Re: [PATCH v2 3/3] qcow2: Rewrite the documentation of qcow2_alloc_cluster_offset()

[Max Reitz]

On 03.09.20 18:37, Alberto Garcia wrote:
> The current text corresponds to an earlier, simpler version of this
> function and it does not explain how it works now.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block/qcow2-cluster.c | 24 ++++++++++++++----------
>  1 file changed, 14 insertions(+), 10 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 25e38daa78..f1ce6afcf5 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -1713,18 +1713,22 @@ out:
>  }
>  
>  /*
> - * alloc_cluster_offset
> + * For a given area on the virtual disk defined by @offset and @bytes,
> + * find the corresponding area on the qcow2 image, allocating new
> + * clusters (or subclusters) if necessary. The result can span a
> + * combination of allocated and previously unallocated clusters.
>   *
> - * For a given offset on the virtual disk, find the cluster offset in qcow2
> - * file. If the offset is not found, allocate a new cluster.
> + * On return, @host_offset is set to the beginning of the requested
> + * area. This area is guaranteed to be contiguous on the qcow2 file
> + * but it can be smaller than initially requested. In this case @bytes
> + * is updated with the actual size.
>   *
> - * If the cluster was already allocated, m->nb_clusters is set to 0 and
> - * other fields in m are meaningless.
> - *
> - * If the cluster is newly allocated, m->nb_clusters is set to the number of
> - * contiguous clusters that have been allocated. In this case, the other
> - * fields of m are valid and contain information about the first allocated
> - * cluster.
> + * If any clusters or subclusters were allocated then @m contains a
> + * list with the information of all the affected regions. Note that
> + * this can happen regardless of whether this function succeeds or
> + * not. The caller is responsible for updating the L2 metadata of the
> + * allocated clusters (on success) or freeing them (on failure), and
> + * for clearing the contents of @m afterwards in both cases.

It’s too bad that preallocate_co() doesn’t do that then, isn’t it...

Max

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