KVM: Don't pre-reserve xarray entries when storing empty/NULL attributesgrafted

Skip the xarray reservation loop when clearing all memory attributes, as
storing NULL only erases the entry and never needs to allocate, so no
reservation (and no cleanup of a failed one) is required in that case.

Suggested-by: Sean Christopherson <seanjc@google.com>
Cc: David Ballesteros <davimaba.v@proton.me>
Signed-off-by: Zeng Chi <zengchi@kylinos.cn>
Link: https://patch.msgid.link/20260921102442.1232375-1-zeng_chi911@163.com
[sean: split to separate patch]
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/scripts/dtc/fstree.c b/scripts/dtc/fstree.c
new file mode 100644
index 000000000..0f9a534ba
--- /dev/null
+++ b/scripts/dtc/fstree.c
@@ -0,0 +1,76 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * (C) Copyright David Gibson <dwg@au1.ibm.com>, IBM Corporation.  2005.
+ */
+
+#include "dtc.h"
+
+#include <dirent.h>
+#include <sys/stat.h>
+
+static struct node *read_fstree(const char *dirname)
+{
+	DIR *d;
+	struct dirent *de;
+	struct stat st;
+	struct node *tree;
+
+	d = opendir(dirname);
+	if (!d)
+		die("Couldn't opendir() \"%s\": %s\n", dirname, strerror(errno));
+
+	tree = build_node(NULL, NULL, NULL);
+
+	while ((de = readdir(d)) != NULL) {
+		char *tmpname;
+
+		if (streq(de->d_name, ".")
+		    || streq(de->d_name, ".."))
+			continue;
+
+		tmpname = join_path(dirname, de->d_name);
+
+		if (stat(tmpname, &st) < 0)
+			die("stat(%s): %s\n", tmpname, strerror(errno));
+
+		if (S_ISREG(st.st_mode)) {
+			struct property *prop;
+			FILE *pfile;
+
+			pfile = fopen(tmpname, "rb");
+			if (! pfile) {
+				fprintf(stderr,
+					"WARNING: Cannot open %s: %s\n",
+					tmpname, strerror(errno));
+			} else {
+				prop = build_property(de->d_name,
+						      data_copy_file(pfile,
+								     st.st_size),
+						      NULL);
+				add_property(tree, prop);
+				fclose(pfile);
+			}
+		} else if (S_ISDIR(st.st_mode)) {
+			struct node *newchild;
+
+			newchild = read_fstree(tmpname);
+			newchild = name_node(newchild, xstrdup(de->d_name));
+			add_child(tree, newchild);
+		}
+
+		free(tmpname);
+	}
+
+	closedir(d);
+	return tree;
+}
+
+struct dt_info *dt_from_fs(const char *dirname)
+{
+	struct node *tree;
+
+	tree = read_fstree(dirname);
+	tree = name_node(tree, "");
+
+	return build_dt_info(DTSF_V1, NULL, tree, guess_boot_cpuid(tree));
+}