Re: [PATCH 03/17] Add xfs_attr_set_defered and xfs_attr_remove_defered

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Wed, Oct 18, 2017 at 03:55:19PM -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.
> 
> Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> ---
>  fs/xfs/libxfs/xfs_attr.c | 58 ++++++++++++++++++++++++++++++++++++++++++++++++
>  fs/xfs/xfs_attr.h        |  7 ++++++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index 5325ec2..59f3502 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -458,6 +458,37 @@ xfs_attr_set(
>  	return error;
>  }
>  
> +int
> +xfs_attr_set_deferred(
> +	struct xfs_inode	*dp,
> +	struct xfs_defer_ops    *dfops,
> +	const unsigned char	*name,
> +	unsigned int		namelen,
> +	unsigned char		*value,
> +	unsigned int		valuelen,
> +	int			flags)
> +{
> +
> +	struct xfs_attr_item     *new;
> +
> +	ASSERT(namelen != 0);
> +	ASSERT(valuelen != 0);
> +
> +	new = kmem_alloc(sizeof(struct xfs_attr_item), KM_SLEEP|KM_NOFS);

Yikes, this is a 66,000 byte allocation.  I wouldn't take it for granted
that we can ask for more than a page's worth of memory.

Seeing as we already know namelen and valuelen, let's go for the
zero length array at the end of the struct approach:

struct xfs_attr_item {
	...
	uint16_t		xattri_namelen;
	uint8_t			xattri_namevalue[0];
};

#define XFS_ATTR_ITEM_SIZEOF(namelen, valuelen)	\
	(sizeof(struct xfs_attr_item) + (namelen) + (valuelen))

new = kmem_alloc(XFS_ATTR_ITEM_SIZEOF(namelen, valuelen), KM...);
if (!new)
	return -ENOMEM;
memcpy(new->xattri_namevalue, name, namelen);
new->xattri_namelen = namelen;
memcpy(&new->xattri_namevalue[namelen], value, valuelen);
...

Assuming there isn't a way to attach the caller's buffers to the attr
item without copying anything(?)  (It would be nice if we could, but
between the defer_add and the defer_finish a lot can happen w.r.t.
variable scope so that might be a bad idea.)

> +	memset(new, 0, sizeof(struct xfs_attr_item));
> +	new->xattri_ino = dp->i_ino;
> +	new->xattri_op_flags = ATTR_OP_FLAGS_SET;
> +	new->xattri_name_len = namelen;
> +	new->xattri_value_len = valuelen;
> +	new->xattri_flags = flags;
> +	memcpy(new->xattri_name, name, namelen);
> +	memcpy(&new->xattri_value, value, valuelen);
> +
> +	xfs_defer_add(dfops, 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.
> @@ -531,6 +562,33 @@ xfs_attr_remove(
>  	return error;
>  }
>  
> +int
> +xfs_attr_remove_deferred(
> +	struct xfs_inode        *dp,
> +	struct xfs_defer_ops    *dfops,
> +	const unsigned char     *name,
> +	unsigned int		namelen,
> +	int                     flags)
> +{
> +
> +	struct xfs_attr_item     *new;
> +
> +	ASSERT(namelen != 0);
> +
> +	new = kmem_alloc(sizeof(struct xfs_attr_item), KM_SLEEP|KM_NOFS);
> +	memset(new, 0, sizeof(struct xfs_attr_item));
> +	new->xattri_ino = dp->i_ino;
> +	new->xattri_op_flags = ATTR_OP_FLAGS_REMOVE;
> +	new->xattri_name_len = namelen;
> +	new->xattri_value_len = 0;
> +	new->xattri_flags = flags;
> +	memcpy(new->xattri_name, name, namelen);
> +
> +	xfs_defer_add(dfops, XFS_DEFER_OPS_TYPE_ATTR, &new->xattri_list);
> +
> +	return 0;
> +}
> +
>  /*========================================================================
>   * External routines when attribute list is inside the inode
>   *========================================================================*/
> diff --git a/fs/xfs/xfs_attr.h b/fs/xfs/xfs_attr.h
> index 34bb4cb..f4a53fd 100644
> --- a/fs/xfs/xfs_attr.h
> +++ b/fs/xfs/xfs_attr.h
> @@ -173,5 +173,12 @@ int xfs_attr_list(struct xfs_inode *dp, char *buffer, int bufsize,
>  int xfs_attr_args_init(struct xfs_da_args *args, struct xfs_inode *dp,
>  		       const unsigned char *name, 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_defer_ops *dfops,
> +			  const unsigned char *name, unsigned int name_len,
> +			  unsigned char *value, unsigned int valuelen,
> +			  int flags);
> +int xfs_attr_remove_deferred(struct xfs_inode *dp, struct xfs_defer_ops *dfops,
> +			    const unsigned char *name, unsigned int namelen,
> +			    int flags);
>  
>  #endif	/* __XFS_ATTR_H__ */
> -- 
> 2.7.4
> 
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