Re: [Qemu-devel] [PATCH v7 03/11] dump-guest-memory: using static DumpState, add DumpStatus

[Peter Xu <peterx@redhat.com>]

On Tue, Feb 16, 2016 at 01:32:00PM +0100, Andrew Jones wrote:
> On Tue, Feb 16, 2016 at 03:50:53PM +0800, Peter Xu wrote:
> > Instead of malloc/free each time for DumpState, make it
> > static. Added DumpStatus to show status for dump.
> 
> I see that the motivation for making DumpState static is for
> dump_in_progress(). DumpState isn't massive, but it isn't tiny
> either, so maybe we should just have a global pointer instead?
> dump_in_progress() can report DUMP_STATUS_NONE when the pointer
> is NULL, or whatever the status is, when it's not.

I chose to use static dump state mostly for the simplicity of
implementation.

If I use a dynamic one, I can save some memory spaces when there is
no dump task, however since it's async dump with dedicated thread, I
need at least a lock to protect the global pointer when to
use/malloc/free it, since there can be concurrent operations (e.g.,
when dump thread finished and trying to free the dump state, one
user might be querying dump status too). So I just chose not to save
the 200+ bytes.

One more thing a static dump state could bring is that, instead of
letting the user know "there is/is't a dump running", we can let him
know something more, like: "no dump started" or "latest dump
finished, with total written bytes XXX". Also, user can always check
for all the information with the last time he/she did the dump
(which I take it as a tiny small enhancement too).

Thanks.
Peter

> 
> drew
> 
> > 
> > This is to be used for detached dump.
> > 
> > Signed-off-by: Peter Xu <peterx@redhat.com>
> > Reviewed-by: Fam Zheng <famz@redhat.com>
> > ---
> >  dump.c                | 21 ++++++++++++++++-----
> >  include/sysemu/dump.h |  2 ++
> >  qapi-schema.json      | 18 ++++++++++++++++++
> >  3 files changed, 36 insertions(+), 5 deletions(-)
> > 
> > diff --git a/dump.c b/dump.c
> > index c4a62d9..434bc60 100644
> > --- a/dump.c
> > +++ b/dump.c
> > @@ -1442,6 +1442,14 @@ static void get_max_mapnr(DumpState *s)
> >      s->max_mapnr = dump_paddr_to_pfn(s, last_block->target_end);
> >  }
> >  
> > +static DumpState dump_state_global = { .status = DUMP_STATUS_NONE };
> > +
> > +static void dump_state_prepare(DumpState *s)
> > +{
> > +    /* zero the struct, setting status to active */
> > +    *s = (DumpState) { .status = DUMP_STATUS_ACTIVE };
> > +}
> > +
> >  static void dump_init(DumpState *s, int fd, bool has_format,
> >                        DumpGuestMemoryFormat format, bool paging, bool has_filter,
> >                        int64_t begin, int64_t length, Error **errp)
> > @@ -1676,24 +1684,27 @@ void qmp_dump_guest_memory(bool paging, const char *file,
> >          return;
> >      }
> >  
> > -    s = g_malloc0(sizeof(DumpState));
> > +    s = &dump_state_global;
> > +    dump_state_prepare(s);
> >  
> >      dump_init(s, fd, has_format, format, paging, has_begin,
> >                begin, length, &local_err);
> >      if (local_err) {
> > -        g_free(s);
> >          error_propagate(errp, local_err);
> > +        s->status = DUMP_STATUS_FAILED;
> >          return;
> >      }
> >  
> >      if (has_format && format != DUMP_GUEST_MEMORY_FORMAT_ELF) {
> > -        create_kdump_vmcore(s, errp);
> > +        create_kdump_vmcore(s, &local_err);
> >      } else {
> > -        create_vmcore(s, errp);
> > +        create_vmcore(s, &local_err);
> >      }
> >  
> > +    s->status = (local_err ? DUMP_STATUS_FAILED : DUMP_STATUS_COMPLETED);
> > +    error_propagate(errp, local_err);
> > +
> >      dump_cleanup(s);
> > -    g_free(s);
> >  }
> >  
> >  DumpGuestMemoryCapability *qmp_query_dump_guest_memory_capability(Error **errp)
> > diff --git a/include/sysemu/dump.h b/include/sysemu/dump.h
> > index 2f04b24..21fc02d 100644
> > --- a/include/sysemu/dump.h
> > +++ b/include/sysemu/dump.h
> > @@ -38,6 +38,7 @@
> >  
> >  #include "sysemu/dump-arch.h"
> >  #include "sysemu/memory_mapping.h"
> > +#include "qapi-types.h"
> >  
> >  typedef struct QEMU_PACKED MakedumpfileHeader {
> >      char signature[16];     /* = "makedumpfile" */
> > @@ -176,6 +177,7 @@ typedef struct DumpState {
> >      off_t offset_page;          /* offset of page part in vmcore */
> >      size_t num_dumpable;        /* number of page that can be dumped */
> >      uint32_t flag_compress;     /* indicate the compression format */
> > +    DumpStatus status;          /* current dump status */
> >  } DumpState;
> >  
> >  uint16_t cpu_to_dump16(DumpState *s, uint16_t val);
> > diff --git a/qapi-schema.json b/qapi-schema.json
> > index caff580..ccd30c8 100644
> > --- a/qapi-schema.json
> > +++ b/qapi-schema.json
> > @@ -2219,6 +2219,24 @@
> >              '*format': 'DumpGuestMemoryFormat'} }
> >  
> >  ##
> > +# @DumpStatus
> > +#
> > +# Describe the status of a long-running background guest memory dump.
> > +#
> > +# @none: no dump-guest-memory has started yet.
> > +#
> > +# @active: there is one dump running in background.
> > +#
> > +# @completed: the last dump has finished successfully.
> > +#
> > +# @failed: the last dump has failed.
> > +#
> > +# Since 2.6
> > +##
> > +{ 'enum': 'DumpStatus',
> > +  'data': [ 'none', 'active', 'completed', 'failed' ] }
> > +
> > +##
> >  # @DumpGuestMemoryCapability:
> >  #
> >  # A list of the available formats for dump-guest-memory
> > -- 
> > 2.4.3
> > 
> >