quick question: what’s the difference between fork() and vfork() system calls ?
quick answer: vfork() system call creates a process that shares the memory address space of its parent.
details:
fork() is implemented by linux as a clone() system call whose flags parameter specifies both a SIGCHLD signal and all the clone flags cleared and whose child_stack parameter is 0.
vfork() is implemented by linux as a clone() system call whose flags parameter specifies both a SGCHLD signal and flags CLONE_VM and CLONE_VFORK and whose second parameter is 0.
[ discussion: copy on write ]
This is a concept of making the process creation using fork() efficient in that instead of copying the parent’s address space while process creation, it is shared but as soon as either of them write on the page, kernel allocates a new page and assigns it to the writer process.
Most of the time, forking is required just to run a new process in which case it’s a waste to copy the whole parent address space.
source* http://whatilearned2day.wordpress.com/2007/02/05/fork-and-vfork/
Some systems have a system call vfork(), which was originally
designed as a lower-overhead version of fork(). Sincefork() involved copying the entire address space of the process,
and was therefore quite expensive, the vfork() function was
introduced (in 3.0BSD).
However, since vfork() was introduced, the
implementation of fork() has improved drastically, most notably
with the introduction of `copy-on-write', where the copying of the
process address space is transparently faked by allowing both processes
to refer to the same physical memory until either of them modify
it. This largely removes the justification for vfork(); indeed, a
large proportion of systems now lack the original functionality ofvfork() completely. For compatibility, though, there may still be
a vfork() call present, that simply calls fork() without
attempting to emulate all of the vfork() semantics.
As a result, it is very unwise to actually make use of any of the
differences between fork() and vfork(). Indeed, it is
probably unwise to use vfork() at all, unless you know exactly
why you want to.
The basic difference between the two is that when a new process is
created with vfork(), the parent process is temporarily
suspended, and the child process might borrow the parent's address
space. This strange state of affairs continues until the child process
either exits, or calls execve(), at which point the parent
process continues.
This means that the child process of a vfork() must be careful to
avoid unexpectedly modifying variables of the parent process. In
particular, the child process must not return from the function
containing the vfork() call, and it must not callexit() (if it needs to exit, it should use _exit();
actually, this is also true for the child of a normal fork()).
Source* http://www.unixguide.net/unix/programming/1.1.2.shtml
During the fork() system call the Kernel makes a copy of the parent process�s address space and attaches it to the child process.But the vfork() system call do not makes any copy of the parent�s address space, so it is faster than the fork() system call. The child process as a result of the vfork() system call executes exec() system call. The child process from vfork() system call executes in the parent�s address space (this can overwrite the parent�s data and stack ) which suspends the parent process until the child process exits.
Source* http://www.kyapoocha.com/unix-interview-questions/difference-between-the-fork-and-vfork-system-call/
During the fork() system call the Kernel makes a copy of the parent process’s address space and attaches it to the child process.
But the vfork() system call do not makes any copy of the parent’s address space, so it is faster than the fork() system call. The child process as a result of the vfork() system call executes exec() system call. The child process from vfork() system call executes in the parent’s address space (this can overwrite the parent’s data and stack ) which suspends the parent process until the child process exits.
Source* http://www.technicalinterview.info/difference-between-the-fork-and-vfork-system-call/
