From: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
To: Kevin Wolf <kwolf@redhat.com>
Cc: qemu-devel@nongnu.org,
Vladimir Sementsov-Ogievskiy <vsementsov@parallels.com>,
stefanha@redhat.com, pbonzini@redhat.com, den@openvz.org,
jsnow@redhat.com
Subject: Re: [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification
Date: Mon, 24 Aug 2015 13:46:06 +0300 [thread overview]
Message-ID: <55DAF5EE.8080003@virtuozzo.com> (raw)
In-Reply-To: <20150610153400.GG4899@noname.str.redhat.com>
On 10.06.2015 18:34, Kevin Wolf wrote:
> Am 08.06.2015 um 17:21 hat Vladimir Sementsov-Ogievskiy geschrieben:
>> From: Vladimir Sementsov-Ogievskiy <vsementsov@parallels.com>
>>
>> Persistent dirty bitmaps will be saved into qcow2 files. It may be used
>> as 'internal' bitmaps (for qcow2 drives) or as 'external' bitmaps for
>> other drives (there may be qcow2 file with zero disk size but with
>> several dirty bitmaps for other drives).
>>
>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>> ---
>> docs/specs/qcow2.txt | 66 ++++++++++++++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 66 insertions(+)
>>
>> diff --git a/docs/specs/qcow2.txt b/docs/specs/qcow2.txt
>> index 121dfc8..0fffba2 100644
>> --- a/docs/specs/qcow2.txt
>> +++ b/docs/specs/qcow2.txt
>> @@ -123,6 +123,7 @@ be stored. Each extension has a structure like the following:
>> 0x00000000 - End of the header extension area
>> 0xE2792ACA - Backing file format name
>> 0x6803f857 - Feature name table
>> + 0x23852875 - Dirty bitmaps
>> other - Unknown header extension, can be safely
>> ignored
>>
>> @@ -166,6 +167,19 @@ the header extension data. Each entry look like this:
>> terminated if it has full length)
>>
>>
>> +== Dirty bitmaps ==
>> +
>> +Dirty bitmaps is an optional header extension. It provides a possibility of
>> +storing dirty bitmaps in qcow2 image. The fields are:
>> +
>> + 0 - 3: nb_dirty_bitmaps
>> + Number of dirty bitmaps contained in the image
>> +
>> + 4 - 11: dirty_bitmaps_offset
>> + Offset into the image file at which the dirty bitmaps table
>> + starts. Must be aligned to a cluster boundary.
>> +
>> +
>> == Host cluster management ==
> You need to use a compatibility flag because for old qemu versions, the
> dirty bitmaps (and associated metadata) are leaked clusters and qemu-img
> check would "repair" them by resetting the refcount to 0.
>
> At second sight, I see that your patches add an autoclear flag.
> Presumably the contents of the dirty bitmaps is outdated when you
> accessed the image with an older version, so this seems right. We just
> need to document it.
>
>> qcow2 manages the allocation of host clusters by maintaining a reference count
>> @@ -360,3 +374,55 @@ Snapshot table entry:
>>
>> variable: Padding to round up the snapshot table entry size to the
>> next multiple of 8.
>> +
>> +
>> +== Dirty bitmaps ==
>> +
>> +The feature supports storing several dirty bitmaps in the qcow2 file.
>> +
>> +=== Cluster mapping ===
>> +
>> +Dirty bitmaps are stored using a ONE-level structure for the mapping of
>> +bitmaps to host clusters. There is only an L1 table.
>> +
>> +The L1 table has a variable size (stored in the Bitmap table entry) and may
>> +use multiple clusters, however it must be contiguous in the image file.
>> +
>> +Given an offset into the bitmap, the offset into the image file can be
>> +obtained as follows:
>> +
>> + offset = l1_table[offset / cluster_size] + (offset % cluster_size)
>> +
>> +L1 table entry:
>> +
>> + Bit 0 - 61: Standard cluster descriptor
>> +
>> + 62 - 63: Reserved
> Stefan already mentioned that we don't have a "L1" when there is only
> one level, and that you shouldn't reuse the cluster descriptors from L2
> tables.
>
>> +=== Bitmap table ===
>> +
>> +A directory of all bitmaps is stored in the bitmap table, a contiguous area in
>> +the image file, whose starting offset and length are given by the header fields
>> +dirty_bitmaps_offset and nb_dirty_bitmaps. The entries of the bitmap table have
>> +variable length, depending on the length of name and extra data.
>> +
>> +Bitmap table entry:
>> +
>> + Byte 0 - 7: Offset into the image file at which the L1 table for the
>> + bitmap starts. Must be aligned to a cluster boundary.
>> +
>> + 8 - 11: Number of entries in the L1 table of the bitmap
> Worth using 64 bits here? This can only cover 4 * 512 GB = 2 TB for the
> smallest possible cluster size. Though it's 65536 * 512 = 32 PB for the
> default, which might be enough for a while.
We store the bitmap in RAM.. I think 2 TB bitmap should not appear,
larger granularity should be used for big disks.
>
>> + 12 - 15: Bitmap granularity in bytes
>> +
>> + 16 - 23: Bitmap size in sectors
> Please don't use sectors, that's a meaningless unit. Bytes is better.
>
>> + 24 - 25: Size of the bitmap name
> We should use a smaller limit than the possible 64k to avoid too large
> memory allocations. Nobody needs really long bitmap names.
>
>> +
>> + variable: The name of the bitmap (not null terminated)
>> +
>> + variable: Padding to round up the bitmap table entry size to the
>> + next multiple of 8.
> Kevin
--
Best regards,
Vladimir
* now, @virtuozzo.com instead of @parallels.com. Sorry for this inconvenience.
next prev parent reply other threads:[~2015-08-24 10:46 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-08 15:21 [Qemu-devel] [PATCH v2 RFC 0/8] block: persistent dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification Vladimir Sementsov-Ogievskiy
2015-06-09 16:01 ` John Snow
2015-06-09 17:03 ` Stefan Hajnoczi
2015-06-10 8:19 ` Vladimir Sementsov-Ogievskiy
2015-06-10 8:49 ` Vladimir Sementsov-Ogievskiy
2015-06-10 13:00 ` Eric Blake
2015-06-11 10:16 ` Vladimir Sementsov-Ogievskiy
2015-06-10 13:24 ` Stefan Hajnoczi
2015-06-11 10:19 ` Vladimir Sementsov-Ogievskiy
2015-06-11 13:03 ` Stefan Hajnoczi
2015-06-11 16:21 ` John Snow
2015-06-12 10:28 ` Stefan Hajnoczi
2015-06-12 15:19 ` John Snow
2015-06-10 15:34 ` Kevin Wolf
2015-06-11 10:25 ` Vladimir Sementsov-Ogievskiy
2015-06-11 16:30 ` John Snow
2015-06-12 8:33 ` Kevin Wolf
2015-08-24 10:46 ` Vladimir Sementsov-Ogievskiy [this message]
2015-08-24 13:30 ` Vladimir Sementsov-Ogievskiy
2015-08-24 14:08 ` Vladimir Sementsov-Ogievskiy
2015-08-24 14:04 ` Vladimir Sementsov-Ogievskiy
2015-08-31 22:21 ` Eric Blake
2015-08-31 22:24 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 2/8] qcow2: add dirty-bitmaps feature Vladimir Sementsov-Ogievskiy
2015-06-09 16:52 ` Stefan Hajnoczi
2015-06-10 14:30 ` Stefan Hajnoczi
2015-06-12 19:02 ` John Snow
2015-06-15 14:42 ` Stefan Hajnoczi
2015-06-23 17:57 ` John Snow
2015-06-24 9:39 ` Stefan Hajnoczi
2015-08-14 17:14 ` Vladimir Sementsov-Ogievskiy
2015-08-26 9:09 ` Stefan Hajnoczi
2015-06-11 23:04 ` John Snow
2015-06-15 14:05 ` Vladimir Sementsov-Ogievskiy
2015-06-15 16:53 ` John Snow
2015-06-12 21:55 ` John Snow
2015-08-26 13:15 ` Vladimir Sementsov-Ogievskiy
2015-08-26 14:14 ` Vladimir Sementsov-Ogievskiy
2015-08-27 12:43 ` Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 3/8] block: store persistent dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 4/8] block: add bdrv_load_dirty_bitmap Vladimir Sementsov-Ogievskiy
2015-06-09 16:01 ` Stefan Hajnoczi
2015-06-10 22:33 ` John Snow
2015-06-11 10:41 ` Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 5/8] qcow2: add qcow2_dirty_bitmap_delete_all Vladimir Sementsov-Ogievskiy
2015-06-08 15:21 ` [Qemu-devel] [PATCH 6/8] qcow2: add autoclear bit for dirty bitmaps Vladimir Sementsov-Ogievskiy
2015-06-09 15:49 ` Stefan Hajnoczi
2015-06-09 15:50 ` Stefan Hajnoczi
2015-08-27 7:45 ` Vladimir Sementsov-Ogievskiy
2015-08-31 11:06 ` Vladimir Sementsov-Ogievskiy
2015-08-31 22:39 ` Eric Blake
2015-08-31 22:50 ` Eric Blake
2015-06-10 23:42 ` John Snow
2015-06-11 8:35 ` Kevin Wolf
2015-06-11 10:49 ` Vladimir Sementsov-Ogievskiy
2015-06-11 16:36 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 7/8] qemu: command line option " Vladimir Sementsov-Ogievskiy
2015-06-11 20:57 ` John Snow
2015-06-12 21:49 ` John Snow
2015-06-08 15:21 ` [Qemu-devel] [PATCH 8/8] iotests: test internal persistent dirty bitmap Vladimir Sementsov-Ogievskiy
2015-06-09 16:17 ` Eric Blake
2015-06-10 15:27 ` [Qemu-devel] [PATCH v2 RFC 0/8] block: persistent dirty bitmaps Stefan Hajnoczi
2015-06-11 11:22 ` Vladimir Sementsov-Ogievskiy
2015-06-11 13:14 ` Stefan Hajnoczi
2015-06-11 20:06 ` Stefan Hajnoczi
2015-06-12 9:58 ` Denis V. Lunev
2015-06-12 10:36 ` Stefan Hajnoczi
2015-08-26 6:26 ` Vladimir Sementsov-Ogievskiy
2015-08-26 9:13 ` Stefan Hajnoczi
2015-06-12 19:34 ` John Snow
2015-06-17 14:29 ` Vladimir Sementsov-Ogievskiy
2015-06-24 0:21 ` John Snow
2015-07-08 12:24 ` Vladimir Sementsov-Ogievskiy
2015-07-08 15:21 ` John Snow
2015-08-27 10:08 ` Vladimir Sementsov-Ogievskiy
-- strict thread matches above, loose matches on Subject: below --
2015-01-13 17:02 [Qemu-devel] [PATCH 0/8] block: persistent dirty bitmaps (RFC) Vladimir Sementsov-Ogievskiy
2015-01-13 17:02 ` [Qemu-devel] [PATCH 1/8] spec: add qcow2-dirty-bitmaps specification Vladimir Sementsov-Ogievskiy
2015-01-27 15:39 ` Eric Blake
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