From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH v3 15/24] xen/dts: Provide an helper to get a DT node from a path provided by a guest Date: Wed, 11 Mar 2015 12:34:51 +0000 Message-ID: <1426077291.21353.234.camel@citrix.com> References: <1421159133-31526-1-git-send-email-julien.grall@linaro.org> <1421159133-31526-16-git-send-email-julien.grall@linaro.org> <1424705450.27930.164.camel@citrix.com> <54EB4EC7.4050502@linaro.org> <1424708838.27930.206.camel@citrix.com> <54FEF868.7090704@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1YVfqw-00015a-VK for xen-devel@lists.xenproject.org; Wed, 11 Mar 2015 12:35:11 +0000 In-Reply-To: <54FEF868.7090704@linaro.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall Cc: xen-devel@lists.xenproject.org, tim@xen.org, stefano.stabellini@citrix.com List-Id: xen-devel@lists.xenproject.org On Tue, 2015-03-10 at 13:58 +0000, Julien Grall wrote: > On 23/02/15 16:27, Ian Campbell wrote: > > On Mon, 2015-02-23 at 16:01 +0000, Julien Grall wrote: > >> Hi Ian, > >> > >> On 23/02/15 15:30, Ian Campbell wrote: > >>> On Tue, 2015-01-13 at 14:25 +0000, Julien Grall wrote: > >>> > >>>> +/* This limit is used by the hypercalls to restrict the size of the path */ > >>>> +#define DEVICE_TREE_MAX_PATHLEN 1024 > >>> > >>> Is this something you've made up or derived from the DT spec/ePAPR etc? > >> > >> I didn't find a such requirements on the spec. > > > > I vaguely recall a limit on the length of a single node name, and a > > limit on the depth which they may nest, which can be multiplied. It's > > probably an unhelpfully large number though, so... > > > >> I chose this number based on the linux pathlen because the path is also > >> used in the sysfs (/sys/firmware/devicetree). > > > > ...that's a good as anything I suppose! > > Hmmm... I'm not so sure about the 1024 limit anymore. Linux is defining > PATH_MAX to 4096 but I don't see many usage in the sysfs code. > > And this value may change from one OS to another. Although, 1024 sounds > a very long path to write in the configuration file... I imagine in practice it will be cut-and-pasted, but yes. > Maybe we should > support alias too? Perhaps 2048 + (optionally, perhaps later) add alias support? 2048 because I assume 4096 being PAGE_SIZE would have some interesting corner cases, especially for a target buffer on the stack. If not then why not go straight for 4096? Ian.