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[54.240.197.227]) by smtp.gmail.com with ESMTPSA id o1-20020a05600c510100b003fe1c332810sm4617535wms.33.2023.10.27.02.01.06 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 27 Oct 2023 02:01:07 -0700 (PDT) Message-ID: <9fb67e52-f262-4cf4-91c2-a42411ba21c4@gmail.com> Date: Fri, 27 Oct 2023 10:01:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 13/28] hw/xen: automatically assign device index to block devices Content-Language: en-US To: David Woodhouse , paul@xen.org, qemu-devel@nongnu.org Cc: Kevin Wolf , Hanna Reitz , Stefano Stabellini , Anthony Perard , =?UTF-8?Q?Marc-Andr=C3=A9_Lureau?= , Paolo Bonzini , "Michael S. Tsirkin" , Marcel Apfelbaum , Richard Henderson , Eduardo Habkost , Jason Wang , Marcelo Tosatti , qemu-block@nongnu.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Bernhard Beschow , Joel Upham References: <20231025145042.627381-1-dwmw2@infradead.org> <20231025145042.627381-14-dwmw2@infradead.org> <74e54da5-9c35-485d-a13c-efac3f81dec2@gmail.com> From: "Durrant, Paul" In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::329; envelope-from=xadimgnik@gmail.com; helo=mail-wm1-x329.google.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paul@xen.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 27/10/2023 09:45, David Woodhouse wrote: > On Fri, 2023-10-27 at 08:30 +0100, Durrant, Paul wrote: >> >>> +    if (blockdev->props.vdev.type == XEN_BLOCK_VDEV_TYPE_INVALID) { >>> +        XenBus *xenbus = XEN_BUS(qdev_get_parent_bus(DEVICE(xendev))); >>> +        char fe_path[XENSTORE_ABS_PATH_MAX + 1]; >>> +        char *value; >>> +        int disk = 0; >>> +        unsigned long idx; >>> + >>> +        /* Find an unoccupied device name */ >> >> Not sure this is going to work is it? What happens if 'hda' or 'sda', or >> 'd0' exists? I think you need to use the core of the code in >> xen_block_set_vdev() to generate names and search all possible encodings >> for each disk. > > Do we care? You're allowed to have *all* of "hda", "sda" and "xvda" at > the same time. If a user explicitly provides "sda" and then provides > another disk without giving it a name, we're allowed to use "xvda". > Maybe sda and xvda can co-exist, but https://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=docs/man/xen-vbd-interface.7.pandoc;h=ba0d159dfa7eaf359922583ccd6d2b413acddb13;hb=HEAD#l125 says that you'll likely run into trouble if hda exists and you happen to create xvda. > Hell, you can also have *separate* backing stores provided as "hda1", > "sda1" and "xvda1". I *might* have tolerated a heckle that this > function should check for at least the latter of those, but when I was > first coding it up I was more inclined to argue "Don't Do That Then". This code is allocating a name automatically so I think the onus is on it not create a needless clash which is likely to have unpredictable results depending on what the guest is. Just avoid any aliasing in the first place and things will be fine. Paul