Re: [PATCH] btrfs: extent-tree: Use round up to replace align macro

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On Tue, Nov 21, 2017 at 04:06:54PM +0800, Qu Wenruo wrote:
> On 2017年11月21日 15:33, Nikolay Borisov wrote:
> > On 21.11.2017 07:54, Qu Wenruo wrote:
> >> @@ -2054,7 +2054,7 @@ static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
> >>  {
> >>  	int j, ret = 0;
> >>  	u64 bytes_left, end;
> >> -	u64 aligned_start = ALIGN(start, 1 << 9);
> >> +	u64 aligned_start = round_up(start, 1 << 9);
> > 
> > nit: 1 << 9 == SZ_512 or essentially sector size however looking at the
> > defines there is SECTOR_SIZE defined in ide.h which we do not include.
> > Or just use 512 no need to obscure it behind a shift.
> 
> I also noticed that while I don't have any good idea which macro should
> be used.
> 
> That SECTOR_SIZE defined in ide.h doesn't sound good to me.

Heh, no we won't include ide.h just to get the macro definition.

> And all other filesystems are using their own definition, without some
> definition in fs/bio level.

That would be useful, as the sectorsize == 512 is part of the bio ABI.

I'd like to convert all the >> 9 shifts to *512 or /512, but this relies
on the compiler to convert namely the division to shifts where we use
u64.
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