[PATCH] btrfs-progs: warn users about the possible dangers of check --repair

[Johannes Thumshirn <jthumshirn@suse.de>]

The manual page of btrfsck clearly states 'btrfs check --repair' is a
dangerous operation.

Although this warning is in place users do not read the manual page and/or
are used to the behaviour of fsck utilities which repair the filesystem,
and thus potentially cause harm.

Similar to 'btrfs balance' without any filters, add a warning and a
countdown, so users can bail out before eventual corrupting the filesystem
more than it already is.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
---
 check/main.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/check/main.c b/check/main.c
index fd05430c1f51..acded927281a 100644
--- a/check/main.c
+++ b/check/main.c
@@ -9970,6 +9970,23 @@ static int cmd_check(const struct cmd_struct *cmd, int argc, char **argv)
 		exit(1);
 	}
 
+	if (repair) {
+		int delay = 10;
+		printf("WARNING:\n\n");
+		printf("\tDo not use --repair unless you are advised to do so by a developer\n");
+		printf("\tor an experienced user, and then only after having accepted that no\n");
+		printf("\tfsck successfully repair all types of filesystem corruption. Eg.\n");
+		printf("\tsome other software or hardware bugs can fatally damage a volume.\n");
+		printf("\tThe operation will start in %d seconds.\n", delay);
+		printf("\tUse Ctrl-C to stop it.\n");
+		while (delay) {
+			printf("%2d", delay--);
+			fflush(stdout);
+			sleep(1);
+		}
+		printf("\nStarting repair.\n");
+	}
+
 	/*
 	 * experimental and dangerous
 	 */
-- 
2.16.4