src/lxc/ringbuf.h

   1 /* SPDX-License-Identifier: LGPL-2.1+ */
   2
   3 #ifndef __LXC_RINGBUF_H
   4 #define __LXC_RINGBUF_H
   5
   6 #include <inttypes.h>
   7 #include <stdbool.h>
   8 #include <stdio.h>
   9 #include <sys/mman.h>
  10
  11 #include "compiler.h"
  12
  13 /**
  14  * lxc_ringbuf - Implements a simple and efficient memory mapped ringbuffer.
  15  * - The "addr" field of struct lxc_ringbuf is considered immutable. Instead the
  16  *   read and write offsets r_off and w_off are used to calculate the current
  17  *   read and write addresses. There should never be a need to use any of those
  18  *   fields directly. Instead use the appropriate helpers below.
  19  * - Callers are expected to synchronize read and write accesses to the
  20  *   ringbuffer.
  21  */
  22 struct lxc_ringbuf {
  23         char *addr; /* start address of the ringbuffer */
  24         uint64_t size; /* total size of the ringbuffer in bytes */
  25         uint64_t r_off; /* read offset */
  26         uint64_t w_off; /* write offset */
  27 };
  28
  29 /**
  30  * lxc_ringbuf_create - Initialize a new ringbuffer.
  31  *
  32  * @param[in] size      Size of the new ringbuffer as a power of 2.
  33  */
  34 __hidden extern int lxc_ringbuf_create(struct lxc_ringbuf *buf, size_t size);
  35 __hidden extern void lxc_ringbuf_move_read_addr(struct lxc_ringbuf *buf, size_t len);
  36 __hidden extern int lxc_ringbuf_write(struct lxc_ringbuf *buf, const char *msg, size_t len);
  37 __hidden extern int lxc_ringbuf_read(struct lxc_ringbuf *buf, char *out, size_t *len);
  38
  39 static inline void lxc_ringbuf_release(struct lxc_ringbuf *buf)
  40 {
  41         if (buf->addr)
  42                 munmap(buf->addr, buf->size * 2);
  43 }
  44
  45 static inline void lxc_ringbuf_clear(struct lxc_ringbuf *buf)
  46 {
  47         buf->r_off = 0;
  48         buf->w_off = 0;
  49 }
  50
  51 static inline uint64_t lxc_ringbuf_used(struct lxc_ringbuf *buf)
  52 {
  53         return buf->w_off - buf->r_off;
  54 }
  55
  56 static inline uint64_t lxc_ringbuf_free(struct lxc_ringbuf *buf)
  57 {
  58         return buf->size - lxc_ringbuf_used(buf);
  59 }
  60
  61 static inline char *lxc_ringbuf_get_read_addr(struct lxc_ringbuf *buf)
  62 {
  63         return buf->addr + buf->r_off;
  64 }
  65
  66 static inline char *lxc_ringbuf_get_write_addr(struct lxc_ringbuf *buf)
  67 {
  68         return buf->addr + buf->w_off;
  69 }
  70
  71 static inline void lxc_ringbuf_move_write_addr(struct lxc_ringbuf *buf, size_t len)
  72 {
  73         buf->w_off += len;
  74 }
  75
  76 #endif /* __LXC_RINGBUF_H */