Re: [PATCH v7 14/19] xfs: Add delay ready attr set routines

Chandan Rajendra
2020-03-03T13:38:48Z

On Sunday, February 23, 2020 7:36 AM 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_iter, which uses a state machine like switch 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.
>
> 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. Finally, xfs_attr_set_args has become a simple loop to
> refresh the transaction until the operation is completed.
>
> Below is a state machine diagram for attr set operations. The XFS_DAS_* states
> indicate places where the function would return -EAGAIN, and then immediately
> resume from after being recalled by the calling function. States marked as a
> "subroutine state" indicate that they belong to a subroutine, and so the calling
> function needs to pass them back to that subroutine to allow it to finish where it
> left off. But they otherwise do not have a role in the calling function other
> than just passing through.
>
> xfs_attr_set_iter()
> â”‚
> v
> need to upgrade
> from sf to leaf? â”€â”€nâ”€â”
> â”‚ â”‚
> y â”‚
> â”‚ â”‚
> V â”‚
> XFS_DAS_ADD_LEAF â”‚
> â”‚ â”‚
> v â”‚
> â”Œâ”€â”€â”€â”€â”€â”€nâ”€â”€ fork has <â”€â”€â”€â”€â”€â”€â”˜
> â”‚ only 1 blk?
> â”‚ â”‚
> â”‚ y
> â”‚ â”‚
> â”‚ v
> â”‚ xfs_attr_leaf_try_add()
> â”‚ â”‚
> â”‚ v
> â”‚ had enough
> â”œâ”€â”€â”€â”€â”€â”€nâ”€â”€ space?
> â”‚ â”‚
> â”‚ y
> â”‚ â”‚
> â”‚ v
> â”‚ XFS_DAS_FOUND_LBLK â”€â”€â”
> â”‚ â”‚
> â”‚ XFS_DAS_FLIP_LFLAG â”€â”€â”¤
> â”‚ (subroutine state) â”‚
> â”‚ â”‚
> â”‚ XFS_DAS_ALLOC_LEAF â”€â”€â”¤
> â”‚ (subroutine state) â”‚
> â”‚ â””â”€>xfs_attr_leaf_addname()
> â”‚ â”‚
> â”‚ v
> â”‚ â”Œâ”€â”€â”€â”€â”€nâ”€â”€ need to
> â”‚ â”‚ alloc blks?
> â”‚ â”‚ â”‚
> â”‚ â”‚ y
> â”‚ â”‚ â”‚
> â”‚ â”‚ v
> â”‚ â”‚ â”Œâ”€>XFS_DAS_ALLOC_LEAF
> â”‚ â”‚ â”‚ â”‚
> â”‚ â”‚ â”‚ v
> â”‚ â”‚ â””â”€â”€yâ”€â”€ need to alloc
> â”‚ â”‚ more blocks?
> â”‚ â”‚ â”‚
> â”‚ â”‚ n
> â”‚ â”‚ â”‚
> â”‚ â”‚ v
> â”‚ â”‚ was this
> â”‚ â””â”€â”€â”€â”€â”€â”€â”€â”€> a rename? â”€â”€nâ”€â”
> â”‚ â”‚ â”‚
> â”‚ y â”‚
> â”‚ â”‚ â”‚
> â”‚ v â”‚
> â”‚ flip incomplete â”‚
> â”‚ flag â”‚
> â”‚ â”‚ â”‚
> â”‚ v â”‚
> â”‚ â”Œâ”€>XFS_DAS_FLIP_LFLAG â”‚
> â”‚ â”‚ â”‚ â”‚
> â”‚ â”‚ v â”‚
> â”‚ â”‚ remove â”‚
> â”‚ â”‚ old name â”‚
> â”‚ â”‚ â”‚ â”‚
> â”‚ â”‚ v â”‚
> â”‚ â””â”€â”€â”€â”€yâ”€â”€ more to â”‚
> â”‚ remove â”‚
> â”‚ â”‚ â”‚
> â”‚ n â”‚
> â”‚ â”‚ â”‚
> â”‚ v â”‚
> â”‚ done <â”€â”€â”€â”€â”€â”€â”˜
> â””â”€â”€â”€â”€> XFS_DAS_LEAF_TO_NODE â”€â”
> â”‚
> XFS_DAS_FOUND_NBLK â”€â”€â”¤
> (subroutine state) â”‚
> â”‚
> XFS_DAS_ALLOC_NODE â”€â”€â”¤
> (subroutine state) â”‚
> â”‚
> XFS_DAS_FLIP_NFLAG â”€â”€â”¤
> (subroutine state) â”‚
> â”‚
> â””â”€>xfs_attr_node_addname()
> â”‚
> v
> find space to store
> attr. Split if needed
> â”‚
> v
> XFS_DAS_FOUND_NBLK
> â”‚
> v
> â”Œâ”€â”€â”€â”€â”€nâ”€â”€ need to
> â”‚ alloc blks?
> â”‚ â”‚
> â”‚ y
> â”‚ â”‚
> â”‚ v
> â”‚ â”Œâ”€>XFS_DAS_ALLOC_NODE
> â”‚ â”‚ â”‚
> â”‚ â”‚ v
> â”‚ â””â”€â”€yâ”€â”€ need to alloc
> â”‚ more blocks?
> â”‚ â”‚
> â”‚ n
> â”‚ â”‚
> â”‚ v
> â”‚ was this
> â””â”€â”€â”€â”€â”€â”€â”€â”€> a rename? â”€â”€nâ”€â”
> â”‚ â”‚
> y â”‚
> â”‚ â”‚
> v â”‚
> flip incomplete â”‚
> flag â”‚
> â”‚ â”‚
> v â”‚
> â”Œâ”€>XFS_DAS_FLIP_NFLAG â”‚
> â”‚ â”‚ â”‚
> â”‚ v â”‚
> â”‚ remove â”‚
> â”‚ old name â”‚
> â”‚ â”‚ â”‚
> â”‚ v â”‚
> â””â”€â”€â”€â”€yâ”€â”€ more to â”‚
> remove â”‚
> â”‚ â”‚
> n â”‚
> â”‚ â”‚
> v â”‚
> done <â”€â”€â”€â”€â”€â”€â”˜
>
> Signed-off-by: Allison Collins <allison.henderson@oracle.com>
> ---
> fs/xfs/libxfs/xfs_attr.c | 368 ++++++++++++++++++++++++++--------------
> fs/xfs/libxfs/xfs_attr.h | 1 +
> fs/xfs/libxfs/xfs_attr_remote.c | 67 +++++++-
> fs/xfs/libxfs/xfs_attr_remote.h | 4 +
> fs/xfs/libxfs/xfs_da_btree.h | 13 ++
> 5 files changed, 319 insertions(+), 134 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index cd3a3f7..4b788f2 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
> @@ -259,9 +260,86 @@ 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_iter(args, &leaf_bp);
> + if (error && error != -EAGAIN)
> + goto out;
> +
> + if (args->dac.flags & XFS_DAC_FINISH_TRANS) {
> + args->dac.flags &= ~XFS_DAC_FINISH_TRANS;
> +
> + err2 = xfs_defer_finish(&args->trans);
> + if (err2) {
> + error = err2;
> + goto out;
> + }
> + }
> +
> + err2 = xfs_trans_roll_inode(&args->trans, args->dp);
> + if (err2) {
> + error = err2;
> + goto out;
> + }
> +
> + 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_iter(
> + 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->dac.dela_state) {
> + case XFS_DAS_ADD_LEAF:
> + goto add_leaf;
> + case XFS_DAS_ALLOC_LEAF:
> + case XFS_DAS_FLIP_LFLAG:
> + case XFS_DAS_FOUND_LBLK:
> + goto leaf;
> + case XFS_DAS_FOUND_NBLK:
> + case XFS_DAS_FLIP_NFLAG:
> + case XFS_DAS_ALLOC_NODE:
> + case XFS_DAS_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,
> @@ -275,17 +353,16 @@ 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) {
> - error2 = xfs_trans_commit(args->trans);
> - args->trans = NULL;
> - return error ? error : error2;
> - }
> +
> + /* Should only be 0, -EEXIST or ENOSPC */
> + 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;
>
> @@ -293,41 +370,48 @@ 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->dac.flags |= XFS_DAC_FINISH_TRANS;
> + args->dac.dela_state = XFS_DAS_ADD_LEAF;
> + return -EAGAIN;
> }
>
> - if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> - error = xfs_attr_leaf_addname(args);
> - if (error != -ENOSPC)
> - return error;
> +add_leaf:
>
> - /*
> - * Commit that transaction so that the node_addname()
> - * call can manage its own transactions.
> - */
> - error = xfs_defer_finish(&args->trans);
> - if (error)
> - return error;
> + /*
> + * 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;
> + }
>
> - /*
> - * Commit the current trans (including the inode) and
> - * start a new one.
> - */
> - error = xfs_trans_roll_inode(&args->trans, dp);
> - if (error)
> + if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> + error = xfs_attr_leaf_try_add(args, *leaf_bp);
> + switch (error) {
> + case -ENOSPC:
> + args->dac.flags |= XFS_DAC_FINISH_TRANS;
> + args->dac.dela_state = XFS_DAS_LEAF_TO_NODE;
> + return -EAGAIN;
> + case 0:
> + args->dac.dela_state = XFS_DAS_FOUND_LBLK;
> + return -EAGAIN;
> + default:
> return error;
> -
> + }
> +leaf:
> + error = xfs_attr_leaf_addname(args);
> + if (error == -ENOSPC) {
> + args->dac.dela_state = XFS_DAS_LEAF_TO_NODE;
> + return -EAGAIN;
> + }
> + return error;
> }
> -
> + args->dac.dela_state = XFS_DAS_LEAF_TO_NODE;
> +node:
> error = xfs_attr_node_addname(args);
> return error;
> }
> @@ -766,28 +850,29 @@ 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, forkoff;
> struct xfs_inode *dp = args->dp;
>
> - 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->dac.dela_state) {
> + case XFS_DAS_FLIP_LFLAG:
> + goto flip_flag;
> + case XFS_DAS_ALLOC_LEAF:
> + goto alloc_leaf;
> + default:
> + break;
> + }
>
> /*
> * If there was an out-of-line value, allocate the blocks we
> @@ -796,7 +881,28 @@ xfs_attr_leaf_addname(
> * maximum size of a transaction and/or hit a deadlock.
> */
> if (args->rmtblkno > 0) {
> - error = xfs_attr_rmtval_set(args);
> +
> + /* Open coded xfs_attr_rmtval_set without trans handling */
> + error = xfs_attr_rmtval_set_init(args);
> + if (error)
> + return error;
> +
> + /*
> + * Roll through the "value", allocating blocks on disk as
> + * required.
> + */
> +alloc_leaf:
> + while (args->dac.blkcnt > 0) {
> + error = xfs_attr_rmtval_set_blk(args);
> + if (error)
> + return error;
> +
> + args->dac.flags |= XFS_DAC_FINISH_TRANS;
> + args->dac.dela_state = XFS_DAS_ALLOC_LEAF;
> + return -EAGAIN;
> + }
> +
> + error = xfs_attr_rmtval_set_value(args);
> if (error)
> return error;
> }
> @@ -815,13 +921,6 @@ xfs_attr_leaf_addname(
> 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;
>
> /*
> * Dismantle the "old" attribute/value pair by removing
> @@ -832,8 +931,17 @@ xfs_attr_leaf_addname(
> args->rmtblkno = args->rmtblkno2;
> args->rmtblkcnt = args->rmtblkcnt2;
> args->rmtvaluelen = args->rmtvaluelen2;
> +
> + args->dac.dela_state = XFS_DAS_FLIP_LFLAG;
> + return -EAGAIN;
> +flip_flag:
> if (args->rmtblkno) {
> - error = xfs_attr_rmtval_remove(args);
> + error = xfs_attr_rmtval_unmap(args);
> +
> + /*
> + * if (error == -EAGAIN), we will repeat this until
> + * args->rmtblkno is zero
> + */
> if (error)
> return error;
> }
Hi Allison,

In the case where args->rmtblkno is non-zero, xfs_attr_rmtval_unmap() invokes
xfs_bunmapi() for unmapping the file block range starting at
args->rmtblkno. If xfs_bunmapi() frees a subset of the range of blocks, it
returns with 'done' set to 0 and in turn xfs_attr_rmtval_unmap() returns with
-EAGAIN error. This will cause xfs_attr_leaf_addname() to return -EAGAIN to
its caller i.e. xfs_attr_set_iter(). In turn xfs_attr_set_iter() returns back
to xfs_attr_set_args(). Here the loop is executed once again and hence
xfs_attr_set_iter() is invoked with args->dac.dela_state set to
XFS_DAS_FLIP_LFLAG. Hence xfs_attr_leaf_addname() is invoked once again with
args->dac.dela_state set to XFS_DAS_FLIP_LFLAG. Here xfs_attr_rmtval_unmap()
is invoked once again with an unmodified args->rmtblkno.

--
chandan