Re: [PATCH v4 17/17] xfs: Add delay ready attr set routines

[Brian Foster <bfoster@redhat.com>]

On Wed, Nov 06, 2019 at 06:28:01PM -0700, Allison Collins 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_later, which uses a state machine to keep track
> of where it was when EAGAIN was returned.  Part of
> xfs_attr_leaf_addname has been factored out into a new helper
> function xfs_attr_leaf_try_add to allow transaction cycling between
> the two routines, and the flipflags logic has been removed since we
> can simply cancel the transaction upon error.  xfs_attr_set_args
> consists of a simple loop to refresh the transaction until the
> operation is completed.
> 
> Signed-off-by: Allison Collins <allison.henderson@oracle.com>
> ---

Pretty much the same fundamental comments here as for the remove patch.
Can we break things down further to avoid much of the jumping into if
branch behavior and such? I also wonder if it might be possible to split
this one up into smaller patches to fix up the leaf/node paths
separately, but additional prep refactoring might simplify things enough
on its own to make that unnecessary..

Brian

>  fs/xfs/libxfs/xfs_attr.c | 435 +++++++++++++++++++++++------------------------
>  fs/xfs/libxfs/xfs_attr.h |   1 +
>  2 files changed, 211 insertions(+), 225 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index 38d5c5c..97e5ae0 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -58,6 +58,7 @@ 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
> @@ -250,9 +251,79 @@ int
>  xfs_attr_set_args(
>  	struct xfs_da_args	*args)
>  {
> +	int			error = 0;
> +	int			err2 = 0;
> +	struct xfs_buf		*leaf_bp = NULL;
> +
> +	do {
> +		error = xfs_attr_set_later(args, &leaf_bp);
> +		if (error && error != -EAGAIN)
> +			goto out;
> +
> +		xfs_trans_log_inode(args->trans, args->dp,
> +				    XFS_ILOG_CORE | XFS_ILOG_ADATA);
> +
> +		err2 = xfs_trans_roll(&args->trans);
> +		if (err2) {
> +			error = err2;
> +			goto out;
> +		}
> +
> +		/* Rejoin inode and leaf if needed */
> +		xfs_trans_ijoin(args->trans, args->dp, 0);
> +		if (leaf_bp) {
> +			xfs_trans_bjoin(args->trans, leaf_bp);
> +			xfs_trans_bhold(args->trans, leaf_bp);
> +		}
> +
> +	} while (error == -EAGAIN);
> +
> +out:
> +	return error;
> +}
> +
> +/*
> + * Set the attribute specified in @args.
> + * This routine is meant to function as a delayed operation, and may return
> + * -EAGAIN when the transaction needs to be rolled.  Calling functions will need
> + * to handle this, and recall the function until a successful error code is
> + * returned.
> + */
> +int
> +xfs_attr_set_later(
> +	struct xfs_da_args	*args,
> +	struct xfs_buf          **leaf_bp)
> +{
>  	struct xfs_inode	*dp = args->dp;
> -	struct xfs_buf          *leaf_bp = NULL;
> -	int			error, error2 = 0;;
> +	int			error = 0;
> +	int			sf_size;
> +
> +	/* State machine switch */
> +	switch (args->dc.dc_state) {
> +	case XFS_DC_SF_TO_LEAF:
> +		goto sf_to_leaf;
> +	case XFS_DC_ALLOC_LEAF:
> +	case XFS_DC_FOUND_LBLK:
> +		goto leaf;
> +	case XFS_DC_FOUND_NBLK:
> +	case XFS_DC_ALLOC_NODE:
> +	case XFS_DC_LEAF_TO_NODE:
> +		goto node;
> +	default:
> +		break;
> +	}
> +
> +	/*
> +	 * New inodes may not have an attribute fork yet. So set the attribute
> +	 * fork appropriately
> +	 */
> +	if (XFS_IFORK_Q((args->dp)) == 0) {
> +		sf_size = sizeof(struct xfs_attr_sf_hdr) +
> +		     XFS_ATTR_SF_ENTSIZE_BYNAME(args->name.len, args->valuelen);
> +		xfs_bmap_set_attrforkoff(args->dp, sf_size, NULL);
> +		args->dp->i_afp = kmem_zone_zalloc(xfs_ifork_zone, 0);
> +		args->dp->i_afp->if_flags = XFS_IFEXTENTS;
> +	}
>  
>  	/*
>  	 * If the attribute list is non-existent or a shortform list,
> @@ -272,21 +343,14 @@ xfs_attr_set_args(
>  		 * Try to add the attr to the attribute list in the inode.
>  		 */
>  		error = xfs_attr_try_sf_addname(dp, args);
> -		if (error != -ENOSPC) {
> -			if (dp->i_mount->m_flags & XFS_MOUNT_WSYNC)
> -				xfs_trans_set_sync(args->trans);
> -
> -			error2 = xfs_trans_commit(args->trans);
> -			args->trans = NULL;
> -			return error ? error : error2;
> -		}
> -
> +		if (error != -ENOSPC)
> +			return error;
>  
>  		/*
>  		 * It won't fit in the shortform, transform to a leaf block.
>  		 * GROT: another possible req'mt for a double-split btree op.
>  		 */
> -		error = xfs_attr_shortform_to_leaf(args, &leaf_bp);
> +		error = xfs_attr_shortform_to_leaf(args, leaf_bp);
>  		if (error)
>  			return error;
>  
> @@ -294,43 +358,42 @@ xfs_attr_set_args(
>  		 * 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.
>  		 */
> -		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;
> -		}
> +
> +		xfs_trans_bhold(args->trans, *leaf_bp);
> +		args->dc.dc_state = XFS_DC_SF_TO_LEAF;
> +		return -EAGAIN;
> +	}
> +sf_to_leaf:
> +
> +	/*
> +	 * After a shortform to leaf conversion, we need to hold the leaf and
> +	 * cylce out the transaction.  When we get back, we need to release
> +	 * the leaf.
> +	 */
> +	if (*leaf_bp != NULL) {
> +		xfs_trans_brelse(args->trans, *leaf_bp);
> +		*leaf_bp = NULL;
>  	}
>  
>  	if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> +		error = xfs_attr_leaf_try_add(args, *leaf_bp);
> +		if (error == -ENOSPC)
> +			args->dc.dc_state = XFS_DC_LEAF_TO_NODE;
> +		else if (error)
> +			return error;
> +		else
> +			args->dc.dc_state = XFS_DC_FOUND_LBLK;
> +		return -EAGAIN;
> +leaf:
>  		error = xfs_attr_leaf_addname(args);
>  		if (error == -ENOSPC) {
> -			/*
> -			 * Commit that transaction so that the node_addname()
> -			 * call can manage its own transactions.
> -			 */
> -			error = xfs_defer_finish(&args->trans);
> -			if (error)
> -				return error;
> -
> -			/*
> -			 * Commit the current trans (including the inode) and
> -			 * start a new one.
> -			 */
> -			error = xfs_trans_roll_inode(&args->trans, dp);
> -			if (error)
> -				return error;
> -
> -			/*
> -			 * Fob the rest of the problem off on the Btree code.
> -			 */
> -			error = xfs_attr_node_addname(args);
> +			args->dc.dc_state = XFS_DC_LEAF_TO_NODE;
> +			return -EAGAIN;
>  		}
>  	} else {
> +		args->dc.dc_state = XFS_DC_LEAF_TO_NODE;
> +node:
>  		error = xfs_attr_node_addname(args);
>  	}
>  	return error;
> @@ -764,27 +827,26 @@ xfs_attr_leaf_try_add(
>   *
>   * This leaf block cannot have a "remote" value, we only call this routine
>   * if bmap_one_block() says there is only one block (ie: no remote blks).
> + *
> + * This routine is meant to function as a delayed operation, and may return
> + * -EAGAIN when the transaction needs to be rolled.  Calling functions will need
> + * to handle this, and recall the function until a successful error code is
> + * returned.
>   */
>  STATIC int
>  xfs_attr_leaf_addname(struct xfs_da_args	*args)
>  {
> -	int			error, forkoff;
> -	struct xfs_buf		*bp = NULL;
> +	int			error, nmap;
>  	struct xfs_inode	*dp = args->dp;
> +	struct xfs_bmbt_irec	*map = &args->dc.map;
>  
> -	trace_xfs_attr_leaf_addname(args);
> -
> -	error = xfs_attr_leaf_try_add(args, bp);
> -	if (error)
> -		return error;
> -
> -	/*
> -	 * Commit the transaction that added the attr name so that
> -	 * later routines can manage their own transactions.
> -	 */
> -	error = xfs_trans_roll_inode(&args->trans, dp);
> -	if (error)
> -		return error;
> +	/* State machine switch */
> +	switch (args->dc.dc_state) {
> +	case XFS_DC_ALLOC_LEAF:
> +		goto alloc_leaf;
> +	default:
> +		break;
> +	}
>  
>  	/*
>  	 * If there was an out-of-line value, allocate the blocks we
> @@ -793,90 +855,58 @@ xfs_attr_leaf_addname(struct xfs_da_args	*args)
>  	 * maximum size of a transaction and/or hit a deadlock.
>  	 */
>  	if (args->rmtblkno > 0) {
> -		error = xfs_attr_rmtval_set(args);
> -		if (error)
> -			return error;
> -	}
>  
> -	/*
> -	 * If this is an atomic rename operation, we must "flip" the
> -	 * incomplete flags on the "new" and "old" attribute/value pairs
> -	 * so that one disappears and one appears atomically.  Then we
> -	 * must remove the "old" attribute/value pair.
> -	 */
> -	if (args->op_flags & XFS_DA_OP_RENAME) {
> -		/*
> -		 * In a separate transaction, set the incomplete flag on the
> -		 * "old" attr and clear the incomplete flag on the "new" attr.
> -		 */
> -		error = xfs_attr3_leaf_flipflags(args);
> -		if (error)
> -			return error;
> -		/*
> -		 * Commit the flag value change and start the next trans in
> -		 * series.
> -		 */
> -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> -		if (error)
> -			return error;
> +		/* Open coded xfs_attr_rmtval_set without trans handling */
>  
> -		/*
> -		 * Dismantle the "old" attribute/value pair by removing
> -		 * a "remote" value (if it exists).
> -		 */
> -		args->index = args->index2;
> -		args->blkno = args->blkno2;
> -		args->rmtblkno = args->rmtblkno2;
> -		args->rmtblkcnt = args->rmtblkcnt2;
> -		args->rmtvaluelen = args->rmtvaluelen2;
> -		if (args->rmtblkno) {
> -			error = xfs_attr_rmtval_remove(args);
> -			if (error)
> -				return error;
> -		}
> +		args->dc.lfileoff = 0;
> +		args->dc.lblkno = 0;
> +		args->dc.blkcnt = 0;
> +		args->rmtblkcnt = 0;
> +		args->rmtblkno = 0;
> +		memset(map, 0, sizeof(struct xfs_bmbt_irec));
>  
> -		/*
> -		 * Read in the block containing the "old" attr, then
> -		 * remove the "old" attr from that block (neat, huh!)
> -		 */
> -		error = xfs_attr3_leaf_read(args->trans, args->dp, args->blkno,
> -					   XFS_DABUF_MAP_NOMAPPING, &bp);
> +		error = xfs_attr_rmt_find_hole(args);
>  		if (error)
>  			return error;
>  
> -		xfs_attr3_leaf_remove(bp, args);
> +		args->dc.blkcnt = args->rmtblkcnt;
> +		args->dc.lblkno = args->rmtblkno;
>  
>  		/*
> -		 * If the result is small enough, shrink it all into the inode.
> +		 * Roll through the "value", allocating blocks on disk as
> +		 * required.
>  		 */
> -		if ((forkoff = xfs_attr_shortform_allfit(bp, dp))) {
> -			error = xfs_attr3_leaf_to_shortform(bp, args, forkoff);
> -			/* bp is gone due to xfs_da_shrink_inode */
> -			if (error)
> -				return error;
> -			error = xfs_defer_finish(&args->trans);
> +alloc_leaf:
> +		while (args->dc.blkcnt > 0) {
> +			nmap = 1;
> +			error = xfs_bmapi_write(args->trans, dp,
> +				  (xfs_fileoff_t)args->dc.lblkno,
> +				  args->dc.blkcnt, XFS_BMAPI_ATTRFORK,
> +				  args->total, map, &nmap);
>  			if (error)
>  				return error;
> -		}
> +			ASSERT(nmap == 1);
> +			ASSERT((map->br_startblock != DELAYSTARTBLOCK) &&
> +			       (map->br_startblock != HOLESTARTBLOCK));
>  
> -		/*
> -		 * Commit the remove and start the next trans in series.
> -		 */
> -		error = xfs_trans_roll_inode(&args->trans, dp);
> +			/* roll attribute extent map forwards */
> +			args->dc.lblkno += map->br_blockcount;
> +			args->dc.blkcnt -= map->br_blockcount;
>  
> -	} else if (args->rmtblkno > 0) {
> -		/*
> -		 * Added a "remote" value, just clear the incomplete flag.
> -		 */
> -		error = xfs_attr3_leaf_clearflag(args);
> +			args->dc.dc_state = XFS_DC_ALLOC_LEAF;
> +			return -EAGAIN;
> +		}
> +
> +		error = xfs_attr_rmtval_set_value(args);
>  		if (error)
>  			return error;
> +	}
>  
> +	if (args->rmtblkno > 0) {
>  		/*
> -		 * Commit the flag value change and start the next trans in
> -		 * series.
> +		 * Added a "remote" value, just clear the incomplete flag.
>  		 */
> -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> +		error = xfs_attr3_leaf_clearflag(args);
>  	}
>  	return error;
>  }
> @@ -1017,16 +1047,23 @@ xfs_attr_node_hasname(
>   *
>   * "Remote" attribute values confuse the issue and atomic rename operations
>   * add a whole extra layer of confusion on top of that.
> + *
> + * This routine is meant to function as a delayed operation, and may return
> + * -EAGAIN when the transaction needs to be rolled.  Calling functions will need
> + * to handle this, and recall the function until a successful error code is
> + *returned.
>   */
>  STATIC int
>  xfs_attr_node_addname(
>  	struct xfs_da_args	*args)
>  {
> -	struct xfs_da_state	*state;
> +	struct xfs_da_state	*state = NULL;
>  	struct xfs_da_state_blk	*blk;
>  	struct xfs_inode	*dp;
> -	struct xfs_mount	*mp;
> -	int			retval, error;
> +	int			retval = 0;
> +	int			error = 0;
> +	int			nmap;
> +	struct xfs_bmbt_irec    *map = &args->dc.map;
>  
>  	trace_xfs_attr_node_addname(args);
>  
> @@ -1034,8 +1071,17 @@ xfs_attr_node_addname(
>  	 * Fill in bucket of arguments/results/context to carry around.
>  	 */
>  	dp = args->dp;
> -	mp = dp->i_mount;
> -restart:
> +
> +	/* State machine switch */
> +	switch (args->dc.dc_state) {
> +	case XFS_DC_FOUND_NBLK:
> +		goto found_nblk;
> +	case XFS_DC_ALLOC_NODE:
> +		goto alloc_node;
> +	default:
> +		break;
> +	}
> +
>  	/*
>  	 * Search to see if name already exists, and get back a pointer
>  	 * to where it should go.
> @@ -1085,19 +1131,12 @@ xfs_attr_node_addname(
>  			error = xfs_attr3_leaf_to_node(args);
>  			if (error)
>  				goto out;
> -			error = xfs_defer_finish(&args->trans);
> -			if (error)
> -				goto out;
>  
>  			/*
> -			 * Commit the node conversion and start the next
> -			 * trans in the chain.
> +			 * Restart routine from the top.  No need to set  the
> +			 * state
>  			 */
> -			error = xfs_trans_roll_inode(&args->trans, dp);
> -			if (error)
> -				goto out;
> -
> -			goto restart;
> +			return -EAGAIN;
>  		}
>  
>  		/*
> @@ -1109,9 +1148,6 @@ xfs_attr_node_addname(
>  		error = xfs_da3_split(state);
>  		if (error)
>  			goto out;
> -		error = xfs_defer_finish(&args->trans);
> -		if (error)
> -			goto out;
>  	} else {
>  		/*
>  		 * Addition succeeded, update Btree hashvals.
> @@ -1126,13 +1162,9 @@ xfs_attr_node_addname(
>  	xfs_da_state_free(state);
>  	state = NULL;
>  
> -	/*
> -	 * Commit the leaf addition or btree split and start the next
> -	 * trans in the chain.
> -	 */
> -	error = xfs_trans_roll_inode(&args->trans, dp);
> -	if (error)
> -		goto out;
> +	args->dc.dc_state = XFS_DC_FOUND_NBLK;
> +	return -EAGAIN;
> +found_nblk:
>  
>  	/*
>  	 * If there was an out-of-line value, allocate the blocks we
> @@ -1141,104 +1173,57 @@ xfs_attr_node_addname(
>  	 * maximum size of a transaction and/or hit a deadlock.
>  	 */
>  	if (args->rmtblkno > 0) {
> -		error = xfs_attr_rmtval_set(args);
> -		if (error)
> -			return error;
> -	}
> +		/* Open coded xfs_attr_rmtval_set without trans handling */
> +		args->dc.lblkno = 0;
> +		args->dc.lfileoff = 0;
> +		args->dc.blkcnt = 0;
> +		args->rmtblkcnt = 0;
> +		args->rmtblkno = 0;
> +		memset(map, 0, sizeof(struct xfs_bmbt_irec));
>  
> -	/*
> -	 * If this is an atomic rename operation, we must "flip" the
> -	 * incomplete flags on the "new" and "old" attribute/value pairs
> -	 * so that one disappears and one appears atomically.  Then we
> -	 * must remove the "old" attribute/value pair.
> -	 */
> -	if (args->op_flags & XFS_DA_OP_RENAME) {
> -		/*
> -		 * In a separate transaction, set the incomplete flag on the
> -		 * "old" attr and clear the incomplete flag on the "new" attr.
> -		 */
> -		error = xfs_attr3_leaf_flipflags(args);
> -		if (error)
> -			goto out;
> -		/*
> -		 * Commit the flag value change and start the next trans in
> -		 * series
> -		 */
> -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> +		error = xfs_attr_rmt_find_hole(args);
>  		if (error)
> -			goto out;
> +			return error;
>  
> +		args->dc.blkcnt = args->rmtblkcnt;
> +		args->dc.lblkno = args->rmtblkno;
>  		/*
> -		 * Dismantle the "old" attribute/value pair by removing
> -		 * a "remote" value (if it exists).
> +		 * Roll through the "value", allocating blocks on disk as
> +		 * required.
>  		 */
> -		args->index = args->index2;
> -		args->blkno = args->blkno2;
> -		args->rmtblkno = args->rmtblkno2;
> -		args->rmtblkcnt = args->rmtblkcnt2;
> -		args->rmtvaluelen = args->rmtvaluelen2;
> -		if (args->rmtblkno) {
> -			error = xfs_attr_rmtval_remove(args);
> +alloc_node:
> +		while (args->dc.blkcnt > 0) {
> +			nmap = 1;
> +			error = xfs_bmapi_write(args->trans, dp,
> +				(xfs_fileoff_t)args->dc.lblkno, args->dc.blkcnt,
> +				XFS_BMAPI_ATTRFORK, args->total, map, &nmap);
>  			if (error)
>  				return error;
> -		}
>  
> -		/*
> -		 * Re-find the "old" attribute entry after any split ops.
> -		 * The INCOMPLETE flag means that we will find the "old"
> -		 * attr, not the "new" one.
> -		 */
> -		args->name.type |= XFS_ATTR_INCOMPLETE;
> -		state = xfs_da_state_alloc();
> -		state->args = args;
> -		state->mp = mp;
> -		state->inleaf = 0;
> -		error = xfs_da3_node_lookup_int(state, &retval);
> -		if (error)
> -			goto out;
> +			ASSERT(nmap == 1);
> +			ASSERT((map->br_startblock != DELAYSTARTBLOCK) &&
> +			       (map->br_startblock != HOLESTARTBLOCK));
>  
> -		/*
> -		 * Remove the name and update the hashvals in the tree.
> -		 */
> -		blk = &state->path.blk[ state->path.active-1 ];
> -		ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
> -		error = xfs_attr3_leaf_remove(blk->bp, args);
> -		xfs_da3_fixhashpath(state, &state->path);
> +			/* roll attribute extent map forwards */
> +			args->dc.lblkno += map->br_blockcount;
> +			args->dc.blkcnt -= map->br_blockcount;
>  
> -		/*
> -		 * Check to see if the tree needs to be collapsed.
> -		 */
> -		if (retval && (state->path.active > 1)) {
> -			error = xfs_da3_join(state);
> -			if (error)
> -				goto out;
> -			error = xfs_defer_finish(&args->trans);
> -			if (error)
> -				goto out;
> +			args->dc.dc_state = XFS_DC_ALLOC_NODE;
> +			return -EAGAIN;
>  		}
>  
> -		/*
> -		 * Commit and start the next trans in the chain.
> -		 */
> -		error = xfs_trans_roll_inode(&args->trans, dp);
> +		error = xfs_attr_rmtval_set_value(args);
>  		if (error)
> -			goto out;
> +			return error;
> +	}
>  
> -	} else if (args->rmtblkno > 0) {
> +	if (args->rmtblkno > 0) {
>  		/*
>  		 * Added a "remote" value, just clear the incomplete flag.
>  		 */
>  		error = xfs_attr3_leaf_clearflag(args);
>  		if (error)
>  			goto out;
> -
> -		 /*
> -		  * Commit the flag value change and start the next trans in
> -		  * series.
> -		  */
> -		error = xfs_trans_roll_inode(&args->trans, args->dp);
> -		if (error)
> -			goto out;
>  	}
>  	retval = error = 0;
>  
> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> index fb8bf5b..c710387 100644
> --- a/fs/xfs/libxfs/xfs_attr.h
> +++ b/fs/xfs/libxfs/xfs_attr.h
> @@ -149,6 +149,7 @@ int xfs_attr_get(struct xfs_inode *ip, struct xfs_name *name,
>  int xfs_attr_set(struct xfs_inode *dp, struct xfs_name *name,
>  		 unsigned char *value, int valuelen, int flags);
>  int xfs_attr_set_args(struct xfs_da_args *args);
> +int xfs_attr_set_later(struct xfs_da_args *args, struct xfs_buf **leaf_bp);
>  int xfs_attr_remove(struct xfs_inode *dp, struct xfs_name *name, int flags);
>  int xfs_has_attr(struct xfs_da_args *args);
>  int xfs_attr_remove_args(struct xfs_da_args *args);
> -- 
> 2.7.4
>