libroot: Add a private __look_up_in_path function.

Refactored out of execvpe. Originally I did this for my attempted
change to posix_spawn, but that change turned out to be wrong and
actually not that beneficial. This bit seems potentially useful,
though, so here it is.

headers/private/libroot/libroot_private.h

@@ -23,6 +23,7 @@ extern int __gABIVersion;
 extern char _single_threaded;
 	/* This determines if a process runs single threaded or not */
 
+status_t __look_up_in_path(const char *name, char *buffer);
 status_t __parse_invoke_line(char *invoker, char ***_newArgs,
 			char * const **_oldArgs, int32 *_argCount, const char *arg0);
 status_t __get_next_image_dependency(image_id id, uint32 *cookie,

src/system/libroot/os/image.cpp

@@ -314,6 +314,55 @@ clear_caches(void *address, size_t length, uint32 flags)
 //	#pragma mark -
 
 
+status_t
+__look_up_in_path(const char *file, char *buffer)
+{
+	// get the PATH
+	const char* paths = getenv("PATH");
+	if (paths == NULL)
+		return B_ENTRY_NOT_FOUND;
+
+	int fileNameLen = strlen(file);
+
+	// iterate through the paths
+	const char* pathEnd = paths - 1;
+	while (pathEnd != NULL) {
+		paths = pathEnd + 1;
+		pathEnd = strchr(paths, ':');
+		int pathLen = (pathEnd ? pathEnd - paths : strlen(paths));
+
+		// We skip empty paths and those that would become too long.
+		// The latter is not really correct, but practically irrelevant.
+		if (pathLen == 0
+			|| pathLen + 1 + fileNameLen >= B_PATH_NAME_LENGTH) {
+			continue;
+		}
+
+		// concatinate the program path
+		char path[B_PATH_NAME_LENGTH];
+		memcpy(path, paths, pathLen);
+		path[pathLen] = '\0';
+
+		if (path[pathLen - 1] != '/')
+			strcat(path, "/");
+		strcat(path, file);
+
+		// check whether it is a file
+		struct stat st;
+		if (stat(path, &st) != 0 || !S_ISREG(st.st_mode))
+			continue;
+
+		// if executable, we've found what we are looking for
+		if (access(path, X_OK) == 0) {
+			strlcpy(buffer, path, B_PATH_NAME_LENGTH);
+			return B_OK;
+		}
+	}
+
+	return B_ENTRY_NOT_FOUND;
+}
+
+
 static char *
 next_argument(char **_start, bool separate)
 {

src/system/libroot/posix/unistd/exec.cpp

@@ -157,50 +157,14 @@ execvpe(const char* file, char* const argv[], char* const environment[])
 
 	// file is just a leaf name, so we have to look it up in the path
 
-	// get the PATH
-	const char* paths = getenv("PATH");
-	if (paths == NULL) {
-		__set_errno(B_ENTRY_NOT_FOUND);
+	char path[B_PATH_NAME_LENGTH];
+	status_t status = __look_up_in_path(file, path);
+	if (status != B_OK) {
+		__set_errno(status);
 		return -1;
 	}
 
-	int fileNameLen = strlen(file);
-
-	// iterate through the paths
-	const char* pathEnd = paths - 1;
-	while (pathEnd != NULL) {
-		paths = pathEnd + 1;
-		pathEnd = strchr(paths, ':');
-		int pathLen = (pathEnd ? pathEnd - paths : strlen(paths));
-
-		// We skip empty paths and those that would become too long.
-		// The latter is not really correct, but practically irrelevant.
-		if (pathLen == 0
-			|| pathLen + 1 + fileNameLen >= B_PATH_NAME_LENGTH) {
-			continue;
-		}
-
-		// concatinate the program path
-		char path[B_PATH_NAME_LENGTH];
-		memcpy(path, paths, pathLen);
-		path[pathLen] = '\0';
-
-		if (path[pathLen - 1] != '/')
-			strcat(path, "/");
-		strcat(path, file);
-
-		// check whether it is a file
-		struct stat st;
-		if (stat(path, &st) != 0 || !S_ISREG(st.st_mode))
-			continue;
-
-		// if executable, execute it
-		if (access(path, X_OK) == 0)
-			return do_exec(path, argv, environment, true);
-	}
-
-	__set_errno(B_ENTRY_NOT_FOUND);
-	return -1;
+	return do_exec(path, argv, environment, true);
 }