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

Chandan Babu R
2020-10-27T13:33:01Z

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

--
chandan