Archipelago » qemu

/* Code to mangle pathnames into those matching a given prefix.

   eg. open("/lib/foo.so") => open("/usr/gnemul/i386-linux/lib/foo.so");

   The assumption is that this area does not change.

*/

#include <sys/types.h>

#include <dirent.h>

#include <unistd.h>

#include <stdlib.h>

#include <string.h>

#include <errno.h>

#include <stdio.h>

#include "qemu.h"

struct pathelem

{

    /* Name of this, eg. lib */

    char *name;

    /* Full path name, eg. /usr/gnemul/x86-linux/lib. */

    char *pathname;

    struct pathelem *parent;

    /* Children */

    unsigned int num_entries;

    struct pathelem *entries[0];

};

static struct pathelem *base;

/* First N chars of S1 match S2, and S2 is N chars long. */

static int strneq(const char *s1, unsigned int n, const char *s2)

{

    unsigned int i;

    for (i = 0; i < n; i++)

        if (s1[i] != s2[i])

            return 0;

    return s2[i] == 0;

}

static struct pathelem *add_entry(struct pathelem *root, const char *name);

static struct pathelem *new_entry(const char *root,

                                  struct pathelem *parent,

                                  const char *name)

{

    struct pathelem *new = malloc(sizeof(*new));

    new->name = strdup(name);

    asprintf(&new->pathname, "%s/%s", root, name);

    new->num_entries = 0;

    return new;

}

#define streq(a,b) (strcmp((a), (b)) == 0)

static struct pathelem *add_dir_maybe(struct pathelem *path)

{

    DIR *dir;

    if ((dir = opendir(path->pathname)) != NULL) {

        struct dirent *dirent;

        while ((dirent = readdir(dir)) != NULL) {

            if (!streq(dirent->d_name,".") && !streq(dirent->d_name,"..")){

                path = add_entry(path, dirent->d_name);

            }

        }

        closedir(dir);

    }

    return path;

}

static struct pathelem *add_entry(struct pathelem *root, const char *name)

{

    root->num_entries++;

    root = realloc(root, sizeof(*root)

                   + sizeof(root->entries[0])*root->num_entries);

    root->entries[root->num_entries-1] = new_entry(root->pathname, root, name);

    root->entries[root->num_entries-1]

        = add_dir_maybe(root->entries[root->num_entries-1]);

    return root;

}

/* This needs to be done after tree is stabalized (ie. no more reallocs!). */

static void set_parents(struct pathelem *child, struct pathelem *parent)

{

    unsigned int i;

    child->parent = parent;

    for (i = 0; i < child->num_entries; i++)

        set_parents(child->entries[i], child);

}

void init_paths(const char *prefix)

{

    if (prefix[0] != '/' ||

        prefix[0] == '\0' ||

        !strcmp(prefix, "/"))

        return;

    base = new_entry("", NULL, prefix+1);

    base = add_dir_maybe(base);

    if (base->num_entries == 0) {

        free (base);

        base = NULL;

    } else {

        set_parents(base, base);

    }

}

/* FIXME: Doesn't handle DIR/.. where DIR is not in emulated dir. */

static const char *

follow_path(const struct pathelem *cursor, const char *name)

{

    unsigned int i, namelen;

    name += strspn(name, "/");

    namelen = strcspn(name, "/");

    if (namelen == 0)

        return cursor->pathname;

    if (strneq(name, namelen, ".."))

        return follow_path(cursor->parent, name + namelen);

    if (strneq(name, namelen, "."))

        return follow_path(cursor, name + namelen);

    for (i = 0; i < cursor->num_entries; i++)

        if (strneq(name, namelen, cursor->entries[i]->name))

            return follow_path(cursor->entries[i], name + namelen);

    /* Not found */

    return NULL;

}

/* Look for path in emulation dir, otherwise return name. */

const char *path(const char *name)

{

    /* Only do absolute paths: quick and dirty, but should mostly be OK.

       Could do relative by tracking cwd. */

    if (!base || name[0] != '/')

        return name;

    return follow_path(base, name) ?: name;

}