[Qemu-devel] [PATCH 1/5] block: added lock image option and callback

["Denis V. Lunev" <den@openvz.org>]

From: Olga Krishtal <okrishtal@virtuozzo.com>

While opening the image we want to be sure that we are the
one who works with image, anf if it is not true -
opening the image for writing should fail.

There are 2 ways at the moment: no lock at all and lock the file
image.

Signed-off-by: Olga Krishtal <okrishtal@virtuozzo.com>
Signed-off-by: Denis V. Lunev <den@openvz.org>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Max Reitz <mreitz@redhat.com>
CC: Eric Blake <eblake@redhat.com>
CC: Fam Zheng <famz@redhat.com>
---
 block.c                   | 41 +++++++++++++++++++++++++++++++++++++++++
 include/block/block.h     |  1 +
 include/block/block_int.h |  1 +
 qapi/block-core.json      |  9 +++++++++
 4 files changed, 52 insertions(+)

diff --git a/block.c b/block.c
index 411edbf..74228b8 100644
--- a/block.c
+++ b/block.c
@@ -40,6 +40,8 @@
 #include "qemu/timer.h"
 #include "qapi-event.h"
 #include "block/throttle-groups.h"
+#include "qapi-types.h"
+#include "qapi/util.h"
 
 #ifdef CONFIG_BSD
 #include <sys/types.h>
@@ -895,6 +897,12 @@ static QemuOptsList bdrv_runtime_opts = {
             .type = QEMU_OPT_BOOL,
             .help = "Ignore flush requests",
         },
+        {
+            .name = "lock",
+            .type = QEMU_OPT_STRING,
+            .help = "How to lock the image: none or lockfile",
+            .def_value_str = "none",
+        },
         { /* end of list */ }
     },
 };
@@ -914,6 +922,8 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file,
     QemuOpts *opts;
     BlockDriver *drv;
     Error *local_err = NULL;
+    const char *lock_image;
+    int lock;
 
     assert(bs->file == NULL);
     assert(options != NULL && bs->options != options);
@@ -1020,6 +1030,18 @@ static int bdrv_open_common(BlockDriverState *bs, BdrvChild *file,
         goto free_and_fail;
     }
 
+    lock_image = qemu_opt_get(opts, "lock");
+    lock = qapi_enum_parse(BdrvLockImage_lookup, lock_image,
+                BDRV_LOCK_IMAGE__MAX, BDRV_LOCK_IMAGE_NONE, &local_err);
+    if (!bs->read_only && lock != BDRV_LOCK_IMAGE_NONE) {
+        ret = bdrv_lock_image(bs, lock);
+        if (ret < 0) {
+            error_setg_errno(errp, -ret, "Could not lock the image");
+            bdrv_close(bs);
+            goto fail_opts;
+        }
+    }
+
     if (bs->encrypted) {
         error_report("Encrypted images are deprecated");
         error_printf("Support for them will be removed in a future release.\n"
@@ -4320,3 +4342,22 @@ void bdrv_refresh_filename(BlockDriverState *bs)
         QDECREF(json);
     }
 }
+
+int bdrv_lock_image(BlockDriverState *bs, BdrvLockImage lock)
+{
+    BlockDriver *drv = bs->drv;
+    if (lock != BDRV_LOCK_IMAGE_LOCKFILE) {
+        return -EOPNOTSUPP;
+    }
+    if (drv != NULL && drv->bdrv_lock_image != NULL) {
+        return bs->drv->bdrv_lock_image(bs, lock);
+    }
+    if (bs->file == NULL) {
+        return -EOPNOTSUPP;
+    }
+    drv = bs->file->bs->drv;
+    if (drv != NULL && drv->bdrv_lock_image != NULL) {
+        return drv->bdrv_lock_image(bs, lock);
+    }
+    return -EOPNOTSUPP;
+}
diff --git a/include/block/block.h b/include/block/block.h
index db8e096..27fc434 100644
--- a/include/block/block.h
+++ b/include/block/block.h
@@ -506,6 +506,7 @@ void bdrv_reset_dirty_bitmap(BdrvDirtyBitmap *bitmap,
 void bdrv_dirty_iter_init(BdrvDirtyBitmap *bitmap, struct HBitmapIter *hbi);
 void bdrv_set_dirty_iter(struct HBitmapIter *hbi, int64_t offset);
 int64_t bdrv_get_dirty_count(BdrvDirtyBitmap *bitmap);
+int bdrv_lock_image(BlockDriverState *bs, BdrvLockImage lock);
 
 void bdrv_enable_copy_on_read(BlockDriverState *bs);
 void bdrv_disable_copy_on_read(BlockDriverState *bs);
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 256609d..755f342 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -135,6 +135,7 @@ struct BlockDriver {
     int (*bdrv_create)(const char *filename, QemuOpts *opts, Error **errp);
     int (*bdrv_set_key)(BlockDriverState *bs, const char *key);
     int (*bdrv_make_empty)(BlockDriverState *bs);
+    int (*bdrv_lock_image)(BlockDriverState *bs, BdrvLockImage lock);
 
     void (*bdrv_refresh_filename)(BlockDriverState *bs, QDict *options);
 
diff --git a/qapi/block-core.json b/qapi/block-core.json
index 1a5d9ce..b82589b 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -2408,3 +2408,12 @@
 ##
 { 'command': 'block-set-write-threshold',
   'data': { 'node-name': 'str', 'write-threshold': 'uint64' } }
+
+##
+# @BdrvLockImage:
+#
+#An enumeration of lock types to lock image file.
+# @none - do not lock the image file
+# @lockfile
+## Since 2.6
+{ 'enum': 'BdrvLockImage', 'data':['none', 'lockfile']}
-- 
2.1.4