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 "config.h"
   7
   8 #include <inttypes.h>
   9 #include <stdbool.h>
  10 #include <stdio.h>
  11 #include <sys/mman.h>
  12
  13 #include "compiler.h"
  14
  15 /**
  16  * lxc_ringbuf - Implements a simple and efficient memory mapped ringbuffer.
  17  * - The "addr" field of struct lxc_ringbuf is considered immutable. Instead the
  18  *   read and write offsets r_off and w_off are used to calculate the current
  19  *   read and write addresses. There should never be a need to use any of those
  20  *   fields directly. Instead use the appropriate helpers below.
  21  * - Callers are expected to synchronize read and write accesses to the
  22  *   ringbuffer.
  23  */
  24 struct lxc_ringbuf {
  25         char *addr; /* start address of the ringbuffer */
  26         uint64_t size; /* total size of the ringbuffer in bytes */
  27         uint64_t r_off; /* read offset */
  28         uint64_t w_off; /* write offset */
  29 };
  30
  31 /**
  32  * lxc_ringbuf_create - Initialize a new ringbuffer.
  33  *
  34  * @param[in] size      Size of the new ringbuffer as a power of 2.
  35  */
  36 __hidden extern int lxc_ringbuf_create(struct lxc_ringbuf *buf, size_t size);
  37 __hidden extern void lxc_ringbuf_move_read_addr(struct lxc_ringbuf *buf, size_t len);
  38 __hidden extern int lxc_ringbuf_write(struct lxc_ringbuf *buf, const char *msg, size_t len);
  39 __hidden extern int lxc_ringbuf_read(struct lxc_ringbuf *buf, char *out, size_t *len);
  40
  41 static inline void lxc_ringbuf_release(struct lxc_ringbuf *buf)
  42 {
  43         if (buf->addr)
  44                 munmap(buf->addr, buf->size * 2);
  45 }
  46
  47 static inline void lxc_ringbuf_clear(struct lxc_ringbuf *buf)
  48 {
  49         buf->r_off = 0;
  50         buf->w_off = 0;
  51 }
  52
  53 static inline uint64_t lxc_ringbuf_used(struct lxc_ringbuf *buf)
  54 {
  55         return buf->w_off - buf->r_off;
  56 }
  57
  58 static inline uint64_t lxc_ringbuf_free(struct lxc_ringbuf *buf)
  59 {
  60         return buf->size - lxc_ringbuf_used(buf);
  61 }
  62
  63 static inline char *lxc_ringbuf_get_read_addr(struct lxc_ringbuf *buf)
  64 {
  65         return buf->addr + buf->r_off;
  66 }
  67
  68 static inline char *lxc_ringbuf_get_write_addr(struct lxc_ringbuf *buf)
  69 {
  70         return buf->addr + buf->w_off;
  71 }
  72
  73 static inline void lxc_ringbuf_move_write_addr(struct lxc_ringbuf *buf, size_t len)
  74 {
  75         buf->w_off += len;
  76 }
  77
  78 #endif /* __LXC_RINGBUF_H */