block/blklogwrites: Add an option for the update interval of the log superblock

This is a way to ensure that the log superblock is periodically
updated. Before, this was only done on flush requests, which may
not be enough if the VM exits abnormally, omitting the final flush.

The default interval is 4096 write requests.

Signed-off-by: Ari Sundholm <[email protected]>
Signed-off-by: Kevin Wolf <[email protected]>

diff --git a/block/blklogwrites.c b/block/blklogwrites.c
index 56154e7325a8f6713e0667ed974249059ab6f9df..63bf6b34a91a4ae216c5e866fad8a8e77c8cc3ef 100644 (file)
--- a/block/blklogwrites.c
+++ b/block/blklogwrites.c
@@ -55,6 +55,7 @@ typedef struct {
     uint32_t sectorbits;
     uint64_t cur_log_sector;
     uint64_t nr_entries;
+    uint64_t update_interval;
 } BDRVBlkLogWritesState;
 
 static QemuOptsList runtime_opts = {
@@ -71,6 +72,11 @@ static QemuOptsList runtime_opts = {
             .type = QEMU_OPT_SIZE,
             .help = "Log sector size",
         },
+        {
+            .name = "log-super-update-interval",
+            .type = QEMU_OPT_NUMBER,
+            .help = "Log superblock update interval (# of write requests)",
+        },
         { /* end of list */ }
     },
 };
@@ -234,6 +240,14 @@ static int blk_log_writes_open(BlockDriverState *bs, QDict *options, int flags,
 
     s->sectorsize = log_sector_size;
     s->sectorbits = blk_log_writes_log2(log_sector_size);
+    s->update_interval = qemu_opt_get_number(opts, "log-super-update-interval",
+                                             4096);
+    if (!s->update_interval) {
+        ret = -EINVAL;
+        error_setg(errp, "Invalid log superblock update interval %"PRIu64,
+                   s->update_interval);
+        goto fail_log;
+    }
 
     ret = 0;
 fail_log:
@@ -360,8 +374,10 @@ static void coroutine_fn blk_log_writes_co_do_log(BlkLogWritesLogReq *lr)
                                             lr->zero_size, 0);
     }
 
-    /* Update super block on flush */
-    if (lr->log_ret == 0 && lr->entry.flags & LOG_FLUSH_FLAG) {
+    /* Update super block on flush or every update interval */
+    if (lr->log_ret == 0 && ((lr->entry.flags & LOG_FLUSH_FLAG)
+        || (s->nr_entries % s->update_interval == 0)))
+    {
         struct log_write_super super = {
             .magic      = cpu_to_le64(WRITE_LOG_MAGIC),
             .version    = cpu_to_le64(WRITE_LOG_VERSION),

diff --git a/qapi/block-core.json b/qapi/block-core.json
index d1753a2ae7d3a717dc907a765c8e811a82e18b4a..38b31250f937dd4e62fa3907424f8b703eec252f 100644 (file)
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -3057,13 +3057,17 @@
 # @log-sector-size: sector size used in logging writes to @file, determines
 #                   granularity of offsets and sizes of writes (default: 512)
 #
+# @log-super-update-interval: interval of write requests after which the log
+#                             super block is updated to disk (default: 4096)
+#
 # Since: 3.0
 ##
 { 'struct': 'BlockdevOptionsBlklogwrites',
   'data': { 'file': 'BlockdevRef',
             'log': 'BlockdevRef',
             '*log-sector-size': 'uint32',
-            '*log-append': 'bool' } }
+            '*log-append': 'bool',
+            '*log-super-update-interval': 'uint64' } }
 
 ##
 # @BlockdevOptionsBlkverify: