On 02/18/2015 03:40 PM, Max Reitz wrote: > Add a refcount_order parameter to qcow2_create2(), use that value for > the image header and for calculating the size required for > preallocation. > > For now, always pass 4. > > This addition requires changes to the calculation of the file size for > the "full" and "falloc" preallocation modes. That in turn is a nice > opportunity to add a comment about that calculation not necessarily > being exact (and that being intentional). > > Signed-off-by: Max Reitz <mre...@redhat.com> > --- > block/qcow2.c | 47 ++++++++++++++++++++++++++++++++++++----------- > 1 file changed, 36 insertions(+), 11 deletions(-) >
> @@ -2010,6 +2022,8 @@ static int qcow2_create(const char *filename, QemuOpts
> *opts, Error **errp)
> size_t cluster_size = DEFAULT_CLUSTER_SIZE;
> PreallocMode prealloc;
> int version = 3;
> + uint64_t refcount_bits = 16;
> + int refcount_order;
> Error *local_err = NULL;
> int ret;
>
> @@ -2064,8 +2078,19 @@ static int qcow2_create(const char *filename, QemuOpts
> *opts, Error **errp)
> goto finish;
> }
>
> + if (version < 3 && refcount_bits != 16) {
> + error_setg(errp, "Different refcount widths than 16 bits require "
> + "compatibility level 1.1 or above (use compat=1.1 or "
> + "greater)");
> + ret = -EINVAL;
> + goto finish;
> + }
> +
> + refcount_order = ffs(refcount_bits) - 1;
ffs() doesn't work on uint64_t (it gives the wrong answer for
0x100000000, for example); you want to use ffsll(). But ffsll() isn't
portable. But we have include/qemu/host-utils.h that gives us ctz64()
which is what we want (where ctz==ffs-1 other than for the special case
of 0). So this should be:
refcount_order = ctz64(refcount_bits);
With that change,
Reviewed-by: Eric Blake <ebl...@redhat.com>
(Hmm, that means that at least qcow2.c:qcow2_create2() has a bug for
calling ffs(size_t), and we probably ought to eradicate other uses of
ffs from the tree - but as a separate followup).
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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