ALSA: core: Use flexible array for card private data

snd_card_new() and snd_devm_card_new() allocate struct snd_card
together with optional driver-private storage. The storage is currently
described only by open-coded sizeof(*card) + extra_size arithmetic, and
snd_card_init() reaches it by manually adding sizeof(struct snd_card) to
the card pointer.

Make the trailing storage explicit with a flexible array member. Use
kzalloc_flex() for the regular allocation path and struct_size() for the
devres allocation size. This documents the layout and avoids open-coded
variable-size object arithmetic.

Align the flexible array to unsigned long long so the driver-private area
does not become less aligned than the old sizeof(struct snd_card) tail
address on 32-bit ABIs.

Signed-off-by: Cássio Gabriel <cassiogabrielcontato@gmail.com>
Link: https://patch.msgid.link/20260531-alsa-card-private-flex-array-v2-1-e4ff67f5bd23@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/include/sound/core.h b/include/sound/core.h
index 4093ec82a0a12bfb267cdde6ff4093434bf25476..4bb76c21c9565971beccf7e0d6a3141f14a0ed65 100644 (file)
--- a/include/sound/core.h
+++ b/include/sound/core.h
@@ -148,6 +148,8 @@ struct snd_card {
        struct snd_mixer_oss *mixer_oss;
        int mixer_oss_change_count;
 #endif
+
+       unsigned char private_data_area[] __aligned(__alignof__(unsigned long long));
 };
 
 #define dev_to_snd_card(p)     container_of(p, struct snd_card, card_dev)

diff --git a/sound/core/init.c b/sound/core/init.c
index 0c316189e94769c055ae5165c403f207dff8ba52..2408160b8ea13de33d43a581c38d1ff5ee38fd23 100644 (file)
--- a/sound/core/init.c
+++ b/sound/core/init.c
@@ -181,7 +181,7 @@ int snd_card_new(struct device *parent, int idx, const char *xid,
 
        if (extra_size < 0)
                extra_size = 0;
-       card = kzalloc(sizeof(*card) + extra_size, GFP_KERNEL);
+       card = kzalloc_flex(*card, private_data_area, extra_size);
        if (!card)
                return -ENOMEM;
 
@@ -232,7 +232,8 @@ int snd_devm_card_new(struct device *parent, int idx, const char *xid,
        int err;
 
        *card_ret = NULL;
-       card = devres_alloc(__snd_card_release, sizeof(*card) + extra_size,
+       card = devres_alloc(__snd_card_release,
+                           struct_size(card, private_data_area, extra_size),
                            GFP_KERNEL);
        if (!card)
                return -ENOMEM;
@@ -280,7 +281,7 @@ static int snd_card_init(struct snd_card *card, struct device *parent,
        int err;
 
        if (extra_size > 0)
-               card->private_data = (char *)card + sizeof(struct snd_card);
+               card->private_data = card->private_data_area;
        if (xid)
                strscpy(card->id, xid, sizeof(card->id));
        err = 0;