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d1fdcab7 PE |
1 | /* Read symbolic links into a buffer without size limitation, relative to fd. |
2 | ||
3 | Copyright (C) 2001, 2003-2004, 2007, 2009-2011 Free Software Foundation, | |
4 | Inc. | |
5 | ||
6 | This program is free software: you can redistribute it and/or modify | |
7 | it under the terms of the GNU General Public License as published by | |
8 | the Free Software Foundation; either version 3 of the License, or | |
9 | (at your option) any later version. | |
10 | ||
11 | This program is distributed in the hope that it will be useful, | |
12 | but WITHOUT ANY WARRANTY; without even the implied warranty of | |
13 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
14 | GNU General Public License for more details. | |
15 | ||
16 | You should have received a copy of the GNU General Public License | |
17 | along with this program. If not, see <http://www.gnu.org/licenses/>. */ | |
18 | ||
19 | /* Written by Paul Eggert, Bruno Haible, and Jim Meyering. */ | |
20 | ||
21 | #include <config.h> | |
22 | ||
23 | #include "careadlinkat.h" | |
24 | ||
25 | #include "allocator.h" | |
26 | ||
27 | #include <errno.h> | |
28 | #include <limits.h> | |
d1fdcab7 PE |
29 | #include <string.h> |
30 | #include <unistd.h> | |
31 | ||
d1fdcab7 PE |
32 | /* Define this independently so that stdint.h is not a prerequisite. */ |
33 | #ifndef SIZE_MAX | |
34 | # define SIZE_MAX ((size_t) -1) | |
35 | #endif | |
36 | ||
37 | #ifndef SSIZE_MAX | |
38 | # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) | |
39 | #endif | |
40 | ||
41 | #if ! HAVE_READLINKAT | |
42 | /* Ignore FD. Get the symbolic link value of FILENAME and put it into | |
43 | BUFFER, with size BUFFER_SIZE. This function acts like readlink | |
44 | but has readlinkat's signature. */ | |
45 | ssize_t | |
46 | careadlinkatcwd (int fd, char const *filename, char *buffer, | |
47 | size_t buffer_size) | |
48 | { | |
49 | (void) fd; | |
50 | return readlink (filename, buffer, buffer_size); | |
51 | } | |
52 | #endif | |
53 | ||
54 | /* Assuming the current directory is FD, get the symbolic link value | |
55 | of FILENAME as a null-terminated string and put it into a buffer. | |
56 | If FD is AT_FDCWD, FILENAME is interpreted relative to the current | |
57 | working directory, as in openat. | |
58 | ||
59 | If the link is small enough to fit into BUFFER put it there. | |
60 | BUFFER's size is BUFFER_SIZE, and BUFFER can be null | |
61 | if BUFFER_SIZE is zero. | |
62 | ||
63 | If the link is not small, put it into a dynamically allocated | |
64 | buffer managed by ALLOC. It is the caller's responsibility to free | |
65 | the returned value if it is nonnull and is not BUFFER. A null | |
66 | ALLOC stands for the standard allocator. | |
67 | ||
68 | The PREADLINKAT function specifies how to read links. | |
69 | ||
70 | If successful, return the buffer address; otherwise return NULL and | |
71 | set errno. */ | |
72 | ||
73 | char * | |
74 | careadlinkat (int fd, char const *filename, | |
75 | char *buffer, size_t buffer_size, | |
76 | struct allocator const *alloc, | |
77 | ssize_t (*preadlinkat) (int, char const *, char *, size_t)) | |
78 | { | |
79 | char *buf; | |
80 | size_t buf_size; | |
81 | size_t buf_size_max = | |
82 | SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; | |
83 | char stack_buf[1024]; | |
84 | ||
9e0e57c7 | 85 | if (! alloc) |
7ec98caf | 86 | alloc = &stdlib_allocator; |
d1fdcab7 PE |
87 | |
88 | if (! buffer_size) | |
89 | { | |
90 | /* Allocate the initial buffer on the stack. This way, in the | |
91 | common case of a symlink of small size, we get away with a | |
92 | single small malloc() instead of a big malloc() followed by a | |
93 | shrinking realloc(). */ | |
94 | buffer = stack_buf; | |
95 | buffer_size = sizeof stack_buf; | |
96 | } | |
97 | ||
98 | buf = buffer; | |
99 | buf_size = buffer_size; | |
100 | ||
101 | do | |
102 | { | |
103 | /* Attempt to read the link into the current buffer. */ | |
104 | ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); | |
105 | size_t link_size; | |
106 | if (link_length < 0) | |
107 | { | |
108 | /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 | |
109 | with errno == ERANGE if the buffer is too small. */ | |
110 | int readlinkat_errno = errno; | |
111 | if (readlinkat_errno != ERANGE) | |
112 | { | |
113 | if (buf != buffer) | |
114 | { | |
9e0e57c7 | 115 | alloc->free (buf); |
d1fdcab7 PE |
116 | errno = readlinkat_errno; |
117 | } | |
118 | return NULL; | |
119 | } | |
120 | } | |
121 | ||
122 | link_size = link_length; | |
123 | ||
124 | if (link_size < buf_size) | |
125 | { | |
126 | buf[link_size++] = '\0'; | |
127 | ||
128 | if (buf == stack_buf) | |
129 | { | |
7ec98caf | 130 | char *b = (char *) alloc->allocate (link_size); |
d1fdcab7 PE |
131 | if (! b) |
132 | break; | |
133 | memcpy (b, buf, link_size); | |
134 | buf = b; | |
135 | } | |
7ec98caf | 136 | else if (link_size < buf_size && buf != buffer && alloc->reallocate) |
d1fdcab7 PE |
137 | { |
138 | /* Shrink BUF before returning it. */ | |
7ec98caf | 139 | char *b = (char *) alloc->reallocate (buf, link_size); |
d1fdcab7 PE |
140 | if (b) |
141 | buf = b; | |
142 | } | |
143 | ||
144 | return buf; | |
145 | } | |
146 | ||
147 | if (buf != buffer) | |
9e0e57c7 | 148 | alloc->free (buf); |
d1fdcab7 PE |
149 | |
150 | if (buf_size <= buf_size_max / 2) | |
151 | buf_size *= 2; | |
152 | else if (buf_size < buf_size_max) | |
153 | buf_size = buf_size_max; | |
154 | else | |
155 | break; | |
7ec98caf | 156 | buf = (char *) alloc->allocate (buf_size); |
d1fdcab7 PE |
157 | } |
158 | while (buf); | |
159 | ||
9e0e57c7 PE |
160 | if (alloc->die) |
161 | alloc->die (); | |
d1fdcab7 PE |
162 | errno = ENOMEM; |
163 | return NULL; | |
164 | } |