check: document mkfs.xfs reliance on fstests exports

There are a number of fstests that employ special (and now unsupported)
XFS filesystem configurations to perform testing in a controlled
environment.  The presence of the QA_CHECK_FS and MSGVERB variables are
used by mkfs.xfs to detect that it's running inside fstests, which
enables the unsupported configurations.  Nobody else should be using
filesystems with tiny logs, non-redundant superblocks, or smaller than
the (new) minimum supported size.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/check b/check
index 2ea2920f76..4b0ebad63b 100755
--- a/check
+++ b/check
@@ -33,6 +33,9 @@ _err_msg=""
 # start the initialisation work now
 iam=check
 
+# mkfs.xfs uses the presence of both of these variables to enable formerly
+# supported tiny filesystem configurations that fstests use for fuzz testing
+# in a controlled environment
 export MSGVERB="text:action"
 export QA_CHECK_FS=${QA_CHECK_FS:=true}