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[Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification
From: |
Avi Kivity |
Subject: |
[Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification |
Date: |
Sun, 10 Oct 2010 11:20:09 +0200 |
User-agent: |
Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.9) Gecko/20100921 Fedora/3.1.4-1.fc13 Lightning/1.0b3pre Thunderbird/3.1.4 |
On 10/08/2010 05:48 PM, Stefan Hajnoczi wrote:
Signed-off-by: Stefan Hajnoczi<address@hidden>
---
docs/specs/qed_spec.txt | 94 +++++++++++++++++++++++++++++++++++++++++++++++
1 files changed, 94 insertions(+), 0 deletions(-)
+Feature bits:
+* QED_F_BACKING_FILE = 0x01. The image uses a backing file.
+* QED_F_NEED_CHECK = 0x02. The image needs a consistency check before use.
Great that QED_F_NEED_CHECK is now non-optional. However, suppose we
add a new structure (e.g. persistent freelist); it's now impossible to
tell whether the structure is updated or not:
1 new qemu opens image
2 writes persistent freelist
3 clears need_check
4 shuts down
5 old qemu opens image
6 doesn't update persistent freelist
7 clears need_check
8 shuts down
The image is now inconsistent, but has need_check cleared.
We can address this by having a third feature bitmask that is
autocleared by guests that don't recognize various bits; so the sequence
becomes:
1 new qemu opens image
2 writes persistent freelist
3 clears need_check
4 sets persistent_freelist
5 shuts down
6 old qemu opens image
7 clears persistent_freelist (and any other bits it doesn't recognize)
8 doesn't update persistent freelist
9 clears need_check
10 shuts down
The image is now consistent, since the persistent freelist has disappeared.
+* QED_CF_BACKING_FORMAT = 0x01. The image has a specific backing file format
stored.
+
It was suggested to have just a bit saying whether the backing format is
raw or not. This way you don't need to store the format.
--
error compiling committee.c: too many arguments to function
- [Qemu-devel] [PATCH v2 0/7] qed: Add QEMU Enhanced Disk format, Stefan Hajnoczi, 2010/10/08
- [Qemu-devel] [PATCH v2 3/7] docs: Add QED image format specification, Stefan Hajnoczi, 2010/10/08
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification,
Avi Kivity <=
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Stefan Hajnoczi, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Avi Kivity, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Stefan Hajnoczi, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Avi Kivity, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Stefan Hajnoczi, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Avi Kivity, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Anthony Liguori, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Avi Kivity, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Anthony Liguori, 2010/10/11
- [Qemu-devel] Re: [PATCH v2 3/7] docs: Add QED image format specification, Avi Kivity, 2010/10/11