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 <be...@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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