Re: [PATCH v2 2/2] xen/device-tree: add a helper to dump an FDT in DTS-like format

["Orzel, Michal" <michal.orzel@xxxxxxx>]

On 12-Oct-26 09:34, Oleksii Kurochko wrote:
> The device tree Xen builds for dom0/hwdom or for a dom0less domain is
> only ever consumed by the guest, so a mistake in it surfaces as an
> obscure failure inside the domain, far away from the code which
> produced the tree.
> 
> Add device_tree_dump(). The output follows dtc's format so that a dump
> can be diffed against the source DTS or fed back to dtc; the value
> formatting heuristics are ported from dtc's utilfdt_print_data() for
> that reason. The walk itself goes through libfdt rather than decoding
> the tag stream by hand as dtc's fdtdump does.
> 
> Dumping a whole tree is only useful while debugging and costs both code
> size and a lot of console output, so it is put under its own option,
> CONFIG_DEVICE_TREE_DUMP. It is separate from CONFIG_DEVICE_TREE_DEBUG
> because the generated tree is often all that is needed, without the rest
> of the device tree debug messages.
> 
> Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
> ---
> Changes in v2:
>  - Dump the device tree generated for dom0/hwdom as well.
>  - Put the dump under its own CONFIG_DEVICE_TREE_DUMP instead of
>    CONFIG_DEVICE_TREE_DEBUG.
>  - Pass the domain to device_tree_dump() and print the "Device tree for"
>    header from it.
>  - Combine isprint() with isascii(), as Xen's isprint() also accepts
>    the characters 0xa0-0xff, unlike the one dtc uses.
>  - Update the commit message.
> ---
> ---
>  xen/Kconfig.debug                       |  10 ++
>  xen/arch/arm/domain_build.c             |   2 +
>  xen/common/device-tree/Makefile         |   1 +
>  xen/common/device-tree/dom0less-build.c |   3 +
>  xen/common/device-tree/fdt-dump.c       | 185 ++++++++++++++++++++++++
>  xen/include/xen/bootfdt.h               |  16 ++
>  6 files changed, 217 insertions(+)
>  create mode 100644 xen/common/device-tree/fdt-dump.c
> 
> diff --git a/xen/Kconfig.debug b/xen/Kconfig.debug
> index d900d926c555..45cff9dbc467 100644
> --- a/xen/Kconfig.debug
> +++ b/xen/Kconfig.debug
> @@ -98,6 +98,16 @@ config DEVICE_TREE_DEBUG
>         logged in the Xen ring buffer.
>         If unsure, say N here.
>  
> +config DEVICE_TREE_DUMP
> +     bool "Dump generated device trees"
> +     depends on DEVICE_TREE_PARSE
> +     help
> +       The device tree Xen generates for dom0/hwdom and for each dom0less
> +       domain is printed on the Xen console in a DTS-like format.
> +       The dump is logged at debug level, so on a non-debug build it is
> +       only shown with "loglvl=all".
That's not correct. loglvl="debug" is enough. That said, I don't find it
particularly necessary for the second part of the sentence to be part of the
help message. If you want to keep it, fix the loglvl.

> +       If unsure, say N here.
> +
>  config SCRUB_DEBUG
>       bool "Page scrubbing test"
>       default DEBUG
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 72d531618045..6a20af23e1bb 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -1705,6 +1705,8 @@ static int __init prepare_dtb_hwdom(struct domain *d, 
> struct kernel_info *kinfo)
>      if ( ret < 0 )
>          goto err;
>  
> +    device_tree_dump(d, kinfo->fdt);
> +
>      return 0;
>  
>    err:
> diff --git a/xen/common/device-tree/Makefile b/xen/common/device-tree/Makefile
> index 9036e455d66a..730d202349eb 100644
> --- a/xen/common/device-tree/Makefile
> +++ b/xen/common/device-tree/Makefile
> @@ -6,6 +6,7 @@ obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += domain-build.init.o
>  obj-$(filter $(CONFIG_DOM0LESS_BOOT),$(CONFIG_HAS_DEVICE_TREE_DISCOVERY)) += 
> dom0less-build.init.o
>  obj-$(CONFIG_DOM0LESS_BOOT) += dom0less-bindings.init.o
>  obj-$(CONFIG_OVERLAY_DTB) += dt-overlay.o
> +obj-$(CONFIG_DEVICE_TREE_DUMP) += fdt-dump.init.o
>  obj-$(CONFIG_HAS_DEVICE_TREE_DISCOVERY) += intc.o
>  obj-$(CONFIG_DOMAIN_BUILD_HELPERS) += kernel.o
>  obj-$(CONFIG_STATIC_EVTCHN) += static-evtchn.init.o
> diff --git a/xen/common/device-tree/dom0less-build.c 
> b/xen/common/device-tree/dom0less-build.c
> index fcbeb8adbd73..24a9c6b1e3e1 100644
> --- a/xen/common/device-tree/dom0less-build.c
> +++ b/xen/common/device-tree/dom0less-build.c
> @@ -1,5 +1,6 @@
>  /* SPDX-License-Identifier: GPL-2.0-only */
>  
> +#include <xen/bootfdt.h>
>  #include <xen/bootinfo.h>
>  #include <xen/device_tree.h>
>  #include <xen/dom0less-build.h>
> @@ -587,6 +588,8 @@ static int __init prepare_dtb_domU(struct domain *d, 
> struct kernel_info *kinfo)
>      if ( ret < 0 )
>          goto err;
>  
> +    device_tree_dump(d, kinfo->fdt);
> +
>      return 0;
>  
>    err:
> diff --git a/xen/common/device-tree/fdt-dump.c 
> b/xen/common/device-tree/fdt-dump.c
> new file mode 100644
> index 000000000000..296ae0d90d12
> --- /dev/null
> +++ b/xen/common/device-tree/fdt-dump.c
> @@ -0,0 +1,185 @@
> +/* SPDX-License-Identifier: GPL-2.0-or-later */
> +/*
> + * Dump a flattened device tree blob in a DTS-like format.
> + *
> + * is_printable_string() and print_value() are derived from
> + * util_is_printable_string() and utilfdt_print_data() in the device tree
> + * compiler (dtc).
> + *
> + * Copyright 2011 The Chromium Authors, All Rights Reserved.
> + * Copyright 2008 Jon Loeliger, Freescale Semiconductor, Inc.
> + * util_is_printable_string contributed by
> + *      Pantelis Antoniou <pantelis.antoniou AT gmail.com>
> + */
> +
> +#include <xen/bootfdt.h>
> +#include <xen/ctype.h>
> +#include <xen/init.h>
> +#include <xen/lib.h>
> +#include <xen/libfdt/libfdt.h>
> +#include <xen/types.h>
> +
> +/* Deeper nodes are still printed, but not indented any further. */
> +#define DUMP_MAX_INDENT_DEPTH 32
> +
> +/* Indentation, in characters, of a node at depth @depth. */
> +static int __init indent_of(int depth)
> +{
> +    return 2 * min(depth, DUMP_MAX_INDENT_DEPTH);
Can we use 4 spaces instead of 2 here and in print_properties() call. It does
look more readable IMO and matches the indentation (1 tab = 4 spaces) of dtc
when converting dtb to dts.

Other than that:
Reviewed-by: Michal Orzel <michal.orzel@xxxxxxx>

~Michal