[PULL,12/42] nbd-server: Use a separate BlockBackend

Commit Message

Kevin Wolf Sept. 5, 2016, 6:13 p.m. UTC

The builtin NBD server uses its own BlockBackend now instead of reusing
the monitor/guest device one.

This means that it has its own writethrough setting now. The builtin
NBD server always uses writeback caching now regardless of whether the
guest device has WCE enabled. qemu-nbd respects the cache mode given on
the command line.

We still need to keep a reference to the monitor BB because we put an
eject notifier on it, but we don't use it for any I/O.

Signed-off-by: Kevin Wolf <[e-mail]>
Reviewed-by: Eric Blake <[e-mail]>
Reviewed-by: Max Reitz <[e-mail]>
---
 block.c             |  2 ++
 blockdev-nbd.c      |  4 ++--
 include/block/nbd.h |  3 ++-
 nbd/server.c        | 25 ++++++++++++++++++++-----
 qemu-nbd.c          |  4 ++--
 5 files changed, 28 insertions(+), 10 deletions(-)

Patch

diff --git a/block.c b/block.c
index 30d64e6..101f8c6 100644
--- a/block.c
+++ b/block.c
@@ -25,6 +25,7 @@ 
 #include "trace.h"
 #include "block/block_int.h"
 #include "block/blockjob.h"
+#include "block/nbd.h"
 #include "qemu/error-report.h"
 #include "qemu/module.h"
 #include "qapi/qmp/qerror.h"
@@ -2206,6 +2207,7 @@  static void bdrv_close(BlockDriverState *bs)
 void bdrv_close_all(void)
 {
     block_job_cancel_sync_all();
+    nbd_export_close_all();
 
     /* Drop references from requests still in flight, such as canceled block
      * jobs whose AIO context has not been polled yet */
diff --git a/blockdev-nbd.c b/blockdev-nbd.c
index 12cae0e..c437d32 100644
--- a/blockdev-nbd.c
+++ b/blockdev-nbd.c
@@ -176,8 +176,8 @@  void qmp_nbd_server_add(const char *device, bool has_writable, bool writable,
         writable = false;
     }
 
-    exp = nbd_export_new(blk, 0, -1, writable ? 0 : NBD_FLAG_READ_ONLY, NULL,
-                         errp);
+    exp = nbd_export_new(blk_bs(blk), 0, -1, writable ? 0 : NBD_FLAG_READ_ONLY,
+                         NULL, false, blk, errp);
     if (!exp) {
         return;
     }
diff --git a/include/block/nbd.h b/include/block/nbd.h
index 1897557..80610ff 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -103,8 +103,9 @@  int nbd_disconnect(int fd);
 typedef struct NBDExport NBDExport;
 typedef struct NBDClient NBDClient;
 
-NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
+NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
                           uint16_t nbdflags, void (*close)(NBDExport *),
+                          bool writethrough, BlockBackend *on_eject_blk,
                           Error **errp);
 void nbd_export_close(NBDExport *exp);
 void nbd_export_get(NBDExport *exp);
diff --git a/nbd/server.c b/nbd/server.c
index 80fbb4d..472f584 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -69,6 +69,7 @@  struct NBDExport {
 
     AioContext *ctx;
 
+    BlockBackend *eject_notifier_blk;
     Notifier eject_notifier;
 };
 
@@ -807,11 +808,18 @@  static void nbd_eject_notifier(Notifier *n, void *data)
     nbd_export_close(exp);
 }
 
-NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
+NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset, off_t size,
                           uint16_t nbdflags, void (*close)(NBDExport *),
+                          bool writethrough, BlockBackend *on_eject_blk,
                           Error **errp)
 {
+    BlockBackend *blk;
     NBDExport *exp = g_malloc0(sizeof(NBDExport));
+
+    blk = blk_new();
+    blk_insert_bs(blk, bs);
+    blk_set_enable_write_cache(blk, !writethrough);
+
     exp->refcount = 1;
     QTAILQ_INIT(&exp->clients);
     exp->blk = blk;
@@ -827,11 +835,14 @@  NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
 
     exp->close = close;
     exp->ctx = blk_get_aio_context(blk);
-    blk_ref(blk);
     blk_add_aio_context_notifier(blk, blk_aio_attached, blk_aio_detach, exp);
 
-    exp->eject_notifier.notify = nbd_eject_notifier;
-    blk_add_remove_bs_notifier(blk, &exp->eject_notifier);
+    if (on_eject_blk) {
+        blk_ref(on_eject_blk);
+        exp->eject_notifier_blk = on_eject_blk;
+        exp->eject_notifier.notify = nbd_eject_notifier;
+        blk_add_remove_bs_notifier(on_eject_blk, &exp->eject_notifier);
+    }
 
     /*
      * NBD exports are used for non-shared storage migration.  Make sure
@@ -844,6 +855,7 @@  NBDExport *nbd_export_new(BlockBackend *blk, off_t dev_offset, off_t size,
     return exp;
 
 fail:
+    blk_unref(blk);
     g_free(exp);
     return NULL;
 }
@@ -914,7 +926,10 @@  void nbd_export_put(NBDExport *exp)
         }
 
         if (exp->blk) {
-            notifier_remove(&exp->eject_notifier);
+            if (exp->eject_notifier_blk) {
+                notifier_remove(&exp->eject_notifier);
+                blk_unref(exp->eject_notifier_blk);
+            }
             blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
                                             blk_aio_detach, exp);
             blk_unref(exp->blk);
diff --git a/qemu-nbd.c b/qemu-nbd.c
index e3571c2..99297a5 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -910,8 +910,8 @@  int main(int argc, char **argv)
         }
     }
 
-    exp = nbd_export_new(blk, dev_offset, fd_size, nbdflags, nbd_export_closed,
-                         &local_err);
+    exp = nbd_export_new(bs, dev_offset, fd_size, nbdflags, nbd_export_closed,
+                         writethrough, NULL, &local_err);
     if (!exp) {
         error_report_err(local_err);
         exit(EXIT_FAILURE);