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      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 #ifdef __linux__
      7 #define _GNU_SOURCE 1
      8 #endif
      9 #include <sys/types.h>
     10 #include <sys/param.h>
     11 #include <dirent.h>
     12 #include <unistd.h>
     13 #include <stdlib.h>
     14 #include <string.h>
     15 #include <errno.h>
     16 #include <stdio.h>
     17 #include "qemu-common.h"
     18 
     19 struct pathelem
     20 {
     21     /* Name of this, eg. lib */
     22     char *name;
     23     /* Full path name, eg. /usr/gnemul/x86-linux/lib. */
     24     char *pathname;
     25     struct pathelem *parent;
     26     /* Children */
     27     unsigned int num_entries;
     28     struct pathelem *entries[0];
     29 };
     30 
     31 static struct pathelem *base;
     32 
     33 /* First N chars of S1 match S2, and S2 is N chars long. */
     34 static int strneq(const char *s1, unsigned int n, const char *s2)
     35 {
     36     unsigned int i;
     37 
     38     for (i = 0; i < n; i++)
     39         if (s1[i] != s2[i])
     40             return 0;
     41     return s2[i] == 0;
     42 }
     43 
     44 static struct pathelem *add_entry(struct pathelem *root, const char *name,
     45                                   unsigned type);
     46 
     47 static struct pathelem *new_entry(const char *root,
     48                                   struct pathelem *parent,
     49                                   const char *name)
     50 {
     51     struct pathelem *new = malloc(sizeof(*new));
     52     new->name = strdup(name);
     53     new->pathname = g_strdup_printf("%s/%s", root, name);
     54     new->num_entries = 0;
     55     return new;
     56 }
     57 
     58 #define streq(a,b) (strcmp((a), (b)) == 0)
     59 
     60 /* Not all systems provide this feature */
     61 #if defined(DT_DIR) && defined(DT_UNKNOWN) && defined(DT_LNK)
     62 # define dirent_type(dirent) ((dirent)->d_type)
     63 # define is_dir_maybe(type) \
     64     ((type) == DT_DIR || (type) == DT_UNKNOWN || (type) == DT_LNK)
     65 #else
     66 # define dirent_type(dirent) (1)
     67 # define is_dir_maybe(type)  (type)
     68 #endif
     69 
     70 static struct pathelem *add_dir_maybe(struct pathelem *path)
     71 {
     72     DIR *dir;
     73 
     74     if ((dir = opendir(path->pathname)) != NULL) {
     75         struct dirent *dirent;
     76 
     77         while ((dirent = readdir(dir)) != NULL) {
     78             if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){
     79                 path = add_entry(path, dirent->d_name, dirent_type(dirent));
     80             }
     81         }
     82         closedir(dir);
     83     }
     84     return path;
     85 }
     86 
     87 static struct pathelem *add_entry(struct pathelem *root, const char *name,
     88                                   unsigned type)
     89 {
     90     struct pathelem **e;
     91 
     92     root->num_entries++;
     93 
     94     root = realloc(root, sizeof(*root)
     95                    + sizeof(root->entries[0])*root->num_entries);
     96     e = &root->entries[root->num_entries-1];
     97 
     98     *e = new_entry(root->pathname, root, name);
     99     if (is_dir_maybe(type)) {
    100         *e = add_dir_maybe(*e);
    101     }
    102 
    103     return root;
    104 }
    105 
    106 /* This needs to be done after tree is stabilized (ie. no more reallocs!). */
    107 static void set_parents(struct pathelem *child, struct pathelem *parent)
    108 {
    109     unsigned int i;
    110 
    111     child->parent = parent;
    112     for (i = 0; i < child->num_entries; i++)
    113         set_parents(child->entries[i], child);
    114 }
    115 
    116 /* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */
    117 static const char *
    118 follow_path(const struct pathelem *cursor, const char *name)
    119 {
    120     unsigned int i, namelen;
    121 
    122     name += strspn(name, "/");
    123     namelen = strcspn(name, "/");
    124 
    125     if (namelen == 0)
    126         return cursor->pathname;
    127 
    128     if (strneq(name, namelen, ".."))
    129         return follow_path(cursor->parent, name + namelen);
    130 
    131     if (strneq(name, namelen, "."))
    132         return follow_path(cursor, name + namelen);
    133 
    134     for (i = 0; i < cursor->num_entries; i++)
    135         if (strneq(name, namelen, cursor->entries[i]->name))
    136             return follow_path(cursor->entries[i], name + namelen);
    137 
    138     /* Not found */
    139     return NULL;
    140 }
    141 
    142 void init_paths(const char *prefix)
    143 {
    144     char pref_buf[PATH_MAX];
    145 
    146     if (prefix[0] == '\0' ||
    147         !strcmp(prefix, "/"))
    148         return;
    149 
    150     if (prefix[0] != '/') {
    151         char *cwd = getcwd(NULL, 0);
    152         size_t pref_buf_len = sizeof(pref_buf);
    153 
    154         if (!cwd)
    155             abort();
    156         pstrcpy(pref_buf, sizeof(pref_buf), cwd);
    157         pstrcat(pref_buf, pref_buf_len, "/");
    158         pstrcat(pref_buf, pref_buf_len, prefix);
    159         free(cwd);
    160     } else
    161         pstrcpy(pref_buf, sizeof(pref_buf), prefix + 1);
    162 
    163     base = new_entry("", NULL, pref_buf);
    164     base = add_dir_maybe(base);
    165     if (base->num_entries == 0) {
    166         free (base);
    167         base = NULL;
    168     } else {
    169         set_parents(base, base);
    170     }
    171 }
    172 
    173 /* Look for path in emulation dir, otherwise return name. */
    174 const char *path(const char *name)
    175 {
    176     /* Only do absolute paths: quick and dirty, but should mostly be OK.
    177        Could do relative by tracking cwd. */
    178     if (!base || !name || name[0] != '/')
    179         return name;
    180 
    181     return follow_path(base, name) ?: name;
    182 }
    183