[PATCH] [4/6] kfifo: add kfifo_out_peek

[Andi Kleen]

In some upcoming code it's useful to peek into a FIFO without
permanentely removing data. This patch implements a new 
kfifo_out_peek() to do this. 

Signed-off-by: Andi Kleen <ak@xxxxxxxxxxxxxxx>

---
 include/linux/kfifo.h |    3 +++
 kernel/kfifo.c        |   21 +++++++++++++++++++++
 2 files changed, 24 insertions(+)

Index: linux/include/linux/kfifo.h
===================================================================
--- linux.orig/include/linux/kfifo.h
+++ linux/include/linux/kfifo.h
@@ -114,6 +114,9 @@ extern unsigned int kfifo_in(struct kfif
 				const void *from, unsigned int len);
 extern __must_check unsigned int kfifo_out(struct kfifo *fifo,
 				void *to, unsigned int len);
+extern __must_check unsigned int kfifo_out_peek(struct kfifo *fifo,
+				void *to, unsigned int len, unsigned offset);
+
 
 /**
  * kfifo_reset - removes the entire FIFO contents
Index: linux/kernel/kfifo.c
===================================================================
--- linux.orig/kernel/kfifo.c
+++ linux/kernel/kfifo.c
@@ -301,6 +301,27 @@ unsigned int kfifo_out(struct kfifo *fif
 }
 EXPORT_SYMBOL(kfifo_out);
 
+/**
+ * kfifo_out_peek - copy some data from the FIFO, but do not remove it
+ * @fifo: the fifo to be used.
+ * @to: where the data must be copied.
+ * @len: the size of the destination buffer.
+ * @offset: offset into the fifo
+ *
+ * This function copies at most @len bytes at @offset from the FIFO
+ * into the @to buffer and returns the number of copied bytes.
+ * The data is not removed from the FIFO.
+ */
+unsigned int kfifo_out_peek(struct kfifo *fifo, void *to, unsigned int len,
+			    unsigned offset)
+{
+	len = min(kfifo_len(fifo), len + offset);
+
+	__kfifo_out_data(fifo, to, len, offset);
+	return len;
+}
+EXPORT_SYMBOL(kfifo_out_peek);
+
 unsigned int __kfifo_out_generic(struct kfifo *fifo,
 	void *to, unsigned int len, unsigned int recsize,
 	unsigned int *total)
--
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