Commit | Line | Data |
---|---|---|
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 | ||
d1fdcab7 PE |
25 | #include <errno.h> |
26 | #include <limits.h> | |
69d9a57d | 27 | #include <stdlib.h> |
d1fdcab7 PE |
28 | #include <string.h> |
29 | #include <unistd.h> | |
30 | ||
d1fdcab7 PE |
31 | /* Define this independently so that stdint.h is not a prerequisite. */ |
32 | #ifndef SIZE_MAX | |
33 | # define SIZE_MAX ((size_t) -1) | |
34 | #endif | |
35 | ||
36 | #ifndef SSIZE_MAX | |
37 | # define SSIZE_MAX ((ssize_t) (SIZE_MAX / 2)) | |
38 | #endif | |
39 | ||
69d9a57d PE |
40 | #include "allocator.h" |
41 | ||
69d9a57d PE |
42 | /* Get the symbolic link value of FILENAME and put it into BUFFER, with |
43 | size BUFFER_SIZE. This function acts like readlink but has | |
44 | readlinkat's signature. */ | |
d1fdcab7 PE |
45 | ssize_t |
46 | careadlinkatcwd (int fd, char const *filename, char *buffer, | |
47 | size_t buffer_size) | |
48 | { | |
69d9a57d PE |
49 | /* FD must be AT_FDCWD here, otherwise the caller is using this |
50 | function in contexts for which it was not meant for. */ | |
51 | if (fd != AT_FDCWD) | |
52 | abort (); | |
d1fdcab7 PE |
53 | return readlink (filename, buffer, buffer_size); |
54 | } | |
d1fdcab7 PE |
55 | |
56 | /* Assuming the current directory is FD, get the symbolic link value | |
57 | of FILENAME as a null-terminated string and put it into a buffer. | |
58 | If FD is AT_FDCWD, FILENAME is interpreted relative to the current | |
59 | working directory, as in openat. | |
60 | ||
61 | If the link is small enough to fit into BUFFER put it there. | |
62 | BUFFER's size is BUFFER_SIZE, and BUFFER can be null | |
63 | if BUFFER_SIZE is zero. | |
64 | ||
65 | If the link is not small, put it into a dynamically allocated | |
66 | buffer managed by ALLOC. It is the caller's responsibility to free | |
67 | the returned value if it is nonnull and is not BUFFER. A null | |
68 | ALLOC stands for the standard allocator. | |
69 | ||
e5b28a7a PE |
70 | The PREADLINKAT function specifies how to read links. It operates |
71 | like POSIX readlinkat() | |
72 | <http://pubs.opengroup.org/onlinepubs/9699919799/functions/readlink.html> | |
73 | but can assume that its first argument is the same as FD. | |
d1fdcab7 PE |
74 | |
75 | If successful, return the buffer address; otherwise return NULL and | |
76 | set errno. */ | |
77 | ||
78 | char * | |
79 | careadlinkat (int fd, char const *filename, | |
80 | char *buffer, size_t buffer_size, | |
81 | struct allocator const *alloc, | |
82 | ssize_t (*preadlinkat) (int, char const *, char *, size_t)) | |
83 | { | |
84 | char *buf; | |
85 | size_t buf_size; | |
86 | size_t buf_size_max = | |
87 | SSIZE_MAX < SIZE_MAX ? (size_t) SSIZE_MAX + 1 : SIZE_MAX; | |
88 | char stack_buf[1024]; | |
89 | ||
9e0e57c7 | 90 | if (! alloc) |
7ec98caf | 91 | alloc = &stdlib_allocator; |
d1fdcab7 PE |
92 | |
93 | if (! buffer_size) | |
94 | { | |
95 | /* Allocate the initial buffer on the stack. This way, in the | |
96 | common case of a symlink of small size, we get away with a | |
97 | single small malloc() instead of a big malloc() followed by a | |
98 | shrinking realloc(). */ | |
99 | buffer = stack_buf; | |
100 | buffer_size = sizeof stack_buf; | |
101 | } | |
102 | ||
103 | buf = buffer; | |
104 | buf_size = buffer_size; | |
105 | ||
106 | do | |
107 | { | |
108 | /* Attempt to read the link into the current buffer. */ | |
109 | ssize_t link_length = preadlinkat (fd, filename, buf, buf_size); | |
110 | size_t link_size; | |
111 | if (link_length < 0) | |
112 | { | |
113 | /* On AIX 5L v5.3 and HP-UX 11i v2 04/09, readlink returns -1 | |
114 | with errno == ERANGE if the buffer is too small. */ | |
115 | int readlinkat_errno = errno; | |
116 | if (readlinkat_errno != ERANGE) | |
117 | { | |
118 | if (buf != buffer) | |
119 | { | |
9e0e57c7 | 120 | alloc->free (buf); |
d1fdcab7 PE |
121 | errno = readlinkat_errno; |
122 | } | |
123 | return NULL; | |
124 | } | |
125 | } | |
126 | ||
127 | link_size = link_length; | |
128 | ||
129 | if (link_size < buf_size) | |
130 | { | |
131 | buf[link_size++] = '\0'; | |
132 | ||
133 | if (buf == stack_buf) | |
134 | { | |
7ec98caf | 135 | char *b = (char *) alloc->allocate (link_size); |
f797625a | 136 | buf_size = link_size; |
d1fdcab7 PE |
137 | if (! b) |
138 | break; | |
139 | memcpy (b, buf, link_size); | |
140 | buf = b; | |
141 | } | |
7ec98caf | 142 | else if (link_size < buf_size && buf != buffer && alloc->reallocate) |
d1fdcab7 PE |
143 | { |
144 | /* Shrink BUF before returning it. */ | |
7ec98caf | 145 | char *b = (char *) alloc->reallocate (buf, link_size); |
d1fdcab7 PE |
146 | if (b) |
147 | buf = b; | |
148 | } | |
149 | ||
150 | return buf; | |
151 | } | |
152 | ||
153 | if (buf != buffer) | |
9e0e57c7 | 154 | alloc->free (buf); |
d1fdcab7 PE |
155 | |
156 | if (buf_size <= buf_size_max / 2) | |
157 | buf_size *= 2; | |
158 | else if (buf_size < buf_size_max) | |
159 | buf_size = buf_size_max; | |
f797625a PE |
160 | else if (buf_size_max < SIZE_MAX) |
161 | { | |
162 | errno = ENAMETOOLONG; | |
163 | return NULL; | |
164 | } | |
d1fdcab7 PE |
165 | else |
166 | break; | |
7ec98caf | 167 | buf = (char *) alloc->allocate (buf_size); |
d1fdcab7 PE |
168 | } |
169 | while (buf); | |
170 | ||
9e0e57c7 | 171 | if (alloc->die) |
f797625a | 172 | alloc->die (buf_size); |
d1fdcab7 PE |
173 | errno = ENOMEM; |
174 | return NULL; | |
175 | } |