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

[Marc-André Lureau]

Hi

On Thu, Sep 14, 2023 at 5:03 AM Stephen Brennan
<stephen.s.brennan@oracle.com> 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/dump/dump-hmp-cmds.c b/dump/dump-hmp-cmds.c
> index b038785fee..1d882e4bd8 100644
> --- a/dump/dump-hmp-cmds.c
> +++ b/dump/dump-hmp-cmds.c
> @@ -24,9 +24,11 @@ void hmp_dump_guest_memory(Monitor *mon, const QDict 
> *qdict)
>      bool has_begin = qdict_haskey(qdict, "begin");
>      bool has_length = qdict_haskey(qdict, "length");
>      bool has_detach = qdict_haskey(qdict, "detach");
> +    bool has_reassembled = qdict_haskey(qdict, "reassembled");
>      int64_t begin = 0;
>      int64_t length = 0;
>      bool detach = false;
> +    bool reassembled = false;
>      enum DumpGuestMemoryFormat dump_format = DUMP_GUEST_MEMORY_FORMAT_ELF;
>      char *prot;
>
> @@ -61,11 +63,15 @@ void hmp_dump_guest_memory(Monitor *mon, const QDict 
> *qdict)
>      if (has_detach) {
>          detach = qdict_get_bool(qdict, "detach");
>      }
> +    if (has_reassembled) {
> +        reassembled = qdict_get_bool(qdict, "reassembled");
> +    }
>
>      prot = g_strconcat("file:", file, NULL);
>
>      qmp_dump_guest_memory(paging, prot, true, detach, has_begin, begin,
> -                          has_length, length, true, dump_format, &err);
> +                          has_length, length, true, has_reassembled,
> +                          reassembled, dump_format, &err);
>      hmp_handle_error(mon, err);
>      g_free(prot);
>  }
> diff --git a/dump/dump.c b/dump/dump.c
> index fb9040cfbc..42d4015fb3 100644
> --- a/dump/dump.c
> +++ b/dump/dump.c
> @@ -2089,6 +2089,7 @@ void qmp_dump_guest_memory(bool paging, const char 
> *file,
>                             bool has_detach, bool detach,
>                             bool has_begin, int64_t begin, bool has_length,
>                             int64_t length, bool has_format,
> +                           bool has_reassembled, bool reassembled,
>                             DumpGuestMemoryFormat format, Error **errp)
>  {
>      ERRP_GUARD();
> @@ -2119,6 +2120,12 @@ void qmp_dump_guest_memory(bool paging, const char 
> *file,
>                           "filter");
>          return;
>      }
> +    if (has_reassembled && format != DUMP_GUEST_MEMORY_FORMAT_KDUMP_ZLIB
> +                        && format != DUMP_GUEST_MEMORY_FORMAT_KDUMP_LZO
> +                        && format != DUMP_GUEST_MEMORY_FORMAT_KDUMP_SNAPPY) {
> +        error_setg(errp, "'reassembled' only applies to kdump format");
> +        return;
> +    }
>      if (has_begin && !has_length) {
>          error_setg(errp, QERR_MISSING_PARAMETER, "length");
>          return;
> @@ -2130,6 +2137,9 @@ void qmp_dump_guest_memory(bool paging, const char 
> *file,
>      if (has_detach) {
>          detach_p = detach;
>      }
> +    if (!has_reassembled) {
> +        reassembled = false;
> +    }
>
>      /* check whether lzo/snappy is supported */
>  #ifndef CONFIG_LZO
> @@ -2192,7 +2202,7 @@ void qmp_dump_guest_memory(bool paging, const char 
> *file,
>      dump_state_prepare(s);
>
>      dump_init(s, fd, has_format, format, paging, has_begin,
> -              begin, length, false, errp);
> +              begin, length, reassembled, errp);
>      if (*errp) {
>          qatomic_set(&s->status, DUMP_STATUS_FAILED);
>          return;
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 2cbd0f77a0..c3062da470 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -1085,14 +1085,15 @@ ERST
>
>      {
>          .name       = "dump-guest-memory",
> -        .args_type  = 
> "paging:-p,detach:-d,windmp:-w,zlib:-z,lzo:-l,snappy:-s,filename:F,begin:l?,length:l?",
> -        .params     = "[-p] [-d] [-z|-l|-s|-w] filename [begin length]",
> +        .args_type  = 
> "paging:-p,detach:-d,windmp:-w,zlib:-z,lzo:-l,snappy:-s,reassembled:-R,filename:F,begin:l?,length:l?",
> +        .params     = "[-p] [-d] [-z|-l|-s|-w] [-R] filename [begin length]",
>          .help       = "dump guest memory into file 'filename'.\n\t\t\t"
>                        "-p: do paging to get guest's memory mapping.\n\t\t\t"
>                        "-d: return immediately (do not wait for 
> completion).\n\t\t\t"
>                        "-z: dump in kdump-compressed format, with zlib 
> compression.\n\t\t\t"
>                        "-l: dump in kdump-compressed format, with lzo 
> compression.\n\t\t\t"
>                        "-s: dump in kdump-compressed format, with snappy 
> compression.\n\t\t\t"
> +                      "-R: when using kdump (-z, -l, -s), try to avoid the 
> flattened format.\n\t\t\t"
>                        "-w: dump in Windows crashdump format (can be used 
> instead of ELF-dump converting),\n\t\t\t"
>                        "    for Windows x86 and x64 guests with vmcoreinfo 
> driver only.\n\t\t\t"
>                        "begin: the starting physical address.\n\t\t\t"
> @@ -1115,6 +1116,8 @@ SRST
>      dump in kdump-compressed format, with lzo compression.
>    ``-s``
>      dump in kdump-compressed format, with snappy compression.
> +  ``-R``
> +    when using kdump (-z, -l, -s), try to avoid the flattened format.
>    ``-w``
>      dump in Windows crashdump format (can be used instead of ELF-dump 
> converting),
>      for Windows x64 guests with vmcoreinfo driver only
> 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

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

Will have to be adjusted to return an error if we drop the fallback behaviour.

> +#     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'} }
>
>  ##
>  # @DumpStatus:
> --
> 2.39.3
>


-- 
Marc-André Lureau