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/*
* LD_PRELOAD trick to make Saleae Logic work from a read-only installation
* directory.
*
* Saleae Logic tries to write to the ./Settings/settings.xml file, relative to
* its installation directory. Because the nix store is read-only, we have to
* redirect access to this file somewhere else. Here's the map:
*
* $out/Settings/settings.xml => $HOME/.saleae-logic-settings.xml
*
* This also makes the software multi-user aware :-)
*
* NOTE: The next Logic version is supposed to have command line parameters for
* configuring where the Settings/ directory is located, but until then we have
* to use this.
*
* Usage:
* gcc -shared -fPIC -DOUT="$out" preload.c -o preload.so -ldl
* LD_PRELOAD=$PWD/preload.so ./result/Logic
*
* To see the paths that are modified at runtime, set the environment variable
* PRELOAD_DEBUG to 1 (or anything really; debugging is on as long as the
* variable exists).
*/
#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>
#include <sys/types.h>
#ifndef OUT
#error Missing OUT define - path to the installation directory.
#endif
typedef FILE *(*fopen_func_t)(const char *path, const char *mode);
typedef FILE *(*fopen64_func_t)(const char *path, const char *mode);
/*
* Redirect $out/Settings/settings.xml => $HOME/.saleae-logic-settings.xml. No
* other paths are changed. Path is truncated if bigger than PATH_MAX.
*
* @param pathname Original file path.
* @param buffer Pointer to a buffer of size PATH_MAX bytes that this function
* will write the new redirected path to (if needed).
*
* @return Pointer to the resulting path. It will either be equal to the
* pathname or buffer argument.
*/
static const char *redirect(const char *pathname, char *buffer)
{
const char *homepath;
const char *new_path;
static char have_warned;
homepath = getenv("HOME");
if (!homepath) {
homepath = "/";
if (!have_warned && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: WARNING: HOME is unset, using \"/\" (root) instead.\n");
have_warned = 1;
}
}
new_path = pathname;
if (strcmp(OUT "/Settings/settings.xml", pathname) == 0) {
snprintf(buffer, PATH_MAX, "%s/.saleae-logic-settings.xml", 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;
char buffer[PATH_MAX];
fopen_func_t orig_fopen;
orig_fopen = (fopen_func_t)dlsym(RTLD_NEXT, "fopen");
path = redirect(pathname, buffer);
fp = orig_fopen(path, mode);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: fopen(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
}
return fp;
}
FILE *fopen64(const char *pathname, const char *mode)
{
FILE *fp;
const char *path;
char buffer[PATH_MAX];
fopen64_func_t orig_fopen64;
orig_fopen64 = (fopen64_func_t)dlsym(RTLD_NEXT, "fopen64");
path = redirect(pathname, buffer);
fp = orig_fopen64(path, mode);
if (path != pathname && getenv("PRELOAD_DEBUG")) {
fprintf(stderr, "preload_debug: fopen64(\"%s\", \"%s\") => \"%s\": fp=%p\n", pathname, mode, path, fp);
}
return fp;
}
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