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([2a01:e0a:11aa:87f0:ea69:b2b0:2dae:5ef9]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-48c71c0b60fsm5378202f8f.8.2026.10.07.06.17.51 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 07 Oct 2026 06:17:51 -0700 (PDT) Message-ID: <24ad6178-2f3b-4f84-91b5-c1f4fb92a21b@redhat.com> Date: Wed, 7 Oct 2026 15:17:48 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] drm/panic: allow overriding panic QR code URL To: Nahida Buer Cc: dri-devel@lists.freedesktop.org, Javier Martinez Canillas , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , linux-kernel@vger.kernel.org References: <20261002203140.121165-1-me@nahida.im> <20261002222021.149450-1-me@nahida.im> Content-Language: en-US, fr From: Jocelyn Falempe In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 10/3/26 01:03, Nahida Buer wrote: > Thanks for the review. > > My motivation was slightly different from disabling the URL when the > configured endpoint is untrusted or unavailable. I wanted to keep the > URL QR mode while allowing the same kernel image to use a different > reporting endpoint depending on the deployment. > > It also allows enabling the compressed URL mode without rebuilding the > kernel. With an empty CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL, the QR code > contains the raw kmsg. Supplying drm.panic_qr_url= at boot instead > switches it to the URL format, where the kmsg is compressed with zlib. > > This could be useful for a distribution or a locally built kernel image > used on multiple systems: the image can keep a neutral/default > configuration, while individual systems can opt into a specific panic > report collector and compressed QR payload at boot time. > > panic_screen=user or panic_screen=kmsg only disables the URL QR mode; > it does not provide a way to keep that mode while changing or enabling > the reporting endpoint. > > The parameter is read-only after initialization, so it only selects the > endpoint at boot/module load time. > > If keeping the URL fixed at build time is intentional policy for DRM > panic, though, I'm fine with dropping the patch. After thinking more about this, I prefer to keep the URL fixed at build time. I hope it won't refrain you from contributing again. Best regards, -- Jocelyn > > Jocelyn Falempe 于2026年10月3日周六 06:56写道： >> >> On 10/3/26 00:20, 纳西妲 · Nahida wrote: >>> The base URL used for the panic QR code is currently fixed at build time >>> by CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL. Changing the panic report >>> endpoint therefore requires rebuilding the kernel. >>> >>> Add a drm.panic_qr_url module parameter to allow overriding the URL at >>> boot or module load time, while keeping the Kconfig value as the >>> default. >>> >>> Keep the parameter read-only after initialization so the panic path can >>> access it without additional synchronization. >>> >>> Expose the configured URL to the DRM panic helper through an internal >>> getter so the helper can use the runtime value when generating the QR >>> code. >> >> The code looks good, but I think it shouldn't be allowed to change this >> setting at boot time. >> You can already set the drm_panic screen to "user" or "kmsg" in the >> kernel command line if you don't trust the default URL, or if the URL is >> no more reachable. >> It introduces some complexity, and I don't really see the benefit. >> >> Best regards, >> >> -- >> >> Jocelyn> >>> Assisted-by: LLM >>> Signed-off-by: 纳西妲 · Nahida >>> --- >>> v2: >>> - Grow the formatted URL buffer to accommodate the maximum 255-byte >>> runtime base URL. >>> - Reject unexpectedly truncated formatted URLs. >>> - Test the maximum-length runtime URL. >>> >>> v1: https://lore.kernel.org/r/20261002203140.121165-1-me@nahida.im >>> >>> Tested on x86_64: >>> - Full modular build with DRM=m and DRM_KMS_HELPER=m. >>> - QEMU/virtio-gpu runtime override with a non-empty Kconfig default URL. >>> - QEMU/virtio-gpu runtime fallback to the Kconfig default URL. >>> - QEMU/virtio-gpu runtime override with an empty Kconfig default URL. >>> - QEMU/virtio-gpu raw kmsg QR fallback with no configured URL. >>> - QEMU/virtio-gpu runtime override with a 255-byte base URL. >>> >>> drivers/gpu/drm/Kconfig | 9 +++++---- >>> drivers/gpu/drm/drm_panic.c | 9 +++++++++ >>> drivers/gpu/drm/drm_panic_helper.c | 17 +++++++++++------ >>> drivers/gpu/drm/drm_panic_internal.h | 4 ++++ >>> 4 files changed, 29 insertions(+), 10 deletions(-) >>> >>> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig >>> index 61111d50b..3d9d421f0 100644 >>> --- a/drivers/gpu/drm/Kconfig >>> +++ b/drivers/gpu/drm/Kconfig >>> @@ -111,10 +111,11 @@ config DRM_PANIC_SCREEN_QR_CODE_URL >>> string "Base URL of the QR code in the panic screen" >>> depends on DRM_PANIC_SCREEN_QR_CODE >>> help >>> - This option sets the base URL to report the kernel panic. If it's set >>> - the QR code will contain the URL and the kmsg compressed with zlib as >>> - a URL parameter. If it's empty, the QR code will contain the kmsg as >>> - uncompressed text only. >>> + This option sets the default base URL to report the kernel panic. If >>> + it's set the QR code will contain the URL and the kmsg compressed with >>> + zlib as a URL parameter. If it's empty, the QR code will contain the >>> + kmsg as uncompressed text only. It can be overridden with the >>> + drm.panic_qr_url= kernel parameter. >>> There is a demo code in javascript, to decode and uncompress the kmsg >>> data from the URL parameter at https://github.com/kdj0c/panic_report >>> >>> diff --git a/drivers/gpu/drm/drm_panic.c b/drivers/gpu/drm/drm_panic.c >>> index 9fe97c4ed..463544f71 100644 >>> --- a/drivers/gpu/drm/drm_panic.c >>> +++ b/drivers/gpu/drm/drm_panic.c >>> @@ -49,6 +49,15 @@ MODULE_LICENSE("GPL"); >>> static uint panic_qr_version = CONFIG_DRM_PANIC_SCREEN_QR_VERSION; >>> module_param(panic_qr_version, uint, 0644); >>> MODULE_PARM_DESC(panic_qr_version, "maximum version (size) of the QR code"); >>> +static char panic_qr_url[256] = CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL; >>> +module_param_string(panic_qr_url, panic_qr_url, sizeof(panic_qr_url), 0444); >>> +MODULE_PARM_DESC(panic_qr_url, "base URL of the QR code in the panic screen"); >>> + >>> +const char *drm_panic_get_qr_url(void) >>> +{ >>> + return panic_qr_url; >>> +} >>> +EXPORT_SYMBOL_GPL(drm_panic_get_qr_url); >>> #endif >>> >>> static enum drm_panic_type drm_panic_type = -1; >>> diff --git a/drivers/gpu/drm/drm_panic_helper.c b/drivers/gpu/drm/drm_panic_helper.c >>> index 8913c3d22..b0ea0b4e8 100644 >>> --- a/drivers/gpu/drm/drm_panic_helper.c >>> +++ b/drivers/gpu/drm/drm_panic_helper.c >>> @@ -609,17 +609,20 @@ static void drm_panic_helper_qr_exit(void) >>> stream.workspace = NULL; >>> } >>> >>> -static int drm_panic_helper_get_qr_code_url(u8 **qr_image, unsigned int qr_version) >>> +static int drm_panic_helper_get_qr_code_url(u8 **qr_image, unsigned int qr_version, >>> + const char *qr_url) >>> { >>> struct kmsg_dump_iter iter; >>> - char url[256]; >>> + char url[512]; >>> size_t kmsg_len, max_kmsg_size; >>> char *kmsg; >>> int max_qr_data_size, url_len; >>> >>> url_len = snprintf(url, sizeof(url), "%s?a=%s&v=%s&z=", >>> - CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL, >>> - utsname()->machine, utsname()->release); >>> + qr_url, utsname()->machine, utsname()->release); >>> + >>> + if (url_len >= (int)sizeof(url)) >>> + return -E2BIG; >>> >>> max_qr_data_size = drm_panic_helper_qr_max_data_size(qr_version, url_len); >>> max_kmsg_size = min(MAX_ZLIB_RATIO * max_qr_data_size, QR_BUFFER1_SIZE); >>> @@ -686,8 +689,10 @@ static int drm_panic_helper_get_qr_code_raw(u8 **qr_image, unsigned int qr_versi >>> >>> static int drm_panic_helper_get_qr_code(u8 **qr_image, unsigned int qr_version) >>> { >>> - if (strlen(CONFIG_DRM_PANIC_SCREEN_QR_CODE_URL) > 0) >>> - return drm_panic_helper_get_qr_code_url(qr_image, qr_version); >>> + const char *qr_url = drm_panic_get_qr_url(); >>> + >>> + if (qr_url[0]) >>> + return drm_panic_helper_get_qr_code_url(qr_image, qr_version, qr_url); >>> else >>> return drm_panic_helper_get_qr_code_raw(qr_image, qr_version); >>> } >>> diff --git a/drivers/gpu/drm/drm_panic_internal.h b/drivers/gpu/drm/drm_panic_internal.h >>> index fe6d514a0..f33552265 100644 >>> --- a/drivers/gpu/drm/drm_panic_internal.h >>> +++ b/drivers/gpu/drm/drm_panic_internal.h >>> @@ -14,6 +14,10 @@ struct drm_device; >>> >>> #ifdef CONFIG_DRM_PANIC >>> >>> +#if IS_ENABLED(CONFIG_DRM_PANIC_SCREEN_QR_CODE) >>> +const char *drm_panic_get_qr_url(void); >>> +#endif >>> + >>> /** >>> * drm_panic_lock - protect panic printing relevant state >>> * @dev: struct drm_device >>> >>> base-commit: 54e61ea6c492d69a1717018826d8340810c812eb >> >