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/openbmc/qemu/include/sysemu/ |
H A D | dump.h | d43a01db Mon Sep 18 18:32:32 CDT 2023 Stephen Brennan <stephen.s.brennan@oracle.com> dump: Allow directly outputting raw kdump format
The flattened format (currently output by QEMU) is used by makedumpfile only when it is outputting a vmcore to a file which is not seekable. The flattened format functions essentially as a set of instructions of the form "seek to the given offset, then write the given bytes out".
The flattened format can be reconstructed using makedumpfile -R, or makedumpfile-R.pl, but it is a slow process because it requires copying the entire vmcore. The flattened format can also be directly read by crash, but still, it requires a lengthy reassembly phase.
To sum up, the flattened format is not an ideal one: it should only be used on files which are actually not seekable. This is the exact strategy which makedumpfile uses, as seen in the implementation of "write_buffer()" in makedumpfile [1]. However, QEMU has always used the flattened format. For compatibility it is best not to change the default output format without warning. So, add a flag to DumpState which changes the output to use the normal (i.e. raw) format. This flag will be added to the QMP and HMP commands in the next change.
[1]: https://github.com/makedumpfile/makedumpfile/blob/f23bb943568188a2746dbf9b6692668f5a2ac3b6/makedumpfile.c#L5008-L5040
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> [ Marc-André: replace loff_t with off_t ] Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-Id: <20230918233233.1431858-3-stephen.s.brennan@oracle.com>
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/openbmc/qemu/dump/ |
H A D | dump.c | d43a01db Mon Sep 18 18:32:32 CDT 2023 Stephen Brennan <stephen.s.brennan@oracle.com> dump: Allow directly outputting raw kdump format
The flattened format (currently output by QEMU) is used by makedumpfile only when it is outputting a vmcore to a file which is not seekable. The flattened format functions essentially as a set of instructions of the form "seek to the given offset, then write the given bytes out".
The flattened format can be reconstructed using makedumpfile -R, or makedumpfile-R.pl, but it is a slow process because it requires copying the entire vmcore. The flattened format can also be directly read by crash, but still, it requires a lengthy reassembly phase.
To sum up, the flattened format is not an ideal one: it should only be used on files which are actually not seekable. This is the exact strategy which makedumpfile uses, as seen in the implementation of "write_buffer()" in makedumpfile [1]. However, QEMU has always used the flattened format. For compatibility it is best not to change the default output format without warning. So, add a flag to DumpState which changes the output to use the normal (i.e. raw) format. This flag will be added to the QMP and HMP commands in the next change.
[1]: https://github.com/makedumpfile/makedumpfile/blob/f23bb943568188a2746dbf9b6692668f5a2ac3b6/makedumpfile.c#L5008-L5040
Signed-off-by: Stephen Brennan <stephen.s.brennan@oracle.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> [ Marc-André: replace loff_t with off_t ] Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Message-Id: <20230918233233.1431858-3-stephen.s.brennan@oracle.com>
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