source: branches/3.2/mindi-busybox/libbb/read_printf.c

Last change on this file was 3232, checked in by bruno, 6 years ago
  • Update mindi-busybox to 1.21.1
  • Property svn:eol-style set to native
File size: 6.0 KB
Line 
1/* vi: set sw=4 ts=4: */
2/*
3 * Utility routines.
4 *
5 * Copyright (C) 1999-2004 by Erik Andersen <andersen@codepoet.org>
6 *
7 * Licensed under GPLv2 or later, see file LICENSE in this source tree.
8 */
9#include "libbb.h"
10
11
12/* Suppose that you are a shell. You start child processes.
13 * They work and eventually exit. You want to get user input.
14 * You read stdin. But what happens if last child switched
15 * its stdin into O_NONBLOCK mode?
16 *
17 * *** SURPRISE! It will affect the parent too! ***
18 * *** BIG SURPRISE! It stays even after child exits! ***
19 *
20 * This is a design bug in UNIX API.
21 *      fcntl(0, F_SETFL, fcntl(0, F_GETFL) | O_NONBLOCK);
22 * will set nonblocking mode not only on _your_ stdin, but
23 * also on stdin of your parent, etc.
24 *
25 * In general,
26 *      fd2 = dup(fd1);
27 *      fcntl(fd2, F_SETFL, fcntl(fd2, F_GETFL) | O_NONBLOCK);
28 * sets both fd1 and fd2 to O_NONBLOCK. This includes cases
29 * where duping is done implicitly by fork() etc.
30 *
31 * We need
32 *      fcntl(fd2, F_SETFD, fcntl(fd2, F_GETFD) | O_NONBLOCK);
33 * (note SETFD, not SETFL!) but such thing doesn't exist.
34 *
35 * Alternatively, we need nonblocking_read(fd, ...) which doesn't
36 * require O_NONBLOCK dance at all. Actually, it exists:
37 *      n = recv(fd, buf, len, MSG_DONTWAIT);
38 *      "MSG_DONTWAIT:
39 *      Enables non-blocking operation; if the operation
40 *      would block, EAGAIN is returned."
41 * but recv() works only for sockets!
42 *
43 * So far I don't see any good solution, I can only propose
44 * that affected readers should be careful and use this routine,
45 * which detects EAGAIN and uses poll() to wait on the fd.
46 * Thankfully, poll() doesn't care about O_NONBLOCK flag.
47 */
48ssize_t FAST_FUNC nonblock_immune_read(int fd, void *buf, size_t count, int loop_on_EINTR)
49{
50    struct pollfd pfd[1];
51    ssize_t n;
52
53    while (1) {
54        n = loop_on_EINTR ? safe_read(fd, buf, count) : read(fd, buf, count);
55        if (n >= 0 || errno != EAGAIN)
56            return n;
57        /* fd is in O_NONBLOCK mode. Wait using poll and repeat */
58        pfd[0].fd = fd;
59        pfd[0].events = POLLIN;
60        /* note: safe_poll pulls in printf */
61        loop_on_EINTR ? safe_poll(pfd, 1, -1) : poll(pfd, 1, -1);
62    }
63}
64
65// Reads one line a-la fgets (but doesn't save terminating '\n').
66// Reads byte-by-byte. Useful when it is important to not read ahead.
67// Bytes are appended to pfx (which must be malloced, or NULL).
68char* FAST_FUNC xmalloc_reads(int fd, size_t *maxsz_p)
69{
70    char *p;
71    char *buf = NULL;
72    size_t sz = 0;
73    size_t maxsz = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
74
75    goto jump_in;
76
77    while (sz < maxsz) {
78        if ((size_t)(p - buf) == sz) {
79 jump_in:
80            buf = xrealloc(buf, sz + 128);
81            p = buf + sz;
82            sz += 128;
83        }
84        if (nonblock_immune_read(fd, p, 1, /*loop_on_EINTR:*/ 1) != 1) {
85            /* EOF/error */
86            if (p == buf) { /* we read nothing */
87                free(buf);
88                return NULL;
89            }
90            break;
91        }
92        if (*p == '\n')
93            break;
94        p++;
95    }
96    *p = '\0';
97    if (maxsz_p)
98        *maxsz_p  = p - buf;
99    p++;
100    return xrealloc(buf, p - buf);
101}
102
103// Read (potentially big) files in one go. File size is estimated
104// by stat. Extra '\0' byte is appended.
105void* FAST_FUNC xmalloc_read(int fd, size_t *maxsz_p)
106{
107    char *buf;
108    size_t size, rd_size, total;
109    size_t to_read;
110    struct stat st;
111
112    to_read = maxsz_p ? *maxsz_p : (INT_MAX - 4095); /* max to read */
113
114    /* Estimate file size */
115    st.st_size = 0; /* in case fstat fails, assume 0 */
116    fstat(fd, &st);
117    /* /proc/N/stat files report st_size 0 */
118    /* In order to make such files readable, we add small const */
119    size = (st.st_size | 0x3ff) + 1;
120
121    total = 0;
122    buf = NULL;
123    while (1) {
124        if (to_read < size)
125            size = to_read;
126        buf = xrealloc(buf, total + size + 1);
127        rd_size = full_read(fd, buf + total, size);
128        if ((ssize_t)rd_size == (ssize_t)(-1)) { /* error */
129            free(buf);
130            return NULL;
131        }
132        total += rd_size;
133        if (rd_size < size) /* EOF */
134            break;
135        if (to_read <= rd_size)
136            break;
137        to_read -= rd_size;
138        /* grow by 1/8, but in [1k..64k] bounds */
139        size = ((total / 8) | 0x3ff) + 1;
140        if (size > 64*1024)
141            size = 64*1024;
142    }
143    buf = xrealloc(buf, total + 1);
144    buf[total] = '\0';
145
146    if (maxsz_p)
147        *maxsz_p = total;
148    return buf;
149}
150
151#ifdef USING_LSEEK_TO_GET_SIZE
152/* Alternatively, file size can be obtained by lseek to the end.
153 * The code is slightly bigger. Retained in case fstat approach
154 * will not work for some weird cases (/proc, block devices, etc).
155 * (NB: lseek also can fail to work for some weird files) */
156
157// Read (potentially big) files in one go. File size is estimated by
158// lseek to end.
159void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
160{
161    char *buf;
162    size_t size;
163    int fd;
164    off_t len;
165
166    fd = open(filename, O_RDONLY);
167    if (fd < 0)
168        return NULL;
169
170    /* /proc/N/stat files report len 0 here */
171    /* In order to make such files readable, we add small const */
172    size = 0x3ff; /* read only 1k on unseekable files */
173    len = lseek(fd, 0, SEEK_END) | 0x3ff; /* + up to 1k */
174    if (len != (off_t)-1) {
175        xlseek(fd, 0, SEEK_SET);
176        size = maxsz_p ? *maxsz_p : (INT_MAX - 4095);
177        if (len < size)
178            size = len;
179    }
180
181    buf = xmalloc(size + 1);
182    size = read_close(fd, buf, size);
183    if ((ssize_t)size < 0) {
184        free(buf);
185        return NULL;
186    }
187    buf = xrealloc(buf, size + 1);
188    buf[size] = '\0';
189
190    if (maxsz_p)
191        *maxsz_p = size;
192    return buf;
193}
194#endif
195
196// Read (potentially big) files in one go. File size is estimated
197// by stat.
198void* FAST_FUNC xmalloc_open_read_close(const char *filename, size_t *maxsz_p)
199{
200    char *buf;
201    int fd;
202
203    fd = open(filename, O_RDONLY);
204    if (fd < 0)
205        return NULL;
206
207    buf = xmalloc_read(fd, maxsz_p);
208    close(fd);
209    return buf;
210}
211
212/* Die with an error message if we can't read the entire buffer. */
213void FAST_FUNC xread(int fd, void *buf, size_t count)
214{
215    if (count) {
216        ssize_t size = full_read(fd, buf, count);
217        if ((size_t)size != count)
218            bb_error_msg_and_die("short read");
219    }
220}
221
222/* Die with an error message if we can't read one character. */
223unsigned char FAST_FUNC xread_char(int fd)
224{
225    char tmp;
226    xread(fd, &tmp, 1);
227    return tmp;
228}
229
230void* FAST_FUNC xmalloc_xopen_read_close(const char *filename, size_t *maxsz_p)
231{
232    void *buf = xmalloc_open_read_close(filename, maxsz_p);
233    if (!buf)
234        bb_perror_msg_and_die("can't read '%s'", filename);
235    return buf;
236}
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