linux-kernel - [PATCH printk v4 03/14] printk: Use prb_first

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Date: Wed,  7 Feb 2024 14:46:52 +0106
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org
Subject: [PATCH printk v4 03/14] printk: Use prb_first_seq() as base for 32bit seq macros

Note: This change only applies to 32bit architectures. On 64bit
      architectures the macros are NOPs.

Currently prb_next_seq() is used as the base for the 32bit seq
macros __u64seq_to_ulseq() and __ulseq_to_u64seq(). However, in
a follow-up commit, prb_next_seq() will need to make use of the
32bit seq macros.

Use prb_first_seq() as the base for the 32bit seq macros instead
because it is guaranteed to return 64bit sequence numbers without
relying on any 32bit seq macros.

Signed-off-by: John Ogness <john.ogness@...utronix.de>
Reviewed-by: Petr Mladek <pmladek@...e.com>
---
 kernel/printk/printk_ringbuffer.c | 2 +-
 kernel/printk/printk_ringbuffer.h | 8 ++++----
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/printk/printk_ringbuffer.c b/kernel/printk/printk_ringbuffer.c
index fde338606ce8..49a82ccce8e9 100644
--- a/kernel/printk/printk_ringbuffer.c
+++ b/kernel/printk/printk_ringbuffer.c
@@ -1832,7 +1832,7 @@ static int prb_read(struct printk_ringbuffer *rb, u64 seq,
 }
 
 /* Get the sequence number of the tail descriptor. */
-static u64 prb_first_seq(struct printk_ringbuffer *rb)
+u64 prb_first_seq(struct printk_ringbuffer *rb)
 {
 	struct prb_desc_ring *desc_ring = &rb->desc_ring;
 	enum desc_state d_state;
diff --git a/kernel/printk/printk_ringbuffer.h b/kernel/printk/printk_ringbuffer.h
index 12f60c782e46..ee294aaf4aeb 100644
--- a/kernel/printk/printk_ringbuffer.h
+++ b/kernel/printk/printk_ringbuffer.h
@@ -378,6 +378,7 @@ bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq,
 bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq,
 			 struct printk_info *info, unsigned int *line_count);
 
+u64 prb_first_seq(struct printk_ringbuffer *rb);
 u64 prb_first_valid_seq(struct printk_ringbuffer *rb);
 u64 prb_next_seq(struct printk_ringbuffer *rb);
 
@@ -392,12 +393,12 @@ u64 prb_next_seq(struct printk_ringbuffer *rb);
 
 static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq)
 {
+	u64 rb_first_seq = prb_first_seq(rb);
 	u64 seq;
-	u64 rb_next_seq;
 
 	/*
 	 * The provided sequence is only the lower 32 bits of the ringbuffer
-	 * sequence. It needs to be expanded to 64bit. Get the next sequence
+	 * sequence. It needs to be expanded to 64bit. Get the first sequence
 	 * number from the ringbuffer and fold it.
 	 *
 	 * Having a 32bit representation in the console is sufficient.
@@ -406,8 +407,7 @@ static inline u64 __ulseq_to_u64seq(struct printk_ringbuffer *rb, u32 ulseq)
 	 *
 	 * Also the access to the ring buffer is always safe.
 	 */
-	rb_next_seq = prb_next_seq(rb);
-	seq = rb_next_seq - (s32)((u32)rb_next_seq - ulseq);
+	seq = rb_first_seq - (s32)((u32)rb_first_seq - ulseq);
 
 	return seq;
 }
-- 
2.39.2