1 | /* vi: set sw=4 ts=4: */
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2 | /*
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3 | * Utility routines.
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4 | *
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5 | * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
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6 | *
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7 | * Licensed under GPLv2 or later, see file LICENSE in this source tree.
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8 | */
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9 | #include "libbb.h"
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10 |
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11 |
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12 | /* Suppose that you are a shell. You start child processes.
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13 | * They work and eventually exit. You want to get user input.
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14 | * You read stdin. But what happens if last child switched
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15 | * its stdin into O_NONBLOCK mode?
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16 | *
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17 | * *** SURPRISE! It will affect the parent too! ***
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18 | * *** BIG SURPRISE! It stays even after child exits! ***
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19 | *
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20 | * This is a design bug in UNIX API.
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21 | * fcntl(0, F_SETFL, fcntl(0, F_GETFL) | O_NONBLOCK);
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22 | * will set nonblocking mode not only on _your_ stdin, but
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23 | * also on stdin of your parent, etc.
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24 | *
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25 | * In general,
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26 | * fd2 = dup(fd1);
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27 | * fcntl(fd2, F_SETFL, fcntl(fd2, F_GETFL) | O_NONBLOCK);
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28 | * sets both fd1 and fd2 to O_NONBLOCK. This includes cases
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29 | * where duping is done implicitly by fork() etc.
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30 | *
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31 | * We need
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32 | * fcntl(fd2, F_SETFD, fcntl(fd2, F_GETFD) | O_NONBLOCK);
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33 | * (note SETFD, not SETFL!) but such thing doesn't exist.
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34 | *
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35 | * Alternatively, we need nonblocking_read(fd, ...) which doesn't
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36 | * require O_NONBLOCK dance at all. Actually, it exists:
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37 | * n = recv(fd, buf, len, MSG_DONTWAIT);
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38 | * "MSG_DONTWAIT:
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39 | * Enables non-blocking operation; if the operation
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40 | * would block, EAGAIN is returned."
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41 | * but recv() works only for sockets!
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42 | *
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43 | * So far I don't see any good solution, I can only propose
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44 | * that affected readers should be careful and use this routine,
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45 | * which detects EAGAIN and uses poll() to wait on the fd.
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46 | * Thankfully, poll() doesn't care about O_NONBLOCK flag.
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47 | */
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48 | ssize_t FAST_FUNC nonblock_immune_read(int fd, void *buf, size_t count, int loop_on_EINTR)
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49 | {
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50 | struct pollfd pfd[1];
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51 | ssize_t n;
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52 |
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53 | while (1) {
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54 | n = loop_on_EINTR ? safe_read(fd, buf, count) : read(fd, buf, count);
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55 | if (n >= 0 || errno != EAGAIN)
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56 | return n;
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57 | /* fd is in O_NONBLOCK mode. Wait using poll and repeat */
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58 | pfd[0].fd = fd;
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59 | pfd[0].events = POLLIN;
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60 | /* note: safe_poll pulls in printf */
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61 | loop_on_EINTR ? safe_poll(pfd, 1, -1) : poll(pfd, 1, -1);
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62 | }
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63 | }
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64 |
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65 | // Reads one line a-la fgets (but doesn't save terminating '\n').
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66 | // Reads byte-by-byte. Useful when it is important to not read ahead.
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67 | // Bytes are appended to pfx (which must be malloced, or NULL).
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68 | char* FAST_FUNC xmalloc_reads(int fd, size_t *maxsz_p)
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69 | {
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70 | char *p;
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71 | char *buf = NULL;
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72 | size_t sz = 0;
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73 | size_t maxsz = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
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74 |
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75 | goto jump_in;
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76 |
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77 | while (sz < maxsz) {
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78 | if ((size_t)(p - buf) == sz) {
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79 | jump_in:
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80 | buf = xrealloc(buf, sz + 128);
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81 | p = buf + sz;
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82 | sz += 128;
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83 | }
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84 | if (nonblock_immune_read(fd, p, 1, /*loop_on_EINTR:*/ 1) != 1) {
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85 | /* EOF/error */
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86 | if (p == buf) { /* we read nothing */
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87 | free(buf);
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88 | return NULL;
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89 | }
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90 | break;
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91 | }
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92 | if (*p == '\n')
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93 | break;
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94 | p++;
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95 | }
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96 | *p = '\0';
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97 | if (maxsz_p)
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98 | *maxsz_p = p - buf;
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99 | p++;
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100 | return xrealloc(buf, p - buf);
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101 | }
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102 |
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103 | // Read (potentially big) files in one go. File size is estimated
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104 | // by stat. Extra '\0' byte is appended.
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105 | void* FAST_FUNC xmalloc_read(int fd, size_t *maxsz_p)
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106 | {
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107 | char *buf;
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108 | size_t size, rd_size, total;
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109 | size_t to_read;
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110 | struct stat st;
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111 |
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112 | to_read = maxsz_p ? *maxsz_p : (INT_MAX - 4095); /* max to read */
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113 |
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114 | /* Estimate file size */
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115 | st.st_size = 0; /* in case fstat fails, assume 0 */
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116 | fstat(fd, &st);
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117 | /* /proc/N/stat files report st_size 0 */
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118 | /* In order to make such files readable, we add small const */
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119 | size = (st.st_size | 0x3ff) + 1;
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120 |
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121 | total = 0;
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122 | buf = NULL;
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123 | while (1) {
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124 | if (to_read < size)
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125 | size = to_read;
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126 | buf = xrealloc(buf, total + size + 1);
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127 | rd_size = full_read(fd, buf + total, size);
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128 | if ((ssize_t)rd_size == (ssize_t)(-1)) { /* error */
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129 | free(buf);
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130 | return NULL;
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131 | }
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132 | total += rd_size;
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133 | if (rd_size < size) /* EOF */
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134 | break;
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135 | if (to_read <= rd_size)
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136 | break;
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137 | to_read -= rd_size;
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138 | /* grow by 1/8, but in [1k..64k] bounds */
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139 | size = ((total / 8) | 0x3ff) + 1;
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140 | if (size > 64*1024)
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141 | size = 64*1024;
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142 | }
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143 | buf = xrealloc(buf, total + 1);
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144 | buf[total] = '\0';
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145 |
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146 | if (maxsz_p)
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147 | *maxsz_p = total;
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148 | return buf;
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149 | }
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150 |
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151 | #ifdef USING_LSEEK_TO_GET_SIZE
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152 | /* Alternatively, file size can be obtained by lseek to the end.
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153 | * The code is slightly bigger. Retained in case fstat approach
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154 | * will not work for some weird cases (/proc, block devices, etc).
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155 | * (NB: lseek also can fail to work for some weird files) */
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156 |
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157 | // Read (potentially big) files in one go. File size is estimated by
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158 | // lseek to end.
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159 | void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
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160 | {
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161 | char *buf;
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162 | size_t size;
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163 | int fd;
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164 | off_t len;
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165 |
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166 | fd = open(filename, O_RDONLY);
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167 | if (fd < 0)
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168 | return NULL;
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169 |
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170 | /* /proc/N/stat files report len 0 here */
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171 | /* In order to make such files readable, we add small const */
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172 | size = 0x3ff; /* read only 1k on unseekable files */
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173 | len = lseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
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174 | if (len != (off_t)-1) {
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175 | xlseek(fd, 0, SEEK_SET);
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176 | size = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
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177 | if (len < size)
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178 | size = len;
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179 | }
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180 |
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181 | buf = xmalloc(size + 1);
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182 | size = read_close(fd, buf, size);
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183 | if ((ssize_t)size < 0) {
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184 | free(buf);
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185 | return NULL;
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186 | }
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187 | buf = xrealloc(buf, size + 1);
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188 | buf[size] = '\0';
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189 |
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190 | if (maxsz_p)
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191 | *maxsz_p = size;
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192 | return buf;
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193 | }
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194 | #endif
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195 |
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196 | // Read (potentially big) files in one go. File size is estimated
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197 | // by stat.
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198 | void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
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199 | {
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200 | char *buf;
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201 | int fd;
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202 |
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203 | fd = open(filename, O_RDONLY);
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204 | if (fd < 0)
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205 | return NULL;
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206 |
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207 | buf = xmalloc_read(fd, maxsz_p);
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208 | close(fd);
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209 | return buf;
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210 | }
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211 |
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212 | /* Die with an error message if we can't read the entire buffer. */
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213 | void FAST_FUNC xread(int fd, void *buf, size_t count)
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214 | {
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215 | if (count) {
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216 | ssize_t size = full_read(fd, buf, count);
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217 | if ((size_t)size != count)
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218 | bb_error_msg_and_die("short read");
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219 | }
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220 | }
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221 |
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222 | /* Die with an error message if we can't read one character. */
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223 | unsigned char FAST_FUNC xread_char(int fd)
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224 | {
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225 | char tmp;
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226 | xread(fd, &tmp, 1);
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227 | return tmp;
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228 | }
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229 |
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230 | void* FAST_FUNC xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p)
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231 | {
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232 | void *buf = xmalloc_open_read_close(filename, maxsz_p);
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233 | if (!buf)
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234 | bb_perror_msg_and_die("can't read '%s'", filename);
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235 | return buf;
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236 | }
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