From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: Xenstore.h clarifications Date: Fri, 28 Nov 2014 09:58:01 +0000 Message-ID: <1417168681.19852.2.camel@citrix.com> References: <54770242.9000709@bitdefender.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54770242.9000709@bitdefender.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Razvan Cojocaru , Ian Jackson Cc: "xen-devel@lists.xen.org" List-Id: xen-devel@lists.xenproject.org On Thu, 2014-11-27 at 12:51 +0200, Razvan Cojocaru wrote: It's a good idea to CC the relevant maintainers if you want their input. > Hello, > > I know that xc_interface_open() can be safely called several times from > the same process, and that several processes can each have a bunch of > xc_interface handles open, and that I shouldn't use an xc_interface > inherited from the parent in a child process, because xenctrl.h says so. > > Is it safe to assume that the same restrictions / conventions apply to > xs_handles obtained via xs_open()? Xenstore.h is not explicit. Looking > at the code, it would seem safe to assume that it can be used in a > similar manner, but it would be nice to have this confirmed if possible. I think there's a pretty good chance that the same applies to xenstore connections made over the device/shared-ring interface. I'm not really sure about the semantics of a Unix domain socket after a fork, but I don't expect both parent and child could sanely make use of it. So I think the answer is: * Connections made with xs_open(0) (which might be shared page or socket based) are only guaranteed to work in the parent after fork. * Connections made with xs_open(XS_OPEN_SOCKETONLY) will be usable in either the parent or the child after fork, but not both. * xs_daemon_open*() and xs_domain_open() are deprecated synonyms for xs_open(0) * XS_OPEN_READONLY has not bearing on any of this. Ian, does that seem right? Razvan, assuming Ian concurs with the above (or corrects it) then could you knock up a patch to document the result please. Ian.