[PATCH 2/2] pstore: Allow kmsg_bytes parameter to be written at runtime

["Guilherme G. Piccoli" <gpiccoli@igalia.com>]

Currently the kmsg_bytes parameter is read-only in sysfs, though
it can be changed both via command-line at boot-time, and through
the pstore filesystem mount option, at runtime.

Add a module parameter callback in order for users to change kmsg_bytes
via the runtime sysfs interface, the same way they can do it using
the mount option.

Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
---
 fs/pstore/platform.c | 20 +++++++++++++++++++-
 1 file changed, 19 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/platform.c b/fs/pstore/platform.c
index f3a900cf2cfb..185afc3db1a4 100644
--- a/fs/pstore/platform.c
+++ b/fs/pstore/platform.c
@@ -93,7 +93,25 @@ MODULE_PARM_DESC(compress, "compression to use (deflate/none)");
 
 /* How much of the kernel log to snapshot */
 unsigned int kmsg_bytes = CONFIG_PSTORE_DEFAULT_KMSG_BYTES;
-module_param(kmsg_bytes, uint, 0444);
+static int param_set_kmsg_bytes(const char *val, const struct kernel_param *kp)
+{
+	unsigned int num;
+
+	if (kstrtouint(val, 0, &num))
+		return -EINVAL;
+
+	WRITE_ONCE(kmsg_bytes, num);
+
+	return 0;
+}
+
+static const struct kernel_param_ops kmsg_bytes_ops = {
+	.set = param_set_kmsg_bytes,
+	.get = param_get_uint,
+};
+
+module_param_cb(kmsg_bytes, &kmsg_bytes_ops, &kmsg_bytes, 0644);
+__MODULE_PARM_TYPE(kmsg_bytes, "uint");
 MODULE_PARM_DESC(kmsg_bytes, "amount of kernel log to snapshot (in bytes)");
 
 static void *compress_workspace;
-- 
2.50.1