[PATCH] fix "fsck -A" failure on a completely clean fs

[Denys Vlasenko <dvlasenk@xxxxxxxxxx>]

Before remounting root fs and mounting local filesystems
in /etc/fstab, my boot scripts check them for errors with:

if ! fsck -A; then
        echo "fsck exit code: $?. Boot will not continue."
        while true; do sleep 9999; done
fi
mount -o remount,rw /
mount -a

Looks like something very straightforward, right?

I have two filesystems in /etc/fstab:
/dev/sda2 /                       ext4    defaults        1 1
/dev/sda1 /boot                   ext4    defaults        1 2

If I use fsck from util-linux-2.33.2-1.fc31.x86_64 (IOW: rather recent code),
it starts two instances of fsck.ext4 (all is fine with it).

The second one's stdio is redirected (probably to /dev/null),
it is no longer the tty. (Which is fine too).

But now we hit a problem. Second fsck.ext4 flat out refuses to do its job,
even before it looks at the filesystem.

Therefore, this condition does not trigger:
        if (getenv("E2FSCK_FORCE_INTERACTIVE") || (isatty(0) && isatty(1))) {
                ctx->interactive = 1;
        }
and ctx->interactive stays 0.
Therefore, later in main() fsck.ext4 dies with this message:
        if (!(ctx->options & E2F_OPT_PREEN) &&
            !(ctx->options & E2F_OPT_NO) &&
            !(ctx->options & E2F_OPT_YES)) {
                if (!ctx->interactive)
                        fatal_error(ctx,
                                    _("need terminal for interactive repairs"));
        }

This happens BEFORE any repairs are deemed necessary, IOW: it happens ALWAYS,
even if filesystem is completely fine.

IOW: "fsck -A" is *completely unusable* in this scenario.
I believe this is wrong. It is intended to be the generic, fs-agnostic way
to run fsck's on all /etc/fstab filesystems.

I propose to change the code so that this abort happens only if we
indeed need to interactively ask something.

Tested patch attached.

Fedora BZ: https://bugzilla.redhat.com/show_bug.cgi?id=1702342

diff -uprN e2fsprogs-1.44.4.orig/e2fsck/unix.c e2fsprogs-1.44.4/e2fsck/unix.c
--- e2fsprogs-1.44.4.orig/e2fsck/unix.c	2018-08-19 04:26:58.000000000 +0200
+++ e2fsprogs-1.44.4/e2fsck/unix.c	2019-04-23 15:38:55.890507270 +0200
@@ -1439,13 +1439,6 @@ int main (int argc, char *argv[])
 
 	check_mount(ctx);
 
-	if (!(ctx->options & E2F_OPT_PREEN) &&
-	    !(ctx->options & E2F_OPT_NO) &&
-	    !(ctx->options & E2F_OPT_YES)) {
-		if (!ctx->interactive)
-			fatal_error(ctx,
-				    _("need terminal for interactive repairs"));
-	}
 	ctx->superblock = ctx->use_superblock;
 
 	flags = EXT2_FLAG_SKIP_MMP;
diff -uprN e2fsprogs-1.44.4.orig/e2fsck/util.c e2fsprogs-1.44.4/e2fsck/util.c
--- e2fsprogs-1.44.4.orig/e2fsck/util.c	2018-08-19 04:26:58.000000000 +0200
+++ e2fsprogs-1.44.4/e2fsck/util.c	2019-04-23 15:39:27.571448855 +0200
@@ -203,6 +203,14 @@ int ask_yn(e2fsck_t ctx, const char * st
 	const char	*extra_prompt = "";
 	static int	yes_answers;
 
+	if (!(ctx->options & E2F_OPT_PREEN) &&
+	    !(ctx->options & E2F_OPT_NO) &&
+	    !(ctx->options & E2F_OPT_YES)) {
+		if (!ctx->interactive)
+			fatal_error(ctx,
+				    _("need terminal for interactive repairs"));
+	}
+
 #ifdef HAVE_TERMIOS_H
 	struct termios	termios, tmp;