[PATCH 6/6] jffs2: add runtime toggle for write verification

[zhouminqiang]

Write verification is a diagnostic facility that adds read-back
overhead to every write. In production, this overhead is undesirable
unless fault isolation is required.

Add a module parameter jffs2.write_verify (bool, 0644) that defaults
to off when CONFIG_JFFS2_FS_WRITE_VERIFY is enabled. The verification
entry checks READ_ONCE(jffs2_write_verify) and returns immediately
when disabled, avoiding any overhead. The parameter can be toggled at
runtime via /sys/module/jffs2/parameters/write_verify or set at
boot/modprobe time.

Signed-off-by: zhouminqiang <zhouminqiang2 at huawei.com>
---
 fs/jffs2/Kconfig  |  8 ++++++++
 fs/jffs2/writev.c | 23 +++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/fs/jffs2/Kconfig b/fs/jffs2/Kconfig
index 556025a5d438..03dadbd003cd 100644
--- a/fs/jffs2/Kconfig
+++ b/fs/jffs2/Kconfig
@@ -61,6 +61,14 @@ config JFFS2_FS_WRITE_VERIFY
 	  tell transport/program-time corruption from post-commit media
 	  damage.
 
+	  Verification defaults to off when this option is selected and can
+	  be enabled at runtime via sysfs:
+
+	    /sys/module/jffs2/parameters/write_verify
+
+	  Write 0 to disable, 1 to enable.  Boot/modprobe parameter
+	  jffs2.write_verify=0|1 is also supported.
+
 	  If unsure, say 'N'.
 
 config JFFS2_SUMMARY
diff --git a/fs/jffs2/writev.c b/fs/jffs2/writev.c
index fc1eae60c476..b32eb07747f4 100644
--- a/fs/jffs2/writev.c
+++ b/fs/jffs2/writev.c
@@ -9,12 +9,32 @@
  *
  */
 
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include <linux/kernel.h>
+#include <linux/module.h>
 #include <linux/vmalloc.h>
 #include <linux/mtd/mtd.h>
 #include "nodelist.h"
 
 #ifdef CONFIG_JFFS2_FS_WRITE_VERIFY
+/*
+ * Optional read-back after writes.
+ *
+ * Catch cases where data is corrupted after node CRCs are calculated but
+ * before it is correctly programmed -- e.g. in RAM or during DMA/bus
+ * transfer to the flash controller -- so mtd_write() succeeds while the
+ * medium does not match the in-memory image.
+ *
+ * Runtime toggle: /sys/module/jffs2/parameters/write_verify
+ * (also boot/modprobe: jffs2.write_verify=0|1)
+ */
+static bool jffs2_write_verify;
+module_param_named(write_verify, jffs2_write_verify, bool, 0644);
+MODULE_PARM_DESC(write_verify,
+		 "Verify flash writes by reading back (default: N)");
+
+
 int jffs2_verify_write(struct jffs2_sb_info *c, const unsigned char *buf,
 			      uint32_t ofs, size_t len)
 {
@@ -23,6 +43,9 @@ int jffs2_verify_write(struct jffs2_sb_info *c, const unsigned char *buf,
 	char *eccstr;
 	void *verify_buf;
 
+	if (!READ_ONCE(jffs2_write_verify))
+		return 0;
+
 	verify_buf = __vmalloc(len, GFP_NOFS);
 	if (!verify_buf) {
 		pr_warn("%s(): verify buffer allocation failed, skipping verification\n",
-- 
2.52.0