[Qemu-devel] [PATCH v4 11/28] migration: convert post-copy to use QIOChannelBuffer

["Daniel P. Berrange" <berrange@redhat.com>]

The post-copy code does some I/O to/from an intermediate
in-memory buffer rather than direct to the underlying
I/O channel. Switch this code to use QIOChannelBuffer
instead of QEMUSizedBuffer.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 docs/migration.txt      |  4 ++--
 include/sysemu/sysemu.h |  2 +-
 migration/migration.c   | 15 +++++++--------
 migration/savevm.c      | 47 ++++++++++++++++-------------------------------
 4 files changed, 26 insertions(+), 42 deletions(-)

diff --git a/docs/migration.txt b/docs/migration.txt
index fda8d61..11703de 100644
--- a/docs/migration.txt
+++ b/docs/migration.txt
@@ -403,8 +403,8 @@ listen thread:                     --- page -- page -- page -- page -- page --
 
 On receipt of CMD_PACKAGED (1)
    All the data associated with the package - the ( ... ) section in the
-diagram - is read into memory (into a QEMUSizedBuffer), and the main thread
-recurses into qemu_loadvm_state_main to process the contents of the package (2)
+diagram - is read into memory, and the main thread recurses into
+qemu_loadvm_state_main to process the contents of the package (2)
 which contains commands (3,6) and devices (4...)
 
 On receipt of 'postcopy listen' - 3 -(i.e. the 1st command in the package)
diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 3bb8897..ea488de 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -120,7 +120,7 @@ void qemu_savevm_command_send(QEMUFile *f, enum qemu_vm_cmd command,
                               uint16_t len, uint8_t *data);
 void qemu_savevm_send_ping(QEMUFile *f, uint32_t value);
 void qemu_savevm_send_open_return_path(QEMUFile *f);
-int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb);
+int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len);
 void qemu_savevm_send_postcopy_advise(QEMUFile *f);
 void qemu_savevm_send_postcopy_listen(QEMUFile *f);
 void qemu_savevm_send_postcopy_run(QEMUFile *f);
diff --git a/migration/migration.c b/migration/migration.c
index 6b2e128..732ef84 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -34,6 +34,7 @@
 #include "qom/cpu.h"
 #include "exec/memory.h"
 #include "exec/address-spaces.h"
+#include "io/channel-buffer.h"
 
 #define MAX_THROTTLE  (32 << 20)      /* Migration transfer speed throttling */
 
@@ -1449,7 +1450,8 @@ static int await_return_path_close_on_source(MigrationState *ms)
 static int postcopy_start(MigrationState *ms, bool *old_vm_running)
 {
     int ret;
-    const QEMUSizedBuffer *qsb;
+    QIOChannelBuffer *bioc;
+    QEMUFile *fb;
     int64_t time_at_stop = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
     migrate_set_state(&ms->state, MIGRATION_STATUS_ACTIVE,
                       MIGRATION_STATUS_POSTCOPY_ACTIVE);
@@ -1508,11 +1510,9 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
      * So we wrap the device state up in a package with a length at the start;
      * to do this we use a qemu_buf to hold the whole of the device state.
      */
-    QEMUFile *fb = qemu_bufopen("w", NULL);
-    if (!fb) {
-        error_report("Failed to create buffered file");
-        goto fail;
-    }
+    bioc = qio_channel_buffer_new(4096);
+    fb = qemu_fopen_channel_output(QIO_CHANNEL(bioc));
+    object_unref(OBJECT(bioc));
 
     /*
      * Make sure the receiver can get incoming pages before we send the rest
@@ -1526,10 +1526,9 @@ static int postcopy_start(MigrationState *ms, bool *old_vm_running)
     qemu_savevm_send_postcopy_run(fb);
 
     /* <><> end of stuff going into the package */
-    qsb = qemu_buf_get(fb);
 
     /* Now send that blob */
-    if (qemu_savevm_send_packaged(ms->to_dst_file, qsb)) {
+    if (qemu_savevm_send_packaged(ms->to_dst_file, bioc->data, bioc->usage)) {
         goto fail_closefb;
     }
     qemu_fclose(fb);
diff --git a/migration/savevm.c b/migration/savevm.c
index 96e7db5..93b7454 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -50,6 +50,7 @@
 #include "qemu/iov.h"
 #include "block/snapshot.h"
 #include "block/qapi.h"
+#include "io/channel-buffer.h"
 
 
 #ifndef ETH_P_RARP
@@ -760,10 +761,8 @@ void qemu_savevm_send_open_return_path(QEMUFile *f)
  *    0 on success
  *    -ve on error
  */
-int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb)
+int qemu_savevm_send_packaged(QEMUFile *f, const uint8_t *buf, size_t len)
 {
-    size_t cur_iov;
-    size_t len = qsb_get_length(qsb);
     uint32_t tmp;
 
     if (len > MAX_VM_CMD_PACKAGED_SIZE) {
@@ -777,18 +776,7 @@ int qemu_savevm_send_packaged(QEMUFile *f, const QEMUSizedBuffer *qsb)
     trace_qemu_savevm_send_packaged();
     qemu_savevm_command_send(f, MIG_CMD_PACKAGED, 4, (uint8_t *)&tmp);
 
-    /* all the data follows (concatinating the iov's) */
-    for (cur_iov = 0; cur_iov < qsb->n_iov; cur_iov++) {
-        /* The iov entries are partially filled */
-        size_t towrite = MIN(qsb->iov[cur_iov].iov_len, len);
-        len -= towrite;
-
-        if (!towrite) {
-            break;
-        }
-
-        qemu_put_buffer(f, qsb->iov[cur_iov].iov_base, towrite);
-    }
+    qemu_put_buffer(f, buf, len);
 
     return 0;
 }
@@ -1570,39 +1558,36 @@ static int loadvm_postcopy_handle_run(MigrationIncomingState *mis)
 static int loadvm_handle_cmd_packaged(MigrationIncomingState *mis)
 {
     int ret;
-    uint8_t *buffer;
-    uint32_t length;
-    QEMUSizedBuffer *qsb;
+    size_t length;
+    QIOChannelBuffer *bioc;
 
     length = qemu_get_be32(mis->from_src_file);
     trace_loadvm_handle_cmd_packaged(length);
 
     if (length > MAX_VM_CMD_PACKAGED_SIZE) {
-        error_report("Unreasonably large packaged state: %u", length);
+        error_report("Unreasonably large packaged state: %zu", length);
         return -1;
     }
-    buffer = g_malloc0(length);
-    ret = qemu_get_buffer(mis->from_src_file, buffer, (int)length);
+
+    bioc = qio_channel_buffer_new(length);
+    ret = qemu_get_buffer(mis->from_src_file,
+                          bioc->data,
+                          length);
     if (ret != length) {
-        g_free(buffer);
-        error_report("CMD_PACKAGED: Buffer receive fail ret=%d length=%d",
+        object_unref(OBJECT(bioc));
+        error_report("CMD_PACKAGED: Buffer receive fail ret=%d length=%zu",
                      ret, length);
         return (ret < 0) ? ret : -EAGAIN;
     }
+    bioc->usage += length;
     trace_loadvm_handle_cmd_packaged_received(ret);
 
-    /* Setup a dummy QEMUFile that actually reads from the buffer */
-    qsb = qsb_create(buffer, length);
-    g_free(buffer); /* Because qsb_create copies */
-    if (!qsb) {
-        error_report("Unable to create qsb");
-    }
-    QEMUFile *packf = qemu_bufopen("r", qsb);
+    QEMUFile *packf = qemu_fopen_channel_input(QIO_CHANNEL(bioc));
 
     ret = qemu_loadvm_state_main(packf, mis);
     trace_loadvm_handle_cmd_packaged_main(ret);
     qemu_fclose(packf);
-    qsb_free(qsb);
+    object_unref(OBJECT(bioc));
 
     return ret;
 }
-- 
2.5.0