From patchwork Wed Feb  1 03:06:58 2012
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Subject: [RFC,4/7] Qemu: Framework for reopening image files safely
Date: Tue, 31 Jan 2012 17:06:58 -0000
From: Supriya Kannery <supriyak@linux.vnet.ibm.com>
X-Patchwork-Id: 138894
Message-Id: <20120201030658.2990.15176.sendpatchset@skannery.in.ibm.com>
To: qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>,
 Christoph Hellwig <hch@lst.de>, Luiz Capitulino <lcapitulino@redhat.com>

Struct BDRVReopenState along with three reopen related functions
introduced for handling reopening of images safely. This can be
extended by each of the block drivers to reopen respective
image files.

Signed-off-by: Supriya Kannery <supriyak@linux.vnet.ibm.com>


Index: qemu/block.c
===================================================================
--- qemu.orig/block.c
+++ qemu/block.c
@@ -808,10 +808,32 @@ unlink_and_fail:
     return ret;
 }
 
+int bdrv_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs, int flags)
+{
+     BlockDriver *drv = bs->drv;
+
+     return drv->bdrv_reopen_prepare(bs, prs, flags);
+}
+
+void bdrv_reopen_commit(BlockDriverState *bs, BDRVReopenState *rs)
+{
+    BlockDriver *drv = bs->drv;
+
+    drv->bdrv_reopen_commit(bs, rs);
+}
+
+void bdrv_reopen_abort(BlockDriverState *bs, BDRVReopenState *rs)
+{
+    BlockDriver *drv = bs->drv;
+
+    drv->bdrv_reopen_abort(bs, rs);
+}
+
 int bdrv_reopen(BlockDriverState *bs, int bdrv_flags)
 {
     BlockDriver *drv = bs->drv;
     int ret = 0, open_flags;
+    BDRVReopenState *reopen_state = NULL;
 
     /* Quiesce IO for the given block device */
     qemu_aio_flush();
@@ -820,17 +842,32 @@ int bdrv_reopen(BlockDriverState *bs, in
         qerror_report(QERR_DATA_SYNC_FAILED, bs->device_name);
         return ret;
     }
-    open_flags = bs->open_flags;
-    bdrv_close(bs);
 
-    ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
-    if (ret < 0) {
-        /* Reopen failed. Try to open with original flags */
-        qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
-        ret = bdrv_open(bs, bs->filename, open_flags, drv);
+    /* Use driver specific reopen() if available */
+    if (drv->bdrv_reopen_prepare) {
+        ret = bdrv_reopen_prepare(bs, &reopen_state, bdrv_flags);
+         if (ret < 0) {
+            bdrv_reopen_abort(bs, reopen_state);
+            qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
+            return ret;
+        }
+
+        bdrv_reopen_commit(bs, reopen_state);
+        bs->open_flags = bdrv_flags;
+
+    } else {
+       open_flags = bs->open_flags;
+       bdrv_close(bs);
+
+       ret = bdrv_open(bs, bs->filename, bdrv_flags, drv);
         if (ret < 0) {
-            /* Reopen failed with orig and modified flags */
-            abort();
+            /* Reopen failed. Try to open with original flags */
+            qerror_report(QERR_REOPEN_FILE_FAILED, bs->filename);
+            ret = bdrv_open(bs, bs->filename, open_flags, drv);
+            if (ret < 0) {
+                /* Reopen failed with orig and modified flags */
+                bs->drv = NULL;
+            }
         }
     }
 
Index: qemu/block_int.h
===================================================================
--- qemu.orig/block_int.h
+++ qemu/block_int.h
@@ -105,6 +105,13 @@ struct BlockDriver {
     int (*bdrv_probe)(const uint8_t *buf, int buf_size, const char *filename);
     int (*bdrv_probe_device)(const char *filename);
     int (*bdrv_open)(BlockDriverState *bs, int flags);
+
+    /* For handling image reopen for split or non-split files */
+    int (*bdrv_reopen_prepare)(BlockDriverState *bs,
+                               BDRVReopenState **prs,
+                               int flags);
+    void (*bdrv_reopen_commit)(BlockDriverState *bs, BDRVReopenState *rs);
+    void (*bdrv_reopen_abort)(BlockDriverState *bs, BDRVReopenState *rs);
     int (*bdrv_file_open)(BlockDriverState *bs, const char *filename, int flags);
     int (*bdrv_read)(BlockDriverState *bs, int64_t sector_num,
                      uint8_t *buf, int nb_sectors);
@@ -299,6 +306,10 @@ struct BlockDriverState {
     BlockJob *job;
 };
 
+struct BDRVReopenState {
+    BlockDriverState *bs;
+};
+
 struct BlockDriverAIOCB {
     AIOPool *pool;
     BlockDriverState *bs;
Index: qemu/qemu-common.h
===================================================================
--- qemu.orig/qemu-common.h
+++ qemu/qemu-common.h
@@ -210,6 +210,7 @@ typedef struct NICInfo NICInfo;
 typedef struct HCIInfo HCIInfo;
 typedef struct AudioState AudioState;
 typedef struct BlockDriverState BlockDriverState;
+typedef struct BDRVReopenState BDRVReopenState;
 typedef struct DriveInfo DriveInfo;
 typedef struct DisplayState DisplayState;
 typedef struct DisplayChangeListener DisplayChangeListener;
Index: qemu/block.h
===================================================================
--- qemu.orig/block.h
+++ qemu/block.h
@@ -120,6 +120,9 @@ int bdrv_file_open(BlockDriverState **pb
 int bdrv_open(BlockDriverState *bs, const char *filename, int flags,
               BlockDriver *drv);
 int bdrv_reopen(BlockDriverState *bs, int bdrv_flags);
+int bdrv_reopen_prepare(BlockDriverState *bs, BDRVReopenState **prs, int flags);
+void bdrv_reopen_commit(BlockDriverState *bs, BDRVReopenState *rs);
+void bdrv_reopen_abort(BlockDriverState *bs, BDRVReopenState *rs);
 void bdrv_close(BlockDriverState *bs);
 int bdrv_attach_dev(BlockDriverState *bs, void *dev);
 void bdrv_attach_dev_nofail(BlockDriverState *bs, void *dev);