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Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation
From: |
Kirill A. Shutemov |
Subject: |
Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation |
Date: |
Sat, 20 Sep 2008 16:11:39 +0300 |
User-agent: |
Mutt/1.5.18 (2008-05-29) |
On Sat, Sep 20, 2008 at 02:45:57PM +0200, andrzej zaborowski wrote:
> 2008/9/20 Kirill A. Shutemov <address@hidden>:
> > On Sat, Sep 20, 2008 at 04:56:45AM +0200, andrzej zaborowski wrote:
> >> 2008/9/18 Kirill A. Shutemov <address@hidden>:
> >> > vfork() is a kind of fork, not thread despite CLONE_VM
> >>
> >> According to clone(2) it can be either, the only difference is that
> >> vfork() suspends the parent process. So if CLONE_VM is set, I think
> >> still the pthread / clone way should be used and the child thread
> >> should be waited on.
> >
> > vfork() suspends the parent process until a call of execve(2) or _exit(2).
> > If child call execnv(2) it replaces whole process, not only the thread.
> > If child call _exit(2) it stops while process, not only the thread.
>
> Do you mean that's the current behavior in qemu? That's not what clone(2)
> says.
Currently, qemu with NPTL(I've tested on ARM EABI) on CLONE_VM create
thread using pthread interface. Every thread has its own stack.
vfork() is clone() with flags CLONE_VM and CLONE_VFORK.
man vfork(2):
Linux Description
vfork(), just like fork(2), creates a child process of the calling
process. For details and return value and errors, see fork(2).
vfork() is a special case of clone(2). It is used to create new pro-
cesses 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(2).
vfork() differs from fork(2) in that the parent is suspended until
the child makes a call to execve(2) or _exit(2). The child shares
all memory with its parent, including the stack, until execve(2) is
issued by the child. The child must not return from the current
function or call exit(3), but may call _exit(2).
Signal handlers are inherited, but not shared. Signals to the parent
arrive after the child releases the parent's memory.
So, implementation vfork() using pthread is wrong.
--
Regards, Kirill A. Shutemov
+ Belarus, Minsk
+ ALT Linux Team, http://www.altlinux.com/
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- [Qemu-devel] [PATCH] Fix building with 2.6.27 kernel headers, (continued)
- Re: [Qemu-devel] [PATCH] Implement futimesat() syscall, Riku Voipio, 2008/09/19
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- Re: [Qemu-devel] [PATCH] Implement fstatat64() syscall, Kirill A. Shutemov, 2008/09/19
- Re: [Qemu-devel] [PATCH] Swap only altered elements of the grouplist, Riku Voipio, 2008/09/19
- Re: [Qemu-devel] [PATCH] Fix getgroups() syscall emulation, Riku Voipio, 2008/09/19
Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, andrzej zaborowski, 2008/09/19
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, Kirill A. Shutemov, 2008/09/20
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, andrzej zaborowski, 2008/09/20
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation,
Kirill A. Shutemov <=
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, andrzej zaborowski, 2008/09/20
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, Kirill A. Shutemov, 2008/09/20
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, andrzej zaborowski, 2008/09/20
- Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, Kirill A. Shutemov, 2008/09/20
Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation, Kirill A. Shutemov, 2008/09/20