vfork() explained: to use or not to use.
The vfork() call is a special implementation of the fork() call.
vfork() is available on about all unices systems.
From the Linux Man Page:
vfork(2) - Linux man page
NAME
vfork - create a child process and block parent
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Linux Description
vfork(), just like fork, creates a child process of the calling process.
For details and return value and errors, see fork.
vfork() is a special case of clone(2). It is used to create new processes
without copying the page tables of the parent process. It may be useful in
performance sensitive applications where a child will be created which then
immediately issues an execve().
vfork() differs from fork() in that the parent is suspended until the
child makes a call to execve(2) or _exit(2).
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From the Mac OSX man page:
VFORK(2) BSD System Calls Manual VFORK(2)
NAME
vfork -- spawn new process in a virtual memory efficient way
SYNOPSIS
#include <unistd.h>
pid_t
vfork(void);
DESCRIPTION
Vfork() can be used to create new processes without fully copying the
address space of the old process, which is horrendously inefficient in a
paged environment. It is useful when the purpose of fork(2) would have
been to create a new system context for an execve. Vfork() differs from
fork in that the child borrows the parent's memory and thread of control
until a call to execve(2) or an exit (either by a call to exit(2) or
abnormally.) The parent process is suspended while the child is using
its resources.
Vfork() returns 0 in the child's context and (later) the pid of the child
in the parent's context.
Vfork() can normally be used just like fork. It does not work, however,
to return while running in the childs context from the procedure that
called vfork() since the eventual return from vfork() would then return
to a no longer existent stack frame. Be careful, also, to call _exit
rather than exit if you can't execve, since exit will flush and close
standard I/O channels, and thereby mess up the parent processes standard
I/O data structures. (Even with fork it is wrong to call exit since
buffered data would then be flushed twice.)
As you can see from these manual pages the vfork() call has been implemented speed up the inefficient fork() call.
While the vfork() call is useful if you need to launch another process from your running process, you shall take care of it. For example, as shown in POS33, due to the implementation of the vfork() function, the parent process is suspended while the child process executes. If a user sends a signal to the child process, delaying its execution, the parent process (which is privileged) is also blocked. This means that an unprivileged process can cause a privileged process to halt, which is a privilege inversion resulting in a denial of service.
So, yhe best practice is to use the fork() call, however if you need the vfork() for your own project remeber that this call can cause a denial of service without highest privilegies.
Gg1
