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Thu, 09 Jan 2025 00:25:50 -0800 (PST) Message-ID: <1af5c552-ea5e-4cf5-9a80-0e3559aeb403@suse.com> Date: Thu, 9 Jan 2025 09:25:48 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 20/35] xen/console: introduce console_owner_domid() To: Stefano Stabellini Cc: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= , dmukhin@ford.com, xen-devel@lists.xenproject.org, Andrew Cooper , Julien Grall , Bertrand Marquis , Michal Orzel , Denis Mukhin References: <20241205-vuart-ns8250-v1-20-e9aa923127eb@ford.com> <8a5a5a0f-72b0-4336-b0d2-142254319242@suse.com> <121ae72e-6229-40a4-8b9f-4f8b0764b712@suse.com> Content-Language: en-US From: Jan Beulich Autocrypt: addr=jbeulich@suse.com; keydata= xsDiBFk3nEQRBADAEaSw6zC/EJkiwGPXbWtPxl2xCdSoeepS07jW8UgcHNurfHvUzogEq5xk hu507c3BarVjyWCJOylMNR98Yd8VqD9UfmX0Hb8/BrA+Hl6/DB/eqGptrf4BSRwcZQM32aZK 7Pj2XbGWIUrZrd70x1eAP9QE3P79Y2oLrsCgbZJfEwCgvz9JjGmQqQkRiTVzlZVCJYcyGGsD /0tbFCzD2h20ahe8rC1gbb3K3qk+LpBtvjBu1RY9drYk0NymiGbJWZgab6t1jM7sk2vuf0Py O9Hf9XBmK0uE9IgMaiCpc32XV9oASz6UJebwkX+zF2jG5I1BfnO9g7KlotcA/v5ClMjgo6Gl MDY4HxoSRu3i1cqqSDtVlt+AOVBJBACrZcnHAUSuCXBPy0jOlBhxPqRWv6ND4c9PH1xjQ3NP nxJuMBS8rnNg22uyfAgmBKNLpLgAGVRMZGaGoJObGf72s6TeIqKJo/LtggAS9qAUiuKVnygo 3wjfkS9A3DRO+SpU7JqWdsveeIQyeyEJ/8PTowmSQLakF+3fote9ybzd880fSmFuIEJldWxp Y2ggPGpiZXVsaWNoQHN1c2UuY29tPsJgBBMRAgAgBQJZN5xEAhsDBgsJCAcDAgQVAggDBBYC AwECHgECF4AACgkQoDSui/t3IH4J+wCfQ5jHdEjCRHj23O/5ttg9r9OIruwAn3103WUITZee e7Sbg12UgcQ5lv7SzsFNBFk3nEQQCACCuTjCjFOUdi5Nm244F+78kLghRcin/awv+IrTcIWF hUpSs1Y91iQQ7KItirz5uwCPlwejSJDQJLIS+QtJHaXDXeV6NI0Uef1hP20+y8qydDiVkv6l IreXjTb7DvksRgJNvCkWtYnlS3mYvQ9NzS9PhyALWbXnH6sIJd2O9lKS1Mrfq+y0IXCP10eS FFGg+Av3IQeFatkJAyju0PPthyTqxSI4lZYuJVPknzgaeuJv/2NccrPvmeDg6Coe7ZIeQ8Yj t0ARxu2xytAkkLCel1Lz1WLmwLstV30g80nkgZf/wr+/BXJW/oIvRlonUkxv+IbBM3dX2OV8 AmRv1ySWPTP7AAMFB/9PQK/VtlNUJvg8GXj9ootzrteGfVZVVT4XBJkfwBcpC/XcPzldjv+3 HYudvpdNK3lLujXeA5fLOH+Z/G9WBc5pFVSMocI71I8bT8lIAzreg0WvkWg5V2WZsUMlnDL9 mpwIGFhlbM3gfDMs7MPMu8YQRFVdUvtSpaAs8OFfGQ0ia3LGZcjA6Ik2+xcqscEJzNH+qh8V m5jjp28yZgaqTaRbg3M/+MTbMpicpZuqF4rnB0AQD12/3BNWDR6bmh+EkYSMcEIpQmBM51qM EKYTQGybRCjpnKHGOxG0rfFY1085mBDZCH5Kx0cl0HVJuQKC+dV2ZY5AqjcKwAxpE75MLFkr wkkEGBECAAkFAlk3nEQCGwwACgkQoDSui/t3IH7nnwCfcJWUDUFKdCsBH/E5d+0ZnMQi+G0A nAuWpQkjM1ASeQwSHEeAWPgskBQL In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit On 09.01.2025 01:29, Stefano Stabellini wrote: > On Wed, 8 Jan 2025, Denis Mukhin wrote: >> On Wednesday, January 8th, 2025 at 12:35 AM, Roger Pau Monné wrote: >>> On Wed, Jan 08, 2025 at 09:13:02AM +0100, Jan Beulich wrote: >>>> On 08.01.2025 09:04, Roger Pau Monné wrote: >>>>> On Wed, Jan 08, 2025 at 08:28:32AM +0100, Jan Beulich wrote: >>>>>> On 08.01.2025 00:40, Stefano Stabellini wrote: >>>>>>> On Tue, 7 Jan 2025, Jan Beulich wrote: >>>>>>>> On 06.01.2025 19:48, Stefano Stabellini wrote: >>>>>>>>> On Mon, 6 Jan 2025, Jan Beulich wrote: >>>>>>>>>> On 04.01.2025 05:15, Denis Mukhin wrote: >>>>>>>>>>> On Tuesday, December 10th, 2024 at 11:28 PM, Jan Beulich jbeulich@suse.com wrote: >>>>>>>>>>>> On 06.12.2024 05:41, Denis Mukhin via B4 Relay wrote: >>>>>>>>>>>> >>>>>>>>>>>>> From: Denis Mukhin dmukhin@ford.com >>>>>>>>>>>>> >>>>>>>>>>>>> console_owner_domid() is introduced to obtain the "console owner" domain ID. >>>>>>>>>>>>> >>>>>>>>>>>>> The call is used in NS8250 emulator to identify the case when physical xen >>>>>>>>>>>>> console focus is owned by the domain w/ NS8250 emulator, in which case, >>>>>>>>>>>>> messages from guest OS are formatted w/o '(XEN)' prefix. >>>>>>>>>>>> >>>>>>>>>>>> Such messages ought to be processed through guest_printk(), which wants a >>>>>>>>>>>> domain pointer, not a domid_t anyway. Plus isn't that going to be >>>>>>>>>>>> current->domain anyway at the callsite, eliminating the need for such a >>>>>>>>>>>> >>>>>>>>>>>> helper altogether? >>>>>>>>>>> >>>>>>>>>>> If the current domain is owning the physical console and printing, say, Linux >>>>>>>>>>> login prompt, there's no need to add "(XEN)" for every printout; adding timestamps >>>>>>>>>>> can be disabled from Xen command line. >>>>>>>>>> >>>>>>>>>> Surely there shouldn't be (XEN), but without (d) it'll be ambiguous in a log >>>>>>>>>> which domain a message came from. As long as only Dom0 messages are left un- >>>>>>>>>> prefixed, that's likely fine. Yet as soon as multiple domains can issue such >>>>>>>>>> messages (and have console "focus") I think the prefix needs to be there. >>>>>>>>> >>>>>>>>> It looks like we are aligned on the desired behavior, >>>>>>>> >>>>>>>> Hmm, no, I don't think we are. I don't ... >>>>>>>> >>>>>>>>> but for clarity, >>>>>>>>> see https://marc.info/?l=xen-devel&m=173405161613716, also copy/pasted >>>>>>>>> here: >>>>>>>>> >>>>>>>>> I think we should provide a consistent behavior across architectures. >>>>>>>>> The current behavior with vpl011 and dom0less on ARM is the following: >>>>>>>>> >>>>>>>>> - no prefix for Dom0 output >>>>>>>>> - DOM$NUM for DomUs when not in focus, otherwise no prefix >>>>>>>> >>>>>>>> ... view this model as a desirable one. It leaves room for ambiguity. >>>>>>> >>>>>>> Adding a few more people in CC for feedback. >>>>>>> >>>>>>> My priority is to keep the architectures aligned. It might be OK to >>>>>>> change output format, but then let's do it uniformly on ARM as well. >>>>>>> >>>>>>> Jan, please clarify what you think would be better than the above. Is it >>>>>>> the following? I don't think I understood your preference. >>>>>>> >>>>>>> - DOM$NUM for Dom0 and DomUs when not in focus, otherwise no prefix >>>>>> >>>>>> No, I mean like we have it with guest_printk() today. (XEN) for Xen's >>>>>> own messages, (d) for ordinary domains' ones, and no prefix >>>>>> exclusively for the hardware/control domain. What is best to do when >>>>>> hardware and control domains are distinct I'm uncertain - I'd be >>>>>> inclined to suggest that the hardware domain then stay the one without >>>>>> any prefix. >>>>> >>>>> One concern I have with this approach is whether the addition of the >>>>> (d) prefixes will skew output of interactive applications. So far >>>>> the prefix is added to output from all domains different than dom0 >>>>> because the console is not interactive for them, and hence no input >>>>> can be consumed. >>>> >>>> Hmm, that's an aspect I have to admit I didn't think of. >>>> >>>>> If that changes however, and domains different than dom0 can get input >>>>> from the Xen console then I wonder how much the added prefix will skew >>>>> output. Another possible option would be to not print the prefix for >>>>> the domain that has the console input assigned (current target), and >>>>> print it for all other domains (even for dom0 when not in focus). >>>> >>>> That's largely what aiui was proposed. My extra requirement there would >>>> then be that we make sure a log message is always emitted when console >>>> focus shifts, so it's possible to identify the owner for any part of >>>> the log. >>> >>> >>> Indeed, printing console input shifting should be a requirement >>> regardless of how we decide to print the prefix. >> >> Console input focus switch is indicated after pressing Crtl+aaa, e.g.: >> [[ >> ... >> (XEN) [15359.353038] *** Serial input to Xen (type 'CTRL-aaa' to switch input) >> (XEN) [15361.176754] *** Serial input to DOM0 (type 'CTRL-aaa' to switch input) >> (XEN) [15711.297202] *** Serial input to DOM1 (type 'CTRL-aaa' to switch input) >> ... >> ]] > > > Roger, Jan, you should use Xen Dom0less more :-) This is the way it > already works on ARM. Let me expand on my earlier message that was too > terse. > > At boot time, Xen prints messages with the (XEN) prefix as usual: > > (XEN) Brought up 4 CPUs > > When Dom0 starts, it has not prefix (and has input by default): > > [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034] > > When a DomU starts, it has the following prefix (and doesn't have > input): > > (XEN) DOM1: [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034] Which is wrong - this isn't a Xen message. Such messages imo want prefixing (d), as guest_printk() does. Jan > Eventually, both Linuxes finish booting, you can login into Dom0 as > usual. Messages from Dom1, if any, are still printed with (XEN) DOM1 as > prefix. > > You can switch input to Dom1 with Ctrx-aaa, the same way that you do > today to switch between Xen and Dom0. Xen prints a message: > > (XEN) *** Serial input to DOM1 (type 'CTRL-a' three times to switch input) > > Now, as you type, you send characters to Dom1. And Dom1 doesn't have the > DOM1 prefix any longer, while it is still has (XEN) because the message > is printed by Xen on behalf of the domain: > > (XEN) / # echo hello world > (XEN) hello world > > If Dom0 prints anything in the backgrounds, it shows without prefixes: > > hello world from dom0 > > If another domain, dom2, prints anything in the background, it shows > with (XEN) DOM2 prefix: > > (XEN) DOM2: hello from dom2 > > I think it makes sense to be consistent across architectures and we > should default to the same behavior on x86 too. If we want to make > improvements, the one thing I could potentially see changing is adding a > DOM0 prefix to Dom0 messages when Dom0 does not have input. If we do > that, let's do it on both ARM and x86 architectures. > > Cheers, > Stefano