Contents of /tags/mkinitrd-6_3_5/busybox/libbb/xreadlink.c
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Sat Jan 29 14:06:54 2011 UTC (13 years, 7 months ago) by niro
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File size: 2647 byte(s)
Sat Jan 29 14:06:54 2011 UTC (13 years, 7 months ago) by niro
File MIME type: text/plain
File size: 2647 byte(s)
tagged 'mkinitrd-6_3_5'
1 | /* vi: set sw=4 ts=4: */ |
2 | /* |
3 | * xreadlink.c - safe implementation of readlink. |
4 | * Returns a NULL on failure... |
5 | * |
6 | * Licensed under GPLv2, see file LICENSE in this tarball for details. |
7 | */ |
8 | |
9 | #include "libbb.h" |
10 | |
11 | /* |
12 | * NOTE: This function returns a malloced char* that you will have to free |
13 | * yourself. |
14 | */ |
15 | char* FAST_FUNC xmalloc_readlink(const char *path) |
16 | { |
17 | enum { GROWBY = 80 }; /* how large we will grow strings by */ |
18 | |
19 | char *buf = NULL; |
20 | int bufsize = 0, readsize = 0; |
21 | |
22 | do { |
23 | bufsize += GROWBY; |
24 | buf = xrealloc(buf, bufsize); |
25 | readsize = readlink(path, buf, bufsize); |
26 | if (readsize == -1) { |
27 | free(buf); |
28 | return NULL; |
29 | } |
30 | } while (bufsize < readsize + 1); |
31 | |
32 | buf[readsize] = '\0'; |
33 | |
34 | return buf; |
35 | } |
36 | |
37 | /* |
38 | * This routine is not the same as realpath(), which |
39 | * canonicalizes the given path completely. This routine only |
40 | * follows trailing symlinks until a real file is reached and |
41 | * returns its name. If the path ends in a dangling link or if |
42 | * the target doesn't exist, the path is returned in any case. |
43 | * Intermediate symlinks in the path are not expanded -- only |
44 | * those at the tail. |
45 | * A malloced char* is returned, which must be freed by the caller. |
46 | */ |
47 | char* FAST_FUNC xmalloc_follow_symlinks(const char *path) |
48 | { |
49 | char *buf; |
50 | char *lpc; |
51 | char *linkpath; |
52 | int bufsize; |
53 | int looping = MAXSYMLINKS + 1; |
54 | |
55 | buf = xstrdup(path); |
56 | goto jump_in; |
57 | |
58 | while (1) { |
59 | linkpath = xmalloc_readlink(buf); |
60 | if (!linkpath) { |
61 | /* not a symlink, or doesn't exist */ |
62 | if (errno == EINVAL || errno == ENOENT) |
63 | return buf; |
64 | goto free_buf_ret_null; |
65 | } |
66 | |
67 | if (!--looping) { |
68 | free(linkpath); |
69 | free_buf_ret_null: |
70 | free(buf); |
71 | return NULL; |
72 | } |
73 | |
74 | if (*linkpath != '/') { |
75 | bufsize += strlen(linkpath); |
76 | buf = xrealloc(buf, bufsize); |
77 | lpc = bb_get_last_path_component_strip(buf); |
78 | strcpy(lpc, linkpath); |
79 | free(linkpath); |
80 | } else { |
81 | free(buf); |
82 | buf = linkpath; |
83 | jump_in: |
84 | bufsize = strlen(buf) + 1; |
85 | } |
86 | } |
87 | } |
88 | |
89 | char* FAST_FUNC xmalloc_readlink_or_warn(const char *path) |
90 | { |
91 | char *buf = xmalloc_readlink(path); |
92 | if (!buf) { |
93 | /* EINVAL => "file: Invalid argument" => puzzled user */ |
94 | const char *errmsg = "not a symlink"; |
95 | int err = errno; |
96 | if (err != EINVAL) |
97 | errmsg = strerror(err); |
98 | bb_error_msg("%s: cannot read link: %s", path, errmsg); |
99 | } |
100 | return buf; |
101 | } |
102 | |
103 | char* FAST_FUNC xmalloc_realpath(const char *path) |
104 | { |
105 | #if defined(__GLIBC__) && !defined(__UCLIBC__) |
106 | /* glibc provides a non-standard extension */ |
107 | /* new: POSIX.1-2008 specifies this behavior as well */ |
108 | return realpath(path, NULL); |
109 | #else |
110 | char buf[PATH_MAX+1]; |
111 | |
112 | /* on error returns NULL (xstrdup(NULL) == NULL) */ |
113 | return xstrdup(realpath(path, buf)); |
114 | #endif |
115 | } |