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

[yuchenlin]

Fam Zheng <address@hidden> 於 2018-09-12 17:34 寫道：
> On Tue, 08/28 11:17, address@hidden wrote: > From: yuchenlin <address@hidden> 
> > > 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 <address@hidden> > --- > 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;
}
}

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