> +void
> +nfs_lock_bio(struct nfs_inode *nfsi)
bio stands for buffered I/O? This could really use a more descriptive
name and/or a comment..
> +{
> + /* Be an optimist! */
> + down_read(&nfsi->io_lock);
> + if (test_bit(NFS_INO_ODIRECT, &nfsi->flags) == 0)
> + return;
> + up_read(&nfsi->io_lock);
So if no direct I/O is going on this locks shared?
> + /* Slow path.... */
> + down_write(&nfsi->io_lock);
> + clear_bit(NFS_INO_ODIRECT, &nfsi->flags);
> + downgrade_write(&nfsi->io_lock);
The whole locking here seems rather confusing. Why not use the XFS
locking model:
buffered write: exclusive
buffered read: shared
direct write: shared (exclusive for pagecache invalidate)
direct read: shared (exclusive for pagecache invalidate)
The nice thing is than in 4.7-rc i_mutex has been replaced with a
rw_mutex so you can just use that in shared mode for direct I/O
as-is without needing any new lock.
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