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