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dmarc=fail (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=xen-devel-bounces@lists.xenproject.org Received: from list by lists.xenproject.org with outflank-mailman.7252.18896 (Exim 4.92) (envelope-from ) id 1kT0hf-0006on-KQ; Thu, 15 Oct 2020 10:41:47 +0000 X-Outflank-Mailman: Message body and most headers restored to incoming version Received: by outflank-mailman (output) from mailman id 7252.18896; Thu, 15 Oct 2020 10:41:47 +0000 X-BeenThere: xen-devel@lists.xenproject.org List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Precedence: list Sender: "Xen-devel" Received: from localhost ([127.0.0.1] helo=lists.xenproject.org) by lists.xenproject.org with esmtp (Exim 4.92) (envelope-from ) id 1kT0hf-0006og-HP; Thu, 15 Oct 2020 10:41:47 +0000 Received: by outflank-mailman (input) for mailman id 7252; Thu, 15 Oct 2020 10:41:45 +0000 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 1kT0hd-0006ob-R0 for xen-devel@lists.xenproject.org; Thu, 15 Oct 2020 10:41:45 +0000 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 105b030c-2baf-4ea9-8814-b281e8e673a7; Thu, 15 Oct 2020 10:41:44 +0000 (UTC) Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 95F97B2A1; Thu, 15 Oct 2020 10:41:43 +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 1kT0hd-0006ob-R0 for xen-devel@lists.xenproject.org; Thu, 15 Oct 2020 10:41:45 +0000 X-Inumbo-ID: 105b030c-2baf-4ea9-8814-b281e8e673a7 Received: from mx2.suse.de (unknown [195.135.220.15]) by us1-amaz-eas2.inumbo.com (Halon) with ESMTPS id 105b030c-2baf-4ea9-8814-b281e8e673a7; Thu, 15 Oct 2020 10:41:44 +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=1602758503; 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=EnA6MYaKqf1RrEFuB4VDcWIXxw1nsLktMnw9Xj3eDgo=; b=VC9qCaSZLQZS9A7dLDOzbLNuxSBHRs+Mptg0eH91oJ4O41JYxk63xlrCFe7Rxi3oDydU8C 7zIqa4yX2GDj1aur1dFQIouyicT3DFyJXqLZSkTyG9vTodLGtBZwyOlSyNFrBpQyzm2bCn NRgKi80EzUy2lQmltScRsknTmy0yA6Y= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 95F97B2A1; Thu, 15 Oct 2020 10:41:43 +0000 (UTC) Subject: Re: Getting rid of (many) dynamic link creations in the xen build To: Jan Beulich Cc: "xen-devel@lists.xenproject.org" , Andrew Cooper , Wei Liu , Ian Jackson , George Dunlap References: <85f1eea2-0c8b-de06-b9d8-69f9a7e34ea8@suse.com> <5c9d5d97-10c4-f5de-e4eb-7ae933706240@suse.com> From: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= Message-ID: Date: Thu, 15 Oct 2020 12:41:42 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <5c9d5d97-10c4-f5de-e4eb-7ae933706240@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit 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. > >> The difference between both variants is affecting the public headers >> in xen/include/public/: avoiding even static links would require to >> add another directory or to move those headers to another place in the >> tree (either use xen/include/public/xen/, or some other path */xen), >> leading to the need to change all #include statements in the hypervisor >> using today. >> >> The need for the path to have "xen/" is due to the Xen library headers >> (which are installed on user's machines) are including the public >> hypervisor headers via "#include " and we can't change that >> scheme. A static link can avoid this problem via a different path, but >> without any link we can't do that. >> >> Apart from that decision, lets look which links are created today for >> accessing the header files (I'll assume my series putting the library >> headers to tools/include will be taken, so those links being created >> in staging today are not mentioned) and what can be done to avoid them: >> >> - xen/include/asm -> xen/include/asm-: >> Move all headers from xen/include/asm- to >> xen/arch//include/asm and add that path via "-I" flag to CFLAGS. >> This has the other nice advantages that most architecture specific >> files are now in xen/arch (apart from the public headers) and that we >> can even add generic fallback headers in xen/include/asm in case an >> arch doesn't need a specific header file. > > Iirc Andrew suggested years ago that we follow Linux in this regard > (and XTF already does). My only concern here is the churn this will > cause for backports. Changing a directory name in a patch isn't that hard, IMO. > >> - xen/arch//efi/*.[ch] -> xen/common/efi/*.[ch]: >> Use vpath for the *.c files and the "-I" flag for adding common/efi to >> the include path in the xen/arch//efi/Makefile. > > Fine with me. > >> - tools/include/xen/asm -> xen/include/asm-: >> Add "-Ixen/arch//include" to the CFLAGS. It might be a nice idea >> to move the headers needed by the tools to xen/arch/include/tools/asm >> and use "-Ixen/arch//include/tools" instead, but this would >> require either the same path added to the hypervisor's CFLAGS or a >> modification of the related #include statements. > > Separating headers intended for tools consumption is okay with me, > but I dislike the tools/ infix in the path you suggest. Since there > can't possibly be any shared prototypes, how about defs/ or some > such not specifically naming either of the consuming components > (and thus visually excluding the other)? I have absolutely no preferences for the naming. defs is fine IMO. > > Of course, the further asm/ underneath is kind of ugly because of > being largely unnecessary. Perhaps we could have just > xen/arch/include/defs/ and use #include ? Yes, that should work, too. > >> - tools/include/xen/foreign -> tools/include/xen-foreign: >> Get rid of tools/include/xen-foreign and generate the headers directly >> in xen/include/public/foreign instead. > > Except that conceptually building in tools/ would better not alter > the xen/ subtree in any way. I meant to generate the headers from the hypervisor build instead. > >> - tools/include/xen/sys -> tools/include/xen-sys/: >> Move the headers from tools/include/xen-sys/ to >> tools/include//xen/sys/ and add the appropriate path to CFLAGS. > > Not very nice imo because of the otherwise pointless intermediate > directories, but if we truly need to minimize symlink usage, then > so be it. > >> - tools/include/xen/lib//* -> xen/include/xen/lib//*: >> Move xen/include/xen/lib/ to xen/include/tools/lib/ and >> add "-Ixen/include/tools" to the CFLAGS of tools. > > Why not -Ixen/include/xen without any movement? Perhaps because This would open up most of the hypervisor private headers to be easily includable by tools. > -Ixen/include/tools wouldn't work either, due to code using > > #include /xyz.h> > > ? I.e. you really mean Move xen/include/xen/lib/ to > xen/include/tools/xen/lib/? Not very nice. I have to admit > I can't see why the header in xen/include/xen/lib// don't > use > > #include "xyz.h" > > But then this would leave the problem with xen/lib//*.c > using similar #include-s. Would dropping xen/ from the paths > perhaps help, moving xen/include/xen/lib/* to xen/include/lib/*? > Istr suggesting this when the lib/ subtrees were introduced ... This would at least eliminate one directory level. > >> - tools/include/xen/libelf/* -> xen/include/xen/*: >> Move the affected headers from xen/include/xen to >> xen/include/tools/libelf and reuse the above set CFLAGS. > > Why not xen/include/libelf/ or xen/include/lib/elf/? > libelf-private.h has distinct #include-s for Xen and the tools > anyway. All that's needed is that these headers don't sit in a > directory where headers also live which are not supposed to be > visible. That is correct. Juergen