[PATCH 0/3] printk: add macros to simplify handling struct va_format

[PATCH 0/3] printk: add macros to simplify handling struct va_format

[Andrzej Hajda]

This patchset contains patch abstracting out most common bits of va_format uses
into small macro. The macro works as a forwarder of variadic args to va_format
call.
Rough estimates based on dirty cocci script suggests about 180-230 users
could be converted, allowing to remove about 1100-1300 lines of code.
Of course, I do not plan to do it in mass. I just provide two patches to
show the usage and potential.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
Andrzej Hajda (3):
      printk: add macros to simplify handling struct va_format
      drivers/core: use va_format_call helper
      mm: use va_format_call helper

 drivers/base/core.c    | 32 ++++++--------------------------
 include/linux/printk.h | 30 ++++++++++++++++++++++++++++++
 mm/page_alloc.c        | 14 ++++----------
 mm/slub.c              | 10 +---------
 4 files changed, 41 insertions(+), 45 deletions(-)
---
base-commit: 37a098cc87aafdf4de147851cbf350bb66c51b45
change-id: 20251126-va_format_call-41053ef60fd7

Best regards,
-- 
Andrzej Hajda <andrzej.hajda@intel.com>

[PATCH 1/3] printk: add macros to simplify handling struct va_format

[Andrzej Hajda]

struct va_format is used to facilitate implementation of
variadic functions. Most of variadic users do not parse
arguments one by one, they just forward them to some
helper via va_format pointer. Introduced helpers simplifies
it more.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
 include/linux/printk.h | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 45c663124c9bd3b294031d839f1253f410313faa..6fd817ce29a66b33a804b660c2b770efa110ee7e 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -87,6 +87,36 @@ struct va_format {
 	va_list *va;
 };
 
+/* Special macro used only by callers of va_format_call to position va_format argument */
+#define va_format_arg (&vaf)
+
+/**
+ * va_format_call() - forward variable arguments to va_format aware function
+ * @_fmt: format used by @_func function
+ * @_func: function which should be called
+ * @_args: arguments passed to @_func. Exactly one of them must be va_format_arg,
+ *         to indicate position of *va_format type arg in arguments of @_func.
+ *
+ * Many variadic functions just forwards their variadic arguments to some helper
+ * function via va_format pointer. It involves few common steps encapsulated in
+ * this macro. The macro is accompanied by va_format_arg macro, described above.
+ * Sample implementation of common helper:
+ * void dev_err(struct device *dev, const char* fmt, ...)
+ * {
+ *    va_format_call(fmt, pr_err, "%s %s: %pV", dev_driver_string(dev),
+ *                   dev_name(dev), va_format_arg);
+ * }
+ */
+#define va_format_call(_fmt, _func, _args...)			\
+({								\
+	va_list ap;						\
+	struct va_format vaf = { .fmt = _fmt, .va = &ap };	\
+								\
+	va_start(ap, _fmt);					\
+	_func(_args);						\
+	va_end(ap);						\
+})
+
 /*
  * FW_BUG
  * Add this to a message where you are sure the firmware is buggy or behaves

-- 
2.43.0

[PATCH 2/3] drivers/core: use va_format_call helper

[Andrzej Hajda]

It simplifies the code and makes it more clear.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
 drivers/base/core.c | 32 ++++++--------------------------
 1 file changed, 6 insertions(+), 26 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index f69dc9c8595455d85bf7eda5d4abce1ed7cb5166..513e5ef8a6dabaec0aee0778c1338a9d72e66892 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -4943,35 +4943,15 @@ static void __dev_printk(const char *level, const struct device *dev,
 void _dev_printk(const char *level, const struct device *dev,
 		 const char *fmt, ...)
 {
-	struct va_format vaf;
-	va_list args;
-
-	va_start(args, fmt);
-
-	vaf.fmt = fmt;
-	vaf.va = &args;
-
-	__dev_printk(level, dev, &vaf);
-
-	va_end(args);
+	va_format_call(fmt, __dev_printk, level, dev, va_format_arg);
 }
 EXPORT_SYMBOL(_dev_printk);
 
-#define define_dev_printk_level(func, kern_level)		\
-void func(const struct device *dev, const char *fmt, ...)	\
-{								\
-	struct va_format vaf;					\
-	va_list args;						\
-								\
-	va_start(args, fmt);					\
-								\
-	vaf.fmt = fmt;						\
-	vaf.va = &args;						\
-								\
-	__dev_printk(kern_level, dev, &vaf);			\
-								\
-	va_end(args);						\
-}								\
+#define define_dev_printk_level(func, kern_level)				\
+void func(const struct device *dev, const char *fmt, ...)			\
+{										\
+	va_format_call(fmt, __dev_printk, kern_level, dev, va_format_arg);	\
+}										\
 EXPORT_SYMBOL(func);
 
 define_dev_printk_level(_dev_emerg, KERN_EMERG);

-- 
2.43.0

[PATCH 3/3] mm: use va_format_call helper

[Andrzej Hajda]

It simplifies the code and makes it more clear.

Signed-off-by: Andrzej Hajda <andrzej.hajda@intel.com>
---
 mm/page_alloc.c | 14 ++++----------
 mm/slub.c       | 10 +---------
 2 files changed, 5 insertions(+), 19 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ed82ee55e66afffafcf6360b13da410119f2898d..cd0b17ea4de0a3262fae117fac7f427a7396978f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3940,22 +3940,16 @@ static void warn_alloc_show_mem(gfp_t gfp_mask, nodemask_t *nodemask)
 
 void warn_alloc(gfp_t gfp_mask, nodemask_t *nodemask, const char *fmt, ...)
 {
-	struct va_format vaf;
-	va_list args;
 	static DEFINE_RATELIMIT_STATE(nopage_rs, 10*HZ, 1);
 
 	if ((gfp_mask & __GFP_NOWARN) ||
 	     !__ratelimit(&nopage_rs) ||
 	     ((gfp_mask & __GFP_DMA) && !has_managed_dma()))
 		return;
-
-	va_start(args, fmt);
-	vaf.fmt = fmt;
-	vaf.va = &args;
-	pr_warn("%s: %pV, mode:%#x(%pGg), nodemask=%*pbl",
-			current->comm, &vaf, gfp_mask, &gfp_mask,
-			nodemask_pr_args(nodemask));
-	va_end(args);
+	va_format_call(fmt, pr_warn,
+		       "%s: %pV, mode:%#x(%pGg), nodemask=%*pbl",
+		       current->comm, va_format_arg, gfp_mask, &gfp_mask,
+		       nodemask_pr_args(nodemask));
 
 	cpuset_print_current_mems_allowed();
 	pr_cont("\n");
diff --git a/mm/slub.c b/mm/slub.c
index 1a5fc34290421ea32e6f5bba8acc87b53a9774b5..786c5a4195d44d5c40b3c9009ff52a3b836bfe23 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1161,17 +1161,9 @@ static void slab_bug(struct kmem_cache *s, const char *fmt, ...)
 __printf(2, 3)
 static void slab_fix(struct kmem_cache *s, const char *fmt, ...)
 {
-	struct va_format vaf;
-	va_list args;
-
 	if (slab_add_kunit_errors())
 		return;
-
-	va_start(args, fmt);
-	vaf.fmt = fmt;
-	vaf.va = &args;
-	pr_err("FIX %s: %pV\n", s->name, &vaf);
-	va_end(args);
+	va_format_call(fmt, pr_err, "FIX %s: %pV\n", s->name, va_format_arg);
 }
 
 static void print_trailer(struct kmem_cache *s, struct slab *slab, u8 *p)

-- 
2.43.0