Re: [PATCH for-7.2 v2 14/20] qmp/hmp, device_tree.c: introduce dumpdtb

[Daniel Henrique Barboza]

On 8/8/22 00:30, David Gibson wrote:
> On Fri, Aug 05, 2022 at 06:39:42AM -0300, Daniel Henrique Barboza wrote:
> > To save the FDT blob we have the '-machine dumpdtb=<file>' property.
> > With this property set, the machine saves the FDT in <file> and exit.
> > The created file can then be converted to plain text dts format using
> > 'dtc'.
> >
> > There's nothing particularly sophisticated into saving the FDT that
> > can't be done with the machine at any state, as long as the machine has
> > a valid FDT to be saved.
> >
> > The 'dumpdtb' command receives a 'filename' paramenter and, if a valid
> > FDT is available, it'll save it in a file 'filename'. In short, this is
> > a '-machine dumpdtb' that can be fired on demand via QMP/HMP.
> >
> > A valid FDT consists of a FDT that was created using libfdt being
> > retrieved via 'current_machine->fdt' in device_tree.c. This condition is
> > met by most FDT users in QEMU.
>
> On spapr at least, the fdt can change at runtime (due to hotplugs).
> So we need to think about concurrency between fdt updates and dumping
> it with this command.  I'm assuming it's protected by the BQL, but I'm
> wondering if we should outright state that somewhere for clarity.

Your assumption is right. It is protected by BQL since it's always executed
in-band. To not hold BQL we would need to declare an extra flag "allow-oob"
to execute the command out-of-band.

I'll mention in the commit msg that we're holding BQL. I'll do the same for
the 'info fdt' commit msg.


Thanks,


Daniel


> > Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
> > ---
> >   hmp-commands.hx              | 13 +++++++++++++
> >   include/monitor/hmp.h        |  1 +
> >   include/sysemu/device_tree.h |  1 +
> >   monitor/hmp-cmds.c           | 12 ++++++++++++
> >   monitor/qmp-cmds.c           | 13 +++++++++++++
> >   qapi/machine.json            | 17 +++++++++++++++++
> >   softmmu/device_tree.c        | 18 ++++++++++++++++++
> >   7 files changed, 75 insertions(+)
> >
> > diff --git a/hmp-commands.hx b/hmp-commands.hx
> > index 182e639d14..d2554e9701 100644
> > --- a/hmp-commands.hx
> > +++ b/hmp-commands.hx
> > @@ -1800,3 +1800,16 @@ ERST
> >                         "\n\t\t\t\t\t limit on a specified virtual cpu",
> >           .cmd        = hmp_cancel_vcpu_dirty_limit,
> >       },
> > +
> > +SRST
> > +``dumpdtb`` *filename*
> > +  Save the FDT in the 'filename' file to be decoded using dtc.
> > +  Requires 'libfdt' support.
> > +ERST
> > +    {
> > +        .name       = "dumpdtb",
> > +        .args_type  = "filename:s",
> > +        .params     = "[filename] file to save the FDT",
> > +        .help       = "save the FDT in the 'filename' file to be decoded using 
> > dtc",
> > +        .cmd        = hmp_dumpdtb,
> > +    },
> > diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> > index a618eb1e4e..d7f324da59 100644
> > --- a/include/monitor/hmp.h
> > +++ b/include/monitor/hmp.h
> > @@ -134,6 +134,7 @@ void hmp_calc_dirty_rate(Monitor *mon, const QDict *qdict);
> >   void hmp_set_vcpu_dirty_limit(Monitor *mon, const QDict *qdict);
> >   void hmp_cancel_vcpu_dirty_limit(Monitor *mon, const QDict *qdict);
> >   void hmp_info_vcpu_dirty_limit(Monitor *mon, const QDict *qdict);
> > +void hmp_dumpdtb(Monitor *mon, const QDict *qdict);
> >   void hmp_human_readable_text_helper(Monitor *mon,
> >                                       HumanReadableText *(*qmp_handler)(Error 
> > **));
> >   void hmp_info_stats(Monitor *mon, const QDict *qdict);
> > diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
> > index ef060a9759..bf7684e4ed 100644
> > --- a/include/sysemu/device_tree.h
> > +++ b/include/sysemu/device_tree.h
> > @@ -136,6 +136,7 @@ int qemu_fdt_add_path(void *fdt, const char *path);
> >       } while (0)
> >   
> >   void qemu_fdt_dumpdtb(void *fdt, int size);
> > +void qemu_fdt_qmp_dumpdtb(const char *filename, Error **errp);
> >   
> >   /**
> >    * qemu_fdt_setprop_sized_cells_from_array:
> > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> > index c6cd6f91dd..d23ec85f9d 100644
> > --- a/monitor/hmp-cmds.c
> > +++ b/monitor/hmp-cmds.c
> > @@ -2472,3 +2472,15 @@ exit:
> >   exit_no_print:
> >       error_free(err);
> >   }
> > +
> > +void hmp_dumpdtb(Monitor *mon, const QDict *qdict)
> > +{
> > +    const char *filename = qdict_get_str(qdict, "filename");
> > +    Error *local_err = NULL;
> > +
> > +    qmp_dumpdtb(filename, &local_err);
> > +
> > +    if (local_err) {
> > +        error_report_err(local_err);
> > +    }
> > +}
> > diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
> > index 7314cd813d..8415aca08c 100644
> > --- a/monitor/qmp-cmds.c
> > +++ b/monitor/qmp-cmds.c
> > @@ -45,6 +45,7 @@
> >   #include "hw/intc/intc.h"
> >   #include "hw/rdma/rdma.h"
> >   #include "monitor/stats.h"
> > +#include "sysemu/device_tree.h"
> >   
> >   NameInfo *qmp_query_name(Error **errp)
> >   {
> > @@ -596,3 +597,15 @@ bool apply_str_list_filter(const char *string, strList 
> > *list)
> >       }
> >       return false;
> >   }
> > +
> > +#ifdef CONFIG_FDT
> > +void qmp_dumpdtb(const char *filename, Error **errp)
> > +{
> > +    return qemu_fdt_qmp_dumpdtb(filename, errp);
> > +}
> > +#else
> > +void qmp_dumpdtb(const char *filename, Error **errp)
> > +{
> > +    error_setg(errp, "dumpdtb requires libfdt");
> > +}
> > +#endif
> > diff --git a/qapi/machine.json b/qapi/machine.json
> > index 6afd1936b0..aeb013f3dd 100644
> > --- a/qapi/machine.json
> > +++ b/qapi/machine.json
> > @@ -1664,3 +1664,20 @@
> >        '*size': 'size',
> >        '*max-size': 'size',
> >        '*slots': 'uint64' } }
> > +
> > +##
> > +# @dumpdtb:
> > +#
> > +# Save the FDT in dtb format. Requires 'libfdt' support.
> > +#
> > +# @filename: name of the FDT file to be created
> > +#
> > +# Since: 7.2
> > +#
> > +# Example:
> > +#   {"execute": "dumpdtb"}
> > +#    "arguments": { "filename": "/tmp/fdt.dtb" } }
> > +#
> > +##
> > +{ 'command': 'dumpdtb',
> > +  'data': { 'filename': 'str' } }
> > diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> > index 6ca3fad285..cd487ddd4d 100644
> > --- a/softmmu/device_tree.c
> > +++ b/softmmu/device_tree.c
> > @@ -643,3 +643,21 @@ out:
> >       g_free(propcells);
> >       return ret;
> >   }
> > +
> > +void qemu_fdt_qmp_dumpdtb(const char *filename, Error **errp)
> > +{
> > +    int size;
> > +
> > +    if (!current_machine->fdt) {
> > +        error_setg(errp, "Unable to find the machine FDT");
> > +        return;
> > +    }
> > +
> > +    size = fdt_totalsize(current_machine->fdt);
> > +
> > +    if (g_file_set_contents(filename, current_machine->fdt, size, NULL)) {
> > +        return;
> > +    }
> > +
> > +    error_setg(errp, "Error when saving machine FDT to file %s", filename);
> > +}