Message-ID: <2085970.qGmQXvoWho@blindfold>
Date:   Fri, 20 Apr 2018 11:37:07 +0200
From:   Richard Weinberger <richard@....at>
To:     Quentin Schulz <quentin.schulz@...tlin.com>
Cc:     dedekind1@...il.com, dwmw2@...radead.org,
        computersforpeace@...il.com, boris.brezillon@...tlin.com,
        marek.vasut@...il.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com
Subject: Re: [PATCH 2/2] ubi: introduce ubi.nocheck parameter to skip CRC check when attaching ubi vol

Quentin,

Am Freitag, 20. April 2018, 10:52:41 CEST schrieb Quentin Schulz:
> There's already ECC on NAND pages so there may be no need for one to
> check the CRC of a UBI volume.
> 
> Let's introduce a ubi.nocheck parameter that let one skip the CRC check
> when attaching a UBI volume.
> 
> This also drastically speeds kernel boot by removing a potentially
> useless check, e.g. I gained 3.2s on boot time of a SPEAr600-based board
> for a ~20MB UBI volume used as rootfs.

You mean at *open* time of a *static* UBI volume?
So I guess the use case is having a read-only filesystem on top of ubiblock?

> Signed-off-by: Quentin Schulz <quentin.schulz@...tlin.com>
> ---
>  drivers/mtd/ubi/kapi.c | 70 +++++++++++++++++++++++++++++++++++++++++++-
>  drivers/mtd/ubi/ubi.h  |  6 ++++-
>  drivers/mtd/ubi/vtbl.c | 24 ++++++++++++++-
>  3 files changed, 99 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
> index d4b2e87..d604cd5 100644
> --- a/drivers/mtd/ubi/kapi.c
> +++ b/drivers/mtd/ubi/kapi.c
> @@ -28,6 +28,9 @@
>  #include <asm/div64.h>
>  #include "ubi.h"
>  
> +struct ubivol_param ubinocheck_param[UBIVOL_MAX_DEVICES];
> +int ubinocheck_devs;
> +
>  /**
>   * ubi_do_get_device_info - get information about UBI device.
>   * @ubi: UBI device description object
> @@ -865,3 +868,70 @@ int ubi_unregister_volume_notifier(struct notifier_block *nb)
>  	return blocking_notifier_chain_unregister(&ubi_notifiers, nb);
>  }
>  EXPORT_SYMBOL_GPL(ubi_unregister_volume_notifier);
> +
> +static int __init ubinocheckvol_set_param(const char *val,
> +					  const struct kernel_param *kp)
> +{
> +	int i, ret;
> +	size_t len;
> +	struct ubivol_param *param;
> +	char buf[UBIVOL_PARAM_LEN];
> +	char *pbuf = &buf[0];
> +	char *tokens[UBIVOL_PARAM_COUNT];
> +
> +	if (!val)
> +		return -EINVAL;
> +
> +	len = strnlen(val, UBIVOL_PARAM_LEN);
> +	if (len == 0) {
> +		pr_warn("UBI: nocheck: empty 'nocheck=' parameter - ignored\n");
> +		return 0;
> +	}
> +
> +	if (len == UBIVOL_PARAM_LEN) {
> +		pr_err("UBI: nocheck: parameter \"%s\" is too long, max. is %d\n",
> +		       val, UBIVOL_PARAM_LEN);
> +		return -EINVAL;
> +	}
> +
> +	strcpy(buf, val);
> +
> +	/* Get rid of the final newline */
> +	if (buf[len - 1] == '\n')
> +		buf[len - 1] = '\0';
> +
> +	for (i = 0; i < UBIVOL_PARAM_COUNT; i++)
> +		tokens[i] = strsep(&pbuf, ",");
> +
> +	param = &ubinocheck_param[ubinocheck_devs];
> +	if (tokens[1]) {
> +		/* Two parameters: can be 'ubi, vol_id' or 'ubi, vol_name' */
> +		ret = kstrtoint(tokens[0], 10, &param->ubi_num);
> +		if (ret < 0)
> +			return -EINVAL;
> +
> +		/* Second param can be a number or a name */
> +		ret = kstrtoint(tokens[1], 10, &param->vol_id);
> +		if (ret < 0) {
> +			param->vol_id = -1;
> +			strcpy(param->name, tokens[1]);
> +		}
> +	}
>

Do we really need this per volume? If your flash is trustworthy, it should not matter.
Having it per UBI instance instead of volume would make the code less complicated.

> +	ubinocheck_devs++;
> +
> +	return 0;
> +}
> +
> +static const struct kernel_param_ops ubinocheckvol_param_ops = {
> +	.set	= ubinocheckvol_set_param,
> +};
> +module_param_cb(nocheck, &ubinocheckvol_param_ops, NULL, 0);
> +MODULE_PARM_DESC(nocheck,
> +		 "Disable CRC check for UBI volumes. Parameter format: nocheck=dev,[num|name]>.\n"
> +		 "Multiple \"nocheck\" parameters may be specified.\n"
> +		 "Examples\n"
> +		 "Using the UBI device, and the volume name:\n"
> +		 "ubi.nocheck=0,rootfs\n"
> +		 "Using both UBI device number and UBI volume number:\n"
> +		 "ubi.nocheck=0,0\n");
> diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
> index 4cc6ec9..2bd89b4 100644
> --- a/drivers/mtd/ubi/ubi.h
> +++ b/drivers/mtd/ubi/ubi.h
> @@ -825,6 +825,12 @@ struct ubivol_param {
>  	char name[UBIVOL_PARAM_LEN + 1];
>  };
>  
> +/* Numbers of elements set in the @ubinocheck_param array */
> +extern int ubinocheck_devs;
> +
> +/* MTD devices specification parameters */
> +extern struct ubivol_param ubinocheck_param[UBIVOL_MAX_DEVICES];
> +
>  #include "debug.h"
>  
>  extern struct kmem_cache *ubi_wl_entry_slab;
> diff --git a/drivers/mtd/ubi/vtbl.c b/drivers/mtd/ubi/vtbl.c
> index 263743e..06b6cfd 100644
> --- a/drivers/mtd/ubi/vtbl.c
> +++ b/drivers/mtd/ubi/vtbl.c
> @@ -534,9 +534,10 @@ static int init_volumes(struct ubi_device *ubi,
>  			const struct ubi_attach_info *ai,
>  			const struct ubi_vtbl_record *vtbl)
>  {
> -	int i, reserved_pebs = 0;
> +	int i, j, reserved_pebs = 0;
>  	struct ubi_ainf_volume *av;
>  	struct ubi_volume *vol;
> +	struct ubivol_param *param;
>  
>  	for (i = 0; i < ubi->vtbl_slots; i++) {
>  		cond_resched();
> @@ -620,6 +621,27 @@ static int init_volumes(struct ubi_device *ubi,
>  			(long long)(vol->used_ebs - 1) * vol->usable_leb_size;
>  		vol->used_bytes += av->last_data_size;
>  		vol->last_eb_bytes = av->last_data_size;
> +
> +		for (j = 0; j < ubinocheck_devs; j++) {
> +			param = &ubinocheck_param[j];
> +
> +			if (vol->ubi->ubi_num != param->ubi_num)
> +				continue;
> +			if (vol->vol_id == param->vol_id) {
> +				ubi_msg(vol->ubi,
> +					"skipping CRC check for volume %d",
> +					vol->vol_id);
> +				vol->checked = true;

Please don't abuse the checked flag.
A new one a la "skip_check" does not hurt.
But again, I don't think we need it per volume.

Also don't forget to add the nocheck parameter to the ioctl() interface, such that
you can specify it also with ubiattach...

Thanks,
//richard

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