From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mailman by lists.gnu.org with tmda-scanned (Exim 4.43) id 1Kh2Ek-0002sY-CS for qemu-devel@nongnu.org; Sat, 20 Sep 2008 09:10:58 -0400 Received: from exim by lists.gnu.org with spam-scanned (Exim 4.43) id 1Kh2Eh-0002sJ-UA for qemu-devel@nongnu.org; Sat, 20 Sep 2008 09:10:56 -0400 Received: from [199.232.76.173] (port=34913 helo=monty-python.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1Kh2Eh-0002sG-Jy for qemu-devel@nongnu.org; Sat, 20 Sep 2008 09:10:55 -0400 Received: from fg-out-1718.google.com ([72.14.220.155]:7060) by monty-python.gnu.org with esmtp (Exim 4.60) (envelope-from ) id 1Kh2Eh-0007f0-BV for qemu-devel@nongnu.org; Sat, 20 Sep 2008 09:10:55 -0400 Received: by fg-out-1718.google.com with SMTP id l26so1436938fgb.8 for ; Sat, 20 Sep 2008 06:10:52 -0700 (PDT) Date: Sat, 20 Sep 2008 16:11:39 +0300 From: "Kirill A. Shutemov" Subject: Re: [Qemu-devel] [PATCH] Fix vfork() syscall emulation Message-ID: <20080920131134.GA26850@localhost.localdomain> References: <1221750426-14863-1-git-send-email-kirill@shutemov.name> <20080920064556.GA24679@localhost.localdomain> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="9jxsPFA5p3P2qPhR" Content-Disposition: inline In-Reply-To: Reply-To: qemu-devel@nongnu.org List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: andrzej zaborowski Cc: qemu-devel@nongnu.org, Paul Brook --9jxsPFA5p3P2qPhR Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Sep 20, 2008 at 02:45:57PM +0200, andrzej zaborowski wrote: > 2008/9/20 Kirill A. Shutemov : > > On Sat, Sep 20, 2008 at 04:56:45AM +0200, andrzej zaborowski wrote: > >> 2008/9/18 Kirill A. Shutemov : > >> > 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. >=20 > 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.=20 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. --=20 Regards, Kirill A. Shutemov + Belarus, Minsk + ALT Linux Team, http://www.altlinux.com/ --9jxsPFA5p3P2qPhR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.9 (GNU/Linux) iEYEARECAAYFAkjU9oYACgkQbWYnhzC5v6p/BwCfU/YBbiiGMBa2DCA+S6eJUuaI 8JEAn2333OhLTtuAcHrBzw05bbJxLg8P =xusg -----END PGP SIGNATURE----- --9jxsPFA5p3P2qPhR--