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Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 7/25/19 11:57 AM, Max Reitz wrote: > Compressed writes generally have to write full clusters, not just in > theory but also in practice when it comes to vmdk's streamOptimized > subformat. It currently is just silently broken for writes with > non-zero in-cluster offsets: > > $ qemu-img create -f vmdk -o subformat=streamOptimized foo.vmdk 1M > $ qemu-io -c 'write 4k 4k' -c 'read 4k 4k' foo.vmdk > wrote 4096/4096 bytes at offset 4096 > 4 KiB, 1 ops; 00.01 sec (443.724 KiB/sec and 110.9309 ops/sec) > read failed: Invalid argument > > (The technical reason is that vmdk_write_extent() just writes the > incomplete compressed data actually to offset 4k. When reading the > data, vmdk_read_extent() looks at offset 0 and finds the compressed data > size to be 0, because that is what it reads from there. This yields an > error.) > > For incomplete writes with zero in-cluster offsets, the error path when > reading the rest of the cluster is a bit different, but the result is > the same: > > $ qemu-img create -f vmdk -o subformat=streamOptimized foo.vmdk 1M > $ qemu-io -c 'write 0k 4k' -c 'read 4k 4k' foo.vmdk > wrote 4096/4096 bytes at offset 0 > 4 KiB, 1 ops; 00.01 sec (362.641 KiB/sec and 90.6603 ops/sec) > read failed: Invalid argument > > (Here, vmdk_read_extent() finds the data and then sees that the > uncompressed data is short.) > > It is better to reject invalid writes than to make the user believe they > might have succeeded and then fail when trying to read it back. > > Signed-off-by: Max Reitz > --- > block/vmdk.c | 10 ++++++++++ > 1 file changed, 10 insertions(+) > > diff --git a/block/vmdk.c b/block/vmdk.c > index db6acfc31e..641acacfe0 100644 > --- a/block/vmdk.c > +++ b/block/vmdk.c > @@ -1731,6 +1731,16 @@ static int vmdk_write_extent(VmdkExtent *extent, int64_t cluster_offset, > if (extent->compressed) { > void *compressed_data; > > + /* Only whole clusters */ > + if (offset_in_cluster || > + n_bytes > (extent->cluster_sectors * SECTOR_SIZE) || > + (n_bytes < (extent->cluster_sectors * SECTOR_SIZE) && > + offset + n_bytes != extent->end_sector * SECTOR_SIZE)) > + { > + ret = -EINVAL; > + goto out; > + } > + > if (!extent->has_marker) { > ret = -EINVAL; > goto out; > What does this look like from a guest's perspective? Is there something that enforces the alignment in the graph for us? Or is it the case that indeed guests (or users via qemu-io) can request invalid writes and we will halt the VM in those cases (in preference to corrupting the disk)?