[PATCH 3/3] Document the use of BTRFS_UNIT in man page.

[Goffredo Baroncelli <kreijack@gmail.com>]

From: Goffredo Baroncelli <kreijack@inwind.it>

---
 man/btrfs.8.in |   14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/man/btrfs.8.in b/man/btrfs.8.in
index 9222580..fe7a5e3 100644
--- a/man/btrfs.8.in
+++ b/man/btrfs.8.in
@@ -355,6 +355,20 @@ not enough to read all the resolved results. The max value one can set is 64k.
 \fBbtrfs\fR returns a zero exist status if it succeeds. Non zero is returned in
 case of failure.
 
+.SH ENVIRONMENTAL VARIABLES
+\fBBTRFS_UNIT\fR set the kind of suffix for the number output by \fBbtrfs\fR. 
+Possible values:
+.RS
+.IP BTRFS_UNIT=IEC
+The number have the IEC suffix: e.g. KiB = 1024 bytes, MiB = 1024 KiB...
+.IP BTRFS_UNIT=SI 
+The number have the SI suffix: e.g. KB = 1000 bytes, MB = 1000 KB...
+.IP BTRFS_UNIT=COMPACT
+For compatibility; the number have the SI suffix but the unit is multiply
+of power of two. E.g. KB = 1024 bytes, MB = 1024 KiB...
+There is no space between the number and the suffix.
+.RE
+
 .SH AVAILABILITY
 .B btrfs
 is part of btrfs-progs. Btrfs filesystem is currently under heavy development,
-- 
1.7.10.4