xfsprogs: document environment variables

Document the various environment variables used in the code,
almost all are for debugging.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Eric Sandeen <sandeen@sandeen.net>

diff --git a/doc/README-env-vars.txt b/doc/README-env-vars.txt
new file mode 100644 (file)
index 0000000..eec59a8
--- /dev/null
+++ b/doc/README-env-vars.txt
@@ -0,0 +1,26 @@
+Several environment variables are used within the code, primarily for
+for debugging purposes; they are documented here.  In most cases simply
+setting the environment variable enables the behavior, but in some
+cases the value assigned influences behavior as well, as noted below.
+
+General
+-------
+LIBXFS_LEAK_CHECK            -- warn and exit(1) if zone-allocated memory
+                                is leaked at exit.
+xfs_fsr
+-------
+FSRXFSTEST                   -- enable -C nfrag in theory coalesces into
+                                nfrag extents.  Doesn't work.
+xfs_scrub
+---------
+Known debug tweaks (pass -d and set the environment variable):
+XFS_SCRUB_FORCE_ERROR        -- pretend all metadata is corrupt
+XFS_SCRUB_FORCE_REPAIR       -- repair all metadata even if it's ok
+XFS_SCRUB_NO_KERNEL          -- pretend there is no kernel ioctl
+XFS_SCRUB_NO_SCSI_VERIFY     -- disable SCSI VERIFY (if present)
+XFS_SCRUB_PHASE              -- run only this scrub phase
+XFS_SCRUB_THREADS            -- start exactly this number of threads
+
+Available even in non-debug mode:
+SERVICE_MODE                 -- compress all error codes to 1 for LSB
+                                service action compliance