Re: [PATCH for-7.2 v3 15/20] qmp/hmp, device_tree.c: introduce 'info fdt' command

[Dr. David Alan Gilbert]

* Daniel Henrique Barboza (danielhb413@gmail.com) wrote:
> Reading the FDT requires that the user saves the fdt_blob and then use
> 'dtc' to read the contents. Saving the file and using 'dtc' is a strong
> use case when we need to compare two FDTs, but it's a lot of steps if
> you want to do quick check on a certain node or property.
> 
> 'info fdt' retrieves FDT nodes (and properties, later on) and print it
> to the user. This can be used to check the FDT on running machines
> without having to save the blob and use 'dtc'.
> 
> The implementation is based on the premise that the machine thas a FDT
> created using libfdt and pointed by 'machine->fdt'. As long as this
> pre-requisite is met the machine should be able to support it.
> 
> For now we're going to add the required QMP/HMP boilerplate and the
> capability of printing the name of the properties of a given node. Next
> patches will extend 'info fdt' to be able to print nodes recursively,
> and then individual properties.
> 
> This command will always be executed in-band (i.e. holding BQL),
> avoiding potential race conditions with machines that might change the
> FDT during runtime (e.g. PowerPC 'pseries' machine).
> 
> 'info fdt' is not something that we expect to be used aside from debugging,
> so we're implementing it in QMP as 'x-query-fdt'.
> 
> This is an example of 'info fdt' fetching the '/chosen' node of the
> pSeries machine:
> 
> (qemu) info fdt /chosen
> chosen {
>     ibm,architecture-vec-5;
>     rng-seed;
>     ibm,arch-vec-5-platform-support;
>     linux,pci-probe-only;
>     stdout-path;
>     linux,stdout-path;
>     qemu,graphic-depth;
>     qemu,graphic-height;
>     qemu,graphic-width;
> }
> 
> And the same node for the aarch64 'virt' machine:
> 
> (qemu) info fdt /chosen
> chosen {
>     stdout-path;
>     rng-seed;
>     kaslr-seed;
> }
> 
> Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
> Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>

For HMP:
Acked-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  hmp-commands-info.hx         | 13 ++++++++++
>  include/monitor/hmp.h        |  1 +
>  include/sysemu/device_tree.h |  4 +++
>  monitor/hmp-cmds.c           | 13 ++++++++++
>  monitor/qmp-cmds.c           | 12 +++++++++
>  qapi/machine.json            | 19 +++++++++++++++
>  softmmu/device_tree.c        | 47 ++++++++++++++++++++++++++++++++++++
>  7 files changed, 109 insertions(+)
> 
> diff --git a/hmp-commands-info.hx b/hmp-commands-info.hx
> index 188d9ece3b..743b48865d 100644
> --- a/hmp-commands-info.hx
> +++ b/hmp-commands-info.hx
> @@ -921,3 +921,16 @@ SRST
>    ``stats``
>      Show runtime-collected statistics
>  ERST
> +
> +    {
> +        .name       = "fdt",
> +        .args_type  = "nodepath:s",
> +        .params     = "nodepath",
> +        .help       = "show firmware device tree node given its path",
> +        .cmd        = hmp_info_fdt,
> +    },
> +
> +SRST
> +  ``info fdt``
> +    Show a firmware device tree node given its path. Requires libfdt.
> +ERST
> diff --git a/include/monitor/hmp.h b/include/monitor/hmp.h
> index d7f324da59..c0883dd1e3 100644
> --- a/include/monitor/hmp.h
> +++ b/include/monitor/hmp.h
> @@ -135,6 +135,7 @@ 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_info_fdt(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 bf7684e4ed..057d13e397 100644
> --- a/include/sysemu/device_tree.h
> +++ b/include/sysemu/device_tree.h
> @@ -14,6 +14,8 @@
>  #ifndef DEVICE_TREE_H
>  #define DEVICE_TREE_H
>  
> +#include "qapi/qapi-types-common.h"
> +
>  void *create_device_tree(int *sizep);
>  void *load_device_tree(const char *filename_path, int *sizep);
>  #ifdef CONFIG_LINUX
> @@ -137,6 +139,8 @@ int qemu_fdt_add_path(void *fdt, const char *path);
>  
>  void qemu_fdt_dumpdtb(void *fdt, int size);
>  void qemu_fdt_qmp_dumpdtb(const char *filename, Error **errp);
> +HumanReadableText *qemu_fdt_qmp_query_fdt(const char *nodepath,
> +                                          Error **errp);
>  
>  /**
>   * qemu_fdt_setprop_sized_cells_from_array:
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index d23ec85f9d..accde90380 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -2484,3 +2484,16 @@ void hmp_dumpdtb(Monitor *mon, const QDict *qdict)
>          error_report_err(local_err);
>      }
>  }
> +
> +void hmp_info_fdt(Monitor *mon, const QDict *qdict)
> +{
> +    const char *nodepath = qdict_get_str(qdict, "nodepath");
> +    Error *err = NULL;
> +    g_autoptr(HumanReadableText) info = qmp_x_query_fdt(nodepath, &err);
> +
> +    if (hmp_handle_error(mon, err)) {
> +        return;
> +    }
> +
> +    monitor_printf(mon, "%s", info->human_readable_text);
> +}
> diff --git a/monitor/qmp-cmds.c b/monitor/qmp-cmds.c
> index 8415aca08c..db2c6aa7da 100644
> --- a/monitor/qmp-cmds.c
> +++ b/monitor/qmp-cmds.c
> @@ -603,9 +603,21 @@ void qmp_dumpdtb(const char *filename, Error **errp)
>  {
>      return qemu_fdt_qmp_dumpdtb(filename, errp);
>  }
> +
> +HumanReadableText *qmp_x_query_fdt(const char *nodepath, Error **errp)
> +{
> +    return qemu_fdt_qmp_query_fdt(nodepath, errp);
> +}
>  #else
>  void qmp_dumpdtb(const char *filename, Error **errp)
>  {
>      error_setg(errp, "dumpdtb requires libfdt");
>  }
> +
> +HumanReadableText *qmp_x_query_fdt(const char *nodepath, Error **errp)
> +{
> +    error_setg(errp, "this command requires libfdt");
> +
> +    return NULL;
> +}
>  #endif
> diff --git a/qapi/machine.json b/qapi/machine.json
> index aeb013f3dd..96cff541ca 100644
> --- a/qapi/machine.json
> +++ b/qapi/machine.json
> @@ -1681,3 +1681,22 @@
>  ##
>  { 'command': 'dumpdtb',
>    'data': { 'filename': 'str' } }
> +
> +##
> +# @x-query-fdt:
> +#
> +# Query for FDT element (node or property). Requires 'libfdt'.
> +#
> +# @nodepath: the path of the FDT node to be retrieved
> +#
> +# Features:
> +# @unstable: This command is meant for debugging.
> +#
> +# Returns: FDT node
> +#
> +# Since: 7.2
> +##
> +{ 'command': 'x-query-fdt',
> +  'data': { 'nodepath': 'str' },
> +  'returns': 'HumanReadableText',
> +  'features': [ 'unstable' ]  }
> diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
> index cd487ddd4d..3fb07b537f 100644
> --- a/softmmu/device_tree.c
> +++ b/softmmu/device_tree.c
> @@ -18,6 +18,7 @@
>  #endif
>  
>  #include "qapi/error.h"
> +#include "qapi/type-helpers.h"
>  #include "qemu/error-report.h"
>  #include "qemu/option.h"
>  #include "qemu/bswap.h"
> @@ -661,3 +662,49 @@ void qemu_fdt_qmp_dumpdtb(const char *filename, Error 
> **errp)
>  
>      error_setg(errp, "Error when saving machine FDT to file %s", filename);
>  }
> +
> +static void fdt_format_node(GString *buf, int node, int depth)
> +{
> +    const struct fdt_property *prop = NULL;
> +    const char *propname = NULL;
> +    void *fdt = current_machine->fdt;
> +    int padding = depth * 4;
> +    int property = 0;
> +    int prop_size;
> +
> +    g_string_append_printf(buf, "%*s%s {\n", padding, "",
> +                           fdt_get_name(fdt, node, NULL));
> +
> +    padding += 4;
> +
> +    fdt_for_each_property_offset(property, fdt, node) {
> +        prop = fdt_get_property_by_offset(fdt, property, &prop_size);
> +        propname = fdt_string(fdt, fdt32_to_cpu(prop->nameoff));
> +
> +        g_string_append_printf(buf, "%*s%s;\n", padding, "", propname);
> +    }
> +
> +    padding -= 4;
> +    g_string_append_printf(buf, "%*s}\n", padding, "");
> +}
> +
> +HumanReadableText *qemu_fdt_qmp_query_fdt(const char *nodepath, Error **errp)
> +{
> +    g_autoptr(GString) buf = g_string_new("");
> +    int node;
> +
> +    if (!current_machine->fdt) {
> +        error_setg(errp, "Unable to find the machine FDT");
> +        return NULL;
> +    }
> +
> +    node = fdt_path_offset(current_machine->fdt, nodepath);
> +    if (node < 0) {
> +        error_setg(errp, "node '%s' not found in FDT", nodepath);
> +        return NULL;
> +    }
> +
> +    fdt_format_node(buf, node, 0);
> +
> +    return human_readable_text_from_str(buf);
> +}
> -- 
> 2.37.2
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK