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 char type);
  43
  44 static struct pathelem *new_entry(const char *root,
  45                                   struct pathelem *parent,
  46                                   const char *name)
  47 {
  48     struct pathelem *new = malloc(sizeof(*new));
  49     new->name = strdup(name);
  50     if (asprintf(&new->pathname, "%s/%s", root, name) == -1) {
  51         printf("Cannot allocate memory\n");
  52         exit(1);
  53     }
  54     new->num_entries = 0;
  55     return new;
  56 }
  57
  58 #define streq(a,b) (strcmp((a), (b)) == 0)
  59
  60 /* Not all systems provide this feature */
  61 #if defined(DT_DIR) && defined(DT_UNKNOWN)
  62 # define dirent_type(dirent) ((dirent)->d_type)
  63 # define is_dir_maybe(type)  ((type) == DT_DIR || (type) == DT_UNKNOWN)
  64 #else
  65 # define dirent_type(dirent) (1)
  66 # define is_dir_maybe(type)  (type)
  67 #endif
  68
  69 static struct pathelem *add_dir_maybe(struct pathelem *path)
  70 {
  71     DIR *dir;
  72
  73     if ((dir = opendir(path->pathname)) != NULL) {
  74         struct dirent *dirent;
  75
  76         while ((dirent = readdir(dir)) != NULL) {
  77             if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){
  78                 path = add_entry(path, dirent->d_name, dirent_type(dirent));
  79             }
  80         }
  81         closedir(dir);
  82     }
  83     return path;
  84 }
  85
  86 static struct pathelem *add_entry(struct pathelem *root, const char *name,
  87                                   unsigned char type)
  88 {
  89     struct pathelem **e;
  90
  91     root->num_entries++;
  92
  93     root = realloc(root, sizeof(*root)
  94                    + sizeof(root->entries[0])*root->num_entries);
  95     e = &root->entries[root->num_entries-1];
  96
  97     *e = new_entry(root->pathname, root, name);
  98     if (is_dir_maybe(type)) {
  99         *e = add_dir_maybe(*e);
 100     }
 101
 102     return root;
 103 }
 104
 105 /* This needs to be done after tree is stabilized (ie. no more reallocs!). */
 106 static void set_parents(struct pathelem *child, struct pathelem *parent)
 107 {
 108     unsigned int i;
 109
 110     child->parent = parent;
 111     for (i = 0; i < child->num_entries; i++)
 112         set_parents(child->entries[i], child);
 113 }
 114
 115 /* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
 116 static const char *
 117 follow_path(const struct pathelem *cursor, const char *name)
 118 {
 119     unsigned int i, namelen;
 120
 121     name += strspn(name, "/");
 122     namelen = strcspn(name, "/");
 123
 124     if (namelen == 0)
 125         return cursor->pathname;
 126
 127     if (strneq(name, namelen, ".."))
 128         return follow_path(cursor->parent, name + namelen);
 129
 130     if (strneq(name, namelen, "."))
 131         return follow_path(cursor, name + namelen);
 132
 133     for (i = 0; i < cursor->num_entries; i++)
 134         if (strneq(name, namelen, cursor->entries[i]->name))
 135             return follow_path(cursor->entries[i], name + namelen);
 136
 137     /* Not found */
 138     return NULL;
 139 }
 140
 141 void init_paths(const char *prefix)
 142 {
 143     char pref_buf[PATH_MAX];
 144
 145     if (prefix[0] == '\0' ||
 146         !strcmp(prefix, "/"))
 147         return;
 148
 149     if (prefix[0] != '/') {
 150         char *cwd = getcwd(NULL, 0);
 151         size_t pref_buf_len = sizeof(pref_buf);
 152
 153         if (!cwd)
 154             abort();
 155         pstrcpy(pref_buf, sizeof(pref_buf), cwd);
 156         pstrcat(pref_buf, pref_buf_len, "/");
 157         pstrcat(pref_buf, pref_buf_len, prefix);
 158         free(cwd);
 159     } else
 160         pstrcpy(pref_buf, sizeof(pref_buf), prefix + 1);
 161
 162     base = new_entry("", NULL, pref_buf);
 163     base = add_dir_maybe(base);
 164     if (base->num_entries == 0) {
 165         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 }