linux-user/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 <dirent.h>
   8 #include <unistd.h>
   9 #include <stdlib.h>
  10 #include <string.h>
  11 #include <errno.h>
  12 #include <stdio.h>
  13 #include "qemu.h"
  14
  15 struct pathelem
  16 {
  17     /* Name of this, eg. lib */
  18     char *name;
  19     /* Full path name, eg. /usr/gnemul/x86-linux/lib. */
  20     char *pathname;
  21     struct pathelem *parent;
  22     /* Children */
  23     unsigned int num_entries;
  24     struct pathelem *entries[0];
  25 };
  26
  27 static struct pathelem *base;
  28
  29 /* First N chars of S1 match S2, and S2 is N chars long. */
  30 static int strneq(const char *s1, unsigned int n, const char *s2)
  31 {
  32     unsigned int i;
  33
  34     for (i = 0; i < n; i++)
  35         if (s1[i] != s2[i])
  36             return 0;
  37     return s2[i] == 0;
  38 }
  39
  40 static struct pathelem *add_entry(struct pathelem *root, const char *name);
  41
  42 static struct pathelem *new_entry(const char *root,
  43                                   struct pathelem *parent,
  44                                   const char *name)
  45 {
  46     struct pathelem *new = malloc(sizeof(*new));
  47     new->name = strdup(name);
  48     asprintf(&new->pathname, "%s/%s", root, name);
  49     new->num_entries = 0;
  50     return new;
  51 }
  52
  53 #define streq(a,b) (strcmp((a), (b)) == 0)
  54
  55 static struct pathelem *add_dir_maybe(struct pathelem *path)
  56 {
  57     DIR *dir;
  58
  59     if ((dir = opendir(path->pathname)) != NULL) {
  60         struct dirent *dirent;
  61
  62         while ((dirent = readdir(dir)) != NULL) {
  63             if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){
  64                 path = add_entry(path, dirent->d_name);
  65             }
  66         }
  67         closedir(dir);
  68     }
  69     return path;
  70 }
  71
  72 static struct pathelem *add_entry(struct pathelem *root, const char *name)
  73 {
  74     root->num_entries++;
  75
  76     root = realloc(root, sizeof(*root)
  77                    + sizeof(root->entries[0])*root->num_entries);
  78
  79     root->entries[root->num_entries-1] = new_entry(root->pathname, root, name);
  80     root->entries[root->num_entries-1]
  81         = add_dir_maybe(root->entries[root->num_entries-1]);
  82     return root;
  83 }
  84
  85 /* This needs to be done after tree is stabalized (ie. no more reallocs!). */
  86 static void set_parents(struct pathelem *child, struct pathelem *parent)
  87 {
  88     unsigned int i;
  89
  90     child->parent = parent;
  91     for (i = 0; i < child->num_entries; i++)
  92         set_parents(child->entries[i], child);
  93 }
  94
  95 void init_paths(const char *prefix)
  96 {
  97     if (prefix[0] != '/' ||
  98         prefix[0] == '\0' ||
  99         !strcmp(prefix, "/"))
 100         return;
 101
 102     base = new_entry("", NULL, prefix+1);
 103     base = add_dir_maybe(base);
 104     if (base->num_entries == 0) {
 105         free (base);
 106         base = NULL;
 107     } else {
 108         set_parents(base, base);
 109     }
 110 }
 111
 112 /* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
 113 static const char *
 114 follow_path(const struct pathelem *cursor, const char *name)
 115 {
 116     unsigned int i, namelen;
 117
 118     name += strspn(name, "/");
 119     namelen = strcspn(name, "/");
 120
 121     if (namelen == 0)
 122         return cursor->pathname;
 123
 124     if (strneq(name, namelen, ".."))
 125         return follow_path(cursor->parent, name + namelen);
 126
 127     if (strneq(name, namelen, "."))
 128         return follow_path(cursor, name + namelen);
 129
 130     for (i = 0; i < cursor->num_entries; i++)
 131         if (strneq(name, namelen, cursor->entries[i]->name))
 132             return follow_path(cursor->entries[i], name + namelen);
 133
 134     /* Not found */
 135     return NULL;
 136 }
 137
 138 /* Look for path in emulation dir, otherwise return name. */
 139 const char *path(const char *name)
 140 {
 141     /* Only do absolute paths: quick and dirty, but should mostly be OK.
 142        Could do relative by tracking cwd. */
 143     if (!base || name[0] != '/')
 144         return name;
 145
 146     return follow_path(base, name) ?: name;
 147 }