btrfs-progs: fix build, manpage compression command

man pages for btrfs-progs are compressed by gzip by default. In Makefile
the variable GZIP is use, this evaluates to 'gzip gzip' on my system.
>From man gzip:

> The environment variable GZIP can hold a set of default options for
> gzip. These options are interpreted first and can be overwritten by
> explicit command line parameters.

So using any other variable name fixes this.

Signed-off-by: Christian Hesse <mail@eworm.de>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: doc: fix symlink target for btrfsck.8

The manpage of btrfsck.8 is supposed to link to btrfs-check.8 .

Reported-by: WorMzy Tykashi <wormzy.tykashi@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: Add information about libblkid requirement to INSTALL file

Signed-off-by: Augusto Mecking Caringi <augustocaringi@gmail.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: clarify mkfs.btrfs --alloc-start option

Fedora had a bug where a poor user thought that --alloc-start
meant that the filesystem would be created at that offset into
the device, rather than just starting allocations at that offset.
A subtle difference, but worth clarifying, because the manpage
is misleading on this point.

The original commit log for this option says:

    Add mkfs.btrfs -A offset to control allocation start on devices

    This is a utility option for the resizer, it makes sure to allocate
    at offset bytes in the disk or higher.  It ensures the resizer will have
    something to move when testing it.

so allude to that intended use in the manpage.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
[converted to asciidoc]
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: clarify manpage for btrfstune seeding option

The btrfstune -S option accepts a positive value to enable seeding,
and a zero to disable seeding, negtive is not allowed.

Add "positive, zero, negative" sentences to btrfstune manpage.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>