git: b510eedf7e51 - stable/15 - linuxkpi: Add support for statically-allocated kfifo

The branch stable/15 has been updated by bz:

URL: https://cgit.FreeBSD.org/src/commit/?id=b510eedf7e512019ccac0f5f79e0cb7738dad40b

commit b510eedf7e512019ccac0f5f79e0cb7738dad40b
Author:     Jean-Sébastien Pédron <dumbbell@FreeBSD.org>
AuthorDate: 2025-09-07 08:37:27 +0000
Commit:     Bjoern A. Zeeb <bz@FreeBSD.org>
CommitDate: 2026-04-22 20:56:54 +0000

    linuxkpi: Add support for statically-allocated kfifo
    
    The main difference with the dynamically allocated version is that the
    structure is initialized with `DECLARE_KFIFO()` which takes the number
    of items as an additional argument compared to `DECLARE_KFIFO_PTR()`.
    
    The declared structure is then initialized with `INIT_KFIFO()` which
    sets all fields to 0, except `total` which is computed from the size of
    the array passed to `DECLARE_KFIFO()`.
    
    The amdgpu DRM driver started to used this in Linux 6.10.
    
    Reviewed by:    bz
    Sponsored by:   The FreeBSD Foundation
    Differential Revision: https://reviews.freebsd.org/D54497
    
    (cherry picked from commit 55bd09ae0fc437c9eb135952ac278540b7388add)
---
 sys/compat/linuxkpi/common/include/linux/kfifo.h | 22 ++++++++++++++++++++--
 1 file changed, 20 insertions(+), 2 deletions(-)

diff --git a/sys/compat/linuxkpi/common/include/linux/kfifo.h b/sys/compat/linuxkpi/common/include/linux/kfifo.h
index b9f6ecacd3d1..b0d0c17f07e4 100644
--- a/sys/compat/linuxkpi/common/include/linux/kfifo.h
+++ b/sys/compat/linuxkpi/common/include/linux/kfifo.h
@@ -33,8 +33,26 @@
 #include <linux/slab.h>
 #include <linux/gfp.h>
 
-#define	INIT_KFIFO(x)	0
-#define	DECLARE_KFIFO(x, y, z)
+/*
+ * INIT_KFIFO() is used to initialize the structure declared with
+ * DECLARE_KFIFO(). It doesn't work with DECLARE_KFIFO_PTR().
+ */
+#define	INIT_KFIFO(_kf)							\
+	({								\
+		(_kf).total = nitems((_kf).head);			\
+		(_kf).count = 0;					\
+		(_kf).first = 0;					\
+		(_kf).last = 0;						\
+	})
+
+#define	DECLARE_KFIFO(_name, _type, _size)				\
+	struct kfifo_ ## _name {					\
+		size_t		total;					\
+		size_t		count;					\
+		size_t		first;					\
+		size_t		last;					\
+		_type		head[_size];				\
+	} _name
 
 #define	DECLARE_KFIFO_PTR(_name, _type)					\
 	struct kfifo_ ## _name {					\