Re: [PATCH 2/5] libfdt: Add namelen variants for setprop

Ayush Singh <ayush@xxxxxxxxxxxxxxx> · Tue, 3 Dec 2024 13:01:17 +0530

On 03/12/24 09:42, David Gibson wrote:
Sorry I've taken so long to reply.

On Sat, Nov 16, 2024 at 08:30:20PM +0530, Ayush Singh wrote:
Helper functions to setproperty with length of property name similar to
getprop_namelen variants.

The idea of this patch is good, independent of the rest of the series.
I'm kind of surprised we don't already have a setprop_namelen()
actually.

Unfortunately, this implementation isn't usable as is.

Ok, I will fix things and send this as a separate patch series. I will 
need to make a lot of changes in the rest of the patch series anyway, so 
it should work out well.



Signed-off-by: Ayush Singh <ayush@xxxxxxxxxxxxxxx>
---
  libfdt/fdt_rw.c | 19 +++++++++++++++++
  libfdt/libfdt.h | 63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
  util.h          |  1 +
  3 files changed, 83 insertions(+)

diff --git a/libfdt/fdt_rw.c b/libfdt/fdt_rw.c
index 3621d3651d3f4bd82b7af66c60d023e3139add03..9e66c2332bf4d3868c1388c294a195b152b6aefd 100644
--- a/libfdt/fdt_rw.c
+++ b/libfdt/fdt_rw.c
@@ -7,6 +7,8 @@
  
  #include <fdt.h>
  #include <libfdt.h>
+#include "../util.h"
+#include <assert.h>

libfdt is designed to compile and work in limited environments (early
stage bootloaders, for example).  Therefore it's very limited in what
libc functions it's permitted to use: basically it can only use the
things listed in libfdt_env.h.

assert() is not ok, malloc() is right out.

  #include "libfdt_internal.h"
  
@@ -288,6 +290,23 @@ int fdt_setprop(void *fdt, int nodeoffset, const char *name,
  	return 0;
  }
  
+int fdt_setprop_namelen(void *fdt, int nodeoffset, const char *name,
+			size_t namelen, const void *val, int len)
+{
+	int ret;
+	char *name_temp = xmalloc(namelen + 1);

As noted, we don't use an allocator in libfdt.  In fact that's a large
part of the reason the _namlen() functions exist in the first place.
To add this, you'll need to start with an fdt_get_property_namelen_w()
in terms of fdt_get_property_namelen(), then make
fdt_resize_property_() and fdt_add_property_() take the name length,
then finally fdt_setprop_placeholder_namelen() and
fdt_setprop_namelen().  The current fdt_setprop_placeholder() and
fdt_setprop() can then become trivial wrappers around the namelen
versions (like fdt_getprop() wraps fdt_getprop_namelen()).

+
+	assert(namelen <= strlen(name));
+
+	memcpy(name_temp, name, namelen);
+	name_temp[namelen] = '\0';
+	ret = fdt_setprop(fdt, nodeoffset, name_temp, val, len);
+
+	free(name_temp);
+
+	return ret;
+}
+
  int fdt_appendprop(void *fdt, int nodeoffset, const char *name,
  		   const void *val, int len)
  {
diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h
index 96782bc57b8412d73dff92d6e0ad494ec0a23909..999b3800dff5c001b9c1babf370d45024c81a9aa 100644
--- a/libfdt/libfdt.h
+++ b/libfdt/libfdt.h
@@ -1690,6 +1690,38 @@ int fdt_set_name(void *fdt, int nodeoffset, const char *name);
  int fdt_setprop(void *fdt, int nodeoffset, const char *name,
  		const void *val, int len);
  
+/**
+ * fdt_setprop_namelen - create or change a property
+ * @fdt: pointer to the device tree blob
+ * @nodeoffset: offset of the node whose property to change
+ * @name: name of the property to change
+ * @namelen: length of the name
+ * @val: pointer to data to set the property value to
+ * @len: length of the property value
+ *
+ * fdt_setprop_namelen() sets the value of the named property in the given
+ * node to the given value and length, creating the property if it
+ * does not already exist.
+ *
+ * This function may insert or delete data from the blob, and will
+ * therefore change the offsets of some existing nodes.
+ *
+ * returns:
+ *	0, on success
+ *	-FDT_ERR_NOSPACE, there is insufficient free space in the blob to
+ *		contain the new property value
+ *	-FDT_ERR_BADOFFSET, nodeoffset did not point to FDT_BEGIN_NODE tag
+ *	-FDT_ERR_BADLAYOUT,
+ *	-FDT_ERR_BADMAGIC,
+ *	-FDT_ERR_BADVERSION,
+ *	-FDT_ERR_BADSTATE,
+ *	-FDT_ERR_BADSTRUCTURE,
+ *	-FDT_ERR_BADLAYOUT,
+ *	-FDT_ERR_TRUNCATED, standard meanings
+ */
+int fdt_setprop_namelen(void *fdt, int nodeoffset, const char *name,
+			size_t namelen, const void *val, int len);
+
  /**
   * fdt_setprop_placeholder - allocate space for a property
   * @fdt: pointer to the device tree blob
@@ -1839,6 +1871,37 @@ static inline int fdt_setprop_cell(void *fdt, int nodeoffset, const char *name,
  #define fdt_setprop_string(fdt, nodeoffset, name, str) \
  	fdt_setprop((fdt), (nodeoffset), (name), (str), strlen(str)+1)
  
+/**
+ * fdt_setprop_namelen_string - set a property to a string value
+ * @fdt: pointer to the device tree blob
+ * @nodeoffset: offset of the node whose property to change
+ * @name: name of the property to change
+ * @str: string value for the property
+ *
+ * fdt_setprop_namelen_string() sets the value of the named property in the
+ * given node to the given string value (using the length of the
+ * string to determine the new length of the property), or creates a
+ * new property with that value if it does not already exist.
+ *
+ * This function may insert or delete data from the blob, and will
+ * therefore change the offsets of some existing nodes.
+ *
+ * returns:
+ *	0, on success
+ *	-FDT_ERR_NOSPACE, there is insufficient free space in the blob to
+ *		contain the new property value
+ *	-FDT_ERR_BADOFFSET, nodeoffset did not point to FDT_BEGIN_NODE tag
+ *	-FDT_ERR_BADLAYOUT,
+ *	-FDT_ERR_BADMAGIC,
+ *	-FDT_ERR_BADVERSION,
+ *	-FDT_ERR_BADSTATE,
+ *	-FDT_ERR_BADSTRUCTURE,
+ *	-FDT_ERR_BADLAYOUT,
+ *	-FDT_ERR_TRUNCATED, standard meanings
+ */
+#define fdt_setprop_namelen_string(fdt, nodeoffset, name, namelen, str)    \
+	fdt_setprop_namelen((fdt), (nodeoffset), (name), (namelen), (str), \
+			    strlen(str) + 1)
  
  /**
   * fdt_setprop_empty - set a property to an empty value
diff --git a/util.h b/util.h
index 800f2e2c55b150d3c30101d1e1f1daaa0e4e3264..3e2ebaabe1e8c7e9ad6821ac2ca17a72e7f4f57d 100644
--- a/util.h
+++ b/util.h
@@ -6,6 +6,7 @@
  #include <stdarg.h>
  #include <stdbool.h>
  #include <getopt.h>
+#include <stdio.h>
  
  /*
   * Copyright 2011 The Chromium Authors, All Rights Reserved.



Ayush Singh








