mkinitrd-6_2_0/libbb/xreadlink.c

/* vi: set sw=4 ts=4: */
/*
 *  xreadlink.c - safe implementation of readlink.
 *  Returns a NULL on failure...
 */

#include "libbb.h"

/*
 * NOTE: This function returns a malloced char* that you will have to free
 * yourself.
 */
char* FAST_FUNC xmalloc_readlink(const char *path)
{
	enum { GROWBY = 80 }; /* how large we will grow strings by */

	char *buf = NULL;
	int bufsize = 0, readsize = 0;

	do {
		bufsize += GROWBY;
		buf = xrealloc(buf, bufsize);
		readsize = readlink(path, buf, bufsize);
		if (readsize == -1) {
			free(buf);
			return NULL;
		}
	} while (bufsize < readsize + 1);

	buf[readsize] = '\0';

	return buf;
}

/*
 * This routine is not the same as realpath(), which
 * canonicalizes the given path completely. This routine only
 * follows trailing symlinks until a real file is reached and
 * returns its name. If the path ends in a dangling link or if
 * the target doesn't exist, the path is returned in any case.
 * Intermediate symlinks in the path are not expanded -- only
 * those at the tail.
 * A malloced char* is returned, which must be freed by the caller.
 */
char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
{
	char *buf;
	char *lpc;
	char *linkpath;
	int bufsize;
	int looping = MAXSYMLINKS + 1;

	buf = xstrdup(path);
	goto jump_in;

	while (1) {
		linkpath = xmalloc_readlink(buf);
		if (!linkpath) {
			/* not a symlink, or doesn't exist */
			if (errno == EINVAL || errno == ENOENT)
				return buf;
			goto free_buf_ret_null;
		}

		if (!--looping) {
			free(linkpath);
 free_buf_ret_null:
			free(buf);
			return NULL;
		}

		if (*linkpath != '/') {
			bufsize += strlen(linkpath);
			buf = xrealloc(buf, bufsize);
			lpc = bb_get_last_path_component_strip(buf);
			strcpy(lpc, linkpath);
			free(linkpath);
		} else {
			free(buf);
			buf = linkpath;
 jump_in:
			bufsize = strlen(buf) + 1;
		}
	}
}

char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
{
	char *buf = xmalloc_readlink(path);
	if (!buf) {
		/* EINVAL => "file: Invalid argument" => puzzled user */
		bb_error_msg("%s: cannot read link (not a symlink?)", path);
	}
	return buf;
}

/* UNUSED */
#if 0
char* FAST_FUNC xmalloc_realpath(const char *path)
{
#if defined(__GLIBC__) && !defined(__UCLIBC__)
	/* glibc provides a non-standard extension */
	return realpath(path, NULL);
#else
	char buf[PATH_MAX+1];

	/* on error returns NULL (xstrdup(NULL) ==NULL) */
	return xstrdup(realpath(path, buf));
#endif
}
#endif
1	niro	532	/* vi: set sw=4 ts=4: */
2			/*
3			* xreadlink.c - safe implementation of readlink.
4			* Returns a NULL on failure...
5			*/
6
7			#include "libbb.h"
8
9			/*
10			* NOTE: This function returns a malloced char* that you will have to free
11	niro	816	* yourself.
12	niro	532	*/
13	niro	816	char* FAST_FUNC xmalloc_readlink(const char *path)
14	niro	532	{
15			enum { GROWBY = 80 }; /* how large we will grow strings by */
16
17			char *buf = NULL;
18			int bufsize = 0, readsize = 0;
19
20			do {
21	niro	816	bufsize += GROWBY;
22			buf = xrealloc(buf, bufsize);
23			readsize = readlink(path, buf, bufsize);
24	niro	532	if (readsize == -1) {
25			free(buf);
26			return NULL;
27			}
28	niro	816	} while (bufsize < readsize + 1);
29	niro	532
30			buf[readsize] = '\0';
31
32			return buf;
33			}
34
35	niro	816	/*
36			* This routine is not the same as realpath(), which
37			* canonicalizes the given path completely. This routine only
38			* follows trailing symlinks until a real file is reached and
39			* returns its name. If the path ends in a dangling link or if
40			* the target doesn't exist, the path is returned in any case.
41			* Intermediate symlinks in the path are not expanded -- only
42			* those at the tail.
43			* A malloced char* is returned, which must be freed by the caller.
44			*/
45			char* FAST_FUNC xmalloc_follow_symlinks(const char *path)
46	niro	532	{
47	niro	816	char *buf;
48			char *lpc;
49			char *linkpath;
50			int bufsize;
51			int looping = MAXSYMLINKS + 1;
52
53			buf = xstrdup(path);
54			goto jump_in;
55
56			while (1) {
57			linkpath = xmalloc_readlink(buf);
58			if (!linkpath) {
59			/* not a symlink, or doesn't exist */
60			if (errno == EINVAL \|\| errno == ENOENT)
61			return buf;
62			goto free_buf_ret_null;
63			}
64
65			if (!--looping) {
66			free(linkpath);
67			free_buf_ret_null:
68			free(buf);
69			return NULL;
70			}
71
72			if (*linkpath != '/') {
73			bufsize += strlen(linkpath);
74			buf = xrealloc(buf, bufsize);
75			lpc = bb_get_last_path_component_strip(buf);
76			strcpy(lpc, linkpath);
77			free(linkpath);
78			} else {
79			free(buf);
80			buf = linkpath;
81			jump_in:
82			bufsize = strlen(buf) + 1;
83			}
84			}
85			}
86
87			char* FAST_FUNC xmalloc_readlink_or_warn(const char *path)
88			{
89			char *buf = xmalloc_readlink(path);
90			if (!buf) {
91			/* EINVAL => "file: Invalid argument" => puzzled user */
92			bb_error_msg("%s: cannot read link (not a symlink?)", path);
93			}
94			return buf;
95			}
96
97			/* UNUSED */
98			#if 0
99			char* FAST_FUNC xmalloc_realpath(const char *path)
100			{
101	niro	532	#if defined(__GLIBC__) && !defined(__UCLIBC__)
102			/* glibc provides a non-standard extension */
103			return realpath(path, NULL);
104			#else
105			char buf[PATH_MAX+1];
106
107			/* on error returns NULL (xstrdup(NULL) ==NULL) */
108			return xstrdup(realpath(path, buf));
109			#endif
110			}
111	niro	816	#endif