Hi, On Wed, Jan 20, 2021 at 10:38:36AM +0100, Jaroslav Kysela wrote: > Dne 20. 01. 21 v 10:27 Takashi Iwai napsal(a): > > On Wed, 20 Jan 2021 09:55:41 +0100, > > Takashi Sakamoto wrote: > >> > >> ALSA control core allows usespace application to register control element > >> set by call of ioctl(2) with SNDRV_CTL_IOCTL_ELEM_ADD request. The added > >> control element set is called as 'user-defined'. Currently sound card has > >> limitation on the number of the user-defined control element set up > >> to 32. > >> > >> The limitation is inconvenient to drivers in ALSA firewire stack since > >> the drivers expect userspace applications to implement function to > >> control device functionalities such as mixing and routing. As the > >> userspace application, snd-firewire-ctl-services project starts: > >> https://github.com/alsa-project/snd-firewire-ctl-services/ > >> > >> The project supports many devices supported by ALSA firewire stack. The > >> limitation is mostly good since routing and mixing controls can be > >> represented by control element set, which includes control element with > >> the same parameters. Nevertheless, it's actually inconvenient to device > >> which has many varied functionalities. For example, plugin effect such as > >> channel strip and reverb has many parameters. For the case, many control > >> elements are required to configure the parameters and control element set > >> cannot aggregates controls for the parameters. At present, below models > >> are implemented with the control elements and actually add control element > >> sets over 32: > >> > >> * Apogee Emsemble (snd-bebob-ctl-service) > >> * TC Electronic Konnekt 24d (snd-dice-ctl-service) > >> * TC Electronic Studio Konnekt 48 (snd-dice-ctl-service) > >> * TC Electronic Konnekt Live (snd-dice-ctl-service) > >> * TC Electronic Impact Twin (snd-dice-ctl-service) > >> > >> It could be investigated to increase the number; e.g. quadruple to the > >> current (=128), however it's hard to find criteria about the number for > >> existent sound card. This commit just removes the limitation for the > >> reason. ALSA control core uses UINT_MAX as the maximum number of control > >> elements added to a sound card. It's limitation for both in-kernel driver > >> and userspace application. > >> > >> Signed-off-by: Takashi Sakamoto <o-takashi@xxxxxxxxxxxxx> > > > > I'm still worried by the unlimited number of possible additions. > > Did you check what would happen if you run a test program to add > > user-space ctls (with the max count) in a loop repeatedly? If that > > doesn't blow up too much, it might be OK. Otherwise we have to add > > some practical limits. > > > > So, let's prove that it's absolutely safe to release the limit at > > first. > > I agree. The UINT_MAX limit is really big in my eyes. The condition was added > to check for the insane allocations. I basically agree to increase this limit > (512, 1024?), but it should not be UINT_MAX. Thanks for your comments. I have no objection to relax current limitation instead of removal. Either 512 or 1024 (of course 32), it just comes from multiples of 2 and seems not to be reasonable for the practical limits. However, as I note in the commit message, I cannot find no criteria for the limitation. In this time, 40-50 control element sets are enough for the service program, thus I'll post v2 patch with 128 as limitation enough large to the requirement. Thanks Takashi Sakamoto
