kfifo: add kfifo_out_linear{,_ptr}()

These are helpers which are going to be used in the serial layer. We
need a wrapper around kfifo which provides us with a tail (sometimes
"tail" offset, sometimes a pointer) to the kfifo data. And which returns
count of available data -- but not larger than to the end of the buffer
(hence _linear in the names). I.e. something like CIRC_CNT_TO_END() in
the legacy circ_buf.

This patch adds such two helpers.

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: Stefani Seibold <stefani@seibold.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://lore.kernel.org/r/20240405060826.2521-4-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 26 insertions, 0 deletions

diff --git a/lib/kfifo.c b/lib/kfifo.c
index 958099cc4914..a36bfdbdb17d 100644
--- a/lib/kfifo.c
+++ b/lib/kfifo.c
@@ -163,6 +163,19 @@ unsigned int __kfifo_out_peek(struct __kfifo *fifo,
 }
 EXPORT_SYMBOL(__kfifo_out_peek);
 
+unsigned int __kfifo_out_linear(struct __kfifo *fifo,
+		unsigned int *tail, unsigned int n)
+{
+	unsigned int size = fifo->mask + 1;
+	unsigned int off = fifo->out & fifo->mask;
+
+	if (tail)
+		*tail = off;
+
+	return min3(n, fifo->in - fifo->out, size - off);
+}
+EXPORT_SYMBOL(__kfifo_out_linear);
+
 unsigned int __kfifo_out(struct __kfifo *fifo,
 		void *buf, unsigned int len)
 {
@@ -473,6 +486,19 @@ unsigned int __kfifo_out_peek_r(struct __kfifo *fifo, void *buf,
 }
 EXPORT_SYMBOL(__kfifo_out_peek_r);
 
+unsigned int __kfifo_out_linear_r(struct __kfifo *fifo,
+		unsigned int *tail, unsigned int n, size_t recsize)
+{
+	if (fifo->in == fifo->out)
+		return 0;
+
+	if (tail)
+		*tail = fifo->out + recsize;
+
+	return min(n, __kfifo_peek_n(fifo, recsize));
+}
+EXPORT_SYMBOL(__kfifo_out_linear_r);
+
 unsigned int __kfifo_out_r(struct __kfifo *fifo, void *buf,
 		unsigned int len, size_t recsize)
 {