1VFORK(2) 386BSD Programmer's Manual VFORK(2) 2 3NNAAMMEE 4 vvffoorrkk - spawn new process in a virtual memory efficient way 5 6SSYYNNOOPPSSIISS 7 ##iinncclluuddee <<uunniissttdd..hh>> 8 9 _i_n_t 10 vvffoorrkk(_v_o_i_d) 11 12DDEESSCCRRIIPPTTIIOONN 13 VVffoorrkk() can be used to create new processes without fully copying the 14 address space of the old process, which is horrendously inefficient in a 15 paged environment. It is useful when the purpose of fork(2) would have 16 been to create a new system context for an execve. VVffoorrkk() differs from 17 fork in that the child borrows the parent's memory and thread of control 18 until a call to execve(2) or an exit (either by a call to exit(2) or 19 abnormally.) The parent process is suspended while the child is using 20 its resources. 21 22 VVffoorrkk() returns 0 in the child's context and (later) the pid of the child 23 in the parent's context. 24 25 VVffoorrkk() can normally be used just like fork. It does not work, however, 26 to return while running in the childs context from the procedure that 27 called vvffoorrkk() since the eventual return from vvffoorrkk() would then return 28 to a no longer existent stack frame. Be careful, also, to call _exit 29 rather than exit if you can't execve, since exit will flush and close 30 standard I/O channels, and thereby mess up the parent processes standard 31 I/O data structures. (Even with fork it is wrong to call exit since 32 buffered data would then be flushed twice.) 33 34SSEEEE AALLSSOO 35 fork(2), execve(2), sigvec(2), wait(2), 36 37DDIIAAGGNNOOSSTTIICCSS 38 Same as for fork. 39 40BBUUGGSS 41 This system call will be eliminated when proper system sharing mechanisms 42 are implemented. Users should not depend on the memory sharing semantics 43 of vfork as it will, in that case, be made synonymous to fork. 44 45 To avoid a possible deadlock situation, processes that are children in 46 the middle of a vvffoorrkk() are never sent SIGTTOU or SIGTTIN signals; 47 rather, output or ioctl(2) calls are allowed and input attempts result in 48 an end-of-file indication. 49 50HHIISSTTOORRYY 51 The vvffoorrkk function call appeared in 3.0BSD. 52 534th Berkeley Distribution March 10, 1991 1 54 55 56 57 58 59 60 61 62 63 64 65 66 67