[1/2,v2] UBI: Add initial support for scatter gather

Adds a new set of functions to deal with scatter gather.
ubi_eba_read_leb_sg() will read from a LEB into a scatter gather list.
The new data structure struct ubi_sgl will be used within UBI to
hold the scatter gather list itself and metadata to have a cursor
within the list.

Signed-off-by: Richard Weinberger <richard@nod.at>
Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
---
 drivers/mtd/ubi/eba.c   | 56 +++++++++++++++++++++++++++++
 drivers/mtd/ubi/kapi.c  | 95 +++++++++++++++++++++++++++++++++++++++++--------
 drivers/mtd/ubi/ubi.h   |  3 ++
 include/linux/mtd/ubi.h | 46 ++++++++++++++++++++++++
 4 files changed, 185 insertions(+), 15 deletions(-)

Am 10.01.2015 um 22:52 schrieb Richard Weinberger:
> Adds a new set of functions to deal with scatter gather.
> ubi_eba_read_leb_sg() will read from a LEB into a scatter gather list.
> The new data structure struct ubi_sgl will be used within UBI to
> hold the scatter gather list itself and metadata to have a cursor
> within the list.
> 
> Signed-off-by: Richard Weinberger <richard@nod.at>
> Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

Can I please get a Reviewed-by for this patch?

Thanks,
//richard

On 01/10/2015 06:52 PM, Richard Weinberger wrote:
> Adds a new set of functions to deal with scatter gather.
> ubi_eba_read_leb_sg() will read from a LEB into a scatter gather list.
> The new data structure struct ubi_sgl will be used within UBI to
> hold the scatter gather list itself and metadata to have a cursor
> within the list.
> 
> Signed-off-by: Richard Weinberger <richard@nod.at>
> Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

Three nitpicks below, and my

Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>

> ---
>  drivers/mtd/ubi/eba.c   | 56 +++++++++++++++++++++++++++++
>  drivers/mtd/ubi/kapi.c  | 95 +++++++++++++++++++++++++++++++++++++++++--------
>  drivers/mtd/ubi/ubi.h   |  3 ++
>  include/linux/mtd/ubi.h | 46 ++++++++++++++++++++++++
>  4 files changed, 185 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
> index b698534..0aaf707 100644
> --- a/drivers/mtd/ubi/eba.c
> +++ b/drivers/mtd/ubi/eba.c
> @@ -481,6 +481,62 @@ out_unlock:
>  }
>  
>  /**
> + * ubi_eba_read_leb_sg - read data into a scatter gather list.
> + * @ubi: UBI device description object
> + * @vol: volume description object
> + * @lnum: logical eraseblock number
> + * @sgl: UBI scatter gather list to store the read data
> + * @offset: offset from where to read
> + * @len: how many bytes to read
> + * @check: data CRC check flag
> + *
> + * This function works exactly like ubi_eba_read_leb(). But instead of
> + * storing the read data into a buffer it writes to an UBI scatter gather
> + * list.
> + */
> +int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
> +			struct ubi_sgl *sgl, int lnum, int offset, int len,
> +			int check)
> +{
> +	int to_read;
> +	int ret;
> +	struct scatterlist *sg;
> +
> +	for (;;) {
> +		ubi_assert(sgl->list_pos < UBI_MAX_SG_COUNT);
> +		sg = &sgl->sg[sgl->list_pos];
> +		if (len < sg->length - sgl->page_pos)
> +			to_read = len;
> +		else
> +			to_read = sg->length - sgl->page_pos;
> +
> +		ret = ubi_eba_read_leb(ubi, vol, lnum,
> +				       sg_virt(sg) + sgl->page_pos, offset,
> +				       to_read, check);
> +		if (ret < 0)
> +			goto out;

Matter of taste, but isn't it better to just return here?

> +
> +		offset += to_read;
> +		len -= to_read;
> +		if (!len) {
> +			sgl->page_pos += to_read;
> +			if (sgl->page_pos == sg->length) {
> +				sgl->list_pos++;
> +				sgl->page_pos = 0;
> +			}
> +
> +			break;
> +		}
> +
> +		sgl->list_pos++;
> +		sgl->page_pos = 0;
> +	}
> +
> +out:
> +	return ret;
> +}
> +
> +/**
>   * recover_peb - recover from write failure.
>   * @ubi: UBI device description object
>   * @pnum: the physical eraseblock to recover
> diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
> index f3bab66..d0055a2 100644
> --- a/drivers/mtd/ubi/kapi.c
> +++ b/drivers/mtd/ubi/kapi.c
> @@ -355,6 +355,43 @@ void ubi_close_volume(struct ubi_volume_desc *desc)
>  EXPORT_SYMBOL_GPL(ubi_close_volume);
>  
>  /**
> + * leb_read_sanity_check - does sanity checks on read requests.
> + * @desc: volume descriptor
> + * @lnum: logical eraseblock number to read from
> + * @offset: offset within the logical eraseblock to read from
> + * @len: how many bytes to read
> + *
> + * This function is used by ubi_leb_read() and ubi_leb_read_sg()
> + * to perfrom sanity checks.

s/perfrom/perform

> + */
> +static int leb_read_sanity_check(struct ubi_volume_desc *desc, int lnum,
> +				 int offset, int len)
> +{
> +	struct ubi_volume *vol = desc->vol;
> +	struct ubi_device *ubi = vol->ubi;
> +	int vol_id = vol->vol_id;
> +
> +	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
> +	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
> +	    offset + len > vol->usable_leb_size)
> +		return -EINVAL;
> +
> +	if (vol->vol_type == UBI_STATIC_VOLUME) {
> +		if (vol->used_ebs == 0)
> +			/* Empty static UBI volume */
> +			return 0;
> +		if (lnum == vol->used_ebs - 1 &&
> +		    offset + len > vol->last_eb_bytes)
> +			return -EINVAL;
> +	}
> +
> +	if (vol->upd_marker)
> +		return -EBADF;
> +
> +	return 0;
> +}
> +
> +/**
>   * ubi_leb_read - read data.
>   * @desc: volume descriptor
>   * @lnum: logical eraseblock number to read from
> @@ -390,22 +427,10 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
>  
>  	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
>  
> -	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
> -	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
> -	    offset + len > vol->usable_leb_size)
> -		return -EINVAL;
> -
> -	if (vol->vol_type == UBI_STATIC_VOLUME) {
> -		if (vol->used_ebs == 0)
> -			/* Empty static UBI volume */
> -			return 0;
> -		if (lnum == vol->used_ebs - 1 &&
> -		    offset + len > vol->last_eb_bytes)
> -			return -EINVAL;
> -	}
> +	err = leb_read_sanity_check(desc, lnum, offset, len);
> +	if (err < 0)
> +		return err;
>  
> -	if (vol->upd_marker)
> -		return -EBADF;
>  	if (len == 0)
>  		return 0;
>  
> @@ -419,6 +444,46 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
>  }
>  EXPORT_SYMBOL_GPL(ubi_leb_read);
>  
> +
> +/**
> + * ubi_leb_read_sg - read data into a scatter gather list.
> + * @desc: volume descriptor
> + * @lnum: logical eraseblock number to read from
> + * @buf: buffer where to store the read data
> + * @offset: offset within the logical eraseblock to read from
> + * @len: how many bytes to read
> + * @check: whether UBI has to check the read data's CRC or not.
> + *
> + * This function works exactly like ubi_leb_read_sg(). But instead of
> + * storing the read data into a buffer it writes to an UBI scatter gather
> + * list.
> + */
> +int ubi_leb_read_sg(struct ubi_volume_desc *desc, int lnum, struct ubi_sgl *sgl,
> +		    int offset, int len, int check)
> +{
> +	struct ubi_volume *vol = desc->vol;
> +	struct ubi_device *ubi = vol->ubi;
> +	int err, vol_id = vol->vol_id;
> +
> +	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
> +
> +	err = leb_read_sanity_check(desc, lnum, offset, len);
> +	if (err < 0)
> +		return err;
> +
> +	if (len == 0)
> +		return 0;
> +
> +	err = ubi_eba_read_leb_sg(ubi, vol, sgl, lnum, offset, len, check);
> +	if (err && mtd_is_eccerr(err) && vol->vol_type == UBI_STATIC_VOLUME) {
> +		ubi_warn(ubi, "mark volume %d as corrupted", vol_id);
> +		vol->corrupted = 1;
> +	}
> +
> +	return err;
> +}
> +EXPORT_SYMBOL_GPL(ubi_leb_read_sg);
> +
>  /**
>   * ubi_leb_write - write data.
>   * @desc: volume descriptor
> diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
> index ee7ac0b..a5283cf 100644
> --- a/drivers/mtd/ubi/ubi.h
> +++ b/drivers/mtd/ubi/ubi.h
> @@ -791,6 +791,9 @@ int ubi_eba_unmap_leb(struct ubi_device *ubi, struct ubi_volume *vol,
>  		      int lnum);
>  int ubi_eba_read_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
>  		     void *buf, int offset, int len, int check);
> +int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
> +			struct ubi_sgl *sgl, int lnum, int offset, int len,
> +			int check);
>  int ubi_eba_write_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
>  		      const void *buf, int offset, int len);
>  int ubi_eba_write_leb_st(struct ubi_device *ubi, struct ubi_volume *vol,
> diff --git a/include/linux/mtd/ubi.h b/include/linux/mtd/ubi.h
> index c3918a0..3d5916d 100644
> --- a/include/linux/mtd/ubi.h
> +++ b/include/linux/mtd/ubi.h
> @@ -23,11 +23,16 @@
>  
>  #include <linux/ioctl.h>
>  #include <linux/types.h>
> +#include <linux/scatterlist.h>
>  #include <mtd/ubi-user.h>
>  
>  /* All voumes/LEBs */
>  #define UBI_ALL -1
>  
> +/* Maximum number of scatter gather list entries,
> + * we use only 64 to have a lower memory foot print. */

Multilines comments style is:

/*
 *
 */

> +#define UBI_MAX_SG_COUNT 64
> +
>  /*
>   * enum ubi_open_mode - UBI volume open mode constants.
>   *
> @@ -116,6 +121,35 @@ struct ubi_volume_info {
>  };
>  
>  /**
> + * struct ubi_sgl - UBI scatter gather list data structure.
> + * @list_pos: current position in @sg[]
> + * @page_pos: current position in @sg[@list_pos]
> + * @sg: the scatter gather list itself
> + *
> + * ubi_sgl is a wrapper around a scatter list which keeps track of the
> + * current position in the list and the current list item such that
> + * it can be used across multiple ubi_leb_read_sg() calls.
> + */
> +struct ubi_sgl {
> +	int list_pos;
> +	int page_pos;
> +	struct scatterlist sg[UBI_MAX_SG_COUNT];
> +};
> +
> +/**
> + * ubi_sgl_init - initialize an UBI scatter gather list data structure.
> + * @usgl: the UBI scatter gather struct itself
> + *
> + * Please note that you still have to use sg_init_table() or any adequate
> + * function to initialize the unterlaying struct scatterlist.
> + */
> +static inline void ubi_sgl_init(struct ubi_sgl *usgl)
> +{
> +	usgl->list_pos = 0;
> +	usgl->page_pos = 0;
> +}
> +
> +/**
>   * struct ubi_device_info - UBI device description data structure.
>   * @ubi_num: ubi device number
>   * @leb_size: logical eraseblock size on this UBI device
> @@ -210,6 +244,8 @@ int ubi_unregister_volume_notifier(struct notifier_block *nb);
>  void ubi_close_volume(struct ubi_volume_desc *desc);
>  int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
>  		 int len, int check);
> +int ubi_leb_read_sg(struct ubi_volume_desc *desc, int lnum, struct ubi_sgl *sgl,
> +		   int offset, int len, int check);
>  int ubi_leb_write(struct ubi_volume_desc *desc, int lnum, const void *buf,
>  		  int offset, int len);
>  int ubi_leb_change(struct ubi_volume_desc *desc, int lnum, const void *buf,
> @@ -230,4 +266,14 @@ static inline int ubi_read(struct ubi_volume_desc *desc, int lnum, char *buf,
>  {
>  	return ubi_leb_read(desc, lnum, buf, offset, len, 0);
>  }
> +
> +/*
> + * This function is the same as the 'ubi_leb_read_sg()' function, but it does
> + * not provide the checking capability.
> + */
> +static inline int ubi_read_sg(struct ubi_volume_desc *desc, int lnum,
> +			      struct ubi_sgl *sgl, int offset, int len)
> +{
> +	return ubi_leb_read_sg(desc, lnum, sgl, offset, len, 0);
> +}
>  #endif /* !__LINUX_UBI_H__ */
>

Am 28.01.2015 um 00:36 schrieb Ezequiel Garcia:
> On 01/10/2015 06:52 PM, Richard Weinberger wrote:
>> Adds a new set of functions to deal with scatter gather.
>> ubi_eba_read_leb_sg() will read from a LEB into a scatter gather list.
>> The new data structure struct ubi_sgl will be used within UBI to
>> hold the scatter gather list itself and metadata to have a cursor
>> within the list.
>>
>> Signed-off-by: Richard Weinberger <richard@nod.at>
>> Tested-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> 
> Three nitpicks below, and my
> 
> Reviewed-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
> 
>> ---
>>  drivers/mtd/ubi/eba.c   | 56 +++++++++++++++++++++++++++++
>>  drivers/mtd/ubi/kapi.c  | 95 +++++++++++++++++++++++++++++++++++++++++--------
>>  drivers/mtd/ubi/ubi.h   |  3 ++
>>  include/linux/mtd/ubi.h | 46 ++++++++++++++++++++++++
>>  4 files changed, 185 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/mtd/ubi/eba.c b/drivers/mtd/ubi/eba.c
>> index b698534..0aaf707 100644
>> --- a/drivers/mtd/ubi/eba.c
>> +++ b/drivers/mtd/ubi/eba.c
>> @@ -481,6 +481,62 @@ out_unlock:
>>  }
>>  
>>  /**
>> + * ubi_eba_read_leb_sg - read data into a scatter gather list.
>> + * @ubi: UBI device description object
>> + * @vol: volume description object
>> + * @lnum: logical eraseblock number
>> + * @sgl: UBI scatter gather list to store the read data
>> + * @offset: offset from where to read
>> + * @len: how many bytes to read
>> + * @check: data CRC check flag
>> + *
>> + * This function works exactly like ubi_eba_read_leb(). But instead of
>> + * storing the read data into a buffer it writes to an UBI scatter gather
>> + * list.
>> + */
>> +int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
>> +			struct ubi_sgl *sgl, int lnum, int offset, int len,
>> +			int check)
>> +{
>> +	int to_read;
>> +	int ret;
>> +	struct scatterlist *sg;
>> +
>> +	for (;;) {
>> +		ubi_assert(sgl->list_pos < UBI_MAX_SG_COUNT);
>> +		sg = &sgl->sg[sgl->list_pos];
>> +		if (len < sg->length - sgl->page_pos)
>> +			to_read = len;
>> +		else
>> +			to_read = sg->length - sgl->page_pos;
>> +
>> +		ret = ubi_eba_read_leb(ubi, vol, lnum,
>> +				       sg_virt(sg) + sgl->page_pos, offset,
>> +				       to_read, check);
>> +		if (ret < 0)
>> +			goto out;
> 
> Matter of taste, but isn't it better to just return here?

After dealing with a lot of nasty bugs in error paths in other projects I've started
using the principle of a single function exit path.
But in this case a "return ret;" is also perfectly fine as the "out" label does no cleanup.

Will fix before pushing.

>> +
>> +		offset += to_read;
>> +		len -= to_read;
>> +		if (!len) {
>> +			sgl->page_pos += to_read;
>> +			if (sgl->page_pos == sg->length) {
>> +				sgl->list_pos++;
>> +				sgl->page_pos = 0;
>> +			}
>> +
>> +			break;
>> +		}
>> +
>> +		sgl->list_pos++;
>> +		sgl->page_pos = 0;
>> +	}
>> +
>> +out:
>> +	return ret;
>> +}
>> +
>> +/**
>>   * recover_peb - recover from write failure.
>>   * @ubi: UBI device description object
>>   * @pnum: the physical eraseblock to recover
>> diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
>> index f3bab66..d0055a2 100644
>> --- a/drivers/mtd/ubi/kapi.c
>> +++ b/drivers/mtd/ubi/kapi.c
>> @@ -355,6 +355,43 @@ void ubi_close_volume(struct ubi_volume_desc *desc)
>>  EXPORT_SYMBOL_GPL(ubi_close_volume);
>>  
>>  /**
>> + * leb_read_sanity_check - does sanity checks on read requests.
>> + * @desc: volume descriptor
>> + * @lnum: logical eraseblock number to read from
>> + * @offset: offset within the logical eraseblock to read from
>> + * @len: how many bytes to read
>> + *
>> + * This function is used by ubi_leb_read() and ubi_leb_read_sg()
>> + * to perfrom sanity checks.
> 
> s/perfrom/perform

Thx.

> 
>> + */
>> +static int leb_read_sanity_check(struct ubi_volume_desc *desc, int lnum,
>> +				 int offset, int len)
>> +{
>> +	struct ubi_volume *vol = desc->vol;
>> +	struct ubi_device *ubi = vol->ubi;
>> +	int vol_id = vol->vol_id;
>> +
>> +	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
>> +	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
>> +	    offset + len > vol->usable_leb_size)
>> +		return -EINVAL;
>> +
>> +	if (vol->vol_type == UBI_STATIC_VOLUME) {
>> +		if (vol->used_ebs == 0)
>> +			/* Empty static UBI volume */
>> +			return 0;
>> +		if (lnum == vol->used_ebs - 1 &&
>> +		    offset + len > vol->last_eb_bytes)
>> +			return -EINVAL;
>> +	}
>> +
>> +	if (vol->upd_marker)
>> +		return -EBADF;
>> +
>> +	return 0;
>> +}
>> +
>> +/**
>>   * ubi_leb_read - read data.
>>   * @desc: volume descriptor
>>   * @lnum: logical eraseblock number to read from
>> @@ -390,22 +427,10 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
>>  
>>  	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
>>  
>> -	if (vol_id < 0 || vol_id >= ubi->vtbl_slots || lnum < 0 ||
>> -	    lnum >= vol->used_ebs || offset < 0 || len < 0 ||
>> -	    offset + len > vol->usable_leb_size)
>> -		return -EINVAL;
>> -
>> -	if (vol->vol_type == UBI_STATIC_VOLUME) {
>> -		if (vol->used_ebs == 0)
>> -			/* Empty static UBI volume */
>> -			return 0;
>> -		if (lnum == vol->used_ebs - 1 &&
>> -		    offset + len > vol->last_eb_bytes)
>> -			return -EINVAL;
>> -	}
>> +	err = leb_read_sanity_check(desc, lnum, offset, len);
>> +	if (err < 0)
>> +		return err;
>>  
>> -	if (vol->upd_marker)
>> -		return -EBADF;
>>  	if (len == 0)
>>  		return 0;
>>  
>> @@ -419,6 +444,46 @@ int ubi_leb_read(struct ubi_volume_desc *desc, int lnum, char *buf, int offset,
>>  }
>>  EXPORT_SYMBOL_GPL(ubi_leb_read);
>>  
>> +
>> +/**
>> + * ubi_leb_read_sg - read data into a scatter gather list.
>> + * @desc: volume descriptor
>> + * @lnum: logical eraseblock number to read from
>> + * @buf: buffer where to store the read data
>> + * @offset: offset within the logical eraseblock to read from
>> + * @len: how many bytes to read
>> + * @check: whether UBI has to check the read data's CRC or not.
>> + *
>> + * This function works exactly like ubi_leb_read_sg(). But instead of
>> + * storing the read data into a buffer it writes to an UBI scatter gather
>> + * list.
>> + */
>> +int ubi_leb_read_sg(struct ubi_volume_desc *desc, int lnum, struct ubi_sgl *sgl,
>> +		    int offset, int len, int check)
>> +{
>> +	struct ubi_volume *vol = desc->vol;
>> +	struct ubi_device *ubi = vol->ubi;
>> +	int err, vol_id = vol->vol_id;
>> +
>> +	dbg_gen("read %d bytes from LEB %d:%d:%d", len, vol_id, lnum, offset);
>> +
>> +	err = leb_read_sanity_check(desc, lnum, offset, len);
>> +	if (err < 0)
>> +		return err;
>> +
>> +	if (len == 0)
>> +		return 0;
>> +
>> +	err = ubi_eba_read_leb_sg(ubi, vol, sgl, lnum, offset, len, check);
>> +	if (err && mtd_is_eccerr(err) && vol->vol_type == UBI_STATIC_VOLUME) {
>> +		ubi_warn(ubi, "mark volume %d as corrupted", vol_id);
>> +		vol->corrupted = 1;
>> +	}
>> +
>> +	return err;
>> +}
>> +EXPORT_SYMBOL_GPL(ubi_leb_read_sg);
>> +
>>  /**
>>   * ubi_leb_write - write data.
>>   * @desc: volume descriptor
>> diff --git a/drivers/mtd/ubi/ubi.h b/drivers/mtd/ubi/ubi.h
>> index ee7ac0b..a5283cf 100644
>> --- a/drivers/mtd/ubi/ubi.h
>> +++ b/drivers/mtd/ubi/ubi.h
>> @@ -791,6 +791,9 @@ int ubi_eba_unmap_leb(struct ubi_device *ubi, struct ubi_volume *vol,
>>  		      int lnum);
>>  int ubi_eba_read_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
>>  		     void *buf, int offset, int len, int check);
>> +int ubi_eba_read_leb_sg(struct ubi_device *ubi, struct ubi_volume *vol,
>> +			struct ubi_sgl *sgl, int lnum, int offset, int len,
>> +			int check);
>>  int ubi_eba_write_leb(struct ubi_device *ubi, struct ubi_volume *vol, int lnum,
>>  		      const void *buf, int offset, int len);
>>  int ubi_eba_write_leb_st(struct ubi_device *ubi, struct ubi_volume *vol,
>> diff --git a/include/linux/mtd/ubi.h b/include/linux/mtd/ubi.h
>> index c3918a0..3d5916d 100644
>> --- a/include/linux/mtd/ubi.h
>> +++ b/include/linux/mtd/ubi.h
>> @@ -23,11 +23,16 @@
>>  
>>  #include <linux/ioctl.h>
>>  #include <linux/types.h>
>> +#include <linux/scatterlist.h>
>>  #include <mtd/ubi-user.h>
>>  
>>  /* All voumes/LEBs */
>>  #define UBI_ALL -1
>>  
>> +/* Maximum number of scatter gather list entries,
>> + * we use only 64 to have a lower memory foot print. */
> 
> Multilines comments style is:
> 
> /*
>  *
>  */

Correct. I wonder why checkpatch.pl did not bark on that.

Thanks,
//richard