[PATCH v6 14/14] qmp/hmp, device_tree.c: introduce dumpdtb

[Daniel Henrique Barboza <danielhb413@gmail.com>]

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.

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).

Cc: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: Markus Armbruster <armbru@redhat.com>
Cc: Alistair Francis <alistair.francis@wdc.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>
---
 hmp-commands.hx              | 15 +++++++++++++++
 include/sysemu/device_tree.h |  1 +
 monitor/misc.c               |  1 +
 qapi/machine.json            | 18 ++++++++++++++++++
 softmmu/device_tree.c        | 31 +++++++++++++++++++++++++++++++
 5 files changed, 66 insertions(+)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 182e639d14..9a3e57504f 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -1800,3 +1800,18 @@ ERST
                       "\n\t\t\t\t\t limit on a specified virtual cpu",
         .cmd        = hmp_cancel_vcpu_dirty_limit,
     },
+
+#if defined(CONFIG_FDT)
+SRST
+``dumpdtb`` *filename*
+  Save the FDT in the 'filename' file to be decoded using dtc.
+  Requires 'libfdt' support.
+ERST
+    {
+        .name       = "dumpdtb",
+        .args_type  = "filename:F",
+        .params     = "filename",
+        .help       = "save the FDT in the 'filename' file to be decoded using dtc",
+        .cmd        = hmp_dumpdtb,
+    },
+#endif
diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
index ef060a9759..e7c5441f56 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 hmp_dumpdtb(Monitor *mon, const QDict *qdict);
 
 /**
  * qemu_fdt_setprop_sized_cells_from_array:
diff --git a/monitor/misc.c b/monitor/misc.c
index 3d2312ba8d..e7dd63030b 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -49,6 +49,7 @@
 #include "sysemu/blockdev.h"
 #include "sysemu/sysemu.h"
 #include "sysemu/tpm.h"
+#include "sysemu/device_tree.h"
 #include "qapi/qmp/qdict.h"
 #include "qapi/qmp/qerror.h"
 #include "qapi/qmp/qstring.h"
diff --git a/qapi/machine.json b/qapi/machine.json
index 6afd1936b0..f968a5d343 100644
--- a/qapi/machine.json
+++ b/qapi/machine.json
@@ -1664,3 +1664,21 @@
      '*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' },
+  'if': 'CONFIG_FDT' }
diff --git a/softmmu/device_tree.c b/softmmu/device_tree.c
index 6ca3fad285..cdd41b6de6 100644
--- a/softmmu/device_tree.c
+++ b/softmmu/device_tree.c
@@ -26,6 +26,9 @@
 #include "hw/loader.h"
 #include "hw/boards.h"
 #include "qemu/config-file.h"
+#include "qapi/qapi-commands-machine.h"
+#include "qapi/qmp/qdict.h"
+#include "monitor/hmp.h"
 
 #include <libfdt.h>
 
@@ -643,3 +646,31 @@ out:
     g_free(propcells);
     return ret;
 }
+
+void qmp_dumpdtb(const char *filename, Error **errp)
+{
+    g_autoptr(GError) err = NULL;
+    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, &err)) {
+        error_setg(errp, "Error saving FDT to file %s: %s",
+                   filename, err->message);
+    }
+}
+
+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);
+
+    hmp_handle_error(mon, local_err);
+}
-- 
2.37.2