src/lxc/ringbuf.h

   1 /* liblxcapi
   2  *
   3  * Copyright © 2017 Christian Brauner <christian.brauner@ubuntu.com>.
   4  * Copyright © 2017 Canonical Ltd.
   5  *
   6  * This program is free software; you can redistribute it and/or modify
   7  * it under the terms of the GNU General Public License version 2, as
   8  * published by the Free Software Foundation.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License along
  16  * with this program; if not, write to the Free Software Foundation, Inc.,
  17  * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
  18  */
  19
  20 #ifndef __LXC_RINGBUF_H
  21 #define __LXC_RINGBUF_H
  22
  23 #include <inttypes.h>
  24 #include <stdbool.h>
  25 #include <stdio.h>
  26 #include <sys/mman.h>
  27
  28 /**
  29  * lxc_ringbuf - Implements a simple and efficient memory mapped ringbuffer.
  30  * - The "addr" field of struct lxc_ringbuf is considered immutable. Instead the
  31  *   read and write offsets r_off and w_off are used to calculate the current
  32  *   read and write addresses. There should never be a need to use any of those
  33  *   fields directly. Instead use the appropriate helpers below.
  34  * - Callers are expected to synchronize read and write accesses to the
  35  *   ringbuffer.
  36  */
  37 struct lxc_ringbuf {
  38         char *addr; /* start address of the ringbuffer */
  39         uint64_t size; /* total size of the ringbuffer in bytes */
  40         uint64_t r_off; /* read offset */
  41         uint64_t w_off; /* write offset */
  42 };
  43
  44 /**
  45  * lxc_ringbuf_create - Initialize a new ringbuffer.
  46  *
  47  * @param[in] size      Size of the new ringbuffer as a power of 2.
  48  */
  49 extern int lxc_ringbuf_create(struct lxc_ringbuf *buf, size_t size);
  50 extern void lxc_ringbuf_move_read_addr(struct lxc_ringbuf *buf, size_t len);
  51 extern int lxc_ringbuf_write(struct lxc_ringbuf *buf, const char *msg, size_t len);
  52 extern int lxc_ringbuf_read(struct lxc_ringbuf *buf, char *out, size_t *len);
  53
  54 static inline void lxc_ringbuf_release(struct lxc_ringbuf *buf)
  55 {
  56         munmap(buf->addr, buf->size * 2);
  57 }
  58
  59 static inline void lxc_ringbuf_clear(struct lxc_ringbuf *buf)
  60 {
  61         buf->r_off = 0;
  62         buf->w_off = 0;
  63 }
  64
  65 static inline uint64_t lxc_ringbuf_used(struct lxc_ringbuf *buf)
  66 {
  67         return buf->w_off - buf->r_off;
  68 }
  69
  70 static inline uint64_t lxc_ringbuf_free(struct lxc_ringbuf *buf)
  71 {
  72         return buf->size - lxc_ringbuf_used(buf);
  73 }
  74
  75 static inline char *lxc_ringbuf_get_read_addr(struct lxc_ringbuf *buf)
  76 {
  77         return buf->addr + buf->r_off;
  78 }
  79
  80 static inline char *lxc_ringbuf_get_write_addr(struct lxc_ringbuf *buf)
  81 {
  82         return buf->addr + buf->w_off;
  83 }
  84
  85 static inline void lxc_ringbuf_move_write_addr(struct lxc_ringbuf *buf, size_t len)
  86 {
  87         buf->w_off += len;
  88 }
  89
  90 #endif /* __LXC_RINGBUF_H */