btrfs-progs: random fixes for usage string of btrfs scrub

- Add missing description about "-R" option in the command
  usage of "btrfs scrub resume".

- Add missing comma to avoid the following misformatted command
  usage of "btrfs scrub start". See the line of "-R" option.

===
usage: btrfs scrub start [-BdqrRf] [-c ioprio_class -n ioprio_classdata] <path>|<device>

    Start a new scrub

    -B     do not background
    -d     stats per device (-B only)
    -q     be quiet
    -r     read only mode
    -R     raw print mode, print full data instead of summary-c     set ioprio class (see ionice(1) manpage)
    -n     set ioprio classdata (see ionice(1) manpage)
    -f     force to skip checking whether scrub has started/resumed in userspace
           this is useful when scrub stats record file is damaged
===

Signed-off-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: avoid to use numeric literal for the size of uuid buffer

Replace a numeric literal to more descriptive macro for
the size of uuid buffer.

Signed-of-by: Satoru Takeuchi <takeuchi_satoru@jp.fujitsu.com>

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: add ask_user confirmation for btrfstune clear seeding flag

If we do the following:
	# mkfs.btrfs -f <dev>
	# mount <dev> <mnt>
	# dd if=/dev/urandom of=<mnt>/data bs=1M count=100
	# umount <dev>
	# btrfstune -S 1 <dev> 		<--- make seeding device
	# mount <dev> <mnt>
	# btrfs dev add -f <dev2> <mnt>
	# umount <dev>
	# btrfstune -S 0 <dev>		<--- clear seeding flag
	# mount <dev2> <mnt>		<=== new device not mountable

When mounting the new device, btrfs will check whether
the seeding flag is set when try to open seeding device.
If the user clears the seeding flag of the seeding device,
the new device will not be mountable. Even set the seeding
flag back will not recovery this problem, because the generation
has been changed. So clear the seeding flag has the chance to
damage the derived new fs.

So I add user confirmation check when clearing seeding flag.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: fix unaligned loads in receive

A user reported corruption after receiving subvolumes.  Turning up the
logging during the receive showed that the commands and string
attributes were being received correctly but the u64 attrbutes were
sometimes corrupted by having variable number of low order bytes
introduced.

It turned out they were on a platform that corrupts unaligned userspace
loads.  Loading the u64s from the unaligned pointers into the received
command stream with get_unaligned() fixed the problem.

Reported-By: Klaus Holler <kho@gmx.at>
Tested-By: Klaus Holler <kho@gmx.at>
Signed-off-by: Zach Brown <zab@zabbo.net>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: Fix spelling in btrfs sub list help

"below", not "bellow"

Signed-off-by: Hugo Mills <hugo@carfax.org.uk>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: mkfs make --uuid require an argument

$ mkfs.btrfs --uuid 1234... /dev/sdx
Error: error checking 1234...  status: No such file or directory

Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: check: do not require argument for --subvol-extents

$ btrfs check --subvol-extents /dev/sdx
ERROR: /dev/sdx is not a valid numeric value.

Signed-off-by: David Sterba <dsterba@suse.cz>