Re: [PATCH 2/2] ubi: introduce ubi.nocheck parameter to skip CRC check when attaching ubi vol

[Quentin Schulz]

Hi Richard,

On Fri, Apr 20, 2018 at 11:37:07AM +0200, Richard Weinberger wrote:
> 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?
> 

Turns out I forgot some important information and poorly worded my
commit log :)

Yes sorry, I have a squashfs (read-only by design) as the image of one
static UBI volume.

And yes, I meant when opening a static UBI volume.

Quentin

> > Signed-off-by: Quentin Schulz <quentin.schulz@xxxxxxxxxxx>
> > ---
> >  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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