[PATCH 15/28] orangefs: Use seq_buf for debug help string generation

orangefs_prepare_debugfs_help_string() constructs the debugfs help text in
a dynamically allocated buffer using repeated strlcat() calls across
keyword loops, rescanning the buffer on every append.

In preparation for removing the deprecated strlcat() API[1], use struct
seq_buf to build the help string. This tracks the write position across
the loops, allows formatting each keyword line with a single
seq_buf_printf() call, and checks for truncation via
seq_buf_has_overflowed().

Additionally, replace the final strlcat() call that copies the completed
string into debug_help_string with strscpy().

Link: https://github.com/KSPP/linux/issues/370 [1]
Cc: codemender-patching+linux@google.com
Assisted-by: Gemini:gemini-2.0-flash-exp [shell_command_run, editor_update_file]
Signed-off-by: Bill Wendling <morbo@google.com>
---
Cc: Russell King <linux@armlinux.org.uk>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: WANG Xuerui <kernel@xen0n.name>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
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Cc: Dave Hansen <dave.hansen@linux.intel.com>
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Cc: "Thomas Hellström" <thomas.hellstrom@linux.intel.com>
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Cc: Andrew Lunn <andrew+netdev@lunn.ch>
Cc: "David S. Miller" <davem@davemloft.net>
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---
 fs/orangefs/orangefs-debugfs.c | 36 +++++++++++++---------------------
 1 file changed, 14 insertions(+), 22 deletions(-)

diff --git a/fs/orangefs/orangefs-debugfs.c b/fs/orangefs/orangefs-debugfs.c
index 9f94919a6bc6..6e2f9887eab4 100644
--- a/fs/orangefs/orangefs-debugfs.c
+++ b/fs/orangefs/orangefs-debugfs.c

@@ -37,6 +37,7 @@
  */
 #include <linux/debugfs.h>
 #include <linux/slab.h>
+#include <linux/seq_buf.h>
 
 #include <linux/uaccess.h>
 

@@ -623,10 +624,10 @@ int orangefs_prepare_debugfs_help_string(int at_boot)
 	char *client_title = "Client Debug Keywords:\n";
 	char *kernel_title = "Kernel Debug Keywords:\n";
 	size_t string_size =  DEBUG_HELP_STRING_SIZE;
-	size_t result_size;
 	size_t i;
 	char *new;
 	int rc = -EINVAL;
+	struct seq_buf s;
 
 	gossip_debug(GOSSIP_UTILS_DEBUG, "%s: start\n", __func__);
 

@@ -640,17 +641,14 @@ int orangefs_prepare_debugfs_help_string(int at_boot)
 		goto out;
 	}
 
+	seq_buf_init(&s, new, string_size);
+
 	/*
-	 * strlcat(dst, src, size) will append at most
-	 * "size - strlen(dst) - 1" bytes of src onto dst,
-	 * null terminating the result, and return the total
-	 * length of the string it tried to create.
-	 *
 	 * We'll just plow through here building our new debug
-	 * help string and let strlcat take care of assuring that
+	 * help string and let seq_buf take care of assuring that
 	 * dst doesn't overflow.
 	 */
-	strlcat(new, client_title, string_size);
+	seq_buf_puts(&s, client_title);
 
 	if (!at_boot) {
 

@@ -665,24 +663,18 @@ int orangefs_prepare_debugfs_help_string(int at_boot)
 			goto out;
 		}
 
-		for (i = 0; i < cdm_element_count; i++) {
-			strlcat(new, "\t", string_size);
-			strlcat(new, cdm_array[i].keyword, string_size);
-			strlcat(new, "\n", string_size);
-		}
+		for (i = 0; i < cdm_element_count; i++)
+			seq_buf_printf(&s, "\t%s\n", cdm_array[i].keyword);
 	}
 
-	strlcat(new, "\n", string_size);
-	strlcat(new, kernel_title, string_size);
+	seq_buf_puts(&s, "\n");
+	seq_buf_puts(&s, kernel_title);
 
-	for (i = 0; i < num_kmod_keyword_mask_map; i++) {
-		strlcat(new, "\t", string_size);
-		strlcat(new, s_kmod_keyword_mask_map[i].keyword, string_size);
-		result_size = strlcat(new, "\n", string_size);
-	}
+	for (i = 0; i < num_kmod_keyword_mask_map; i++)
+		seq_buf_printf(&s, "\t%s\n", s_kmod_keyword_mask_map[i].keyword);
 
 	/* See if we tried to put too many bytes into "new"... */
-	if (result_size >= string_size) {
+	if (seq_buf_has_overflowed(&s)) {
 		kfree(new);
 		goto out;
 	}

@@ -692,7 +684,7 @@ int orangefs_prepare_debugfs_help_string(int at_boot)
 	} else {
 		mutex_lock(&orangefs_help_file_lock);
 		memset(debug_help_string, 0, DEBUG_HELP_STRING_SIZE);
-		strlcat(debug_help_string, new, string_size);
+		strscpy(debug_help_string, new, DEBUG_HELP_STRING_SIZE);
 		mutex_unlock(&orangefs_help_file_lock);
 		kfree(new);
 	}

-- 
2.55.0.1032.g73a4cd73de-goog