Re: [PATCH v4 08/17] xfs: Factor out xfs_attr_leaf_addname helper

Allison Collins
2019-11-09T21:41:09Z

On 11/8/19 1:57 PM, Darrick J. Wong wrote:
> On Wed, Nov 06, 2019 at 06:27:52PM -0700, Allison Collins wrote:
>> Factor out new helper function xfs_attr_leaf_try_add.
>> Because new delayed attribute routines cannot roll
>> transactions, we carve off the parts of
>> xfs_attr_leaf_addname that we can use. This will help
>> to reduce repetitive code later when we introduce
>> delayed attributes.
>>
>> Signed-off-by: Allison Collins <allison.henderson@oracle.com>
>> ---
>> fs/xfs/libxfs/xfs_attr.c | 84 +++++++++++++++++++++++++++++-------------------
>> 1 file changed, 51 insertions(+), 33 deletions(-)
>>
>> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
>> index 212995f..dda2eba 100644
>> --- a/fs/xfs/libxfs/xfs_attr.c
>> +++ b/fs/xfs/libxfs/xfs_attr.c
>> @@ -305,10 +305,33 @@ xfs_attr_set_args(
>> }
>> }
>>
>> - if (xfs_bmap_one_block(dp, XFS_ATTR_FORK))
>> + if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
>> error = xfs_attr_leaf_addname(args);
>> - else
>> + 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);
>> + }
>> + } else {
>> error = xfs_attr_node_addname(args);
>> + }
>> return error;
>
>
>> }
>>
>> @@ -601,21 +624,12 @@ xfs_attr_shortform_addname(xfs_da_args_t *args)
>> * External routines when attribute list is one block
>> *========================================================================*/
>>
>> -/*
>> - * Add a name to the leaf attribute list structure
>> - *
>> - * 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).
>> - */
>> STATIC int
>> -xfs_attr_leaf_addname(
>> - struct xfs_da_args *args)
>> +xfs_attr_leaf_try_add(
>
> (total stream of consciousness here...)
>
> AFAICT the old _addname function's responsibilities were:
>
> 1 Try to add a new attr key entry to the leaf block, with INCOMPLETE set
> if it's a rename op or we need to set a remote value.
> 2 If there wasn't space in the leaf block, convert to node format, call
> the node version of this function, and exit.
> 3 Allocating blocks for the remote attr value and writing them, if
> applicable
> 4 If it's a rename operation, clearing the INCOMPLETE flag on the new
> entry; setting it on the old entry; and then removing the old entry.
> 5 Clearing the INCOMPLETE flag on the new entry when we're done writing
> a remote value (if applicable)
>
> I think we arrive at this split so that we don't have a transaction roll
> in the middle of the function, right? And also to make the "convert to
> node format and roll" bits go elsewhere?
>
> The way I'm thinking about how to accomplish this is...
>
> xfs_attr_leaf_addname should be renamed xfs_attr_leaf_setname, and then
> hoist (1) into a separate function, move (2) into xfs_attr_set_args, and
> hoist (4) into a separate function.
>
> ...ok, so let's test how closely my understanding fits the changes made
> in this patch:
>
> _try_add is basically (1).
>
> Most of (2) happened, though the call to xfs_attr3_leaf_to_node ought to
> go into the caller so that the conversion stays with the defer_finish
> and roll.
>
> (4) could still be done, maybe as a separate prep patch.
>

I think you're on the right track. Perhaps the diff made it look a
little crazier than it seems. Maybe its easier to describe it as this:

I renamed xfs_attr_leaf_addname to xfs_attr_leaf_try_add,
and then deleted (2) out of the body of the function. The upper half
(1) became the helper function, and lower half (3, 4, and 5) became the
new xfs_attr_leaf_addname, which now calls the helper at the start of
the routine. Finally (2) got factored up into the caller.

Hope that helps some :-) The point of all this being to jigsaw out (1)
into a stand alone routine that we can use later in delayed attrs.

> Hm, ok, I think I understand what this patch does. The call site in
> xfs_attr_set_args would be clearer (and less indenty) if it looked like:
>
> if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> error = xfs_attr_leaf_addname(args);
> if (error == 0 || error != -ENOSPC)
> return error;
>
> /* Promote the attribute list to node format. */
> error = xfs_attr3_leaf_to_node(args);
> if (error)
> return error;
I think this part here is already taken care of in
xfs_attr_leaf_addname, but otherwise, I think the rest of this is
equivalent. Will update in the next set.

Thanks for the reviews!
Allison

>
> /*
> * 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;
> }
>
> return xfs_attr_node_addname(args);
>
> But otherwise it looks decent, assuming I understood any of it. :)
>
> --D
>
>> + struct xfs_da_args *args,
>> + struct xfs_buf *bp)
>> {
>> - struct xfs_buf *bp;
>> - int retval, error, forkoff;
>> - struct xfs_inode *dp = args->dp;
>> -
>> - trace_xfs_attr_leaf_addname(args);
>> + int retval, error;
>>
>> /*
>> * Look up the given attribute in the leaf block. Figure out if
>> @@ -661,31 +675,35 @@ xfs_attr_leaf_addname(
>> retval = xfs_attr3_leaf_add(bp, args);
>> if (retval == -ENOSPC) {
>> /*
>> - * Promote the attribute list to the Btree format, then
>> - * Commit that transaction so that the node_addname() call
>> - * can manage its own transactions.
>> + * Promote the attribute list to the Btree format.
>> + * Unless an error occurs, retain the -ENOSPC retval
>> */
>> error = xfs_attr3_leaf_to_node(args);
>> if (error)
>> return error;
>> - error = xfs_defer_finish(&args->trans);
>> - if (error)
>> - return error;
>> + }
>> + return retval;
>> +}
>>
>> - /*
>> - * 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 whole rest of the problem off on the Btree code.
>> - */
>> - error = xfs_attr_node_addname(args);
>> +/*
>> + * Add a name to the leaf attribute list structure
>> + *
>> + * 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).
>> + */
>> +STATIC int
>> +xfs_attr_leaf_addname(struct xfs_da_args *args)
>> +{
>> + int error, forkoff;
>> + struct xfs_buf *bp = NULL;
>> + 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
>> --
>> 2.7.4
>>