| Message ID | 345629775.1268590.1401202679338.JavaMail.root@meituan.com |
|---|---|
| State | New |
| Headers | show |
On Tue, May 27, 2014 at 10:57:59PM +0800, 蒙聪 wrote: > cow2_alloc_cluster_offset() sets the host_offset pointing to the first > byte of the cluster referenced by guest_offset other than to the exact > byte referenced by guest_offset. In this case, preallocate() fails to > extend the image large enough. > > This bug can be reproduced by following steps: > > $ /home/cmeng/work/qemu/qemu-git/qemu-img create -f qcow2 -o cluster_size=2M,preallocation=metadata t1 25G > Formatting 't1', fmt=qcow2 size=26843545600 encryption=off cluster_size=2097152 preallocation='metadata' lazy_refcounts=off > > $ ll t1 > -rw-r--r-- 1 cmeng cmeng 26851940352 May 27 21:20 t1 > > $ ./qcow2.py t1 get-cluster-offset 52428799 > l1_size, 1 l1_table_offset, 6291456 cluster_bits, 21 cluster_size, 2097152 l2_entries_per_cluster, 262144 > l1_entry (l1_refcount, l2_offset) : (1L, 8388608L) > l2_entry (l2_compressed, l2_refcount_is_one, (cluster_offset, read_as_zero)) : (0L, 1L, (26851934208L, 0L)) > final offset : 26854030848 > > I modified qcow2.py to get the offset into the host image file of the > last sector of the virutal image. As shown above, the offset is > 26854030848, which is a little bigger than 26851940352, the size of t1. > > Signed-off-by: Cong Meng <mengcong@meituan.com> > --- > block/qcow2.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/block/qcow2.c b/block/qcow2.c > index a4b97e8..c315fb7 100644 > --- a/block/qcow2.c > +++ b/block/qcow2.c > @@ -1538,6 +1538,7 @@ static int preallocate(BlockDriverState *bs) > int num; > int ret; > QCowL2Meta *meta; > + BDRVQcowState *s = bs->opaque; > > nb_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS; > offset = 0; > @@ -1582,6 +1583,8 @@ static int preallocate(BlockDriverState *bs) > if (host_offset != 0) { > uint8_t buf[BDRV_SECTOR_SIZE]; > memset(buf, 0, BDRV_SECTOR_SIZE); > + host_offset += offset_into_cluster(s, > + offset - (num << BDRV_SECTOR_BITS)); > ret = bdrv_write(bs->file, (host_offset >> BDRV_SECTOR_BITS) + num - 1, > buf, 1); I don't understand what problem this calculation is supposed to fix. Can you explain the root cause? It seems that the issue stems from: while (nb_sectors) { num = MIN(nb_sectors, INT_MAX >> BDRV_SECTOR_BITS); ret = qcow2_alloc_cluster_offset(bs, offset, &num, &host_offset, &meta); INT_MAX >> BDRV_SECTOR_BITS is not a multiple of cluster size. That means 'num' will not be a multiple of cluster size, even though full clusters were allocated by qcow2_alloc_cluster_offset(). Try changing it to: (INT_MAX & ~(s->cluster_size - 1)) >> BDRV_SECTOR_BITS Now the loop will allocate full clusters until the last iteration. Stefan
diff --git a/block/qcow2.c b/block/qcow2.c index a4b97e8..c315fb7 100644 --- a/block/qcow2.c +++ b/block/qcow2.c @@ -1538,6 +1538,7 @@ static int preallocate(BlockDriverState *bs) int num; int ret; QCowL2Meta *meta; + BDRVQcowState *s = bs->opaque; nb_sectors = bdrv_getlength(bs) >> BDRV_SECTOR_BITS; offset = 0; @@ -1582,6 +1583,8 @@ static int preallocate(BlockDriverState *bs) if (host_offset != 0) { uint8_t buf[BDRV_SECTOR_SIZE]; memset(buf, 0, BDRV_SECTOR_SIZE); + host_offset += offset_into_cluster(s, + offset - (num << BDRV_SECTOR_BITS)); ret = bdrv_write(bs->file, (host_offset >> BDRV_SECTOR_BITS) + num - 1, buf, 1); if (ret < 0) {
cow2_alloc_cluster_offset() sets the host_offset pointing to the first byte of the cluster referenced by guest_offset other than to the exact byte referenced by guest_offset. In this case, preallocate() fails to extend the image large enough. This bug can be reproduced by following steps: $ /home/cmeng/work/qemu/qemu-git/qemu-img create -f qcow2 -o cluster_size=2M,preallocation=metadata t1 25G Formatting 't1', fmt=qcow2 size=26843545600 encryption=off cluster_size=2097152 preallocation='metadata' lazy_refcounts=off $ ll t1 -rw-r--r-- 1 cmeng cmeng 26851940352 May 27 21:20 t1 $ ./qcow2.py t1 get-cluster-offset 52428799 l1_size, 1 l1_table_offset, 6291456 cluster_bits, 21 cluster_size, 2097152 l2_entries_per_cluster, 262144 l1_entry (l1_refcount, l2_offset) : (1L, 8388608L) l2_entry (l2_compressed, l2_refcount_is_one, (cluster_offset, read_as_zero)) : (0L, 1L, (26851934208L, 0L)) final offset : 26854030848 I modified qcow2.py to get the offset into the host image file of the last sector of the virutal image. As shown above, the offset is 26854030848, which is a little bigger than 26851940352, the size of t1. Signed-off-by: Cong Meng <mengcong@meituan.com> --- block/qcow2.c | 3 +++ 1 file changed, 3 insertions(+)