[Qemu-devel] [PATCH v2 6/8] migration/ram: ensure write persistence on loading normal pages to PMEM

[Haozhong Zhang]

When loading a normal page to persistent memory, load its data by
libpmem function pmem_memcpy_nodrain() instead of memcpy(). Combined
with a call to pmem_drain() at the end of memory loading, we can
guarantee all those normal pages are persistenly loaded to PMEM.

Signed-off-by: Haozhong Zhang <address@hidden>
---
 include/migration/qemu-file-types.h |  1 +
 include/qemu/pmem.h                 |  6 ++++++
 migration/qemu-file.c               | 41 ++++++++++++++++++++++++++++---------
 migration/ram.c                     |  6 +++++-
 4 files changed, 43 insertions(+), 11 deletions(-)

diff --git a/include/migration/qemu-file-types.h 
b/include/migration/qemu-file-types.h
index bd6d7dd7f9..bb5c547498 100644
--- a/include/migration/qemu-file-types.h
+++ b/include/migration/qemu-file-types.h
@@ -34,6 +34,7 @@ void qemu_put_be16(QEMUFile *f, unsigned int v);
 void qemu_put_be32(QEMUFile *f, unsigned int v);
 void qemu_put_be64(QEMUFile *f, uint64_t v);
 size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size);
+size_t qemu_get_buffer_to_pmem(QEMUFile *f, uint8_t *buf, size_t size);
 
 int qemu_get_byte(QEMUFile *f);
 
diff --git a/include/qemu/pmem.h b/include/qemu/pmem.h
index 861d8ecc21..77ee1fc4eb 100644
--- a/include/qemu/pmem.h
+++ b/include/qemu/pmem.h
@@ -26,6 +26,12 @@ pmem_memcpy_persist(void *pmemdest, const void *src, size_t 
len)
     return memcpy(pmemdest, src, len);
 }
 
+static inline void *
+pmem_memcpy_nodrain(void *pmemdest, const void *src, size_t len)
+{
+    return memcpy(pmemdest, src, len);
+}
+
 static inline void *pmem_memset_nodrain(void *pmemdest, int c, size_t len)
 {
     return memset(pmemdest, c, len);
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 2ab2bf362d..7e573010d9 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -26,6 +26,7 @@
 #include "qemu-common.h"
 #include "qemu/error-report.h"
 #include "qemu/iov.h"
+#include "qemu/pmem.h"
 #include "migration.h"
 #include "qemu-file.h"
 #include "trace.h"
@@ -471,15 +472,8 @@ size_t qemu_peek_buffer(QEMUFile *f, uint8_t **buf, size_t 
size, size_t offset)
     return size;
 }
 
-/*
- * Read 'size' bytes of data from the file into buf.
- * 'size' can be larger than the internal buffer.
- *
- * It will return size bytes unless there was an error, in which case it will
- * return as many as it managed to read (assuming blocking fd's which
- * all current QEMUFile are)
- */
-size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size)
+static size_t
+qemu_get_buffer_common(QEMUFile *f, uint8_t *buf, size_t size, bool is_pmem)
 {
     size_t pending = size;
     size_t done = 0;
@@ -492,7 +486,11 @@ size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t 
size)
         if (res == 0) {
             return done;
         }
-        memcpy(buf, src, res);
+        if (!is_pmem) {
+            memcpy(buf, src, res);
+        } else {
+            pmem_memcpy_nodrain(buf, src, res);
+        }
         qemu_file_skip(f, res);
         buf += res;
         pending -= res;
@@ -501,6 +499,29 @@ size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t 
size)
     return done;
 }
 
+/*
+ * Read 'size' bytes of data from the file into buf.
+ * 'size' can be larger than the internal buffer.
+ *
+ * It will return size bytes unless there was an error, in which case it will
+ * return as many as it managed to read (assuming blocking fd's which
+ * all current QEMUFile are)
+ */
+size_t qemu_get_buffer(QEMUFile *f, uint8_t *buf, size_t size)
+{
+    return qemu_get_buffer_common(f, buf, size, false);
+}
+
+/*
+ * Mostly the same as qemu_get_buffer(), except that
+ * 1) it's for the case that 'buf' is in the persistent memory, and
+ * 2) it takes necessary operations to ensure the data persistence in 'buf'.
+ */
+size_t qemu_get_buffer_to_pmem(QEMUFile *f, uint8_t *buf, size_t size)
+{
+    return qemu_get_buffer_common(f, buf, size, true);
+}
+
 /*
  * Read 'size' bytes of data from the file.
  * 'size' can be larger than the internal buffer.
diff --git a/migration/ram.c b/migration/ram.c
index 5a0e503818..5a79bbff64 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -2950,7 +2950,11 @@ static int ram_load(QEMUFile *f, void *opaque, int 
version_id)
             break;
 
         case RAM_SAVE_FLAG_PAGE:
-            qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
+            if (!is_pmem) {
+                qemu_get_buffer(f, host, TARGET_PAGE_SIZE);
+            } else {
+                qemu_get_buffer_to_pmem(f, host, TARGET_PAGE_SIZE);
+            }
             break;
 
         case RAM_SAVE_FLAG_COMPRESS_PAGE:
-- 
2.14.1