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