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