In message <20080501122136.bc2215c9.akpm@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton writes:
> On Thu, 1 May 2008 13:18:09 -0400
> Erez Zadok <ezk@xxxxxxxxxxxxx> wrote:
>
> > In message <20080430101704.9cbd6384.akpm@xxxxxxxxxxxxxxxxxxxx>, Andrew Morton writes:
> > [...[
> > > Can we avoid having to think?
> > >
> > > void fsstack_copy_inode_size(struct inode *dst, const struct inode *src)
> > > {
> > > blkcnt_t i_blocks;
> > > loff_t i_size;
> > >
> > > i_size = i_size_read(src);
> > > spin_lock_32bit(&src->i_lock);
> > > i_blocks = src->i_blocks;
> > > spin_unlock_32bit(&src->i_lock);
> > >
> > > i_size_write(dst, i_size);
> > > spin_lock_32bit(&dst->i_lock)
> > > dst->i_blocks = i_blocks;
> > > spin_unlock_32bit(&dst->i_lock)
> > > }
> >
> > I can't find spin_[um]lock_32bit anywhere (checkd latest mmotm and linus's
> > tree). I therefore assume this was just your way of saying I should:
> >
> > #if BITS_PER_LONG == 32
> > spin_unlock(&dst->i_lock);
> > #endif
>
> Nope, it was my way of suggesting that you implement it ;)
> include/linux/spinlock.h would be a good place.
Sure, I can implement it and submit a patch. But I've got two questions
first:
1. i_size_read has a tri-state behaviour:
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
// play with seqcount
#elif BITS_PER_LONG==32 && defined(CONFIG_PREEMPT)
// wrap in preempt_disable/enable
#else
// just return value
#endif
Shouldn't the same be done for i_blocks, with matching i_blocks_read(),
i_blocks_write(), and adding an inode->i_blocks_seqcount field?
2. I've rewritten your suggested code a bit to reduce stack use. Modulo
having 32-bit spin_lock/unlock variants, do you see any problem with this
code below? My testing of it so far on 32/64-bit SMP/UMP have all
passed.
void fsstack_copy_inode_size(struct inode *dst, struct inode *src)
{
#if BITS_PER_LONG == 32
blkcnt_t i_blocks;
spin_lock(&src->i_lock);
i_blocks = src->i_blocks;
spin_unlock(&src->i_lock);
spin_lock(&dst->i_lock);
dst->i_blocks = i_blocks;
spin_unlock(&dst->i_lock);
#else
dst->i_blocks = src->i_blocks;
#endif
i_size_write(dst, i_size_read(src));
}
Thanks,
Erez.
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