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