e2fsck: Support a negative argument to -C to suppress progress information

If a negative progress argument is given to -C, initially suppress the
progress information.  It can be enabled later by sending the e2fsck
process a SIGUSR1 signal.

Addresses-Launchpad-Bug: #203323
Addresses-Sourceforge-Bug: #1926023

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
2 files changed