gamemode: Add function to resolve the wine preloader executable

This commit adds a function to resolve a wine preloader binary into its
original windows binary.

Signed-off-by: Kai Krakow <kai@kaishome.de>

daemon/gamemode.c

@@ -38,6 +38,7 @@ POSSIBILITY OF SUCH DAMAGE.
 #include "ioprio.h"
 #include "logging.h"
 
+#include <ctype.h>
 #include <fcntl.h>
 #include <linux/limits.h>
 #include <linux/sched.h>
@@ -741,6 +742,116 @@ static char *game_mode_lookup_user_home(void)
 	return home ? strdup(home) : NULL;
 }
 
+/**
+ * Attempt to resolve the exe for wine-preloader.
+ * This function is used if game_mode_context_find_exe() identified the
+ * process as wine-preloader. Returns NULL when resolve fails.
+ */
+static char *game_mode_resolve_wine_preloader(pid_t pid)
+{
+	char buffer[PATH_MAX];
+	char *proc_path = NULL, *wine_exe = NULL, *wineprefix = NULL;
+	int proc_fd = -1;
+
+	if (!(proc_path = safe_snprintf(buffer, "/proc/%d", pid)))
+		goto fail;
+
+	/* Open the directory, we are potentially reading multiple files from it */
+	if (-1 == (proc_fd = open(proc_path, O_RDONLY | O_CLOEXEC)))
+		goto fail_proc;
+
+	/* Open the command line */
+	int fd = openat(proc_fd, "cmdline", O_RDONLY | O_CLOEXEC);
+	if (fd != -1) {
+		FILE *stream = fdopen(fd, "r");
+		if (stream) {
+			char *argv = NULL;
+			size_t args = 0;
+			int argc = 0;
+			while (!wine_exe && (argc++ < 2) && (getdelim(&argv, &args, 0, stream) != -1)) {
+				/* If we see the wine loader here, we have to use the next argument */
+				if (strtail(argv, "/wine") || strtail(argv, "/wine64"))
+					continue;
+				free(wine_exe); // just in case
+				/* Check presence of the drive letter, we assume that below */
+				wine_exe = args > 2 && argv[1] == ':' ? strndup(argv, args) : NULL;
+			}
+			free(argv);
+			fclose(stream);
+		} else
+			close(fd);
+	}
+
+	/* Did we get wine exe from cmdline? */
+	if (wine_exe)
+		LOG_MSG("Detected wine exe for client %d [%s].\n", pid, wine_exe);
+	else
+		goto fail_cmdline;
+
+	/* Open the process environment and find the WINEPREFIX */
+	errno = 0;
+	if (!(wineprefix = game_mode_lookup_proc_env(proc_fd, "WINEPREFIX"))) {
+		/* Lookup user home instead only if there was no error */
+		char *home = NULL;
+		if (errno == 0)
+			home = game_mode_lookup_user_home();
+
+		/* Append "/.wine" if we found the user home */
+		if (home)
+			wineprefix = safe_snprintf(buffer, "%s/.wine", home);
+
+		/* Cleanup and check result */
+		free(home);
+		if (!wineprefix)
+			goto fail_env;
+	}
+
+	/* Wine prefix was detected, log this for diagnostics */
+	LOG_MSG("Detected wine prefix for client %d: '%s'\n", pid, wineprefix);
+
+	/* Convert Windows to Unix path separators */
+	char *ix = wine_exe;
+	while (ix != NULL)
+		(ix = strchr(ix, '\\')) && (*ix++ = '/');
+
+	/* Convert the drive letter to lcase because wine handles it this way in the prefix */
+	wine_exe[0] = (char)tolower(wine_exe[0]);
+
+	/* Convert relative wine exe path to full unix path */
+	char *wine_path = safe_snprintf(buffer, "%s/dosdevices/%s", wineprefix, wine_exe);
+	free(wine_exe);
+	wine_exe = wine_path ? realpath(wine_path, NULL) : NULL;
+	free(wine_path);
+
+	/* Fine? Successo? Fortuna! */
+	if (wine_exe)
+		LOG_MSG("Successfully mapped wine client %d [%s].\n", pid, wine_exe);
+	else
+		goto fail;
+
+error_cleanup:
+	close(proc_fd);
+	free(wineprefix);
+	free(proc_path);
+	return wine_exe;
+
+fail:
+	LOG_ERROR("Unable to find wine executable for client %d: %s\n", pid, strerror(errno));
+	goto error_cleanup;
+
+fail_cmdline:
+	LOG_ERROR("Wine loader has no accepted cmdline for client %d yet, deferring.\n", pid);
+	goto error_cleanup;
+
+fail_env:
+	LOG_ERROR("Failed to access process environment in '%s': %s\n", proc_path, strerror(errno));
+	goto error_cleanup;
+
+fail_proc:
+	LOG_ERROR("Failed to access process data in '%s': %s\n", proc_path, strerror(errno));
+	goto error_cleanup;
+}
+
 /**
  * Attempt to locate the exe for the process.
  * We might run into issues if the process is running under an odd umask.