linux-ext4 - Re: [PATCH] ext4: use ext4_fc_tl_mem in fast-commit replay path

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Date:   Thu, 12 Jan 2023 11:10:07 +0100
From:   Jan Kara <jack@...e.cz>
To:     Eric Biggers <ebiggers@...nel.org>
Cc:     Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org,
        Ye Bin <yebin10@...wei.com>
Subject: Re: [PATCH] ext4: use ext4_fc_tl_mem in fast-commit replay path

On Wed 11-01-23 10:30:19, Eric Biggers wrote:
> On Wed, Jan 11, 2023 at 03:43:27PM +0100, Jan Kara wrote:
> > On Fri 16-12-22 21:02:12, Eric Biggers wrote:
> > > From: Eric Biggers <ebiggers@...gle.com>
> > > 
> > > To avoid 'sparse' warnings about missing endianness conversions, don't
> > > store native endianness values into struct ext4_fc_tl.  Instead, use a
> > > separate struct type, ext4_fc_tl_mem.
> > > 
> > > Fixes: dcc5827484d6 ("ext4: factor out ext4_fc_get_tl()")
> > > Cc: Ye Bin <yebin10@...wei.com>
> > > Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> > 
> > Looks good to me. Just one nit below:
> > 
> > > -static inline void ext4_fc_get_tl(struct ext4_fc_tl *tl, u8 *val)
> > > +static inline void ext4_fc_get_tl(struct ext4_fc_tl_mem *tl, u8 *val)
> > >  {
> > > -	memcpy(tl, val, EXT4_FC_TAG_BASE_LEN);
> > > -	tl->fc_len = le16_to_cpu(tl->fc_len);
> > > -	tl->fc_tag = le16_to_cpu(tl->fc_tag);
> > > +	struct ext4_fc_tl tl_disk;
> > > +
> > > +	memcpy(&tl_disk, val, EXT4_FC_TAG_BASE_LEN);
> > > +	tl->fc_len = le16_to_cpu(tl_disk.fc_len);
> > > +	tl->fc_tag = le16_to_cpu(tl_disk.fc_tag);
> > >  }
> > 
> > So why not just:
> > 
> > 	struct ext4_fc_tl *tl_disk = (struct ext4_fc_tl *)val;
> > 
> > instead of memcpy?
> 
> That would result in unaligned memory accesses.

Indeed. Thanks for explanation! Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR