Re: [Qemu-devel] [PATCH v6 05/10] block: Add bdrv_copy_dirty_bitmap and bdrv_reset_dirty_bitmap

[John Snow]

On 11/07/2014 10:16 AM, Vladimir Sementsov-Ogievskiy wrote:
from [PATCH v6 02/10]
+void qmp_block_dirty_bitmap_remove(const char *device, const char *name,
+                                   Error **errp)
+{
+    BlockDriverState *bs;
+    BdrvDirtyBitmap *bitmap;
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    if (!name || name[0] == '\0') {
+        error_setg(errp, "Bitmap name cannot be empty");
+        return;
+    }
+    bitmap = bdrv_find_dirty_bitmap(bs, name);
+    if (!bitmap) {
+        error_setg(errp, "Dirty bitmap not found: %s", name);
+        return;
+    }
+
+    bdrv_dirty_bitmap_make_anon(bs, bitmap);
+    bdrv_release_dirty_bitmap(bs, bitmap);
+}

from [PATCH v6 05/10]:
+void qmp_block_dirty_bitmap_enable(const char *device, const char *name,
+                                   Error **errp)
+{
+    BlockDriverState *bs;
+    BdrvDirtyBitmap *bitmap;
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    bitmap = bdrv_find_dirty_bitmap(bs, name);
+    if (!bitmap) {
+        error_setg(errp, "Dirty bitmap not found: %s", name);
+        return;
+    }
+
+    bdrv_enable_dirty_bitmap(bs, bitmap);
+}
+
+void qmp_block_dirty_bitmap_disable(const char *device, const char *name,
+                                    Error **errp)
+{
+    BlockDriverState *bs;
+    BdrvDirtyBitmap *bitmap;
+
+    bs = bdrv_find(device);
+    if (!bs) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return;
+    }
+
+    bitmap = bdrv_find_dirty_bitmap(bs, name);
+    if (!bitmap) {
+        error_setg(errp, "Dirty bitmap not found: %s", name);
+        return;
+    }
+
+    bdrv_disable_dirty_bitmap(bs, bitmap);
+}
+

there is one inconsistence:

you have check
+    if (!name || name[0] == '\0') {
+        error_setg(errp, "Bitmap name cannot be empty");
+        return;
+    }
when accessing bitmap in qmp_block_dirty_bitmap_remove, but not in
qmp_block_dirty_bitmap_{enable,disable}.

In qmp_block_dirty_bitmap_{enable,disable} I don't think it's a problem 
if we don't check the name here -- it just means that we're not going to 
be able to find the name (since it's invalid) and the function will 
error out anyway.

I don't think a change is warranted, necessarily, unless we factor out 
the error checking: see below.

Also, I think it'll be better to put similar part of these three
functions into one separate function to avoid duplicates, like

static BdrvDirtyBitmap *bitmap find_dirty_bitmap(const char *device, const char 
*name,
                                    Error **errp)
{
     BlockDriverState *bs;
     BdrvDirtyBitmap *bitmap;

     // most simple error condition earlier
     if (!name || name[0] == '\0') {
         error_setg(errp, "Bitmap name cannot be empty");
         return NULL;
     }

     bs = bdrv_find(device);
     if (!bs) {
         error_set(errp, QERR_DEVICE_NOT_FOUND, device);
         return NULL;
     }

     bitmap = bdrv_find_dirty_bitmap(bs, name);
     if (!bitmap) {
         error_setg(errp, "Dirty bitmap not found: %s", name);
         return NULL;
     }

     return bitmap;
}


I think normally I would agree, but since qmp_block_dirty_bitmap_remove 
needs to use the BlockDriverState anyway, part of this error-checking 
routine gets duplicated regardless, unless you add another return 
parameter to give you the BlockDriverState back as well, and you lose 
the single purpose nature of factoring it out.

I will keep the redundancy of the error-checking of this patch in mind 
as I clean it up for v7...

--
Best regards,
Vladimir