of seeking, the \fIwrite\fP starts at a position
70: given by the pointer associated with
71: .IR d ,
72: see
73: .IR lseek (2).
74: Upon return from
75: .IR write ,
76: the pointer is incremented by the number of bytes actually written.
77: .PP
78: Objects that are not capable of seeking always write from the current
79: position. The value of the pointer associated with such an object
80: is undefined.
81: .PP
82: If the real user is not the super-user, then
83: .I write
84: clears the set-user-id bit on a file.
85: This prevents penetration of system security
86: by a user who
87: \*(lqcaptures\*(rq a writable set-user-id file
88: owned by the super-user.
89: .PP
90: When using non-blocking I/O on objects such as sockets that are subject
91: to flow control,
92: .I write
93: and
94: .I writev
95: may write fewer bytes than requested;
96: the return value must be noted,
97: and the remainder of the operation should be retried when possible.
98: .SH "RETURN VALUE
99: Upon successful completion the number of bytes actually written
100: is returned. Otherwise a \-1 is returned and the global variable
101: .I errno
102: is set to indicate the error.
103: .SH ERRORS
104: .I Write
105: and
106: .I writev
107: will fail and the file pointer will remain unchanged if one or more
108: of the following are true:
109: .TP 15
110: [EBADF]
111: \fID\fP is not a valid descriptor open for writing.
112: .TP 15
113: [EPIPE]
114: An attempt is made to write to a pipe that is not open
115: for reading by any process.
116: .TP 15
117: [EPIPE]
118: An attempt is made to write to a socket of type SOCK_STREAM
119: that is not connected to a peer socket.
120: .TP 15
121: [EFBIG]
122: An attempt was made to write a file that exceeds the process's
123: file size limit or the maximum file size.
124: .TP 15
125: [EFAULT]
126: Part of \fIiov\fP or data to be written to the file
127: points outside the process's allocated address space.
128: .TP 15
129: [EINVAL]
130: The pointer associated with
131: .I d
132: was negative.
133: .TP 15
134: [ENOSPC]
135: There is no free space remaining on the file system
136: containing the file.
137: .TP 15
138: [EDQUOT]
139: The user's quota of disk blocks on the file system
140: containing the file has been exhausted.
141: .TP 15
142: [EIO]
143: An I/O error occurred while reading from or writing to the file system.
144: .TP 15
145: [EWOULDBLOCK]
146: The file was marked for non-blocking I/O,
147: and no data could be written immediately.
148: .PP
149: In addition,
150: .I writev
151: may return one of the following errors:
152: .TP 15
153: [EINVAL]
154: .I Iovcnt
155: was less than or equal to 0, or greater than 16.
156: .TP 15
157: [EINVAL]
158: One of the
159: .I iov_len
160: values in the
161: .I iov
162: array was negative.
163: .TP 15
164: [EINVAL]
165: The sum of the
166: .I iov_len
167: values in the
168: .I iov
169: array overflowed a 32-bit integer.
170: .SH "SEE ALSO"
171: fcntl(2), lseek(2), open(2), pipe(2), select(2)
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