git: 27b932e32fab - main - sound: Safely remove channel from list in one pass

The branch main has been updated by christos:

URL: https://cgit.FreeBSD.org/src/commit/?id=27b932e32faba1137ff307d05b787d837ccadda8

commit 27b932e32faba1137ff307d05b787d837ccadda8
Author:     Florian Walpen <dev@submerge.ch>
AuthorDate: 2025-01-21 11:59:12 +0000
Commit:     Christos Margiolis <christos@FreeBSD.org>
CommitDate: 2025-01-21 12:00:52 +0000

    sound: Safely remove channel from list in one pass
    
    The CHN_REMOVE_SAFE() macro did two traversals of the channel list to
    remove a channel, one to check whether the channel is an element of the
    list, and a second traversal through SLIST_REMOVE(). Reduce this to one
    traversal, while still preventing a NULL dereference in case the channel
    in question is not present in the list.
    
    While here, rename the macro arguments to something more descriptive.
    
    MFC after:      1 week
    Reviewed by:    christos
    Differential Revision:  https://reviews.freebsd.org/D48207
---
 sys/dev/sound/pcm/channel.h | 25 +++++++++++++++----------
 1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/sys/dev/sound/pcm/channel.h b/sys/dev/sound/pcm/channel.h
index 67f5019f4727..58fedd284ecb 100644
--- a/sys/dev/sound/pcm/channel.h
+++ b/sys/dev/sound/pcm/channel.h
@@ -175,6 +175,7 @@ struct pcm_channel {
 #define CHN_LINK(y)			y.link
 #define CHN_EMPTY(x, y)			SLIST_EMPTY(CHN_HEAD(x, y))
 #define CHN_FIRST(x, y)			SLIST_FIRST(CHN_HEAD(x, y))
+#define CHN_NEXT(elm, list)		SLIST_NEXT((elm), CHN_LINK(list))
 
 #define CHN_FOREACH(x, y, z)						\
 	SLIST_FOREACH(x, CHN_HEAD(y, z), CHN_LINK(z))
@@ -188,8 +189,8 @@ struct pcm_channel {
 #define CHN_INSERT_AFTER(x, y, z)					\
 	SLIST_INSERT_AFTER(x, y, CHN_LINK(z))
 
-#define CHN_REMOVE(x, y, z)						\
-	SLIST_REMOVE(CHN_HEAD(x, z), y, pcm_channel, CHN_LINK(z))
+#define CHN_REMOVE(holder, elm, list)					\
+	SLIST_REMOVE(CHN_HEAD(holder, list), elm, pcm_channel, CHN_LINK(list))
 
 #define CHN_INSERT_HEAD_SAFE(x, y, z)		do {			\
 	struct pcm_channel *t = NULL;					\
@@ -211,14 +212,18 @@ struct pcm_channel {
 		CHN_INSERT_AFTER(x, y, z);				\
 } while (0)
 
-#define CHN_REMOVE_SAFE(x, y, z)		do {			\
-	struct pcm_channel *t = NULL;					\
-	CHN_FOREACH(t, x, z) {						\
-		if (t == y)						\
-			break;						\
-	} 								\
-	if (t == y)							\
-		CHN_REMOVE(x, y, z);					\
+#define CHN_REMOVE_SAFE(holder, elm, list)	do {			\
+	if (CHN_FIRST(holder, list) == (elm)) {				\
+		SLIST_REMOVE_HEAD(CHN_HEAD(holder, list), CHN_LINK(list)); \
+	} else {							\
+		struct pcm_channel *t = NULL;				\
+		CHN_FOREACH(t, holder, list) {				\
+			if (CHN_NEXT(t, list) == (elm)) {		\
+				SLIST_REMOVE_AFTER(t, CHN_LINK(list));	\
+				break;					\
+			}						\
+		}							\
+	}								\
 } while (0)
 
 #define CHN_INSERT_SORT(w, x, y, z)		do {			\