From 78807eb24454077acbdde7b86ecdb19181c677c1 Mon Sep 17 00:00:00 2001
From: Vitaliy Filippov <vitalif@yourcmc.ru>
Date: Wed, 27 Nov 2019 11:35:11 +0300
Subject: [PATCH] Fix journal space check (do not overwrite the beginning of
 the journal)

---
 blockstore_journal.cpp | 8 ++++----
 blockstore_journal.h   | 1 +
 2 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/blockstore_journal.cpp b/blockstore_journal.cpp
index 937c19ec..047dccce 100644
--- a/blockstore_journal.cpp
+++ b/blockstore_journal.cpp
@@ -7,12 +7,12 @@ blockstore_journal_check_t::blockstore_journal_check_t(blockstore *bs)
     next_pos = bs->journal.next_free;
     next_sector = bs->journal.cur_sector;
     next_in_pos = bs->journal.in_sector_pos;
+    right_dir = next_pos >= bs->journal.used_start;
 }
 
 // Check if we can write <required> entries of <size> bytes and <data_after> data bytes after them to the journal
 int blockstore_journal_check_t::check_available(blockstore_operation *op, int required, int size, int data_after)
 {
-    bool wrapped = false;
     while (1)
     {
         int fits = (512 - next_in_pos) / size;
@@ -30,7 +30,7 @@ int blockstore_journal_check_t::check_available(blockstore_operation *op, int re
         if (next_pos >= bs->journal.len)
         {
             next_pos = 512;
-            wrapped = true;
+            right_dir = false;
         }
         next_in_pos = 0;
         if (bs->journal.sector_info[next_sector].usage_count > 0)
@@ -49,11 +49,11 @@ int blockstore_journal_check_t::check_available(blockstore_operation *op, int re
         next_pos = next_pos + data_after;
         if (next_pos > bs->journal.len)
         {
-            wrapped = true;
             next_pos = 512 + data_after;
+            right_dir = false;
         }
     }
-    if (wrapped && next_pos >= bs->journal.used_start)
+    if (!right_dir && next_pos >= bs->journal.used_start-512)
     {
         // No space in the journal. Wait for it.
         op->wait_for = WAIT_JOURNAL;
diff --git a/blockstore_journal.h b/blockstore_journal.h
index e2ff8192..7773c8c5 100644
--- a/blockstore_journal.h
+++ b/blockstore_journal.h
@@ -137,6 +137,7 @@ struct blockstore_journal_check_t
     blockstore *bs;
     uint64_t next_pos, next_sector, next_in_pos;
     int sectors_required;
+    bool right_dir; // writing to the end or the beginning of the ring buffer
 
     blockstore_journal_check_t(blockstore *bs);
     int check_available(blockstore_operation *op, int required, int size, int data_after);