[PATCH v7 18/18] pstore/blk: Introduce "best_effort" mode

[Kees Cook <keescook@chromium.org>]

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@chromium.org>
---
 fs/pstore/blk.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c
index 0dea8ded2de2..ad46860d5a78 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
  *
@@ -376,7 +380,8 @@ static int __register_pstore_blk(struct pstore_blk_info *info)
 	}
 
 	/* only allow driver matching the @blkdev */
-	if (!binfo.devt || MAJOR(binfo.devt) != info->major) {
+	if (!binfo.devt || (!best_effort &&
+			    MAJOR(binfo.devt) != info->major)) {
 		pr_debug("invalid major %u (expect %u)\n",
 				info->major, MAJOR(binfo.devt));
 		ret = -ENODEV;
@@ -479,6 +484,20 @@ int pstore_blk_get_config(struct pstore_blk_config *info)
 }
 EXPORT_SYMBOL_GPL(pstore_blk_get_config);
 
+static int __init pstore_blk_init(void)
+{
+	struct pstore_blk_info info = { };
+	int ret = 0;
+
+	mutex_lock(&pstore_blk_lock);
+	if (!pstore_zone_info && best_effort && blkdev[0])
+		ret = __register_pstore_blk(&info);
+	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