Re: [PATCH v13 03/10] xfs: Add delay ready attr set routines

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Oct 27, 2020 at 07:02:55PM +0530, Chandan Babu R wrote:
> On Friday 23 October 2020 12:04:28 PM IST Allison Henderson wrote:
> > This patch modifies the attr set routines to be delay ready. This means
> > they no longer roll or commit transactions, but instead return -EAGAIN
> > to have the calling routine roll and refresh the transaction.  In this
> > series, xfs_attr_set_args has become xfs_attr_set_iter, which uses a
> > state machine like switch to keep track of where it was when EAGAIN was
> > returned. See xfs_attr.h for a more detailed diagram of the states.
> > 
> > Two new helper functions have been added: xfs_attr_rmtval_set_init and
> > xfs_attr_rmtval_set_blk.  They provide a subset of logic similar to
> > xfs_attr_rmtval_set, but they store the current block in the delay attr
> > context to allow the caller to roll the transaction between allocations.
> > This helps to simplify and consolidate code used by
> > xfs_attr_leaf_addname and xfs_attr_node_addname. xfs_attr_set_args has
> > now become a simple loop to refresh the transaction until the operation
> > is completed.  Lastly, xfs_attr_rmtval_remove is no longer used, and is
> > removed.
> 
> One nit. xfs_attr_rmtval_remove()'s prototype declaration needs to be removed
> from xfs_attr_remote.h.
> 
> > 
> > Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> > ---
> >  fs/xfs/libxfs/xfs_attr.c        | 370 ++++++++++++++++++++++++++--------------
> >  fs/xfs/libxfs/xfs_attr.h        | 126 +++++++++++++-
> >  fs/xfs/libxfs/xfs_attr_remote.c |  99 +++++++----
> >  fs/xfs/libxfs/xfs_attr_remote.h |   4 +
> >  fs/xfs/xfs_trace.h              |   1 -
> >  5 files changed, 439 insertions(+), 161 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > index 6ca94cb..95c98d7 100644
> > --- a/fs/xfs/libxfs/xfs_attr.c
> > +++ b/fs/xfs/libxfs/xfs_attr.c
> > @@ -44,7 +44,7 @@ STATIC int xfs_attr_shortform_addname(xfs_da_args_t *args);
> >   * Internal routines when attribute list is one block.
> >   */
> >  STATIC int xfs_attr_leaf_get(xfs_da_args_t *args);
> > -STATIC int xfs_attr_leaf_addname(xfs_da_args_t *args);
> > +STATIC int xfs_attr_leaf_addname(struct xfs_delattr_context *dac);
> >  STATIC int xfs_attr_leaf_removename(xfs_da_args_t *args);
> >  STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
> >  
> > @@ -52,12 +52,15 @@ STATIC int xfs_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
> >   * Internal routines when attribute list is more than one block.
> >   */
> >  STATIC int xfs_attr_node_get(xfs_da_args_t *args);
> > -STATIC int xfs_attr_node_addname(xfs_da_args_t *args);
> > +STATIC int xfs_attr_node_addname(struct xfs_delattr_context *dac);
> >  STATIC int xfs_attr_node_removename_iter(struct xfs_delattr_context *dac);
> >  STATIC int xfs_attr_node_hasname(xfs_da_args_t *args,
> >  				 struct xfs_da_state **state);
> >  STATIC int xfs_attr_fillstate(xfs_da_state_t *state);
> >  STATIC int xfs_attr_refillstate(xfs_da_state_t *state);
> > +STATIC int xfs_attr_leaf_try_add(struct xfs_da_args *args, struct xfs_buf *bp);
> > +STATIC int xfs_attr_set_iter(struct xfs_delattr_context *dac,
> > +			     struct xfs_buf **leaf_bp);
> >  
> >  int
> >  xfs_inode_hasattr(
> > @@ -218,8 +221,11 @@ xfs_attr_is_shortform(
> >  
> >  /*
> >   * Attempts to set an attr in shortform, or converts short form to leaf form if
> > - * there is not enough room.  If the attr is set, the transaction is committed
> > - * and set to NULL.
> > + * there is not enough room.  This function is meant to operate as a helper
> > + * routine to the delayed attribute functions.  It returns -EAGAIN to indicate
> > + * that the calling function should roll the transaction, and then proceed to
> > + * add the attr in leaf form.  This subroutine does not expect to be recalled
> > + * again like the other delayed attr routines do.
> >   */
> >  STATIC int
> >  xfs_attr_set_shortform(
> > @@ -227,16 +233,16 @@ xfs_attr_set_shortform(
> >  	struct xfs_buf		**leaf_bp)
> >  {
> >  	struct xfs_inode	*dp = args->dp;
> > -	int			error, error2 = 0;
> > +	int			error = 0;
> >  
> >  	/*
> >  	 * Try to add the attr to the attribute list in the inode.
> >  	 */
> >  	error = xfs_attr_try_sf_addname(dp, args);
> > +
> > +	/* Should only be 0, -EEXIST or ENOSPC */
> >  	if (error != -ENOSPC) {
> > -		error2 = xfs_trans_commit(args->trans);
> > -		args->trans = NULL;
> > -		return error ? error : error2;
> > +		return error;
> >  	}
> >  	/*
> >  	 * It won't fit in the shortform, transform to a leaf block.  GROT:
> > @@ -249,18 +255,10 @@ xfs_attr_set_shortform(
> >  	/*
> >  	 * Prevent the leaf buffer from being unlocked so that a concurrent AIL
> >  	 * push cannot grab the half-baked leaf buffer and run into problems
> > -	 * with the write verifier. Once we're done rolling the transaction we
> > -	 * can release the hold and add the attr to the leaf.
> > +	 * with the write verifier.
> >  	 */
> >  	xfs_trans_bhold(args->trans, *leaf_bp);
> > -	error = xfs_defer_finish(&args->trans);
> > -	xfs_trans_bhold_release(args->trans, *leaf_bp);
> > -	if (error) {
> > -		xfs_trans_brelse(args->trans, *leaf_bp);
> > -		return error;
> > -	}
> > -
> > -	return 0;
> > +	return -EAGAIN;
> >  }
> >  
> >  /*
> > @@ -268,7 +266,7 @@ xfs_attr_set_shortform(
> >   * also checks for a defer finish.  Transaction is finished and rolled as
> >   * needed, and returns true of false if the delayed operation should continue.
> >   */
> > -int
> > +STATIC int
> >  xfs_attr_trans_roll(
> >  	struct xfs_delattr_context	*dac)
> >  {
> > @@ -297,61 +295,130 @@ int
> >  xfs_attr_set_args(
> >  	struct xfs_da_args	*args)
> >  {
> > -	struct xfs_inode	*dp = args->dp;
> > -	struct xfs_buf          *leaf_bp = NULL;
> > -	int			error = 0;
> > +	struct xfs_buf			*leaf_bp = NULL;
> > +	int				error = 0;
> > +	struct xfs_delattr_context	dac = {
> > +		.da_args	= args,
> > +	};
> > +
> > +	do {
> > +		error = xfs_attr_set_iter(&dac, &leaf_bp);
> > +		if (error != -EAGAIN)
> > +			break;
> > +
> > +		error = xfs_attr_trans_roll(&dac);
> > +		if (error)
> > +			return error;
> > +
> > +		if (leaf_bp) {
> > +			xfs_trans_bjoin(args->trans, leaf_bp);
> > +			xfs_trans_bhold(args->trans, leaf_bp);
> > +		}
> 
> When xfs_attr_set_iter() causes a "short form" attribute list to be converted
> to "leaf form", leaf_bp would point to an xfs_buf which has been added to the
> transaction and also XFS_BLI_HOLD flag is set on the buffer (last statement in
> xfs_attr_set_shortform()). XFS_BLI_HOLD flag makes sure that the new
> transaction allocated by xfs_attr_trans_roll() would continue to have leaf_bp
> in the transaction's item list. Hence I think the above calls to
> xfs_trans_bjoin() and xfs_trans_bhold() are not required.

I /think/ the defer ops will rejoin the buffer each time it rolls, which
means that xfs_attr_trans_roll returns with the buffer already joined to
the transaction?  And I think you're right that the bhold isn't needed,
because holding is dictated by the lower levels (i.e. _set_iter).

> Please let me know if I am missing something obvious here.

The entire function goes away by the end of the series. :)

--D

> 
> -- 
> chandan
> 
> 
>