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annotate buffer_static.c @ 712:8295148e8f44

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buffer: rename internal 'used' member to a more obvious name It really keeps track of the number of readable bytes in the buffer. In other words, it keeps track of the size - hence the new name. Signed-off-by: Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
author Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
date Tue, 19 Mar 2019 14:43:26 -0400
parents 0fa2f6606c5e
children 1c4d7ff0a682
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1 /*
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2 * Copyright (c) 2017-2019 Josef 'Jeff' Sipek <jeffpc@josefsipek.net>
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3 *
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4 * Permission is hereby granted, free of charge, to any person obtaining a copy
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5 * of this software and associated documentation files (the "Software"), to deal
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6 * in the Software without restriction, including without limitation the rights
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7 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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8 * copies of the Software, and to permit persons to whom the Software is
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9 * furnished to do so, subject to the following conditions:
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10 *
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11 * The above copyright notice and this permission notice shall be included in
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12 * all copies or substantial portions of the Software.
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13 *
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14 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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15 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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16 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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17 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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18 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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19 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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20 * SOFTWARE.
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21 */
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22
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23 #include "buffer_impl.h"
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24
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25 /*
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26 * Static buffers
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27 *
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28 * Since we have a borrowed buffer we must never allow:
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29 *
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30 * - resizing of the buffer
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31 * - freeing of the buffer
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32 *
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33 * Conveniently, if we leave the realloc op NULL, the generic code returns
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34 * -ENOTSUP for us. Leaving the free op NULL turns it into a no-op.
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35 *
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36 * There is a slight difference between the read-only and read-write
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37 * variants. Namely, the read-only variant does not support *any* writes or
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38 * changes to the (apparent) buffer size. In both cases, -EROFS is
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39 * returned. The read-write variant allows changes to the amount of used
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40 * space, truncation, etc. as long as the result fits within the borrowed
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41 * buffer.
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42 */
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43
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44 static int static_buffer_check_append_ro(struct buffer *buffer, const void *data,
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45 size_t size)
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46 {
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47 return -EROFS;
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48 }
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49
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50 static int static_buffer_check_append_rw(struct buffer *buffer, const void *data,
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51 size_t size)
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52 {
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53 if ((buffer->size + size) <= buffer->allocsize)
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54 return 0;
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55
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56 return -ENOSPC;
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57 }
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58
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59 static int static_buffer_check_truncate_ro(struct buffer *buffer, size_t size)
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60 {
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61 return -EROFS;
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62 }
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63
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64 static int static_buffer_check_truncate_rw(struct buffer *buffer, size_t size)
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65 {
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66 if (size <= buffer->allocsize)
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67 return 0;
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68
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69 return -ENOSPC;
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70 }
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71
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72 static int static_buffer_check_write_ro(struct buffer *buffer, const void *buf,
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73 size_t len, size_t off)
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74 {
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75 return -EROFS;
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76 }
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77
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78 static int static_buffer_check_write_rw(struct buffer *buffer, const void *buf,
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79 size_t len, size_t off)
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80 {
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81 if ((off + len) <= buffer->allocsize)
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82 return 0;
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83
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84 return -ENOSPC;
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85 }
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86
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87 /* a read-only static buffer */
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88 const struct buffer_ops static_buffer_ro = {
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89 .check_append = static_buffer_check_append_ro,
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90 .check_truncate = static_buffer_check_truncate_ro,
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91 .check_write = static_buffer_check_write_ro,
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92
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93 .clear = generic_buffer_clear_panic,
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94 .copyin = generic_buffer_copyin_panic,
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95 .copyout = generic_buffer_copyout_memcpy,
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96 };
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97
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98 /* a read-write static buffer */
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99 const struct buffer_ops static_buffer_rw = {
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100 .check_append = static_buffer_check_append_rw,
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101 .check_truncate = static_buffer_check_truncate_rw,
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102 .check_write = static_buffer_check_write_rw,
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103
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104 .clear = generic_buffer_clear_memset,
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105 .copyin = generic_buffer_copyin_memcpy,
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106 .copyout = generic_buffer_copyout_memcpy,
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107 };