Commit | Line | Data |
---|---|---|
55c2faba WJ |
1 | .\" Copyright (c) 1980, 1991 Regents of the University of California. |
2 | .\" All rights reserved. | |
3 | .\" | |
4 | .\" Redistribution and use in source and binary forms, with or without | |
5 | .\" modification, are permitted provided that the following conditions | |
6 | .\" are met: | |
7 | .\" 1. Redistributions of source code must retain the above copyright | |
8 | .\" notice, this list of conditions and the following disclaimer. | |
9 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
10 | .\" notice, this list of conditions and the following disclaimer in the | |
11 | .\" documentation and/or other materials provided with the distribution. | |
12 | .\" 3. All advertising materials mentioning features or use of this software | |
13 | .\" must display the following acknowledgement: | |
14 | .\" This product includes software developed by the University of | |
15 | .\" California, Berkeley and its contributors. | |
16 | .\" 4. Neither the name of the University nor the names of its contributors | |
17 | .\" may be used to endorse or promote products derived from this software | |
18 | .\" without specific prior written permission. | |
19 | .\" | |
20 | .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND | |
21 | .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE | |
22 | .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE | |
23 | .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE | |
24 | .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL | |
25 | .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS | |
26 | .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) | |
27 | .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT | |
28 | .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY | |
29 | .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF | |
30 | .\" SUCH DAMAGE. | |
31 | .\" | |
32 | .\" @(#)vfork.2 6.3 (Berkeley) 3/10/91 | |
33 | .\" | |
34 | .Dd March 10, 1991 | |
35 | .Dt VFORK 2 | |
36 | .Os BSD 4 | |
37 | .Sh NAME | |
38 | .Nm vfork | |
39 | .Nd spawn new process in a virtual memory efficient way | |
40 | .Sh SYNOPSIS | |
41 | .Fd #include <unistd.h> | |
42 | .Ft int | |
43 | .Fn vfork void | |
44 | .Sh DESCRIPTION | |
45 | .Fn Vfork | |
46 | can be used to create new processes without fully copying the address | |
47 | space of the old process, which is horrendously inefficient in a paged | |
48 | environment. It is useful when the purpose of | |
49 | .Xr fork 2 | |
50 | would have been to create a new system context for an | |
51 | .Xr execve . | |
52 | .Fn Vfork | |
53 | differs from | |
54 | .Xr fork | |
55 | in that the child borrows the parent's memory and thread of | |
56 | control until a call to | |
57 | .Xr execve 2 | |
58 | or an exit (either by a call to | |
59 | .Xr exit 2 | |
60 | or abnormally.) | |
61 | The parent process is suspended while the child is using its resources. | |
62 | .Pp | |
63 | .Fn Vfork | |
64 | returns 0 in the child's context and (later) the pid of the child in | |
65 | the parent's context. | |
66 | .Pp | |
67 | .Fn Vfork | |
68 | can normally be used just like | |
69 | .Xr fork . | |
70 | It does not work, however, to return while running in the childs context | |
71 | from the procedure that called | |
72 | .Fn vfork | |
73 | since the eventual return from | |
74 | .Fn vfork | |
75 | would then return to a no longer existent stack frame. | |
76 | Be careful, also, to call | |
77 | .Xr _exit | |
78 | rather than | |
79 | .Xr exit | |
80 | if you can't | |
81 | .Xr execve , | |
82 | since | |
83 | .Xr exit | |
84 | will flush and close standard I/O channels, and thereby mess up the | |
85 | parent processes standard I/O data structures. | |
86 | (Even with | |
87 | .Xr fork | |
88 | it is wrong to call | |
89 | .Xr exit | |
90 | since buffered data would then be flushed twice.) | |
91 | .Sh SEE ALSO | |
92 | .Xr fork 2 , | |
93 | .Xr execve 2 , | |
94 | .Xr sigvec 2 , | |
95 | .Xr wait 2 , | |
96 | .Sh DIAGNOSTICS | |
97 | Same as for | |
98 | .Xr fork . | |
99 | .Sh BUGS | |
100 | This system call will be eliminated when proper system sharing | |
101 | mechanisms are implemented. | |
102 | Users should not depend on the memory | |
103 | sharing semantics of | |
104 | .Xr vfork | |
105 | as it will, in that case, be made synonymous to | |
106 | .Xr fork . | |
107 | .Pp | |
108 | To avoid a possible deadlock situation, | |
109 | processes that are children in the middle | |
110 | of a | |
111 | .Fn vfork | |
112 | are never sent | |
113 | .Dv SIGTTOU | |
114 | or | |
115 | .Dv SIGTTIN | |
116 | signals; rather, | |
117 | output or | |
118 | .Xr ioctl 2 | |
119 | calls | |
120 | are allowed | |
121 | and input attempts result in an end-of-file indication. | |
122 | .Sh HISTORY | |
123 | The | |
124 | .Nm | |
125 | function call appeared in | |
126 | .Bx 3.0 . |