Auto-guess atomic_write_size from /sys

src/blockstore/blockstore_disk.cpp

@@ -52,6 +52,8 @@ void blockstore_disk_t::parse_config(std::map<std::string, std::string> & config
     meta_format = stoull_full(config["meta_format"]);
     atomic_write_size = (config.find("atomic_write_size") != config.end()
         ? parse_size(config["atomic_write_size"]) : 4096);
+    use_atomic_flag = config.find("use_atomic_flag") != config.end() &&
+        (config["use_atomic_flag"] == "true" || config["use_atomic_flag"] == "1" || config["use_atomic_flag"] == "yes");
     if (config.find("data_io") == config.end() &&
         config.find("meta_io") == config.end() &&
         config.find("journal_io") == config.end())

src/blockstore/blockstore_disk.h

@@ -36,6 +36,8 @@ struct blockstore_disk_t
     uint32_t meta_block_size = 4096;
     // Atomic write size of the data block device
     uint32_t atomic_write_size = 4096;
+    // Whether we should set RWF_ATOMIC on atomic writes
+    bool use_atomic_flag = false;
     // Sparse write tracking granularity. 4 KB is a good choice. Must be a multiple of disk_alignment
     uint32_t bitmap_granularity = 4096;
     // Data checksum type, BLOCKSTORE_CSUM_NONE or BLOCKSTORE_CSUM_CRC32C

src/blockstore/blockstore_internal.h

@@ -48,3 +48,7 @@
 #define COPY_BUF_COALESCED  0x10
 #define COPY_BUF_PADDED     0x20
 #define COPY_BUF_SKIP_CSUM  0x40
+
+#ifndef RWF_ATOMIC
+#define RWF_ATOMIC 0x40
+#endif

src/blockstore/blockstore_write.cpp

@@ -444,6 +444,8 @@ resume_10:
     data->iov = (struct iovec){ op->buf, op->len };
     data->callback = [this, op](ring_data_t *data) { handle_write_event(data, op); };
     io_uring_prep_writev(sqe, dsk.data_fd, &data->iov, 1, dsk.data_offset + PRIV(op)->location + op->offset);
+    if (dsk.use_atomic_flag)
+        sqe->rw_flags = RWF_ATOMIC;
     PRIV(op)->pending_ops++;
     PRIV(op)->op_state = 7;
     return 1;