On Fri, Nov 15, 2013 at 09:29:43AM +0800, Hu Tao wrote:
> On Wed, Nov 13, 2013 at 07:03:03AM +0100, Peter Lieven wrote:
> > What is your use case for this seris? QCOW2 creation or converting
> > anything to QCOW2? For the later case you could use "qemu-img convert -S 0
> > ..."
> > starting in 1.8.
>
> The former. Seems "qemu-img convert -S 0" do the same thing but at
> converting time, maybe we can share some code. But let me dig the
> code first.
The purpose is to using posix_fallocate() to preallocate space, other
than writing zeros to do it. Because the latter is pretty slow.
>
> >
> > Peter
> >
> > Hu Tao wrote:
> > > This adds a preallocation=full mode to qcow2 image creation, which
> > > creates a non-sparse image file.
> > >
> > > Signed-off-by: Hu Tao <hu...@cn.fujitsu.com>
> > > ---
> > > block/qcow2.c | 28 ++++++++++++++++++++++------
> > > 1 file changed, 22 insertions(+), 6 deletions(-)
> > >
> > > diff --git a/block/qcow2.c b/block/qcow2.c
> > > index 359030f..d3ca6cf 100644
> > > --- a/block/qcow2.c
> > > +++ b/block/qcow2.c
> > > @@ -1385,7 +1385,13 @@ static int
> > > qcow2_change_backing_file(BlockDriverState *bs,
> > > return qcow2_update_header(bs);
> > > }
> > >
> > > -static int preallocate(BlockDriverState *bs)
> > > +enum prealloc_mode {
> > > + PREALLOC_OFF = 0,
> > > + PREALLOC_METADATA,
> > > + PREALLOC_FULL,
> > > +};
> > > +
> > > +static int preallocate(BlockDriverState *bs, enum prealloc_mode mode)
> > > {
> > > uint64_t nb_sectors;
> > > uint64_t offset;
> > > @@ -1394,9 +1400,12 @@ static int preallocate(BlockDriverState *bs)
> > > int ret;
> > > QCowL2Meta *meta;
> > >
> > > + assert(mode != PREALLOC_OFF);
> > > +
> > > nb_sectors = bdrv_getlength(bs) >> 9;
> > > offset = 0;
> > >
> > > + /* First allocate metadata in _really_ big chunks */
> > > while (nb_sectors) {
> > > num = MIN(nb_sectors, INT_MAX >> 9);
> > > ret = qcow2_alloc_cluster_offset(bs, offset, 0, num, &num,
> > > @@ -1424,6 +1433,11 @@ static int preallocate(BlockDriverState *bs)
> > > offset += num << 9;
> > > }
> > >
> > > + /* Then write zeros to the cluster data, if requested */
> > > + if (mode == PREALLOC_FULL) {
> > > + bdrv_zero_init(bs->file, offset, bdrv_getlength(bs));
> > > + }
> > > +
> > > /*
> > > * It is expected that the image file is large enough to actually
> > > contain
> > > * all of the allocated clusters (otherwise we get failing reads
> > > after
> > > @@ -1572,11 +1586,11 @@ static int qcow2_create2(const char *filename,
> > > int64_t total_size,
> > > }
> > > }
> > >
> > > - /* And if we're supposed to preallocate metadata, do that now */
> > > + /* And if we're supposed to preallocate data, do that now */
> > > if (prealloc) {
> > > BDRVQcowState *
> >
