Re: [Devel] [PATCH hci-8.1 0/3] dm-qcow2: keep images of a read-only table unmodified

[Alexander Ivanov <alexander.ivanov@virtuozzo.com>]

On 10/29/26 12:42, Konstantin Khorenko wrote:
> Three things found while reviewing the series, none of them for it.
> Please fix them separately.
>
> - A v3 image with header_length < 104 is not rejected. The only check
>    is header_length < sizeof(struct QCowHeader), and only when the
>    compression bit is set. qemu fails such an image with "qcow2 header
>    too short". For us the extension parser then starts inside the
>    header.
>
> - For a v2 image hdr->header_length is never set, so it stays 0 from
>    kzalloc() and the extensions are parsed from offset 0 of the header
>    instead of 72. qemu sets header_length = 72 for v2.
>
> - The table mode is still tested against FMODE_WRITE in
>    qcow2_check_convert_hdr(), qcow2_attach_file(),
>    qcow2_truncate_preallocations(), qcow2_postsuspend() and
>    qcow2_preresume(), while the series switched to BLK_OPEN_WRITE. Same
>    value today, but dm_table_get_mode() returns blk_mode_t. The is_ro
>    in qcow2_check_convert_hdr() has only a commented-out user and can go.
>
>
> Please file appropriate tasks and fix them separately.

Created tasks:
https://virtuozzo.atlassian.net/browse/VSTOR-152393

https://virtuozzo.atlassian.net/browse/VSTOR-152394

https://virtuozzo.atlassian.net/browse/VSTOR-152395

> --
> Best regards,
>
> Konstantin Khorenko,
> Virtuozzo Linux Kernel Team
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