util/path.c

   1 /* Code to mangle pathnames into those matching a given prefix.
   2    eg. open("/lib/foo.so") => open("/usr/gnemul/i386-linux/lib/foo.so");
   3
   4    The assumption is that this area does not change.
   5 */
   6 #include <sys/types.h>
   7 #include <sys/param.h>
   8 #include <dirent.h>
   9 #include <unistd.h>
  10 #include <stdlib.h>
  11 #include <string.h>
  12 #include <errno.h>
  13 #include <stdio.h>
  14 #include "qemu-common.h"
  15
  16 struct pathelem
  17 {
  18     /* Name of this, eg. lib */
  19     char *name;
  20     /* Full path name, eg. /usr/gnemul/x86-linux/lib. */
  21     char *pathname;
  22     struct pathelem *parent;
  23     /* Children */
  24     unsigned int num_entries;
  25     struct pathelem *entries[0];
  26 };
  27
  28 static struct pathelem *base;
  29
  30 /* First N chars of S1 match S2, and S2 is N chars long. */
  31 static int strneq(const char *s1, unsigned int n, const char *s2)
  32 {
  33     unsigned int i;
  34
  35     for (i = 0; i < n; i++)
  36         if (s1[i] != s2[i])
  37             return 0;
  38     return s2[i] == 0;
  39 }
  40
  41 static struct pathelem *add_entry(struct pathelem *root, const char *name,
  42                                   unsigned type);
  43
  44 static struct pathelem *new_entry(const char *root,
  45                                   struct pathelem *parent,
  46                                   const char *name)
  47 {
  48     struct pathelem *new = g_malloc(sizeof(*new));
  49     new->name = g_strdup(name);
  50     new->pathname = g_strdup_printf("%s/%s", root, name);
  51     new->num_entries = 0;
  52     return new;
  53 }
  54
  55 #define streq(a,b) (strcmp((a), (b)) == 0)
  56
  57 /* Not all systems provide this feature */
  58 #if defined(DT_DIR) && defined(DT_UNKNOWN) && defined(DT_LNK)
  59 # define dirent_type(dirent) ((dirent)->d_type)
  60 # define is_dir_maybe(type) \
  61     ((type) == DT_DIR || (type) == DT_UNKNOWN || (type) == DT_LNK)
  62 #else
  63 # define dirent_type(dirent) (1)
  64 # define is_dir_maybe(type)  (type)
  65 #endif
  66
  67 static struct pathelem *add_dir_maybe(struct pathelem *path)
  68 {
  69     DIR *dir;
  70
  71     if ((dir = opendir(path->pathname)) != NULL) {
  72         struct dirent *dirent;
  73
  74         while ((dirent = readdir(dir)) != NULL) {
  75             if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){
  76                 path = add_entry(path, dirent->d_name, dirent_type(dirent));
  77             }
  78         }
  79         closedir(dir);
  80     }
  81     return path;
  82 }
  83
  84 static struct pathelem *add_entry(struct pathelem *root, const char *name,
  85                                   unsigned type)
  86 {
  87     struct pathelem **e;
  88
  89     root->num_entries++;
  90
  91     root = g_realloc(root, sizeof(*root)
  92                    + sizeof(root->entries[0])*root->num_entries);
  93     e = &root->entries[root->num_entries-1];
  94
  95     *e = new_entry(root->pathname, root, name);
  96     if (is_dir_maybe(type)) {
  97         *e = add_dir_maybe(*e);
  98     }
  99
 100     return root;
 101 }
 102
 103 /* This needs to be done after tree is stabilized (ie. no more reallocs!). */
 104 static void set_parents(struct pathelem *child, struct pathelem *parent)
 105 {
 106     unsigned int i;
 107
 108     child->parent = parent;
 109     for (i = 0; i < child->num_entries; i++)
 110         set_parents(child->entries[i], child);
 111 }
 112
 113 /* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
 114 static const char *
 115 follow_path(const struct pathelem *cursor, const char *name)
 116 {
 117     unsigned int i, namelen;
 118
 119     name += strspn(name, "/");
 120     namelen = strcspn(name, "/");
 121
 122     if (namelen == 0)
 123         return cursor->pathname;
 124
 125     if (strneq(name, namelen, ".."))
 126         return follow_path(cursor->parent, name + namelen);
 127
 128     if (strneq(name, namelen, "."))
 129         return follow_path(cursor, name + namelen);
 130
 131     for (i = 0; i < cursor->num_entries; i++)
 132         if (strneq(name, namelen, cursor->entries[i]->name))
 133             return follow_path(cursor->entries[i], name + namelen);
 134
 135     /* Not found */
 136     return NULL;
 137 }
 138
 139 void init_paths(const char *prefix)
 140 {
 141     char pref_buf[PATH_MAX];
 142
 143     if (prefix[0] == '\0' ||
 144         !strcmp(prefix, "/"))
 145         return;
 146
 147     if (prefix[0] != '/') {
 148         char *cwd = getcwd(NULL, 0);
 149         size_t pref_buf_len = sizeof(pref_buf);
 150
 151         if (!cwd)
 152             abort();
 153         pstrcpy(pref_buf, sizeof(pref_buf), cwd);
 154         pstrcat(pref_buf, pref_buf_len, "/");
 155         pstrcat(pref_buf, pref_buf_len, prefix);
 156         free(cwd);
 157     } else
 158         pstrcpy(pref_buf, sizeof(pref_buf), prefix + 1);
 159
 160     base = new_entry("", NULL, pref_buf);
 161     base = add_dir_maybe(base);
 162     if (base->num_entries == 0) {
 163         g_free(base->pathname);
 164         g_free(base->name);
 165         g_free(base);
 166         base = NULL;
 167     } else {
 168         set_parents(base, base);
 169     }
 170 }
 171
 172 /* Look for path in emulation dir, otherwise return name. */
 173 const char *path(const char *name)
 174 {
 175     /* Only do absolute paths: quick and dirty, but should mostly be OK.
 176        Could do relative by tracking cwd. */
 177     if (!base || !name || name[0] != '/')
 178         return name;
 179
 180     return follow_path(base, name) ?: name;
 181 }