On Mon, Aug 29, 2022 at 07:00:55PM -0300, Daniel Henrique Barboza wrote: > > > On 8/29/22 00:34, David Gibson wrote: > > On Fri, Aug 26, 2022 at 11:11:44AM -0300, Daniel Henrique Barboza 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; > > > }; > > > > So, I'm reasonably convinced allowing dumping the whole dtb from > > qmp/hmp is useful. I'm less convined that info fdt is worth the > > additional complexity it incurs. Note that as well as being able to > > decompile a whole dtb using dtc, you can also extract and list > > specific properties from a dtb blob using the 'fdtget' tool which is > > part of the dtc tree. > > What's your opinion on patch 21/21, where 'dumpdtb' can write a formatted > FDT in a file with an extra option? That was possible because of the > format helpers introduced for 'info fdt'. The idea is that since we're > able to format a FDT in DTS format, we can also write the FDT in text > format without relying on DTC to decode it.
Since it's mostly the same code, I think it's reasonable to throw in if the info fdt stuff is there, but I don't think it's worth including without that. As a whole, I remain dubious that (info fdt + dumpdts) is worth the complexity cost. People with more practical experience debugging the embedded ARM platforms might have a different opinion if they thing info fdt would be really useful though. > If we think that this 'dumpdtb' capability is worth having, I can respin > the patches without 'info fdt' but adding these helpers to enable this > 'dumpdtb' support. If not, then we can just remove patches 15-21 and > be done with it. > > > Thanks, > > > Daniel > > > > > > > > > Cc: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > Acked-by: Dr. David Alan Gilbert <dgilb...@redhat.com> > > > Signed-off-by: Daniel Henrique Barboza <danielhb...@gmail.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 1c7bfd3b9d..93a4103afa 100644 > > > --- a/monitor/hmp-cmds.c > > > +++ b/monitor/hmp-cmds.c > > > @@ -2484,3 +2484,16 @@ void hmp_dumpdtb(Monitor *mon, const QDict *qdict) > > > hmp_handle_error(mon, 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..6b15f6ace2 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); > > > +} > > > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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