linux-kernel - Re: [PATCH] ALSA: sound: Increase max size of components field

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Message-ID: <318f2ed3-57e6-495c-a773-4a094a3784cb@perex.cz>
Date: Thu, 23 Oct 2025 13:56:26 +0200
From: Jaroslav Kysela <perex@...ex.cz>
To: Maciej Strozek <mstrozek@...nsource.cirrus.com>,
 Takashi Iwai <tiwai@...e.com>
Cc: alsa-devel@...a-project.org, patches@...nsource.cirrus.com,
 linux-sound@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: sound: Increase max size of components field

On 10/23/25 11:27, Maciej Strozek wrote:
> The components field of snd_card can run out of space in new systems which
> use many audio devices, hence increase its size to 256 bytes.

> @@ -1069,7 +1069,7 @@ struct snd_ctl_card_info {
>   	unsigned char longname[80];	/* name + info text about soundcard */
>   	unsigned char reserved_[16];	/* reserved for future (was ID of mixer) */
>   	unsigned char mixername[80];	/* visual mixer identification */
> -	unsigned char components[128];	/* card components / fine identification, delimited with one space (AC97 etc..) */
> +	unsigned char components[256];	/* card components / fine identification, delimited with one space (AC97 etc..) */
Unfortunately, this change will introduce kABI breakage (ioctl number change - 
structure size).

You can probably define another struct snd_ctl_card_info and 
SNDRV_CTL_IOCTL_CARD_INFO and update alsa-lib to use it depending the protocol 
version.

Or, we may introduce a separate ioctl for the components string. The stripped 
components string in struct snd_ctl_card_info may have a special ASCII mark 
like '>' at the end of string specifying the availability of the complete 
string through another ioctl. I would prefer this solution.

Also, the components string may be dynamic in the kernel structure (pointer) 
to save some space. 256 bytes is not small number.

					Jaroslav

-- 
Jaroslav Kysela <perex@...ex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.