Implemented GUI with zenity

Now the program is completely functional and is using zenity dialogues.
`sources` directory was renamed to `src`. UI related stuff was moved to
`src/gui/ui`.

src/sourcefs.c

@@ -0,0 +1,116 @@
+#define _GNU_SOURCE
+
+#include "sourcefs.h"
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+static struct source_files_handle {
+  int root_fd;
+} handle;
+
+const char *source_filename_translate(const char *filename) {
+  if (strcmp("/", filename) == 0) {
+    return ".";
+  } else {
+    return filename + 1;
+  }
+}
+
+int source_init(const char *root_path) {
+  int root_fd = open(root_path, O_PATH);
+
+  if (root_fd == -1) {
+    return -1;
+  }
+
+  handle.root_fd = root_fd;
+
+  return 0;
+}
+
+int source_mkdir(const char *filename, mode_t mode) {
+  const char *relative_filename = source_filename_translate(filename);
+  return mkdirat(handle.root_fd, relative_filename, mode);
+}
+
+int source_unlink(const char *filename) {
+  const char *relative_filename = source_filename_translate(filename);
+  return unlinkat(handle.root_fd, relative_filename, 0);
+}
+
+int source_stat(const char *restrict filename, struct stat *restrict statbuf) {
+  const char *relative_filename = source_filename_translate(filename);
+  return fstatat(handle.root_fd, relative_filename, statbuf, 0);
+}
+
+int source_rmdir(const char *filename) {
+  const char *relative_filename = source_filename_translate(filename);
+  return unlinkat(handle.root_fd, relative_filename, AT_REMOVEDIR);
+}
+
+int source_symlink(const char *target, const char *linkpath) {
+  const char *relative_linkpath = source_filename_translate(linkpath);
+  return symlinkat(target, handle.root_fd, relative_linkpath);
+}
+
+DIR *source_opendir(const char *filename) {
+  const char *relative_filename = source_filename_translate(filename);
+  int fd = openat(handle.root_fd, relative_filename, NULL);
+  if (fd < 0) {
+    perror("Openat failed");
+    return NULL;
+  }
+  DIR *dir_pointer = fdopendir(fd);
+  return dir_pointer;
+}
+
+int source_rename(const char *oldpath, const char *newpath) {
+  const char *relative_oldpath = source_filename_translate(oldpath);
+  const char *relative_newpath = source_filename_translate(newpath);
+  return renameat(handle.root_fd, relative_oldpath, handle.root_fd,
+                  relative_newpath);
+}
+
+int source_link(const char *oldpath, const char *newpath) {
+  const char *relative_oldpath = source_filename_translate(oldpath);
+  const char *relative_newpath = source_filename_translate(newpath);
+  return linkat(handle.root_fd, relative_oldpath, handle.root_fd,
+                relative_newpath, 0);
+  // NOTE: perhaps the flags here need to be reevaluated.
+}
+
+int source_chmod(const char *filename, mode_t mode) {
+  const char *relative_filename = source_filename_translate(filename);
+  return fchmodat(handle.root_fd, relative_filename, mode, 0);
+  // NOTE: perhaps the flags here need to be reevaluated.
+}
+
+int source_chown(const char *filename, uid_t owner, gid_t group) {
+  const char *relative_filename = source_filename_translate(filename);
+  return fchownat(handle.root_fd, filename, owner, group, AT_SYMLINK_NOFOLLOW);
+}
+
+int source_truncate(const char *filename, off_t length) {
+  const char *relative_filename = source_filename_translate(filename);
+  int fd = openat(handle.root_fd, relative_filename, NULL);
+  if (fd < 0) {
+    perror("Openat failed");
+    return -1;
+  }
+  return ftruncate(fd, length);
+}
+
+int source_open(const char *filename, int flags) {
+  const char *relative_filename = source_filename_translate(filename);
+  return openat(handle.root_fd, relative_filename, flags);
+}
+
+int source_create(const char *filename, int flags, mode_t mode) {
+  const char *relative_filename = source_filename_translate(filename);
+  return openat(handle.root_fd, relative_filename, flags, mode);
+}