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Re: [Qemu-devel] [PATCH v6 04/24] qcow2: Only return status from qcow2_g

From: Eric Blake
Subject: Re: [Qemu-devel] [PATCH v6 04/24] qcow2: Only return status from qcow2_get_refcount
Date: Wed, 11 Feb 2015 08:47:00 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0

On 02/10/2015 01:28 PM, Max Reitz wrote:
> Refcounts can theoretically be of type uint64_t; in order to be able to
> represent the full range, qcow2_get_refcount() cannot use a single
> variable to represent both all refcount values and also keep some values
> reserved for errors.
> One solution would be to add an Error pointer parameter to
> qcow2_get_refcount(); however, no caller could (currently) pass that
> error message, so it would have to be emitted immediately and be
> passed to the next caller by returning -EIO or something similar.
> Therefore, an Error parameter does not offer any advantages here.
> The solution applied by this patch is simpler to use. Because no caller
> would be able to pass the error message, they would have to print it and
> free it, whereas with this patch the caller only needs to pass the
> returned integer (which is often a no-op from the code perspective,
> because that integer will be stored in a variable "ret" which will be
> returned by the fail path of many callers).
> Signed-off-by: Max Reitz <address@hidden>
> ---
>  block/qcow2-cluster.c  |  8 ++---
>  block/qcow2-refcount.c | 86 
> +++++++++++++++++++++++++++-----------------------
>  block/qcow2.h          |  3 +-
>  3 files changed, 53 insertions(+), 44 deletions(-)

> @@ -744,10 +749,9 @@ int qcow2_alloc_clusters_at(BlockDriverState *bs, 
> uint64_t offset,
>          /* Check how many clusters there are free */
>          cluster_index = offset >> s->cluster_bits;
>          for(i = 0; i < nb_clusters; i++) {
> -            refcount = qcow2_get_refcount(bs, cluster_index++);

Worth fixing the spacing after 'for' while touching here? (might even
already happen later in the series). But not important enough for a
respin, and I won't even care if a maintainer doesn't fold it in.

Reviewed-by: Eric Blake <address@hidden>

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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