Re: [Patch v2 06/15] CIFS: Introduce helper function to get page offset and length in smb_rqst

[Tom Talpey <tom@talpey.com>]

On 6/25/2018 5:14 PM, Long Li wrote:
>> Subject: Re: [Patch v2 06/15] CIFS: Introduce helper function to get page
>> offset and length in smb_rqst
>>
>> On 5/30/2018 3:47 PM, Long Li wrote:
>>> From: Long Li <longli@microsoft.com>
>>>
>>> Introduce a function rqst_page_get_length to return the page offset
>>> and length for a given page in smb_rqst. This function is to be used
>>> by following patches.
>>>
>>> Signed-off-by: Long Li <longli@microsoft.com>
>>> ---
>>>    fs/cifs/cifsproto.h |  3 +++
>>>    fs/cifs/misc.c      | 17 +++++++++++++++++
>>>    2 files changed, 20 insertions(+)
>>>
>>> diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h index
>>> 7933c5f..89dda14 100644
>>> --- a/fs/cifs/cifsproto.h
>>> +++ b/fs/cifs/cifsproto.h
>>> @@ -557,4 +557,7 @@ int cifs_alloc_hash(const char *name, struct
>> crypto_shash **shash,
>>>    		    struct sdesc **sdesc);
>>>    void cifs_free_hash(struct crypto_shash **shash, struct sdesc
>>> **sdesc);
>>>
>>> +extern void rqst_page_get_length(struct smb_rqst *rqst, unsigned int
>> page,
>>> +				unsigned int *len, unsigned int *offset);
>>> +
>>>    #endif			/* _CIFSPROTO_H */
>>> diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c index 96849b5..e951417
>>> 100644
>>> --- a/fs/cifs/misc.c
>>> +++ b/fs/cifs/misc.c
>>> @@ -905,3 +905,20 @@ cifs_free_hash(struct crypto_shash **shash,
>> struct sdesc **sdesc)
>>>    		crypto_free_shash(*shash);
>>>    	*shash = NULL;
>>>    }
>>> +
>>> +/**
>>> + * rqst_page_get_length - obtain the length and offset for a page in
>>> +smb_rqst
>>> + * Input: rqst - a smb_rqst, page - a page index for rqst
>>> + * Output: *len - the length for this page, *offset - the offset for
>>> +this page  */ void rqst_page_get_length(struct smb_rqst *rqst,
>>> +unsigned int page,
>>> +				unsigned int *len, unsigned int *offset) {
>>> +	*len = rqst->rq_pagesz;
>>> +	*offset = (page == 0) ? rqst->rq_offset : 0;
>>
>> Really? Page 0 always has a zero offset??
> 
> I think you are misreading this line. The offset for page 0 is rq_offset, the offset for all subsequent pages are 0.

Ah, yes, sorry I did read it incorrectly.
>>> +
>>> +	if (rqst->rq_npages == 1 || page == rqst->rq_npages-1)
>>> +		*len = rqst->rq_tailsz;
>>> +	else if (page == 0)
>>> +		*len = rqst->rq_pagesz - rqst->rq_offset; }
>>>
>>
>> This subroutine does what patch 5 does inline. Why not push this patch up in
>> the sequence and use the helper?
> 
> This is actually a little different. This function returns the length and offset for a given page in the request. There might be multiple pages in a request.

Ok, but I still think there is quite a bit of inline computation of
this stuff that would more clearly and more robustly be done in a set
of common functions. If someone ever touches the code to support a
new upper layer, or even integrate with more complex compounding,
things will get ugly fast.

> The other function calculates the total length of all the pages in a request.

Again, a great candidate for a common set of subroutines, IMO.

Tom.