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Thu, 11 Jun 2020 11:31:28 +0000 (UTC) Subject: Re: [PATCH v7 2/5] softmmu/vl: Let -fw_cfg option take a 'gen_id' argument To: minyard@acm.org References: <20200528173141.17495-1-philmd@redhat.com> <20200528173141.17495-3-philmd@redhat.com> <20200609155050.GT2880@minyard.net> From: Laszlo Ersek Message-ID: <6e4b9540-7d5b-0951-2870-bada03e29d83@redhat.com> Date: Thu, 11 Jun 2020 13:31:28 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20200609155050.GT2880@minyard.net> Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=205.139.110.61; envelope-from=lersek@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/06/11 03:29:33 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -30 X-Spam_score: -3.1 X-Spam_bar: --- X-Spam_report: (-3.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-1, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=-0.01, RCVD_IN_MSPIKE_WL=-0.01, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , "=?UTF-8?Q?Daniel_P._Berrang=c3=a9?=" , =?UTF-8?Q?Philippe_Mathieu-Daud=c3=a9?= , qemu-devel@nongnu.org, Gerd Hoffmann Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 06/09/20 17:50, Corey Minyard wrote: > On Fri, May 29, 2020 at 11:50:24AM +0200, Laszlo Ersek wrote: >> Gerd, Corey: there's a question for you near the end, please. >> >> On 05/28/20 19:31, Philippe Mathieu-Daudé wrote: > > snip... > >> >> >> (3) I've noticed another *potential* issue, from looking at the larger >> context. I apologize for missing it in v6. >> >> See commit bab47d9a75a3 ("Sort the fw_cfg file list", 2016-04-07). (I'm >> copying Corey; Gerd is already copied.) From that commit, we have, at >> the end of this function: >> >> /* For legacy, keep user files in a specific global order. */ >> fw_cfg_set_order_override(fw_cfg, FW_CFG_ORDER_OVERRIDE_USER); >> fw_cfg_add_file(fw_cfg, name, buf, size); >> fw_cfg_reset_order_override(fw_cfg); >> >> This takes effect for "file" and "string", but not for "gen_id". Should >> we apply it to "gen_id" as well? (Sorry, I really don't understand what >> commit bab47d9a75a3 is about!) > > I can explain the rationale for that change, but I'm not sure of the > answer to your question. That changes makes sure that the fw_cfg data > remains exactly the same even on newer versions of qemu if the machine > is set the same. This way you can do migrations to newer qemu versions > and anything using fw_cfg won't get confused because the data changes. > > The reason that change was so complex was preserving the order for > migrating from older versions. > > This is only about migration. I'm not sure what gen_id is, but if it's > migrated, it better be future proof. Whenever introducing a new fw_cfg file (*any* new named file), how do we decide whether we need fw_cfg_set_order_override()? Thanks Laszlo > > -corey > >> >> *IF* we want to apply the same logic to "gen_id", then we should >> *perhaps* do, on the "nonempty_str(gen_id)" branch: >> >> size_t fw_cfg_size; >> >> fw_cfg_set_order_override(fw_cfg, FW_CFG_ORDER_OVERRIDE_USER); >> fw_cfg_size = fw_cfg_add_from_generator(fw_cfg, name, gen_id, errp); >> fw_cfg_reset_order_override(fw_cfg); >> return (fw_cfg_size > 0) ? 0 : -1; >> >> I think??? >> >> Or maybe even use FW_CFG_ORDER_OVERRIDE_DEVICE rather than >> FW_CFG_ORDER_OVERRIDE_USER? I don't have the slightest clue. >> >> (I guess if I understood what commit bab47d9a75a3 was about, I'd be less >> in doubt now. But that commit only hints at "avoid[ing] any future >> issues of moving the file creation" -- I don't know what those issues >> were in the first place!) >> >> With (1) optionally fixed, and (2) fixed, I'd be willing to R-b this >> patch; but I'm really thrown off by (3). >> >> Thanks, >> Laszlo >> >> >>> } else { >>> GError *err = NULL; >>> if (!g_file_get_contents(file, &buf, &size, &err)) { >>> >> >