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Re: [PATCH v2 2/6] parallels.txt: fix bitmap L1 table description
From: |
Kevin Wolf |
Subject: |
Re: [PATCH v2 2/6] parallels.txt: fix bitmap L1 table description |
Date: |
Thu, 4 Mar 2021 15:21:45 +0100 |
Am 24.02.2021 um 11:47 hat Vladimir Sementsov-Ogievskiy geschrieben:
> Actually L1 table entry offset is in 512 bytes sectors. Fix the spec.
>
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---
> docs/interop/parallels.txt | 27 +++++++++++++++------------
> 1 file changed, 15 insertions(+), 12 deletions(-)
>
> diff --git a/docs/interop/parallels.txt b/docs/interop/parallels.txt
> index f15bf35bd1..73af9a2c4b 100644
> --- a/docs/interop/parallels.txt
> +++ b/docs/interop/parallels.txt
> @@ -208,21 +208,24 @@ of its data area are:
> 28 - 31: l1_size
> The number of entries in the L1 table of the bitmap.
>
> - variable: l1_table (8 * l1_size bytes)
> - L1 offset table (in bytes)
> + variable: L1 offset table (l1_table), size: 8 * l1_size bytes
>
> -A dirty bitmap is stored using a one-level structure for the mapping to host
> -clusters - an L1 table.
> +Dirty bitmap is stored in the array of clusters inside Parallels Image file.
> +Offsets of these clusters are saved in L1 offset table here. Each L1 table
> +entry is a 64bit integer described below:
I think the English grammar needs some fixes here (missing articles).
If I understand correctly, it's also not really an array, which I would
understand as consecutive clusters.
Maybe something like this:
The dirty bitmap described by this feature extension is stored in a set
of clusters inside the Parallels image file. The offsets of these
clusters are saved in the L1 offset table specified by the feature
extension. Each L1 table entry is a 64 bit integer as described below:
> -Given an offset in bytes into the bitmap data, the offset in bytes into the
> -image file can be obtained as follows:
> +Given an offset in bytes into the bitmap data, corresponding L1 entry is
>
> - offset = l1_table[offset / cluster_size] + (offset % cluster_size)
> + l1_table[offset / cluster_size]
>
> -If an L1 table entry is 0, the corresponding cluster of the bitmap is assumed
> -to be zero.
> +If L1 table entry is 0, all bits in the corresponding cluster of the bitmap
> +are assumed to be 0.
"an L1 table", like before.
> -If an L1 table entry is 1, the corresponding cluster of the bitmap is assumed
> -to have all bits set.
> +If L1 table entry is 1, all bits in the corresponding cluster of the bitmap
> +are assumed to be 1.
Same here.
> -If an L1 table entry is not 0 or 1, it allocates a cluster from the data
> area.
> +If an L1 table entry is not 0 or 1, it contains corresponding cluster offset
"the corresponding cluster offset"
> +(in 512b sectors). Given an offset in bytes into the bitmap data the offset
> in
> +bytes into the image file can be obtained as follows:
> +
> + offset = l1_table[offset / cluster_size] * 512 + (offset % cluster_size)
These changes can be made while applying the patch.
Kevin
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