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/*
* LD_PRELOAD trick to make Eagle (schematic editor and PCB layout tool from
* CadSoft) work from a read-only installation directory.
*
* When Eagle starts, it looks for the license file in <eagle>/bin/eagle.key
* (where <eagle> is the install path). If eagle.key is not found, Eagle checks
* for write access to <eagle>/bin/, shows a license dialog to the user and
* then attempts to write a license file to <eagle>/bin/.
*
* This will of course fail when Eagle is installed in the read-only Nix store.
* Hence this library that redirects accesses to the those paths in the
* following way:
*
* <eagle>/bin => $HOME
* <eagle>/bin/eagle.key => $HOME/.eagle.key
*
* Also, if copying an example project to ~/eagle/ (in the Eagle GUI), Eagle
* chmod's the destination with read-only permission bits (presumably because
* the source is read-only) and fails to complete the copy operation.
* Therefore, the mode argument in calls to chmod() is OR'ed with the S_IWUSR
* bit (write by owner).
*
* Usage:
* gcc -shared -fPIC -DEAGLE_PATH="$out/eagle-${version}" eagle_fixer.c -o eagle_fixer.so -ldl
* LD_PRELOAD=$PWD/eagle_fixer.so ./result/bin/eagle
*
* To see the paths that are modified at runtime, set the environment variable
* EAGLE_FIXER_DEBUG to 1.
*/
#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <dlfcn.h>
#include <limits.h>
#include <sys/stat.h>
#ifndef EAGLE_PATH
#error Missing EAGLE_PATH, path to the eagle-${version} installation directory.
#endif
typedef FILE *(*fopen_func_t)(const char *path, const char *mode);
typedef int (*access_func_t)(const char *pathname, int mode);
typedef int (*chmod_func_t)(const char *path, mode_t mode);
/*
* Map <eagle>/bin to $HOME and <eagle>/bin/eagle.key to $HOME/.eagle.key
*
* Path is truncated if bigger than PATH_MAX. It's not threadsafe, but that's
* OK.
*/
static const char *redirect(const char *pathname)
{
static char buffer[PATH_MAX];
const char *homepath;
const char *new_path;
static int have_warned;
homepath = getenv("HOME");
if (!homepath) {
homepath = "/";
if (!have_warned && getenv("EAGLE_FIXER_DEBUG")) {
fprintf(stderr, "eagle_fixer: HOME is unset, using \"/\" (root) instead.\n");
have_warned = 1;
}
}
new_path = pathname;
if (strcmp(EAGLE_PATH "/bin", pathname) == 0) {
/* redirect to $HOME */
new_path = homepath;
} else if (strcmp(EAGLE_PATH "/bin/eagle.key", pathname) == 0) {
/* redirect to $HOME/.eagle.key */
snprintf(buffer, PATH_MAX, "%s/.eagle.key", homepath);
buffer[PATH_MAX-1] = '\0';
new_path = buffer;
}
return new_path;
}
FILE *fopen(const char *pathname, const char *mode)
{
FILE *fp;
const char *path;
fopen_func_t orig_fopen;
orig_fopen = (fopen_func_t)dlsym(RTLD_NEXT, "fopen");
path = redirect(pathname);
fp = orig_fopen(path, mode);
if (path != pathname && getenv("EAGLE_FIXER_DEBUG")) {
fprintf(stderr, "eagle_fixer: fopen(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
}
return fp;
}
int access(const char *pathname, int mode)
{
int ret;
const char *path;
access_func_t orig_access;
orig_access = (access_func_t)dlsym(RTLD_NEXT, "access");
path = redirect(pathname);
ret = orig_access(path, mode);
if (path != pathname && getenv("EAGLE_FIXER_DEBUG")) {
fprintf(stderr, "eagle_fixer: access(\"%s\", %d) => \"%s\": ret=%d\n", pathname, mode, path, ret);
}
return ret;
}
int chmod(const char *pathname, mode_t mode)
{
int ret;
mode_t new_mode;
chmod_func_t orig_chmod;
orig_chmod = (chmod_func_t)dlsym(RTLD_NEXT, "chmod");
new_mode = mode | S_IWUSR;
ret = orig_chmod(pathname, new_mode);
if (getenv("EAGLE_FIXER_DEBUG")) {
fprintf(stderr, "eagle_fixer: chmod(\"%s\", %o) => %o: ret=%d\n", pathname, mode, new_mode, ret);
}
return ret;
}
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