Re: [Qemu-devel] [PATCH] vmdk: align end of file to a sector boundary

[Fam Zheng <famz@redhat.com>]

On Wed, 09/12 17:52, yuchenlin wrote:
> 
> Fam Zheng <famz@redhat.com> 於 2018-09-12 17:34 寫道：
> > On Tue, 08/28 11:17, yuchenlin@synology.com wrote: > From: yuchenlin <yuchenlin@synology.com> > > There is a rare case which the size of last compressed cluster > is larger than the cluster size, which will cause the file is > not aligned at the sector boundary. I don't understand. Doesn't it mean that if you force the alignment by truncating out the extra bytes, some data is lost?   
> 
> You can take qcow2_co_pwritev_compressed in block/qcow2.c as an example.
> The bdrv_getlength will return the length in bytes which is always a multiple of BDRV_SECTOR_SIZE.
> After truncates this size, the vmdk is extended to align sector size.
> > > > Signed-off-by: yuchenlin <yuchenlin@synology.com> > --- > block/vmdk.c | 18 ++++++++++++++++++ > 1 file changed, 18 insertions(+) > > diff --git a/block/vmdk.c b/block/vmdk.c > index a9d0084e36..a8ae7c65d2 100644 > --- a/block/vmdk.c > +++ b/block/vmdk.c > @@ -1698,6 +1698,24 @@ static int coroutine_fn > vmdk_co_pwritev_compressed(BlockDriverState *bs, uint64_t offset, > uint64_t bytes, QEMUIOVector *qiov) > { > + if (bytes == 0) { Where is this bytes == 0 condition from?
> 
> From the end of convert_do_copy in qemu-img.c.
> 
> if (s->compressed && !s->ret) {
> /* signal EOF to align */
> ret = blk_pwrite_compressed(s->target, 0, NULL, 0);
> if (ret < 0) {
> return ret;
> }
> }

I see. Please mention this in the comment of the if check.

Fam

> 
> It signals the EOF to the block driver.
> > > + /* align end of file to a sector boundary. */ > + BDRVVmdkState *s = bs->opaque; > + int i, ret; > + int64_t length; > + > + for (i = 0; i < s->num_extents; i++) { > + length = bdrv_getlength(s->extents[i].file->bs); > + if (length < 0) { > + return length; > + } > + ret = bdrv_truncate(s->extents[i].file, length, PREALLOC_MODE_OFF, NULL); > + if (ret < 0) { > + return ret; > + } > + } > + return 0; > + } > return vmdk_co_pwritev(bs, offset, bytes, qiov, 0); > } > > -- > 2.17.0 > Fam
> 
> 
> yuchenlin
>