[patch v2] bio-integrity: use hardware sectors instead of block

[patch v2] bio-integrity: use hardware sectors instead of block

[Dan Carpenter]

Smatch tagged this code as suspicious because we never use the
"nr_sectors" variable.  Looking at the code, we did intend to use 
"nr_sectors" instead of "sectors" when we call bio_integrity_mark_tail().

The difference between "sectors" and "nr_sectors" is that "sectors" is in
terms of 512 byte sectors and "nr_sectors" is in terms of hardware 
sectors.  They are only different for 4k sector devices.

Also I changed the name because as Jamie Lokier points out, "that code is
so asking for the variable to be called 'hw_sectors'."

Signed-off-by: Dan Carpenter <error27@gmail.com>

diff --git a/fs/bio-integrity.c b/fs/bio-integrity.c
index 612a5c3..d8cd1e2 100644
--- a/fs/bio-integrity.c
+++ b/fs/bio-integrity.c
@@ -667,16 +667,16 @@ void bio_integrity_trim(struct bio *bio, unsigned int offset,
 {
 	struct bio_integrity_payload *bip = bio->bi_integrity;
 	struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
-	unsigned int nr_sectors;
+	unsigned int hw_sectors;
 
 	BUG_ON(bip = NULL);
 	BUG_ON(bi = NULL);
 	BUG_ON(!bio_flagged(bio, BIO_CLONED));
 
-	nr_sectors = bio_integrity_hw_sectors(bi, sectors);
+	hw_sectors = bio_integrity_hw_sectors(bi, sectors);
 	bip->bip_sector = bip->bip_sector + offset;
 	bio_integrity_mark_head(bip, offset * bi->tuple_size);
-	bio_integrity_mark_tail(bip, sectors * bi->tuple_size);
+	bio_integrity_mark_tail(bip, hw_sectors * bi->tuple_size);
 }
 EXPORT_SYMBOL(bio_integrity_trim);
 
  

Re: [patch v2] bio-integrity: use hardware sectors instead of block layer sectors

[Martin K. Petersen]

>>>>> "Dan" = Dan Carpenter <error27@gmail.com> writes:

Dan,

This one bitrotted in my mailbox for a while because it conflicted with
something else I was working on and then it slipped through the cracks.
Sorry about that.


Dan> The difference between "sectors" and "nr_sectors" is that "sectors"
Dan> is in terms of 512 byte sectors and "nr_sectors" is in terms of
Dan> hardware sectors.  They are only different for 4k sector devices.

Dan> Also I changed the name because as Jamie Lokier points out, "that
Dan> code is so asking for the variable to be called 'hw_sectors'."

The change is obviously functionally correct.  But I object to the
notion of hw_sectors.  The 1:1 mapping of DIF tuples and logical blocks
is even going away in SBC3.  So let's not perpetuate that.

I have a patch in my queue that gets rid of all the hw_sector references
in the integrity code.  I'll make sure to include your fix.

So thanks for spotting this.  I obviously haven't tested PI drives with
a 4KB logical block size in combination with device mapper...

-- 
Martin K. Petersen	Oracle Linux Engineering

Re: [patch v2] bio-integrity: use hardware sectors instead of block

[Jonathan Nieder]

Hi,

On 2010-05-17, Martin K. Petersen wrote:

> The change is obviously functionally correct.  But I object to the
> notion of hw_sectors.  The 1:1 mapping of DIF tuples and logical blocks
> is even going away in SBC3.  So let's not perpetuate that.
>
> I have a patch in my queue that gets rid of all the hw_sector references
> in the integrity code.  I'll make sure to include your fix.
>
> So thanks for spotting this.  I obviously haven't tested PI drives with
> a 4KB logical block size in combination with device mapper...

I'm just curious: did anything come of this?  Nowadays gcc 4.6 warns
about the same unused nr_sector var smatch warned about, so new
readers are coming to the same question of why this function doesn't
use hardware sectors.