From: Alberto Garcia <berto@igalia.com>
To: Max Reitz <mreitz@redhat.com>, qemu-devel@nongnu.org
Cc: Kevin Wolf <kwolf@redhat.com>,
Anton Nefedov <anton.nefedov@virtuozzo.com>,
qemu-block@nongnu.org,
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>,
"Denis V . Lunev" <den@openvz.org>
Subject: Re: [RFC PATCH v2 05/26] qcow2: Document the Extended L2 Entries feature
Date: Wed, 30 Oct 2019 23:38:01 +0100 [thread overview]
Message-ID: <w51y2x1eu5y.fsf@maestria.local.igalia.com> (raw)
In-Reply-To: <0c738172-732f-eee0-3396-5a9576a4addf@redhat.com>
On Wed 30 Oct 2019 05:23:30 PM CET, Max Reitz wrote:
>> +Subcluster Allocation Bitmap (for standard clusters):
>> +
>> + Bit 0 - 31: Allocation status (one bit per subcluster)
>> +
>> + 1: the subcluster is allocated. In this case the
>> + host cluster offset field must contain a valid
>> + offset.
>> + 0: the subcluster is not allocated. In this case
>> + read requests shall go to the backing file or
>> + return zeros if there is no backing file data.
>> +
>> + Bits are assigned starting from the most significant one.
>> + (i.e. bit x is used for subcluster 31 - x)
>
> I seem to remember that someone proposed this bit ordering to you, but
> I wonder why. So far everything in qcow2 starts from the least
> significant bit, for example refcounts (“If refcount_bits implies a
> sub-byte width, note that bit 0 means the least significant bit in
> this context”), feature bits, and sub-byte structure descriptions in
> general (which you reference directly with “bit x”).
>
> Soo... What’s the reason for doing it the other way around here?
The reason is that I thought that it would be better for debugging
purposes. If I do an hexdump of the L2 table to see what's going on then
starting from the most significant bit gives me a better visual image of
what subclusters are allocated.
In other words, if the first two subclusters are allocated I think this
representation
11000000 00000000 00000000 00000000 (c0 00 00 00)
is more natural than this one
00000000 00000000 00000000 00000011 (00 00 00 03)
But I don't have a very strong opinion so I'm open to changing it.
Berto
next prev parent reply other threads:[~2019-10-30 22:44 UTC|newest]
Thread overview: 65+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-26 21:25 [RFC PATCH v2 00/26] Add subcluster allocation to qcow2 Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 01/26] qcow2: Add calculate_l2_meta() Alberto Garcia
2019-10-28 12:50 ` Vladimir Sementsov-Ogievskiy
2019-10-30 15:56 ` Alberto Garcia
2019-10-30 12:04 ` Max Reitz
2019-10-30 16:02 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 02/26] qcow2: Split cluster_needs_cow() out of count_cow_clusters() Alberto Garcia
2019-10-28 13:55 ` Vladimir Sementsov-Ogievskiy
2019-10-26 21:25 ` [RFC PATCH v2 03/26] qcow2: Process QCOW2_CLUSTER_ZERO_ALLOC clusters in handle_copied() Alberto Garcia
2019-10-30 14:24 ` Max Reitz
2019-11-13 14:25 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 04/26] qcow2: Add get_l2_entry() and set_l2_entry() Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 05/26] qcow2: Document the Extended L2 Entries feature Alberto Garcia
2019-10-30 16:23 ` Max Reitz
2019-10-30 22:38 ` Alberto Garcia [this message]
2019-10-26 21:25 ` [RFC PATCH v2 06/26] qcow2: Add dummy has_subclusters() function Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 07/26] qcow2: Add subcluster-related fields to BDRVQcow2State Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 08/26] qcow2: Add offset_to_sc_index() Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 09/26] qcow2: Add l2_entry_size() Alberto Garcia
2019-10-30 16:47 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 10/26] qcow2: Update get/set_l2_entry() and add get/set_l2_bitmap() Alberto Garcia
2019-10-30 16:55 ` Max Reitz
2019-11-14 13:57 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 11/26] qcow2: Add qcow2_get_subcluster_type() Alberto Garcia
2019-11-04 12:35 ` Max Reitz
2019-11-04 15:01 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 12/26] qcow2: Handle QCOW2_CLUSTER_UNALLOCATED_SUBCLUSTER Alberto Garcia
2019-11-04 12:57 ` Max Reitz
2019-11-04 13:03 ` Alberto Garcia
2019-11-04 13:10 ` Max Reitz
2019-11-07 14:44 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 13/26] qcow2: Add subcluster support to calculate_l2_meta() Alberto Garcia
2019-11-04 14:21 ` Max Reitz
2019-11-08 15:18 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 14/26] qcow2: Add subcluster support to qcow2_get_cluster_offset() Alberto Garcia
2019-11-04 14:58 ` Max Reitz
2019-11-08 15:42 ` Alberto Garcia
2019-11-11 8:42 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 15/26] qcow2: Add subcluster support to zero_in_l2_slice() Alberto Garcia
2019-11-04 15:04 ` Max Reitz
2019-11-04 15:10 ` Max Reitz
2019-11-14 15:31 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 16/26] qcow2: Add subcluster support to discard_in_l2_slice() Alberto Garcia
2019-11-04 15:07 ` Max Reitz
2019-11-14 15:33 ` Alberto Garcia
2019-11-14 16:22 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 17/26] qcow2: Add subcluster support to check_refcounts_l2() Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 18/26] qcow2: Add subcluster support to expand_zero_clusters_in_l1() Alberto Garcia
2019-11-05 11:05 ` Max Reitz
2019-11-14 15:43 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 19/26] qcow2: Fix offset calculation in handle_dependencies() Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 20/26] qcow2: Update L2 bitmap in qcow2_alloc_cluster_link_l2() Alberto Garcia
2019-11-05 11:43 ` Max Reitz
2019-11-14 16:30 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 21/26] qcow2: Clear the L2 bitmap when allocating a compressed cluster Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 22/26] qcow2: Add subcluster support to handle_alloc_space() Alberto Garcia
2019-11-05 12:05 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 23/26] qcow2: Restrict qcow2_co_pwrite_zeroes() to full clusters only Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 24/26] qcow2: Add the 'extended_l2' option and the QCOW2_INCOMPAT_EXTL2 bit Alberto Garcia
2019-11-05 12:47 ` Max Reitz
2019-11-15 13:35 ` Alberto Garcia
2019-10-26 21:25 ` [RFC PATCH v2 25/26] qcow2: Allow preallocation and backing files if extended_l2 is set Alberto Garcia
2019-11-05 13:11 ` Max Reitz
2019-10-26 21:25 ` [RFC PATCH v2 26/26] iotests: Add tests for qcow2 images with extended L2 entries Alberto Garcia
2019-11-05 13:32 ` [RFC PATCH v2 00/26] Add subcluster allocation to qcow2 Max Reitz
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=w51y2x1eu5y.fsf@maestria.local.igalia.com \
--to=berto@igalia.com \
--cc=anton.nefedov@virtuozzo.com \
--cc=den@openvz.org \
--cc=kwolf@redhat.com \
--cc=mreitz@redhat.com \
--cc=qemu-block@nongnu.org \
--cc=qemu-devel@nongnu.org \
--cc=vsementsov@virtuozzo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).