utils: add helper functions useful for allocating a ring buffer

This creates a mapping with twice the size of the allocated memory. The
second half of that mapping points at the same memory as the first half.

This is useful for ring buffers, because any read starting in the first
half can overflow into the second half as long as the read size is
smaller than the size of the memory area.

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 20 insertions, 0 deletions

diff --git a/utils.h b/utils.h
index d00e76b..803150b 100644
--- a/utils.h
+++ b/utils.h
@@ -23,6 +23,7 @@
 #include <sys/time.h>
 #include <stdint.h>
 #include <stdbool.h>
+#include <unistd.h>
 #include <time.h>
 
 /*
@@ -192,4 +193,23 @@ int b64_decode(const void *src, void *dest, size_t dest_len);
 #define B64_ENCODE_LEN(_len)	((((_len) + 2) / 3) * 4 + 1)
 #define B64_DECODE_LEN(_len)	(((_len) / 4) * 3 + 1)
 
+static inline unsigned int cbuf_order(unsigned int x)
+{
+	return 32 - __builtin_clz(x - 1);
+}
+
+static inline unsigned long cbuf_size(int order)
+{
+	unsigned long page_size = sysconf(_SC_PAGESIZE);
+	unsigned long ret = 1ULL << order;
+
+	if (ret < page_size)
+		ret = page_size;
+
+	return ret;
+}
+
+void *cbuf_alloc(unsigned int order);
+void cbuf_free(void *ptr, unsigned int order);
+
 #endif