Re: [Qemu-devel] [PATCH v4 04/26] qcow2: Only return status from qcow2_get_refcount

[Stefan Hajnoczi]

On Wed, Dec 03, 2014 at 02:37:24PM +0100, 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 | 79 
> +++++++++++++++++++++++++++-----------------------
>  block/qcow2.h          |  3 +-
>  3 files changed, 49 insertions(+), 41 deletions(-)

Reviewed-by: Stefan Hajnoczi <address@hidden>

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