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

[Allison Henderson <allison.henderson@xxxxxxxxxx>]

On 10/19/2017 12:13 PM, Darrick J. Wong wrote:
> 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@xxxxxxxxxx>
> > ---
> >   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);
> ...
Ok, yeah that makes sense.  Will do.
> 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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