bluestore: Fix BlueStore::statfs available amount to not include blue…

…fs min reserved

This fixes OSD crashes because checking osd_failsafe_full_ratio won't work
without accurate statfs information.

Signed-off-by: David Zafman <dzafman@redhat.com>

src/os/bluestore/BlueStore.cc

@@ -5424,8 +5424,10 @@ int BlueStore::statfs(struct store_statfs_t *buf)
   buf->available = alloc->get_free();
 
   if (bluefs) {
-    // part of our shared device is "free" accordingly to BlueFS
-    buf->available += bluefs->get_free(bluefs_shared_bdev);
+    // part of our shared device is "free" according to BlueFS
+    // Don't include bluestore_bluefs_min because that space can't
+    // be used for any other purpose.
+    buf->available += bluefs->get_free(bluefs_shared_bdev) - cct->_conf->bluestore_bluefs_min;
 
     // include dedicated db, too, if that isn't the shared device.
     if (bluefs_shared_bdev != BlueFS::BDEV_DB) {