Re: [Qemu-devel] [PATCH V3] block/vhdx: add check for truncated image files

[Kevin Wolf <kwolf@redhat.com>]

Am 03.09.2019 um 15:35 hat Peter Lieven geschrieben:
> qemu is currently not able to detect truncated vhdx image files.
> Add a basic check if all allocated blocks are reachable at open and
> report all errors during bdrv_co_check.
> 
> Signed-off-by: Peter Lieven <pl@kamp.de>
> ---
> V3: - check for bdrv_getlength failure [Kevin]
>     - use uint32_t for i [Kevin]
>     - check for BAT entry overflow [Kevin]
>     - break on !errcnt in second check
> 
> V2: - add error reporting [Kevin]
>     - use bdrv_getlength instead of bdrv_get_allocated_file_size [Kevin]
>     - factor out BAT entry check and add error reporting for region
>       overlaps
>     - already check on vhdx_open

Something still seems to be wrong with this patch:

    213      fail       [15:50:13] [15:50:14]      (last: 2s)    output mismatch (see 213.out.bad)
    --- /home/kwolf/source/qemu/tests/qemu-iotests/213.out  2019-06-28 14:19:50.065797707 +0200
    +++ /home/kwolf/source/qemu/tests/qemu-iotests/213.out.bad      2019-09-04 15:50:14.582053976 +0200
    @@ -46,10 +46,8 @@
     {"execute": "job-dismiss", "arguments": {"id": "job0"}}
     {"return": {}}

    -image: TEST_IMG
    -file format: IMGFMT
    -virtual size: 32 MiB (33554432 bytes)
    -cluster_size: 268435456
    +qemu-img: VHDX BAT entry 0 offset points after end of file. Image has probably been truncated.
    +qemu-img: Could not open 'TEST_IMG': Could not open 'TEST_IMG': Invalid argument

     === Invalid BlockdevRef ===

I can reproduce this manually with the following qemu-img invocations.
It seems all three options must be given to reproduce the error:

    $ ./qemu-img create -f vhdx -o block_size=268435456,subformat=fixed,block_state_zero=off /tmp/test.vhdx 32M
    Formatting '/tmp/test.vhdx', fmt=vhdx size=33554432 log_size=1048576 block_size=268435456 subformat=fixed block_state_zero=off
    $ ./qemu-img info /tmp/test.vhdx
    qemu-img: VHDX BAT entry 0 offset points after end of file. Image has probably been truncated.
    qemu-img: Could not open '/tmp/test.vhdx': Could not open '/tmp/test.vhdx': Invalid argument

If I add the offsets to the error message (would probably nice to have),
I get:

    qemu-img: VHDX BAT entry 0 offset 8388608 points after end of file (41943040). Image has probably been truncated.

So it seems that the file is large enough to hold 32M + metadata, but we
don't increase the file size to hold a full block (256M). Is this a
problem in the way we create images or are partial blocks at the end
expected?

Kevin