[2725] | 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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[3232] | 48 | ssize_t FAST_FUNC nonblock_immune_read(int fd, void *buf, size_t count, int loop_on_EINTR)
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[2725] | 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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[3232] | 54 | n = loop_on_EINTR ? safe_read(fd, buf, count) : read(fd, buf, count);
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[2725] | 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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[3232] | 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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[2725] | 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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[3232] | 68 | char* FAST_FUNC xmalloc_reads(int fd, size_t *maxsz_p)
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[2725] | 69 | {
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| 70 | char *p;
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[3232] | 71 | char *buf = NULL;
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| 72 | size_t sz = 0;
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[2725] | 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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[3232] | 76 |
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[2725] | 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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[3232] | 84 | if (nonblock_immune_read(fd, p, 1, /*loop_on_EINTR:*/ 1) != 1) {
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| 85 | /* EOF/error */
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[2725] | 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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