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Date:   Wed, 18 Mar 2020 11:42:50 -0700
From:   Kees Cook <keescook@chromium.org>
To:     WeiXiong Liao <liaoweixiong@allwinnertech.com>
Cc:     Anton Vorontsov <anton@enomsg.org>,
        Colin Cross <ccross@android.com>,
        Tony Luck <tony.luck@intel.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Richard Weinberger <richard@nod.at>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        Mauro Carvalho Chehab <mchehab+samsung@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Rob Herring <robh@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mtd@lists.infradead.org
Subject: Re: [PATCH v2 08/11] blkoops: respect for device to pick recorders
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 <1581078355-19647-9-git-send-email-liaoweixiong@allwinnertech.com>
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In the subject and through-out:

s/recorders/pstore front-ends/

On Fri, Feb 07, 2020 at 08:25:52PM +0800, WeiXiong Liao wrote:
> It's one of a series of patches for adaptive to MTD device.

typo: adapting

> 
> MTD device is not block device. The sector of flash (MTD device) will be
> broken if erase over limited cycles. Avoid damaging block so fast, we
> can not write to a sector frequently. So, the recorders of pstore/blk
> like console and ftrace recorder should not be supported.
> 
> Besides, mtd device need aligned write/erase size. To avoid
> over-erasing/writing flash, we should keep a aligned cache and read old
> data to cache before write/erase, which make codes more complex. So,
> pmsg do not be supported now because it writes misaligned.
> 
> How about dmesg? Luckly, pstore/blk keeps several aligned chunks for
> dmesg and uses one by one for wear balance.
> 
> So, MTD device for pstore should pick recorders, that is why the patch
> here.
> 
> Signed-off-by: WeiXiong Liao <liaoweixiong@allwinnertech.com>
> ---
>  Documentation/admin-guide/pstore-block.rst |  9 +++++++++
>  fs/pstore/blkoops.c                        | 29 +++++++++++++++++++++--------
>  include/linux/blkoops.h                    | 14 +++++++++++++-
>  3 files changed, 43 insertions(+), 9 deletions(-)
> 
> diff --git a/Documentation/admin-guide/pstore-block.rst b/Documentation/admin-guide/pstore-block.rst
> index be865dfc1a28..299142b3d8e6 100644
> --- a/Documentation/admin-guide/pstore-block.rst
> +++ b/Documentation/admin-guide/pstore-block.rst
> @@ -166,6 +166,15 @@ It is only required by block device which is registered by
>  ``blkoops_register_blkdev``.  It's the major device number of registered
>  devices, by which blkoops can get the matching driver for @blkdev.
>  
> +flags
> +~~~~~
> +
> +Refer to macro starting with *BLKOOPS_DEV_SUPPORT_* which is defined in
> +*linux/blkoops.h*. They tell us that which pstore/blk recorders this device
> +supports. Default zero means all recorders for compatible, witch is the same

typo: witch -> which

> +as BLKOOPS_DEV_SUPPORT_ALL. Recorder works only when chunk size is not zero
> +and device support.

There are already flags for this, please see "Supported frontends"
in include/linux/pstore.h

> +
>  total_size
>  ~~~~~~~~~~
>  
> diff --git a/fs/pstore/blkoops.c b/fs/pstore/blkoops.c
> index c76bab671b0b..01170b344f00 100644
> --- a/fs/pstore/blkoops.c
> +++ b/fs/pstore/blkoops.c
> @@ -128,9 +128,16 @@ int blkoops_register_device(struct blkoops_device *bo_dev)
>  		return -ENOMEM;
>  	}
>  
> -#define verify_size(name, defsize, alignsize) {				\
> -		long _##name_ = (name);					\
> -		if (_##name_ < 0)					\
> +	/* zero means all recorders for compatible */
> +	if (bo_dev->flags == BLKOOPS_DEV_SUPPORT_DEFAULT)
> +		bo_dev->flags = BLKOOPS_DEV_SUPPORT_ALL;
> +#define verify_size(name, defsize, alignsize, enable) {			\
> +		long _##name_;						\
> +		if (!(enable))						\
> +			_##name_ = 0;					\
> +		else if ((name) >= 0)					\
> +			_##name_ = (name);				\
> +		else							\
>  			_##name_ = (defsize);				\
>  		_##name_ = _##name_ <= 0 ? 0 : (_##name_ * 1024);	\
>  		if (_##name_ & ((alignsize) - 1)) {			\
> @@ -142,10 +149,14 @@ int blkoops_register_device(struct blkoops_device *bo_dev)
>  		bzinfo->name = _##name_;				\
>  	}
>  
> -	verify_size(dmesg_size, DEFAULT_DMESG_SIZE, 4096);
> -	verify_size(pmsg_size, DEFAULT_PMSG_SIZE, 4096);
> -	verify_size(console_size, DEFAULT_CONSOLE_SIZE, 4096);
> -	verify_size(ftrace_size, DEFAULT_FTRACE_SIZE, 4096);
> +	verify_size(dmesg_size, DEFAULT_DMESG_SIZE, 4096,
> +			bo_dev->flags & BLKOOPS_DEV_SUPPORT_DMESG);
> +	verify_size(pmsg_size, DEFAULT_PMSG_SIZE, 4096,
> +			bo_dev->flags & BLKOOPS_DEV_SUPPORT_PMSG);
> +	verify_size(console_size, DEFAULT_CONSOLE_SIZE, 4096,
> +			bo_dev->flags & BLKOOPS_DEV_SUPPORT_CONSOLE);
> +	verify_size(ftrace_size, DEFAULT_FTRACE_SIZE, 4096,
> +			bo_dev->flags & BLKOOPS_DEV_SUPPORT_FTRACE);

I'd kind of prefer this patch be moved much earlier in the series so
that the later additions of front-end support doesn't have to be touched
twice. i.e. when PMSG support is added, it is added as a whole here and
does the flag check in that patch, etc.

>  #undef verify_size
>  	dump_oops = !!(dump_oops < 0 ? DEFAULT_DUMP_OOPS : dump_oops);
>  
> @@ -336,6 +347,7 @@ static ssize_t blkoops_blk_panic_write(const char *buf, size_t size,
>   * register block device to blkoops
>   * @major: the major device number of registering device
>   * @panic_write: the write interface for panic case.
> + * @flags: Refer to macro starting with BLKOOPS_DEV_SUPPORT.
>   *
>   * It is ONLY used for block device to register to blkoops. In this case,
>   * the module parameter @blkdev must be valid. Generic read/write interfaces
> @@ -349,7 +361,7 @@ static ssize_t blkoops_blk_panic_write(const char *buf, size_t size,
>   * panic occurs but pstore/blk does not recover yet, the first zone of dmesg
>   * will be used.
>   */
> -int blkoops_register_blkdev(unsigned int major,
> +int blkoops_register_blkdev(unsigned int major, unsigned int flags,
>  		blkoops_blk_panic_write_op panic_write)
>  {
>  	struct block_device *bdev;
> @@ -372,6 +384,7 @@ int blkoops_register_blkdev(unsigned int major,
>  	if (bo_dev.total_size == 0)
>  		goto err_put_bdev;
>  	bo_dev.panic_write = panic_write ? blkoops_blk_panic_write : NULL;
> +	bo_dev.flags = flags;
>  	bo_dev.read = blkoops_generic_blk_read;
>  	bo_dev.write = blkoops_generic_blk_write;
>  
> diff --git a/include/linux/blkoops.h b/include/linux/blkoops.h
> index 71c596fd4cc8..bc7665d14a98 100644
> --- a/include/linux/blkoops.h
> +++ b/include/linux/blkoops.h
> @@ -6,6 +6,7 @@
>  #include <linux/types.h>
>  #include <linux/blkdev.h>
>  #include <linux/pstore_blk.h>
> +#include <linux/bitops.h>
>  
>  /**
>   * struct blkoops_device - backend blkoops driver structure.
> @@ -14,6 +15,10 @@
>   * blkoops_register_device(). If block device, you are strongly recommended
>   * to use blkoops_register_blkdev().
>   *
> + * @flags:
> + *	Refer to macro starting with BLKOOPS_DEV_SUPPORT_. These macros tell
> + *	us that which pstore/blk recorders this device supports. Zero means
> + *	all recorders for compatible.
>   * @total_size:
>   *	The total size in bytes pstore/blk can use. It must be greater than
>   *	4096 and be multiple of 4096.
> @@ -38,6 +43,13 @@
>   *	On error, negative number should be returned.
>   */
>  struct blkoops_device {
> +	unsigned int flags;
> +#define BLKOOPS_DEV_SUPPORT_ALL		UINT_MAX
> +#define BLKOOPS_DEV_SUPPORT_DEFAULT	(0)
> +#define BLKOOPS_DEV_SUPPORT_DMESG	BIT(0)
> +#define BLKOOPS_DEV_SUPPORT_PMSG	BIT(1)
> +#define BLKOOPS_DEV_SUPPORT_CONSOLE	BIT(2)
> +#define BLKOOPS_DEV_SUPPORT_FTRACE	BIT(3)
>  	unsigned long total_size;
>  	blkz_read_op read;
>  	blkz_write_op write;
> @@ -54,7 +66,7 @@ typedef int (*blkoops_blk_panic_write_op)(const char *buf, sector_t start_sect,
>  
>  int  blkoops_register_device(struct blkoops_device *bo_dev);
>  void blkoops_unregister_device(struct blkoops_device *bo_dev);
> -int  blkoops_register_blkdev(unsigned int major,
> +int  blkoops_register_blkdev(unsigned int major, unsigned int flags,
>  		blkoops_blk_panic_write_op panic_write);
>  void blkoops_unregister_blkdev(unsigned int major);
>  int  blkoops_blkdev_info(dev_t *devt, sector_t *nr_sects, sector_t *start_sect);
> -- 
> 1.9.1
> 

-- 
Kees Cook