lib/byteq.c

   1 /* Copyright (c) 2008, 2009, 2012 Nicira, Inc.
   2  *
   3  * Licensed under the Apache License, Version 2.0 (the "License");
   4  * you may not use this file except in compliance with the License.
   5  * You may obtain a copy of the License at:
   6  *
   7  *     http://www.apache.org/licenses/LICENSE-2.0
   8  *
   9  * Unless required by applicable law or agreed to in writing, software
  10  * distributed under the License is distributed on an "AS IS" BASIS,
  11  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12  * See the License for the specific language governing permissions and
  13  * limitations under the License.
  14  */
  15
  16 #include <config.h>
  17 #include "byteq.h"
  18 #include <errno.h>
  19 #include <string.h>
  20 #include <unistd.h>
  21 #include "util.h"
  22
  23 /* The queue size must be a power of 2. */
  24 BUILD_ASSERT_DECL(!(BYTEQ_SIZE & (BYTEQ_SIZE - 1)));
  25
  26 /* Initializes 'q' as empty. */
  27 void
  28 byteq_init(struct byteq *q)
  29 {
  30     q->head = q->tail = 0;
  31 }
  32
  33 /* Returns the number of bytes current queued in 'q'. */
  34 int
  35 byteq_used(const struct byteq *q)
  36 {
  37     return q->head - q->tail;
  38 }
  39
  40 /* Returns the number of bytes that can be added to 'q' without overflow. */
  41 int
  42 byteq_avail(const struct byteq *q)
  43 {
  44     return BYTEQ_SIZE - byteq_used(q);
  45 }
  46
  47 /* Returns true if no bytes are queued in 'q',
  48  * false if at least one byte is queued.  */
  49 bool
  50 byteq_is_empty(const struct byteq *q)
  51 {
  52     return !byteq_used(q);
  53 }
  54
  55 /* Returns true if 'q' has no room to queue additional bytes,
  56  * false if 'q' has room for at least one more byte.  */
  57 bool
  58 byteq_is_full(const struct byteq *q)
  59 {
  60     return !byteq_avail(q);
  61 }
  62
  63 /* Adds 'c' at the head of 'q', which must not be full. */
  64 void
  65 byteq_put(struct byteq *q, uint8_t c)
  66 {
  67     ovs_assert(!byteq_is_full(q));
  68     *byteq_head(q) = c;
  69     q->head++;
  70 }
  71
  72 /* Adds the 'n' bytes in 'p' at the head of 'q', which must have at least 'n'
  73  * bytes of free space. */
  74 void
  75 byteq_putn(struct byteq *q, const void *p_, size_t n)
  76 {
  77     const uint8_t *p = p_;
  78     ovs_assert(byteq_avail(q) >= n);
  79     while (n > 0) {
  80         size_t chunk = MIN(n, byteq_headroom(q));
  81         memcpy(byteq_head(q), p, chunk);
  82         byteq_advance_head(q, chunk);
  83         p += chunk;
  84         n -= chunk;
  85     }
  86 }
  87
  88 /* Appends null-terminated string 's' to the head of 'q', which must have
  89  * enough space.  The null terminator is not added to 'q'. */
  90 void
  91 byteq_put_string(struct byteq *q, const char *s)
  92 {
  93     byteq_putn(q, s, strlen(s));
  94 }
  95
  96 /* Removes a byte from the tail of 'q' and returns it.  'q' must not be
  97  * empty. */
  98 uint8_t
  99 byteq_get(struct byteq *q)
 100 {
 101     uint8_t c;
 102     ovs_assert(!byteq_is_empty(q));
 103     c = *byteq_tail(q);
 104     q->tail++;
 105     return c;
 106 }
 107
 108 /* Writes as much of 'q' as possible to 'fd'.  Returns 0 if 'q' is fully
 109  * drained by the write, otherwise a positive errno value (e.g. EAGAIN if a
 110  * socket or tty buffer filled up). */
 111 int
 112 byteq_write(struct byteq *q, int fd)
 113 {
 114     while (!byteq_is_empty(q)) {
 115         ssize_t n = write(fd, byteq_tail(q), byteq_tailroom(q));
 116         if (n > 0) {
 117             byteq_advance_tail(q, n);
 118         } else {
 119             ovs_assert(n < 0);
 120             return errno;
 121         }
 122     }
 123     return 0;
 124 }
 125
 126 /* Reads as much possible from 'fd' into 'q'.  Returns 0 if 'q' is completely
 127  * filled up by the read, EOF if end-of-file was reached before 'q' was filled,
 128  * and otherwise a positive errno value (e.g. EAGAIN if a socket or tty buffer
 129  * was drained). */
 130 int
 131 byteq_read(struct byteq *q, int fd)
 132 {
 133     while (!byteq_is_full(q)) {
 134         ssize_t n = read(fd, byteq_head(q), byteq_headroom(q));
 135         if (n > 0) {
 136             byteq_advance_head(q, n);
 137         } else {
 138             return !n ? EOF : errno;
 139         }
 140     }
 141     return 0;
 142 }
 143
 144 /* Returns the number of contiguous bytes of in-use space starting at the tail
 145  * of 'q'. */
 146 int
 147 byteq_tailroom(const struct byteq *q)
 148 {
 149     int used = byteq_used(q);
 150     int tail_to_end = BYTEQ_SIZE - (q->tail & (BYTEQ_SIZE - 1));
 151     return MIN(used, tail_to_end);
 152 }
 153
 154 /* Returns the first in-use byte of 'q', the point at which data is removed
 155  * from 'q'. */
 156 const uint8_t *
 157 byteq_tail(const struct byteq *q)
 158 {
 159     return &q->buffer[q->tail & (BYTEQ_SIZE - 1)];
 160 }
 161
 162 /* Removes 'n' bytes from the tail of 'q', which must have at least 'n' bytes
 163  * of tailroom. */
 164 void
 165 byteq_advance_tail(struct byteq *q, unsigned int n)
 166 {
 167     ovs_assert(byteq_tailroom(q) >= n);
 168     q->tail += n;
 169 }
 170
 171 /* Returns the byte after the last in-use byte of 'q', the point at which new
 172  * data will be added to 'q'. */
 173 uint8_t *
 174 byteq_head(struct byteq *q)
 175 {
 176     return &q->buffer[q->head & (BYTEQ_SIZE - 1)];
 177 }
 178
 179 /* Returns the number of contiguous bytes of free space starting at the head
 180  * of 'q'. */
 181 int
 182 byteq_headroom(const struct byteq *q)
 183 {
 184     int avail = byteq_avail(q);
 185     int head_to_end = BYTEQ_SIZE - (q->head & (BYTEQ_SIZE - 1));
 186     return MIN(avail, head_to_end);
 187 }
 188
 189 /* Adds to 'q' the 'n' bytes after the last currently in-use byte of 'q'.  'q'
 190  * must have at least 'n' bytes of headroom. */
 191 void
 192 byteq_advance_head(struct byteq *q, unsigned int n)
 193 {
 194     ovs_assert(byteq_headroom(q) >= n);
 195     q->head += n;
 196 }