Merge pull request #2887 from brauner/2019-03-01/coding_style_updates

CODING_STYLE.md

@@ -662,3 +662,123 @@ int lxc_attach_run_command(void *payload)
 	return ret;
 }
 ```
+
+## 24) Never use `fgets()`
+
+LXC does not allow the use of `fgets()`. Use `getline()` or other methods
+instead.
+
+## 25) Never allocate memory on the stack
+
+This specifically forbids any usage of `alloca()` in the codebase.
+
+## 26) Use cleanup macros supported by `gcc` and `clang`
+
+LXC has switched from manually cleaning up resources to using cleanup macros
+supported by `gcc` and `clang`:
+```c
+__attribute__((__cleanup__(<my-cleanup-function-wrapper>)))
+```
+We do not allow manually cleanups anymore if there are appropriate macros.
+Currently the following macros are supported:
+```c
+/* close file descriptor */
+__do_close_prot_errno
+
+/* free allocated memory */
+__do_free __attribute__((__cleanup__(__auto_free__)))
+
+/* close FILEs */
+__do_fclose __attribute__((__cleanup__(__auto_fclose__)))
+
+/* close DIRs */
+__do_closedir __attribute__((__cleanup__(__auto_closedir__)))
+```
+For example:
+```c
+void remount_all_slave(void)
+{
+	__do_free char *line = NULL;
+	__do_fclose FILE *f = NULL;
+	__do_close_prot_errno int memfd = -EBADF, mntinfo_fd = -EBADF;
+	int ret;
+	ssize_t copied;
+	size_t len = 0;
+
+	mntinfo_fd = open("/proc/self/mountinfo", O_RDONLY | O_CLOEXEC);
+	if (mntinfo_fd < 0) {
+		SYSERROR("Failed to open \"/proc/self/mountinfo\"");
+		return;
+	}
+
+	memfd = memfd_create(".lxc_mountinfo", MFD_CLOEXEC);
+	if (memfd < 0) {
+		char template[] = P_tmpdir "/.lxc_mountinfo_XXXXXX";
+
+		if (errno != ENOSYS) {
+			SYSERROR("Failed to create temporary in-memory file");
+			return;
+		}
+
+		memfd = lxc_make_tmpfile(template, true);
+		if (memfd < 0) {
+			WARN("Failed to create temporary file");
+			return;
+		}
+	}
+
+again:
+	copied = lxc_sendfile_nointr(memfd, mntinfo_fd, NULL, LXC_SENDFILE_MAX);
+	if (copied < 0) {
+		if (errno == EINTR)
+			goto again;
+
+		SYSERROR("Failed to copy \"/proc/self/mountinfo\"");
+		return;
+	}
+
+	ret = lseek(memfd, 0, SEEK_SET);
+	if (ret < 0) {
+		SYSERROR("Failed to reset file descriptor offset");
+		return;
+	}
+
+	f = fdopen(memfd, "r");
+	if (!f) {
+		SYSERROR("Failed to open copy of \"/proc/self/mountinfo\" to mark all shared. Continuing");
+		return;
+	}
+
+	/*
+	 * After a successful fdopen() memfd will be closed when calling
+	 * fclose(f). Calling close(memfd) afterwards is undefined.
+	 */
+	move_fd(memfd);
+
+	while (getline(&line, &len, f) != -1) {
+		char *opts, *target;
+
+		target = get_field(line, 4);
+		if (!target)
+			continue;
+
+		opts = get_field(target, 2);
+		if (!opts)
+			continue;
+
+		null_endofword(opts);
+		if (!strstr(opts, "shared"))
+			continue;
+
+		null_endofword(target);
+		ret = mount(NULL, target, NULL, MS_SLAVE, NULL);
+		if (ret < 0) {
+			SYSERROR("Failed to make \"%s\" MS_SLAVE", target);
+			ERROR("Continuing...");
+			continue;
+		}
+		TRACE("Remounted \"%s\" as MS_SLAVE", target);
+	}
+	TRACE("Remounted all mount table entries as MS_SLAVE");
+}
+```