bcachefs: twf: convert bch2_stdio_redirect_readline() to darray

We now read the line from the buffer atomically, which means we have to
allow the buffer to grow past STDIO_REDIRECT_BUFSIZE if we're waiting
for a full line - this behaviour is necessary for
stdio_redirect_readline_timeout() in the next patch.
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/error.c

@@ -109,18 +109,21 @@ static enum ask_yn bch2_fsck_ask_yn(struct bch_fs *c)
 	if (!stdio)
 		return YN_NO;
 
-	char buf[100];
+	darray_char line = {};
 	int ret;
 
 	do {
 		bch2_print(c, " (y,n, or Y,N for all errors of this type) ");
 
-		int r = bch2_stdio_redirect_readline(stdio, buf, sizeof(buf) - 1);
-		if (r < 0)
-			return YN_NO;
-		buf[r] = '\0';
-	} while ((ret = parse_yn_response(buf)) < 0);
+		int r = bch2_stdio_redirect_readline(stdio, &line);
+		if (r < 0) {
+			ret = YN_NO;
+			break;
+		}
+		darray_last(line) = '\0';
+	} while ((ret = parse_yn_response(line.data)) < 0);
 
+	darray_exit(&line);
 	return ret;
 }
 #else

fs/bcachefs/thread_with_file.c

@@ -67,9 +67,14 @@ int bch2_run_thread_with_file(struct thread_with_file *thr,
 
 /* stdio_redirect */
 
+static bool stdio_redirect_has_more_input(struct stdio_redirect *stdio, size_t seen)
+{
+	return stdio->input.buf.nr > seen || stdio->done;
+}
+
 static bool stdio_redirect_has_input(struct stdio_redirect *stdio)
 {
-	return stdio->input.buf.nr || stdio->done;
+	return stdio_redirect_has_more_input(stdio, 0);
 }
 
 static bool stdio_redirect_has_output(struct stdio_redirect *stdio)
@@ -181,9 +186,13 @@ static ssize_t thread_with_stdio_write(struct file *file, const char __user *ubu
 		}
 
 		spin_lock(&buf->lock);
-		if (buf->buf.nr < STDIO_REDIRECT_BUFSIZE)
-			darray_make_room_gfp(&buf->buf,
-				min(b, STDIO_REDIRECT_BUFSIZE - buf->buf.nr), GFP_NOWAIT);
+		size_t makeroom = b;
+		if (!buf->waiting_for_line || memchr(buf->buf.data, '\n', buf->buf.nr))
+			makeroom = min_t(ssize_t, makeroom,
+				   max_t(ssize_t, STDIO_REDIRECT_BUFSIZE - buf->buf.nr,
+						  0));
+		darray_make_room_gfp(&buf->buf, makeroom, GFP_NOWAIT);
+
 		b = min(len, darray_room(buf->buf));
 
 		if (b && !copy_from_user_nofault(&darray_top(buf->buf), ubuf, b)) {
@@ -355,43 +364,48 @@ int bch2_stdio_redirect_read(struct stdio_redirect *stdio, char *ubuf, size_t le
 	return ret;
 }
 
-int bch2_stdio_redirect_readline(struct stdio_redirect *stdio, char *ubuf, size_t len)
+int bch2_stdio_redirect_readline(struct stdio_redirect *stdio, darray_char *line)
 {
 	struct stdio_buf *buf = &stdio->input;
-	size_t copied = 0;
-	ssize_t ret = 0;
+	size_t seen = 0;
 again:
-	do {
-		wait_event_timeout(buf->wait, stdio_redirect_has_input(stdio),
+	wait_event_timeout(buf->wait, stdio_redirect_has_more_input(stdio, seen),
 			   sysctl_hung_task_timeout_secs * HZ / 2);
-	} while (!stdio_redirect_has_input(stdio));
 
-	if (stdio->done) {
-		ret = -1;
-		goto out;
-	}
+	if (stdio->done)
+		return -1;
 
 	spin_lock(&buf->lock);
-	size_t b = min(len, buf->buf.nr);
-	char *n = memchr(buf->buf.data, '\n', b);
-	if (n)
-		b = min_t(size_t, b, n + 1 - buf->buf.data);
+	seen = buf->buf.nr;
+	char *n = memchr(buf->buf.data, '\n', seen);
+	if (!n) {
+		buf->waiting_for_line = true;
+		spin_unlock(&buf->lock);
+		goto again;
+	}
+
+	size_t b = n + 1 - buf->buf.data;
+	if (b > line->size) {
+		spin_unlock(&buf->lock);
+		int ret = darray_resize(line, b);
+		if (ret)
+			return ret;
+		seen = 0;
+		goto again;
+	}
+
 	buf->buf.nr -= b;
-	memcpy(ubuf, buf->buf.data, b);
+	memcpy(line->data, buf->buf.data, b);
 	memmove(buf->buf.data,
 		buf->buf.data + b,
 		buf->buf.nr);
-	ubuf += b;
-	len -= b;
-	copied += b;
+	line->nr = b;
+
+	buf->waiting_for_line = false;
 	spin_unlock(&buf->lock);
 
 	wake_up(&buf->wait);
-
-	if (!n && len)
-		goto again;
-out:
-	return copied ?: ret;
+	return 0;
 }
 
 __printf(3, 0)

fs/bcachefs/thread_with_file.h

@@ -71,7 +71,8 @@ int bch2_run_thread_with_stdio(struct thread_with_stdio *,
 int bch2_run_thread_with_stdout(struct thread_with_stdio *,
 				const struct thread_with_stdio_ops *);
 int bch2_stdio_redirect_read(struct stdio_redirect *, char *, size_t);
-int bch2_stdio_redirect_readline(struct stdio_redirect *, char *, size_t);
+
+int bch2_stdio_redirect_readline(struct stdio_redirect *, darray_char *);
 
 __printf(3, 0) ssize_t bch2_stdio_redirect_vprintf(struct stdio_redirect *, bool, const char *, va_list);
 __printf(3, 4) ssize_t bch2_stdio_redirect_printf(struct stdio_redirect *, bool, const char *, ...);

fs/bcachefs/thread_with_file_types.h

@@ -8,6 +8,7 @@ struct stdio_buf {
 	spinlock_t		lock;
 	wait_queue_head_t	wait;
 	darray_char		buf;
+	bool			waiting_for_line;
 };
 
 struct stdio_redirect {