[PATCH] ALSA: hda: Add hda_append_suffix() local helper

[PATCH] ALSA: hda: Add hda_append_suffix() local helper

[Takashi Iwai]

As strlcat() shall be deprecated in future, provide an alternative
just for a simple purpose -- append a suffix string to the given
string buffer -- and use it at appropriate places.  The code isn't
really efficient, but we don't ask for speed here, so let it be.

Link: https://lore.kernel.org/amolHJpiluNmBsDU@dev
Signed-off-by: Takashi Iwai <tiwai@suse.de>
---
 sound/hda/codecs/generic.c   | 4 ++--
 sound/hda/common/hda_local.h | 7 +++++++
 sound/hda/common/jack.c      | 2 +-
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/sound/hda/codecs/generic.c b/sound/hda/codecs/generic.c
index a4623dd67f81..6120f797b45a 100644
--- a/sound/hda/codecs/generic.c
+++ b/sound/hda/codecs/generic.c
@@ -2701,7 +2701,7 @@ static void get_jack_mode_name(struct hda_codec *codec, hda_nid_t pin,
 	struct hda_gen_spec *spec = codec->spec;
 
 	snd_hda_get_pin_label(codec, pin, &spec->autocfg, name, name_len);
-	strlcat(name, " Jack Mode", name_len);
+	hda_append_suffix(name, " Jack Mode", name_len);
 }
 
 static int get_out_jack_num_items(struct hda_codec *codec, hda_nid_t pin)
@@ -5678,7 +5678,7 @@ static void fill_pcm_stream_name(char *str, size_t len, const char *sfx,
 			break;
 		}
 	}
-	strlcat(str, sfx, len);
+	hda_append_suffix(str, sfx, len);
 }
 
 /* copy PCM stream info from @default_str, and override non-NULL entries
diff --git a/sound/hda/common/hda_local.h b/sound/hda/common/hda_local.h
index 98b2c4acebc2..947a3152fdb5 100644
--- a/sound/hda/common/hda_local.h
+++ b/sound/hda/common/hda_local.h
@@ -723,4 +723,11 @@ void snd_hda_codec_display_power(struct hda_codec *codec, bool enable);
 #define codec_dbg(codec, fmt, args...) \
 	dev_dbg(hda_codec_dev(codec), fmt, ##args)
 
+/* append a suffix string safely; equivalent with strlcat() */
+static inline void hda_append_suffix(char *str, const char *suffix, size_t size)
+{
+	size_t len = strnlen(str, size);
+	strscpy(str + len, suffix, size - len);
+}
+
 #endif /* __SOUND_HDA_LOCAL_H */
diff --git a/sound/hda/common/jack.c b/sound/hda/common/jack.c
index c4338f03a54d..1d6b0f0e6f27 100644
--- a/sound/hda/common/jack.c
+++ b/sound/hda/common/jack.c
@@ -615,7 +615,7 @@ static int add_jack_kctl(struct hda_codec *codec, hda_nid_t nid,
 		snd_hda_get_pin_label(codec, nid, cfg, name, sizeof(name));
 	if (phantom_jack)
 		/* Example final name: "Internal Mic Phantom Jack" */
-		strncat(name, " Phantom", sizeof(name) - strlen(name) - 1);
+		hda_append_suffix(name, " Phantom", sizeof(name));
 	err = snd_hda_jack_add_kctl(codec, nid, name, phantom_jack, 0, NULL);
 	if (err < 0)
 		return err;
-- 
2.55.0

Re: [PATCH] ALSA: hda: Add hda_append_suffix() local helper

[Ian Bridges]

On Thu, Jul 30, 2026 at 06:14:03PM +0200, Takashi Iwai wrote:
> As strlcat() shall be deprecated in future, provide an alternative
> just for a simple purpose -- append a suffix string to the given
> string buffer -- and use it at appropriate places.  The code isn't
> really efficient, but we don't ask for speed here, so let it be.

The patch was tested as follows:
 - Applied on today's for-next (f817bac425c5) on top of the two jack
 name cleanup patches. W=1 build of sound/hda/, no new warnings.

 - A userspace harness compared hda_append_suffix() against
 both the kernel strlcat() and the strncat() form in jack.c,
 exhaustively over buffer sizes, fill levels and suffix
 lengths, comparing every byte of the buffer. All cases
 were byte identical, including truncation.

 - A QEMU boot with intel-hda and hda-duplex, comparing the PCM
 stream names, the codec proc dump and the full control
 element list between base and patched kernels. The captures
 were byte identical.

Ian

Reviewed-by: Ian Bridges <icb@fastmail.org>
Tested-by: Ian Bridges <icb@fastmail.org>