fsck: add support for whole-disk locking (-l option)

This feature allows to call multiple independent fsck instances rather
than use only one "fsck -A" process.

The lock uses LOCK_EX flock(2). The lock request is ignored if the
whole-disk is non-rotating disk. The verbose mode (-V) provides
information about disk locking.

Note that "fsck -l" does not care if the device is stacked, for
example if you want to call "fsck -l /dev/md0" and "fsck -l /dev/md1"
then the underlying devices will not be locked. The traditional "fsck
-A" does not run in parallel for stacked devices.

Requested-by: Lennart Poettering <lennart@poettering.net>
Signed-off-by: Karel Zak <kzak@redhat.com>

1 files changed, 12 insertions, 1 deletions

diff --git a/fsck/fsck.8 b/fsck/fsck.8
index 9cf80785d..3d60ac08d 100644
--- a/fsck/fsck.8
+++ b/fsck/fsck.8
@@ -7,7 +7,7 @@
 fsck \- check and repair a Linux file system
 .SH SYNOPSIS
 .B fsck
-.RB [ \-sAVRTMNP ]
+.RB [ \-lsAVRTMNP ]
 .RB [ \-C
 .RI [ fd ]]
 .RB [ \-t
@@ -80,6 +80,17 @@ variable.  Please see the file system-specific checker manual pages for
 further details.
 .SH OPTIONS
 .TP
+.B \-l
+Lock whole-disk device by exclusive
+.BR flock (2).
+This option can be used with one device only (e.g. -A and -l are mutually
+exclusive). This option is recommended when more
+.B fsck (8)
+instances are executed in the same time. The option is ignored when used for
+multiple devices or for non-rotating disk. The fsck does not lock underlying
+devices if executed to check stacked devices (e.g. MD or DM) -- this feature is
+not implemented yet.
+.TP
 .B \-s
 Serialize
 .B fsck