Re: a question for i_inode's i_size in ext2

[Jan Kara <jack@suse.cz>]

  Dear Shin Hong,

>   I have a question of inode's i_size. I found that it is hard to find
> any consistent synchronization mechanism that protects inode's i_size
> field.
>   Is there any lock or synchronization mechanism that consistently
> protects i_size fields of inode objects to avoid data race?
>   In inode's definition in /include/linux/fs.h, there is comment that
> i_lock protects i_size but it is not clear.
  As Ted said, i_size changes use i_mutex to guard them (actually,
the comment you are probably refering to speaks about i_mutex - i_lock is
something different). Reading i_size is a different matter - see
i_size_read function. We use seqlock for that - essentially we use an
atomic counter which is incremented on every change of i_size and check
that it's value before we started reading i_size and after we have
finished reading it has not changed. I hope this helps.

								Honza
-- 
Jan Kara <jack@suse.cz>
SuSE CR Labs