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b=Um4H2o3wihXRCxdr4Ay3XIZwLa+jy5O+xf3lXdHnbSnrsATB9aq2lL6VFvfut2mHYmaDd5 pYrp3VjHooG52UDw== Received: from imap1.dmz-prg2.suse.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by imap1.dmz-prg2.suse.org (Postfix) with ESMTPS id 4434C3EA75; Fri, 6 Mar 2026 10:43:50 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id wow3D+avqmk4SAAAD6G6ig (envelope-from ); Fri, 06 Mar 2026 10:43:50 +0000 Date: Fri, 06 Mar 2026 11:43:49 +0100 Message-ID: <87zf4lutju.wl-tiwai@suse.de> From: Takashi Iwai To: Jaroslav Kysela Cc: Maciej Strozek , Takashi Iwai , linux-kernel@vger.kernel.org, linux-sound@vger.kernel.org, patches@opensource.cirrus.com, alsa-devel@alsa-project.org Subject: Re: [PATCH v3 2/2] ALSA: control: add ioctl to retrieve full card components In-Reply-To: <3174b8c9-8801-4d09-8e30-450899b40ca2@perex.cz> References: <20260303145815.9930-1-mstrozek@opensource.cirrus.com> <20260303145815.9930-2-mstrozek@opensource.cirrus.com> <87seagx6c4.wl-tiwai@suse.de> <87v7fay4l1.wl-tiwai@suse.de> <87pl5iy3z6.wl-tiwai@suse.de> <3174b8c9-8801-4d09-8e30-450899b40ca2@perex.cz> User-Agent: Wanderlust/2.15.9 (Almost Unreal) Emacs/30.2 Mule/6.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Rspamd-Action: no action X-Rspamd-Server: rspamd2.dmz-prg2.suse.org X-Spamd-Result: default: False [-3.51 / 50.00]; BAYES_HAM(-3.00)[100.00%]; MID_CONTAINS_FROM(1.00)[]; NEURAL_HAM_LONG(-1.00)[-1.000]; R_DKIM_ALLOW(-0.20)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; NEURAL_HAM_SHORT(-0.20)[-1.000]; MIME_GOOD(-0.10)[text/plain]; MX_GOOD(-0.01)[]; RCPT_COUNT_SEVEN(0.00)[7]; FUZZY_RATELIMITED(0.00)[rspamd.com]; MIME_TRACE(0.00)[0:+]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; RCVD_TLS_ALL(0.00)[]; DKIM_SIGNED(0.00)[suse.de:s=susede2_rsa,suse.de:s=susede2_ed25519]; FROM_EQ_ENVFROM(0.00)[]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; RCVD_COUNT_TWO(0.00)[2]; TO_MATCH_ENVRCPT_ALL(0.00)[]; DBL_BLOCKED_OPENRESOLVER(0.00)[imap1.dmz-prg2.suse.org:helo,imap1.dmz-prg2.suse.org:rdns]; DKIM_TRACE(0.00)[suse.de:+] X-Rspamd-Queue-Id: 7E1085C178 X-Spam-Flag: NO X-Spam-Score: -3.51 X-Spam-Level: On Fri, 06 Mar 2026 10:39:46 +0100, Jaroslav Kysela wrote: > > On 3/5/26 11:18, Takashi Iwai wrote: > > On Thu, 05 Mar 2026 11:11:40 +0100, > > Maciej Strozek wrote: > >> > >> W dniu czw, 05.03.2026 o godzinie 11∶04 +0100, użytkownik Takashi Iwai > >> napisał: > >>> On Thu, 05 Mar 2026 10:54:35 +0100, > >>> Maciej Strozek wrote: > >>>> > >>>> W dniu wto, 03.03.2026 o godzinie 16∶47 +0100, użytkownik Takashi > >>>> Iwai > >>>> napisał: > >>>>>> > >>>>>> + */ > >>>>>> +struct snd_ctl_card_components { > >>>>>> + int card; > >>>>>> + unsigned int length; > >>>>>> + unsigned char *components; > >>>>>> +}; > >>>>> > >>>>> And the ioctl can serve for two purposes: > >>>>> > >>>>> - When length=0 is set, the kernel stores the current number of > >>>>> bytes > >>>>>   and returns without copying.  User-space can use this mode for > >>>>>   allocating the buffer. > >>>>> > >>>> In alsa-lib all data must be allocated beforehand, so this > >>>> length==0 > >>>> query is not very useful there, it will just go into a [512] array > >>>> anyway. Are there any other users that may benefit from this? > >>> > >>> My suggested API can work even with the fixed size 512, too, if 512 > >>> is > >>> hight enough.  It's just more flexible.  And there is no restriction > >>> about alsa-lib data allocation; the function can query the size then > >>> allocate, too. > >>> > >>> > >>> Takashi > >> > >> OK, will prepare v4 with this, thanks > > > > Well, let's see how others think, too. The API design needs more > > considerations because we can't change it any longer once after > > defined. > > I think that the indirect pointer in ioctl structure is the best at > the moment unless we decide to use the fixed char array. OK, it might be indeed better if the user-space API is something like: int snd_ctl_card_components(snd_ctl_t *ctl, unsigned char *buf, size_t len); Then it's simpler to pass the pointer as is without copying. > But (for > discussion) we may try to be a bit clever and define universal bytes > ioctl which may carry also other things in future like: > > enum { > SND_CTL_CARD_BTYPE_COMPONENTS = 1 > }; So this is for future extensions? > struct snd_ctl_card_bytes { > unsigned int card; // this is duplication with info ioctl > // to be removed? Right, it sounds like superfluous. I thought we were to allow extracting a card info for a different card number, but it doesn't look so. > unsigned int type; // e.g. SND_CTL_CARD_BTYPE_COMPONENTS > unsigned int data_allocated; // overall size of data > unsigned int data_len; // actual data len > unsigned char *data; // pointer to data array > }; > > Scenarios: > > data_allocated = 0 or data == NULL -> driver just returns data_len > data_allocated < data_len -> driver returns -ENOMEM > data_allocated >= data_len -> driver will copy data > > Note that data_len will be zero from the user space for read > operations (driver knows it). But we can eventually use this ioctl to > set some data in future, so data_len/data will be used for the write > operation. In all cases, data_len is filled with the expected data size in return, right? thanks, Takashi