linux-kernel - Re: [Xen-devel] [PATCH v2 07/20] block/xen-blkfront: split get

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Date:	Tue, 21 Jul 2015 14:03:28 +0100
From:	Julien Grall <julien.grall@...rix.com>
To:	Roger Pau Monné <roger.pau@...rix.com>,
	<xen-devel@...ts.xenproject.org>
CC:	<ian.campbell@...rix.com>, <stefano.stabellini@...citrix.com>,
	<linux-kernel@...r.kernel.org>,
	David Vrabel <david.vrabel@...rix.com>,
	"Boris Ostrovsky" <boris.ostrovsky@...cle.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [Xen-devel] [PATCH v2 07/20] block/xen-blkfront: split get_grant
 in 2

Hi,

On 21/07/15 11:30, Roger Pau Monné wrote:
> El 09/07/15 a les 22.42, Julien Grall ha escrit:
>> Prepare the code to support 64KB page granularity. The first
>> implementation will use a full Linux page per indirect and persistent
>> grant. When non-persistent grant is used, each page of a bio request
>> may be split in multiple grant.
>>
>> Furthermore, the field page of the grant structure is only used to copy
>> data from persistent grant or indirect grant. Avoid to set it for other
>> use case as it will have no meaning given the page will be split in
>> multiple grant.
>>
>> Provide 2 functions, to setup indirect grant, the other for bio page.
>>
>> Signed-off-by: Julien Grall <julien.grall@...rix.com>
>> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>> Cc: Roger Pau Monné <roger.pau@...rix.com>
>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
>> Cc: David Vrabel <david.vrabel@...rix.com>
>> ---
>>     Changes in v2:
>>         - Patch added
>> ---
>>  drivers/block/xen-blkfront.c | 85 ++++++++++++++++++++++++++++++--------------
>>  1 file changed, 59 insertions(+), 26 deletions(-)
>>
>> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
>> index 7b81d23..95fd067 100644
>> --- a/drivers/block/xen-blkfront.c
>> +++ b/drivers/block/xen-blkfront.c
>> @@ -242,34 +242,77 @@ out_of_memory:
>>  	return -ENOMEM;
>>  }
>>  
>> -static struct grant *get_grant(grant_ref_t *gref_head,
>> -			       struct page *page,
>> -                               struct blkfront_info *info)
>> +static struct grant *get_free_grant(struct blkfront_info *info)
>>  {
>>  	struct grant *gnt_list_entry;
>> -	unsigned long buffer_mfn;
>>  
>>  	BUG_ON(list_empty(&info->grants));
>>  	gnt_list_entry = list_first_entry(&info->grants, struct grant,
>> -	                                  node);
>> +					  node);
> 
> Stray change?

No the indentation was wrong before.

> 
>>  	list_del(&gnt_list_entry->node);
>>  
>> -	if (gnt_list_entry->gref != GRANT_INVALID_REF) {
>> +	if (gnt_list_entry->gref != GRANT_INVALID_REF)
>>  		info->persistent_gnts_c--;
>> +
>> +	return gnt_list_entry;
>> +}
>> +
>> +static void grant_foreign_access(const struct grant *gnt_list_entry,
>> +				 const struct blkfront_info *info)
> 
> Given that this is just a wrapper I would make it an inline function, or
> even consider removing it and just call
> gnttab_page_grant_foreign_access_ref directly.

I prefer to keep the help as it's used in two place and make the caller
function more readable.

Most of compiler will try to inline even without the inline. This is the
case of gcc where both grant_foreign_access and even get_grant are in
fine inline. If you really want, I can add the inline.

>> +{
>> +	gnttab_page_grant_foreign_access_ref(gnt_list_entry->gref,
>> +					     info->xbdev->otherend_id,
>> +					     gnt_list_entry->page,
>> +					     0);
>> +}
>> +
>> +static struct grant *get_grant(grant_ref_t *gref_head,
>> +			       unsigned long mfn,
>> +			       struct blkfront_info *info)
> 
> Indentation.

Why? The indentation is valid, tabulation of 8 as requested by the
coding style, and will be aligned correctly in your editor. This may not
be the case in your mail reader.

> 
>> +{
>> +	struct grant *gnt_list_entry = get_free_grant(info);
>> +
>> +	if (gnt_list_entry->gref != GRANT_INVALID_REF)
>>  		return gnt_list_entry;
>> +
>> +	/* Assign a gref to this page */
>> +	gnt_list_entry->gref = gnttab_claim_grant_reference(gref_head);
>> +	BUG_ON(gnt_list_entry->gref == -ENOSPC);
>> +	if (info->feature_persistent)
>> +		grant_foreign_access(gnt_list_entry, info);
>> +	else {
>> +		/* Grant access to the MFN passed by the caller */
>> +		gnttab_grant_foreign_access_ref(gnt_list_entry->gref,
>> +			                        info->xbdev->otherend_id,
>> +				                mfn, 0);
>>  	}
>>  
>> +	return gnt_list_entry;
>> +}
>> +
>> +static struct grant *get_indirect_grant(grant_ref_t *gref_head,
>> +					struct blkfront_info *info)
> 
> Indentation.

Ditto.

Regards,

-- 
Julien Grall
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