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From: Max Reitz <mreitz@redhat.com>
To: Alberto Garcia <berto@igalia.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 14/26] qcow2: Add subcluster support to qcow2_get_cluster_offset()
Date: Mon, 11 Nov 2019 09:42:41 +0100	[thread overview]
Message-ID: <e1a91584-ff67-e918-20e7-f96bad5b745b@redhat.com> (raw)
In-Reply-To: <w51ftiys7bv.fsf@maestria.local.igalia.com>


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On 08.11.19 16:42, Alberto Garcia wrote:
> On Mon 04 Nov 2019 03:58:57 PM CET, Max Reitz wrote:

[...]

>>> @@ -514,8 +499,8 @@ int qcow2_get_cluster_offset(BlockDriverState *bs, uint64_t offset,
>>
>> I suppose this is get_subcluster_offset now.
> 
> Hmmm no, this returns the actual host cluster offset, then the caller
> uses offset_into_cluster() to get the final value (which doesn't need to
> be subcluster-aligned anyway).

It still returns the subcluster type, though.  Which makes the whole
thing kind of a weird chimera...  Maybe it would work better if the
subcluster type would be stored in a pointer parameter, so it’d be clear?

But does it have actually have any advantages to on one hand return a
cluster-aligned host offset and on the other return a bytes count that
starts at the mid-cluster offset?  That’s weird already.  Maybe the
offset that’s returned should just not be cluster-aligned and the whole
function be called qcow2_get_host_offset().

I suppose one reason (maybe the only one?) to return aligned offsets is
for compressed clusters.  It would be another kind of magic to return
aligned offsets only for them.  But maybe it’s worth it?  (Judging from
a quick glance, it doesn’t look too difficult to me to modify the
callers to accept a mid-cluster host offset.)

(Another thing I just noticed is that the comment above
qcow2_get_cluster_offset() needs some fixing, because it still refers to
whole clusters.)

Max


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  reply	other threads:[~2019-11-11  8:45 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
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 [this message]
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

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