Re: [PATCH v2 qemu 3/3] dump: Add qmp argument "reassembled"

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Sep 13, 2023 at 06:03:15PM -0700, Stephen Brennan wrote:
> This can be used from QMP command line as "-R" to mirror the
> corresponding flag for makedumpfile. This enables the kdump_reassembled
> flag introduced in the previous patch.
> 
> Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com>
> ---
>  dump/dump-hmp-cmds.c |  8 +++++++-
>  dump/dump.c          | 12 +++++++++++-
>  hmp-commands.hx      |  7 +++++--
>  qapi/dump.json       | 14 +++++++++++++-
>  4 files changed, 36 insertions(+), 5 deletions(-)

> diff --git a/qapi/dump.json b/qapi/dump.json
> index 4ae1f722a9..9cc7c3ea93 100644
> --- a/qapi/dump.json
> +++ b/qapi/dump.json
> @@ -69,6 +69,18 @@
>  #     to dump all guest's memory, please specify the start @begin and
>  #     @length
>  #
> +# @reassembled: if false (the default), the kdump output formats will use the
> +#     "makedumpfile flattened" variant of the format, which is less broadly
> +#     compatible with analysis tools. The flattened dump can be reassembled
> +#     after the fact using the command "makedumpfile -R". If true, Qemu
> +#     attempts to generate the standard kdump format. This requires a
> +#     seekable file as output -- if the output file is not seekable, then
> +#     the flattened format is still generated. The standard format is more
> +#     broadly compatible with debugging tools, but generating it requires a
> +#     seekable output file descriptor, and could use more system memory due
> +#     to page cache utilization. This should be left unspecified for non-kdump
> +#     output formats.
> +#
>  # @format: if specified, the format of guest memory dump.  But non-elf
>  #     format is conflict with paging and filter, ie.  @paging, @begin
>  #     and @length is not allowed to be specified with non-elf @format
> @@ -89,7 +101,7 @@
>  { 'command': 'dump-guest-memory',
>    'data': { 'paging': 'bool', 'protocol': 'str', '*detach': 'bool',
>              '*begin': 'int', '*length': 'int',
> -            '*format': 'DumpGuestMemoryFormat'} }
> +            '*reassembled': 'bool', '*format': 'DumpGuestMemoryFormat'} }

The 'reassembled' flag is changing the meaning of 3 out of the 5
'format' enum values. IMHO, we should just be adding new formats
instead of changing the meaning of existing formats. It is a shame
we have the current 'kdump' naming prefix, but we're stuck with
that for backwards compat, we need a new prefix. I'd suggest
'kdump-raw'. eg

#
# @DumpGuestMemoryFormat:
#
# An enumeration of guest-memory-dump's format.
#
# @elf: elf format
#
# @kdump-zlib: makedumpfile flattened, kdump-compressed format with zlib-compressed
#
# @kdump-lzo: makedumpfile flattened, kdump-compressed format with lzo-compressed
#
# @kdump-snappy: makedumpfile flattened, kdump-compressed format with snappy-compressed
#
# @kdump-raw-zlib: raw assembled kdump-compressed format with zlib-compressed (since 8.2)
#
# @kdump-raw-lzo: raw assembled kdump-compressed format with lzo-compressed (since 8.2)
#
# @kdump-raw-snappy: raw assembled kdump-compressed format with snappy-compressed (since 8.2)
#
# @win-dmp: Windows full crashdump format, can be used instead of ELF
#     converting (since 2.13)
#
# Since: 2.0
##
{ 'enum': 'DumpGuestMemoryFormat',
  'data': [ 'elf',
            'kdump-zlib', 'kdump-lzo', 'kdump-snappy',
            'kdump-raw-zlib', 'kdump-raw-lzo', 'kdump-raw-snappy',
            'win-dmp' ] }


With regards,
Daniel
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