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