Re: [PATCH 5/9] xfs: Add xfs_attr_set_deferred and xfs_attr_remove_deferred

Allison Henderson
2019-04-18T21:28:19Z

On 4/18/19 8:49 AM, Brian Foster wrote:
> On Fri, Apr 12, 2019 at 03:50:32PM -0700, Allison Henderson wrote:
>> These routines set up set and start a new deferred attribute
>> operation. These functions are meant to be called by other
>> code needing to initiate a deferred attribute operation. We
>> will use these routines later in the parent pointer patches.
>>
>
> We probably don't need to reference the parent pointer stuff any more
> for this, right? I'm assuming we'll be converting generic attr
> infrastructure over to this mechanism in subsequent patches..?

Right, some of these comments are a little stale. I will clean then up
a bit.

>
>> Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
>> ---
>> fs/xfs/libxfs/xfs_attr.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++
>> fs/xfs/libxfs/xfs_attr.h | 7 +++++
>> 2 files changed, 87 insertions(+)
>>
>> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
>> index fadd485..c3477fa7 100644
>> --- a/fs/xfs/libxfs/xfs_attr.c
>> +++ b/fs/xfs/libxfs/xfs_attr.c
>> @@ -30,6 +30,7 @@
>> #include "xfs_trans_space.h"
>> #include "xfs_trace.h"
>> #include "xfs_attr_item.h"
>> +#include "xfs_attr.h"
>>
>> /*
>> * xfs_attr.c
>> @@ -429,6 +430,52 @@ xfs_attr_set(
>> goto out_unlock;
>> }
>>
>> +/* Sets an attribute for an inode as a deferred operation */
>> +int
>> +xfs_attr_set_deferred(
>> + struct xfs_inode *dp,
>> + struct xfs_trans *tp,
>> + const unsigned char *name,
>> + unsigned int namelen,
>> + const unsigned char *value,
>> + unsigned int valuelen,
>> + int flags)
>> +{
>> +
>> + struct xfs_attr_item *new;
>> + char *name_value;
>> +
>> + /*
>> + * All set operations must have a name
>> + * but not necessarily a value.
>> + * Generic 062
>
> Comment formatting, also looks like there's some stale text or
> something.
I think I left that as a reminder to myself at one point and forgot to
take it out :-) I believe there was some discussion in earlier reviews
about checking both name and value length, but later I ran into test
cases that expect to be able to set an attribute with no value, so I
guess not. In any case, I will clean up the commentary here.

>
>> + */
>> + if (!namelen) {
>> + ASSERT(0);
>> + return -EFSCORRUPTED;
>
> This is essentially a requested operation from userspace, right? If so,
> I'd think -EINVAL or something makes more sense than -EFSCORRUPTED.

Yeah, I think initially the plan was to have only parent pointers use
the defer operations, but since now we are using them for all attr
operations, it should probably be EINVAL.

>
>> + }
>> +
>> + new = kmem_alloc(XFS_ATTR_ITEM_SIZEOF(namelen, valuelen),
>> + KM_SLEEP|KM_NOFS);
>
> This could get interesting with larger attrs (up to 64k IIRC). We might
> want to consider kmem_alloc_large().

Thats a good point, I'll move it to the larger allocation. Maybe I can
make a test case for it as well.

>
>> + name_value = ((char *)new) + sizeof(struct xfs_attr_item);
>> + memset(new, 0, XFS_ATTR_ITEM_SIZEOF(namelen, valuelen));
>> + new->xattri_ip = dp;
>> + new->xattri_op_flags = XFS_ATTR_OP_FLAGS_SET;
>> + new->xattri_name_len = namelen;
>> + new->xattri_value_len = valuelen;
>> + new->xattri_flags = flags;
>> + memcpy(&name_value[0], name, namelen);
>
> name_value is just a char pointer. Do we need the whole array index just
> to deref thing here? Meh, I guess it's consistent with the value copy
> below. No big deal.
It's not needed. I guess it just looks a little more consistent since
we have things getting copied out at different offsets in the buffer.

>
>> + new->xattri_name = name_value;
>> + new->xattri_value = name_value + namelen;
>> +
>> + if (valuelen > 0)
>> + memcpy(&name_value[namelen], value, valuelen);
>> +
>> + xfs_defer_add(tp, XFS_DEFER_OPS_TYPE_ATTR, &new->xattri_list);
>> +
>> + return 0;
>> +}
>> +
>> /*
>> * Generic handler routine to remove a name from an attribute list.
>> * Transitions attribute list from Btree to shortform as necessary.
>> @@ -513,6 +560,39 @@ xfs_attr_remove(
>> return error;
>> }
>>
>> +/* Removes an attribute for an inode as a deferred operation */
>> +int
>> +xfs_attr_remove_deferred(
>
> Hmm.. I'm kind of wondering if we actually need to defer attr removes.
> Do we have the same kind of challenges for attr removal as for attr
> creation, or is there some future scenario where this is needed?

I suppose we don't have to have it? The motivation was to help break up
the amount of transaction activity that happens on inode
create/rename/remove operations once pptrs go in. Attr remove does not
look as complex as attr set, but I suppose it helps to some degree?

>
>> + struct xfs_inode *dp,
>> + struct xfs_trans *tp,
>> + const unsigned char *name,
>> + unsigned int namelen,
>> + int flags)
>> +{
>> +
>> + struct xfs_attr_item *new;
>> + char *name_value;
>> +
>> + if (!namelen) {
>> + ASSERT(0);
>> + return -EFSCORRUPTED;
>
> Similar comment around -EFSCORRUPTED vs. -EINVAL (or something else..).
Ok, I will change to EINVAL here too.

Thanks again for the reviews!! They are very helpful!

Allison
>
> Brian
>
>> + }
>> +
>> + new = kmem_alloc(XFS_ATTR_ITEM_SIZEOF(namelen, 0), KM_SLEEP|KM_NOFS);
>> + name_value = ((char *)new) + sizeof(struct xfs_attr_item);
>> + memset(new, 0, XFS_ATTR_ITEM_SIZEOF(namelen, 0));
>> + new->xattri_ip = dp;
>> + new->xattri_op_flags = XFS_ATTR_OP_FLAGS_REMOVE;
>> + new->xattri_name_len = namelen;
>> + new->xattri_value_len = 0;
>> + new->xattri_flags = flags;
>> + memcpy(name_value, name, namelen);
>> +
>> + xfs_defer_add(tp, XFS_DEFER_OPS_TYPE_ATTR, &new->xattri_list);
>> +
>> + return 0;
>> +}
>> +
>> /*========================================================================
>> * External routines when attribute list is inside the inode
>> *========================================================================*/
>> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
>> index 92d9a15..83b3621 100644
>> --- a/fs/xfs/libxfs/xfs_attr.h
>> +++ b/fs/xfs/libxfs/xfs_attr.h
>> @@ -175,5 +175,12 @@ bool xfs_attr_namecheck(const void *name, size_t length);
>> int xfs_attr_args_init(struct xfs_da_args *args, struct xfs_inode *dp,
>> const unsigned char *name, size_t namelen, int flags);
>> int xfs_attr_calc_size(struct xfs_da_args *args, int *local);
>> +int xfs_attr_set_deferred(struct xfs_inode *dp, struct xfs_trans *tp,
>> + const unsigned char *name, unsigned int name_len,
>> + const unsigned char *value, unsigned int valuelen,
>> + int flags);
>> +int xfs_attr_remove_deferred(struct xfs_inode *dp, struct xfs_trans *tp,
>> + const unsigned char *name, unsigned int namelen,
>> + int flags);
>>
>> #endif /* __XFS_ATTR_H__ */
>> --
>> 2.7.4
>>