[PATCH v6 18/18] pstore/blk: Introduce "best_effort" mode

[Kees Cook]

In order to use arbitrary block devices as a pstore backend, provide a
new module param named "best_effort", which will allow using any block
device, even if it has not provided a panic_write callback.

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 fs/pstore/blk.c | 19 ++++++++++++++++++-
 1 file changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c
index 3e67bd4557ea..b7c33ef4c646 100644
--- a/fs/pstore/blk.c
+++ b/fs/pstore/blk.c
@@ -51,6 +51,10 @@ static long ftrace_size = -1;
 module_param(ftrace_size, long, 0400);
 MODULE_PARM_DESC(ftrace_size, "ftrace size in kbytes");
 
+static bool best_effort;
+module_param(best_effort, bool, 0400);
+MODULE_PARM_DESC(best_effort, "use best effort to write (i.e. do not require storage driver pstore support, default: off)");
+
 /*
  * blkdev - the block device to use for pstore storage
  *
@@ -388,7 +392,7 @@ static int __register_pstore_blk(unsigned int major, unsigned int flags,
 		return PTR_ERR(binfo);
 
 	/* only allow driver matching the @blkdev */
-	if (!binfo->devt || MAJOR(binfo->devt) != major) {
+	if (!binfo->devt || (!best_effort && MAJOR(binfo->devt) != major)) {
 		pr_debug("invalid major %u (expect %u)\n",
 				major, MAJOR(binfo->devt));
 		return -ENODEV;
@@ -532,6 +536,19 @@ int pstore_blk_usr_info(struct pstore_blk_info *info)
 }
 EXPORT_SYMBOL_GPL(pstore_blk_usr_info);
 
+static int __init pstore_blk_init(void)
+{
+	int ret = 0;
+
+	mutex_lock(&pstore_blk_lock);
+	if (!pstore_zone_info && best_effort && blkdev[0])
+		ret = __register_pstore_blk(0, 0, NULL);
+	mutex_unlock(&pstore_blk_lock);
+
+	return ret;
+}
+late_initcall(pstore_blk_init);
+
 static void __exit pstore_blk_exit(void)
 {
 	mutex_lock(&pstore_blk_lock);
-- 
2.20.1