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Fri, 16 Oct 2020 06:52:43 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 70b5cef0-477e-4eab-b283-597742a6446a; Fri, 16 Oct 2020 06:52:41 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0628CAF30; Fri, 16 Oct 2020 06:52:41 +0000 (UTC) Received: from all-amaz-eas1.inumbo.com ([34.197.232.57] helo=us1-amaz-eas2.inumbo.com) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kTJbX-0007jD-H8 for xen-devel@lists.xenproject.org; Fri, 16 Oct 2020 06:52:43 +0000 X-Inumbo-ID: 70b5cef0-477e-4eab-b283-597742a6446a Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 70b5cef0-477e-4eab-b283-597742a6446a; Fri, 16 Oct 2020 06:52:41 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1602831161; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FU7VEYcmI1s3fO2D5qXBOl6HFx1yAiqrlE49qMsQuI8=; b=pCyLFIf8DqPUs5vNScYGA3RX6wCofxVM/9ofjeSTHhUHmDkmFNe3qqAdchBoSGOD+tleZa n1Xh4UJ3WxJakYgHM+yfwA63oKJCH2WpG7UtvJ5NHqROxeFX2nE1gTSkveWf2dRrFSDPc7 Rl77hdR2Q+a1JGcw2Zvh+7n5YENZbeU= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 0628CAF30; Fri, 16 Oct 2020 06:52:41 +0000 (UTC) Subject: Re: Getting rid of (many) dynamic link creations in the xen build To: Andrew Cooper Cc: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , "xen-devel@lists.xenproject.org" , Wei Liu , Ian Jackson , George Dunlap References: <85f1eea2-0c8b-de06-b9d8-69f9a7e34ea8@suse.com> <5c9d5d97-10c4-f5de-e4eb-7ae933706240@suse.com> From: Jan Beulich Message-ID: Date: Fri, 16 Oct 2020 08:52:42 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit On 15.10.2020 22:52, Andrew Cooper wrote: > On 15/10/2020 11:41, Jürgen Groß wrote: >> On 15.10.20 12:09, Jan Beulich wrote: >>> On 15.10.2020 09:58, Jürgen Groß wrote: >>>> After a short discussion on IRC yesterday I promised to send a mail >>>> how I think we could get rid of creating dynamic links especially >>>> for header files in the Xen build process. >>>> >>>> This will require some restructuring, the amount will depend on the >>>> selected way to proceed: >>>> >>>> - avoid links completely, requires more restructuring >>>> - avoid only dynamically created links, i.e. allowing some static >>>>     links which are committed to git >>> >>> While I like the latter better, I'd like to point out that not all >>> file systems support symlinks, and hence the repo then couldn't be >>> stored on (or the tarball expanded onto) such a file system. Note >>> that this may be just for viewing purposes - I do this typically at >>> home -, i.e. there's no resulting limitation from the build process >>> needing symlinks. Similarly, once we fully support out of tree >>> builds, there wouldn't be any restriction from this as long as just >>> the build tree is placed on a capable file system. >>> >>> As a result I'd like to propose variant 2´: Reduce the number of >>> dynamically created symlinks to a minimum. This said, I have to >>> admit that I haven't really understood yet why symlinks are bad. >>> They exist for exactly such purposes, I would think. >> >> Not the symlinks as such, but the dynamically created ones seem to be >> a problem, as we stumble upon those again and again. > > We have multiple build system bugs every release to do with dynamically > generated symlinks.  Given that symlinks aren't a hard requirement, this > is a massive price to pay, and time which could be better spent doing > other other things. > > Also, they prohibit the ability to build from a read-only source dir. In which way? In an out-of-tree build (see Linux) this gets created in the build tree, not the source one. Or else ... > The asm symlink in particular prevents any attempt to do concurrent > builds of xen.  In some future, I'd love to be able to do concurrent > out-of-tree builds of Xen on different architectures, because elapsed > time to do this is one limiting factor of mine on pre-push sanity checks. ... this wouldn't already be possible there (including varying arch-es built from the same source tree). Jan