linux-kernel - Re: use case for register_pstore

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Message-ID: <202010070007.8FF59EC42@keescook>
Date:   Wed, 7 Oct 2020 00:13:27 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Christoph Hellwig <hch@....de>
Cc:     WeiXiong Liao <gmpy.liaowx@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: use case for register_pstore_blk?

On Tue, Oct 06, 2020 at 05:52:20PM +0200, Christoph Hellwig wrote:
> Hi WeiXiong, hi Kees,
> 
> what is the use case for the code added in commit 17639f67c1d6 
> ("pstore/blk: Introduce backend for block devices").
> 
> This still doesn't have a user, and the API looks really odd to me.

pstore is a beast. :) The API is there so that a blk device can declare
its direct support of pstore (specifically, to provide a panic_write
handler).

The MTD device does this, but yes, that's a good point, there isn't a
blk device user of that entry point yet.

> By our normal kernel rules we should not add new exports without
> users and this should probably be reverted for the 5.9 release.

I don't want to revert the entire patch (I'm still using
__register_pstore_blk by way of pstore/blk's "best_effort" option), but
I wouldn't object to something like this:


diff --git a/fs/pstore/blk.c b/fs/pstore/blk.c
index fcd5563dde06..e0fe21e2cf34 100644
--- a/fs/pstore/blk.c
+++ b/fs/pstore/blk.c
@@ -419,27 +419,6 @@ static int __register_pstore_blk(struct pstore_blk_info *info)
 	return ret;
 }
 
-/**
- * register_pstore_blk() - register block device to pstore/blk
- *
- * @info: details on the desired block device interface
- *
- * Return:
- * * 0		- OK
- * * Others	- something error.
- */
-int register_pstore_blk(struct pstore_blk_info *info)
-{
-	int ret;
-
-	mutex_lock(&pstore_blk_lock);
-	ret = __register_pstore_blk(info);
-	mutex_unlock(&pstore_blk_lock);
-
-	return ret;
-}
-EXPORT_SYMBOL_GPL(register_pstore_blk);
-
 static void __unregister_pstore_blk(unsigned int major)
 {
 	struct pstore_device_info dev = { .read = psblk_generic_blk_read };
@@ -454,19 +433,6 @@ static void __unregister_pstore_blk(unsigned int major)
 	}
 }
 
-/**
- * unregister_pstore_blk() - unregister block device from pstore/blk
- *
- * @major: the major device number of device
- */
-void unregister_pstore_blk(unsigned int major)
-{
-	mutex_lock(&pstore_blk_lock);
-	__unregister_pstore_blk(major);
-	mutex_unlock(&pstore_blk_lock);
-}
-EXPORT_SYMBOL_GPL(unregister_pstore_blk);
-
 /* get information of pstore/blk */
 int pstore_blk_get_config(struct pstore_blk_config *info)
 {
diff --git a/include/linux/pstore_blk.h b/include/linux/pstore_blk.h
index 61e914522b01..2bf07d20ce43 100644
--- a/include/linux/pstore_blk.h
+++ b/include/linux/pstore_blk.h
@@ -46,9 +46,6 @@ struct pstore_blk_info {
 	sector_t start_sect;
 };
 
-int  register_pstore_blk(struct pstore_blk_info *info);
-void unregister_pstore_blk(unsigned int major);
-
 /**
  * struct pstore_device_info - back-end pstore/blk driver structure.
  *

-- 
Kees Cook