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