Re: [PATCH v3 04/19] xfs: Add xfs_has_attr and subroutines

[Brian Foster <bfoster@redhat.com>]

On Thu, Sep 05, 2019 at 03:18:22PM -0700, Allison Collins wrote:
> From: Allison Henderson <allison.henderson@oracle.com>
> 
> This patch adds a new functions to check for the existence of
> an attribute.  Subroutines are also added to handle the cases
> of leaf blocks, nodes or shortform.  Common code that appears
> in existing attr add and remove functions have been factored
> out to help reduce the appearence of duplicated code.  We will
> need these routines later for delayed attributes since delayed
> operations cannot return error codes.
> 
> Signed-off-by: Allison Henderson <allison.henderson@oracle.com>
> Signed-off-by: Allison Collins <allison.henderson@oracle.com>

Extra s-o-b tag?

> ---
>  fs/xfs/libxfs/xfs_attr.c      | 150 +++++++++++++++++++++++++++---------------
>  fs/xfs/libxfs/xfs_attr.h      |   1 +
>  fs/xfs/libxfs/xfs_attr_leaf.c |  92 +++++++++++++++++---------
>  fs/xfs/libxfs/xfs_attr_leaf.h |   2 +
>  4 files changed, 161 insertions(+), 84 deletions(-)
> 
> diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> index 50e099f..a297857 100644
> --- a/fs/xfs/libxfs/xfs_attr.c
> +++ b/fs/xfs/libxfs/xfs_attr.c
> @@ -46,6 +46,7 @@ STATIC int xfs_attr_shortform_addname(xfs_da_args_t *args);
>  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_removename(xfs_da_args_t *args);
> +STATIC int xfs_leaf_has_attr(struct xfs_da_args *args, struct xfs_buf **bp);
>  

The fact that this is not named xfs_attr_leaf_*() kind of stands out
here, particularly since the node variant uses the xfs_attr_* prefix.
Hm? (Same goes for xfs_shortform_has_attr() I suppose..).

>  /*
>   * Internal routines when attribute list is more than one block.
> @@ -53,6 +54,8 @@ STATIC int xfs_attr_leaf_removename(xfs_da_args_t *args);
>  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_removename(xfs_da_args_t *args);
> +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);
>  
> @@ -309,6 +312,32 @@ xfs_attr_set_args(
>  }
>  
>  /*
> + * Return EEXIST if attr is found, or ENOATTR if not
> + */
> +int
> +xfs_has_attr(
> +	struct xfs_da_args      *args)
> +{
> +	struct xfs_inode        *dp = args->dp;
> +	struct xfs_buf		*bp;
> +	int                     error;
> +
> +	if (!xfs_inode_hasattr(dp)) {
> +		error = -ENOATTR;
> +	} else if (dp->i_d.di_aformat == XFS_DINODE_FMT_LOCAL) {
> +		ASSERT(dp->i_afp->if_flags & XFS_IFINLINE);
> +		error = xfs_shortform_has_attr(args, NULL, NULL);
> +	} else if (xfs_bmap_one_block(dp, XFS_ATTR_FORK)) {
> +		error = xfs_leaf_has_attr(args, &bp);
> +		xfs_trans_brelse(args->trans, bp);
> +	} else {
> +		error = xfs_attr_node_hasname(args, NULL);
> +	}
> +
> +	return error;
> +}
> +

FWIW, I think it's preferable to include new functions like this with
the first user. I'm a bit curious about the use of error codes here as
opposed to returning a boolean. I could see being able to handle
unexpected errors as a good reason for doing that, but taking a quick
look ahead, it appears neither caller of xfs_has_attr() does so. ;)

(To be clear, I think keeping the function as is and fixing up the
eventual callers to handle unexpected errors is probably the right thing
to do.).

> +/*
>   * Remove the attribute specified in @args.
>   */
>  int
> @@ -574,26 +603,17 @@ STATIC int
>  xfs_attr_leaf_addname(
>  	struct xfs_da_args	*args)
>  {
> -	struct xfs_inode	*dp;
>  	struct xfs_buf		*bp;
>  	int			retval, error, forkoff;
> +	struct xfs_inode	*dp = args->dp;
>  
>  	trace_xfs_attr_leaf_addname(args);
>  
>  	/*
> -	 * Read the (only) block in the attribute list in.
> -	 */
> -	dp = args->dp;
> -	args->blkno = 0;
> -	error = xfs_attr3_leaf_read(args->trans, args->dp, args->blkno, -1, &bp);
> -	if (error)
> -		return error;
> -

It looks like we lose this unexpected error check here (i.e. suppose we
got -ENOMEM or -EFSCORRUPTED or something that indicates we shouldn't
continue). FWIW, this seems to repeat throughout this patch where we've
invoked the new helpers..

> -	/*
>  	 * Look up the given attribute in the leaf block.  Figure out if
>  	 * the given flags produce an error or call for an atomic rename.
>  	 */
> -	retval = xfs_attr3_leaf_lookup_int(bp, args);
> +	retval = xfs_leaf_has_attr(args, &bp);
>  	if ((args->name.type & ATTR_REPLACE) && (retval == -ENOATTR)) {
>  		xfs_trans_brelse(args->trans, bp);
>  		return retval;
> @@ -745,6 +765,25 @@ xfs_attr_leaf_addname(
>  }
>  
>  /*
> + * Return EEXIST if attr is found, or ENOATTR if not
> + */
> +STATIC int
> +xfs_leaf_has_attr(
> +	struct xfs_da_args      *args,
> +	struct xfs_buf		**bp)
> +{
> +	int                     error = 0;
> +
> +	args->blkno = 0;

This seems misplaced for a helper, but I could be missing context.  Why
not just pass zero directly and leave the args->blkno assignment to the
caller?

> +	error = xfs_attr3_leaf_read(args->trans, args->dp,
> +			args->blkno, XFS_DABUF_MAP_NOMAPPING, bp);
> +	if (error)
> +		return error;
> +
> +	return xfs_attr3_leaf_lookup_int(*bp, args);
> +}
> +
> +/*
>   * Remove a name from the leaf attribute list structure
>   *
>   * This leaf block cannot have a "remote" value, we only call this routine
> @@ -764,12 +803,8 @@ xfs_attr_leaf_removename(
>  	 * Remove the attribute.
>  	 */
>  	dp = args->dp;
> -	args->blkno = 0;
> -	error = xfs_attr3_leaf_read(args->trans, args->dp, args->blkno, -1, &bp);
> -	if (error)
> -		return error;

Lost error check.

>  
> -	error = xfs_attr3_leaf_lookup_int(bp, args);
> +	error = xfs_leaf_has_attr(args, &bp);
>  	if (error == -ENOATTR) {
>  		xfs_trans_brelse(args->trans, bp);
>  		return error;
> @@ -808,12 +843,7 @@ xfs_attr_leaf_get(xfs_da_args_t *args)
>  
>  	trace_xfs_attr_leaf_get(args);
>  
> -	args->blkno = 0;
> -	error = xfs_attr3_leaf_read(args->trans, args->dp, args->blkno, -1, &bp);
> -	if (error)
> -		return error;
> -

^ here too. Not sure if I caught them all, but you get the idea. ;)

> -	error = xfs_attr3_leaf_lookup_int(bp, args);
> +	error = xfs_leaf_has_attr(args, &bp);
>  	if (error != -EEXIST)  {
>  		xfs_trans_brelse(args->trans, bp);
>  		return error;
> @@ -823,6 +853,43 @@ xfs_attr_leaf_get(xfs_da_args_t *args)
>  	return error;
>  }
>  
> +/*
> + * Return EEXIST if attr is found, or ENOATTR if not
> + * statep: If not null is set to point at the found state.  Caller will
> + * 	   be responsible for freeing the state in this case.
> + */
> +STATIC int
> +xfs_attr_node_hasname(
> +	struct xfs_da_args	*args,
> +	struct xfs_da_state	**statep)
> +{
> +	struct xfs_da_state	*state;
> +	struct xfs_inode	*dp;
> +	int			retval, error;
> +
> +	/*
> +	 * Tie a string around our finger to remind us where we are.
> +	 */
> +	dp = args->dp;
> +	state = xfs_da_state_alloc();
> +	state->args = args;
> +	state->mp = dp->i_mount;
> +

No real need for the dp local variable here if it's just to reference
->i_mount. Also I know that comment isn't introduced by this patch, but
any idea what it actually means? It doesn't make much sense to me at a
glance. :P

> +	/*
> +	 * Search to see if name exists, and get back a pointer to it.
> +	 */
> +	error = xfs_da3_node_lookup_int(state, &retval);
> +	if (error == 0)
> +		error = retval;
> +
> +	if (statep != NULL)
> +		*statep = state;
> +	else
> +		xfs_da_state_free(state);
> +
> +	return error;
> +}
> +
>  /*========================================================================
>   * External routines when attribute list size > geo->blksize
>   *========================================================================*/
> @@ -855,17 +922,14 @@ xfs_attr_node_addname(
>  	dp = args->dp;
>  	mp = dp->i_mount;
>  restart:
> -	state = xfs_da_state_alloc();
> -	state->args = args;
> -	state->mp = mp;
> -
>  	/*
>  	 * Search to see if name already exists, and get back a pointer
>  	 * to where it should go.
>  	 */
> -	error = xfs_da3_node_lookup_int(state, &retval);
> -	if (error)

Error check again.

> +	error = xfs_attr_node_hasname(args, &state);
> +	if (error == -EEXIST)
>  		goto out;
> +
>  	blk = &state->path.blk[ state->path.active-1 ];
>  	ASSERT(blk->magic == XFS_ATTR_LEAF_MAGIC);
>  	if ((args->name.type & ATTR_REPLACE) && (retval == -ENOATTR)) {
> @@ -1070,29 +1134,15 @@ xfs_attr_node_removename(
>  {
>  	struct xfs_da_state	*state;
>  	struct xfs_da_state_blk	*blk;
> -	struct xfs_inode	*dp;
>  	struct xfs_buf		*bp;
>  	int			retval, error, forkoff;
> +	struct xfs_inode	*dp = args->dp;
>  
>  	trace_xfs_attr_node_removename(args);
>  
> -	/*
> -	 * Tie a string around our finger to remind us where we are.
> -	 */
> -	dp = args->dp;
> -	state = xfs_da_state_alloc();
> -	state->args = args;
> -	state->mp = dp->i_mount;
> -
> -	/*
> -	 * Search to see if name exists, and get back a pointer to it.
> -	 */
> -	error = xfs_da3_node_lookup_int(state, &retval);
> -	if (error || (retval != -EEXIST)) {
> -		if (error == 0)
> -			error = retval;
> +	error = xfs_attr_node_hasname(args, &state);
> +	if (error != -EEXIST)
>  		goto out;
> -	}
>  
>  	/*
>  	 * If there is an out-of-line value, de-allocate the blocks.
> @@ -1314,20 +1364,14 @@ xfs_attr_node_get(xfs_da_args_t *args)
>  
>  	trace_xfs_attr_node_get(args);
>  
> -	state = xfs_da_state_alloc();
> -	state->args = args;
> -	state->mp = args->dp->i_mount;
> -
>  	/*
>  	 * Search to see if name exists, and get back a pointer to it.
>  	 */
> -	error = xfs_da3_node_lookup_int(state, &retval);
> -	if (error) {
> +	error = xfs_attr_node_hasname(args, &state);
> +	if (error != -EEXIST) {
>  		retval = error;
>  		goto out_release;
>  	}
> -	if (retval != -EEXIST)
> -		goto out_release;
>  
>  	/*
>  	 * Get the value, local or "remote"
> diff --git a/fs/xfs/libxfs/xfs_attr.h b/fs/xfs/libxfs/xfs_attr.h
> index cedb4e2..fb56d81 100644
> --- a/fs/xfs/libxfs/xfs_attr.h
> +++ b/fs/xfs/libxfs/xfs_attr.h
> @@ -150,6 +150,7 @@ int xfs_attr_set(struct xfs_inode *dp, struct xfs_name *name,
>  		 unsigned char *value, int valuelen);
>  int xfs_attr_set_args(struct xfs_da_args *args);
>  int xfs_attr_remove(struct xfs_inode *dp, struct xfs_name *name);
> +int xfs_has_attr(struct xfs_da_args *args);
>  int xfs_attr_remove_args(struct xfs_da_args *args);
>  int xfs_attr_list(struct xfs_inode *dp, char *buffer, int bufsize,
>  		  int flags, struct attrlist_cursor_kern *cursor);
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.c b/fs/xfs/libxfs/xfs_attr_leaf.c
> index 07ce320..a501538 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.c
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.c
> @@ -590,6 +590,53 @@ xfs_attr_shortform_create(xfs_da_args_t *args)
>  }
>  
>  /*
> + * Return EEXIST if attr is found, or ENOATTR if not
> + * args:  args containing attribute name and namelen
> + * sfep:  If not null, pointer will be set to the last attr entry found
> + * basep: If not null, pointer is set to the byte offset of the entry in the
> + *	  list
> + */
> +int
> +xfs_shortform_has_attr(
> +	struct xfs_da_args	 *args,
> +	struct xfs_attr_sf_entry **sfep,
> +	int			 *basep)
> +{
> +	struct xfs_attr_shortform *sf;
> +	struct xfs_attr_sf_entry *sfe;
> +	int			base = sizeof(struct xfs_attr_sf_hdr);
> +	int			size = 0;
> +	int			end;
> +	int			i;
> +
> +	base = sizeof(struct xfs_attr_sf_hdr);
> +	sf = (struct xfs_attr_shortform *)args->dp->i_afp->if_u1.if_data;
> +	sfe = &sf->list[0];
> +	end = sf->hdr.count;
> +	for (i = 0; i < end; sfe = XFS_ATTR_SF_NEXTENTRY(sfe),
> +			base += size, i++) {
> +		size = XFS_ATTR_SF_ENTSIZE(sfe);
> +		if (sfe->namelen != args->name.len)
> +			continue;
> +		if (memcmp(sfe->nameval, args->name.name, args->name.len) != 0)
> +			continue;
> +		if (!xfs_attr_namesp_match(args->name.type, sfe->flags))
> +			continue;
> +		break;
> +	}
> +
> +	if (sfep != NULL)
> +		*sfep = sfe;
> +
> +	if (basep != NULL)
> +		*basep = base;
> +
> +	if (i == end)
> +		return -ENOATTR;
> +	return -EEXIST;

This function seems like it could just return a bool. Eh, I suppose it's
better to be consistent with the other variants if those ones can return
unrelated errors.

> +}
> +
> +/*
>   * Add a name/value pair to the shortform attribute list.
>   * Overflow from the inode has already been checked for.
>   */
> @@ -598,7 +645,7 @@ xfs_attr_shortform_add(xfs_da_args_t *args, int forkoff)
>  {
>  	xfs_attr_shortform_t *sf;
>  	xfs_attr_sf_entry_t *sfe;
> -	int i, offset, size;
> +	int offset, size, error;
>  	xfs_mount_t *mp;
>  	xfs_inode_t *dp;

Nit: might be good to clean up the typedefs here since you do it in the
remove function as well.

>  	struct xfs_ifork *ifp;
> @@ -612,18 +659,10 @@ xfs_attr_shortform_add(xfs_da_args_t *args, int forkoff)
>  	ifp = dp->i_afp;
>  	ASSERT(ifp->if_flags & XFS_IFINLINE);
>  	sf = (xfs_attr_shortform_t *)ifp->if_u1.if_data;
> -	sfe = &sf->list[0];
> -	for (i = 0; i < sf->hdr.count; sfe = XFS_ATTR_SF_NEXTENTRY(sfe), i++) {
> +	error = xfs_shortform_has_attr(args, &sfe, NULL);
>  #ifdef DEBUG
> -		if (sfe->namelen != args->name.len)
> -			continue;
> -		if (memcmp(args->name.name, sfe->nameval, args->name.len) != 0)
> -			continue;
> -		if (!xfs_attr_namesp_match(args->name.type, sfe->flags))
> -			continue;
> -		ASSERT(0);
> +	ASSERT(error != -EEXIST);
>  #endif

Hmm, interesting. So basically this code walks to the end of the list
for the purpose of placement of the new attr and the debug code simply
asserts that we don't find an existing attr. The only thing that
concerns me is that nothing about xfs_shortform_has_attr() indicates
that the output values are important when the lookup fails. The comment
only explains what the values are when a lookup succeeds. Could we
update the comment to elaborate on this use case to prevent somebody
from unknowingly breaking it down the road?

Also, there's no need for the #ifdef DEBUG any more with just the assert
check in that block.

> -	}
>  
>  	offset = (char *)sfe - (char *)sf;
>  	size = XFS_ATTR_SF_ENTSIZE_BYNAME(args->name.len, args->valuelen);
> @@ -668,33 +707,24 @@ xfs_attr_fork_remove(
>  int
>  xfs_attr_shortform_remove(xfs_da_args_t *args)
>  {
> -	xfs_attr_shortform_t *sf;
> -	xfs_attr_sf_entry_t *sfe;
> -	int base, size=0, end, totsize, i;
> -	xfs_mount_t *mp;
> -	xfs_inode_t *dp;
> +	struct xfs_attr_shortform	*sf;
> +	struct xfs_attr_sf_entry	*sfe;
> +	int				base, size = 0, end, totsize;
> +	struct xfs_mount		*mp;
> +	struct xfs_inode		*dp;
> +	int				error;
>  
>  	trace_xfs_attr_sf_remove(args);
>  
>  	dp = args->dp;
>  	mp = dp->i_mount;
> -	base = sizeof(xfs_attr_sf_hdr_t);
>  	sf = (xfs_attr_shortform_t *)dp->i_afp->if_u1.if_data;
> -	sfe = &sf->list[0];
>  	end = sf->hdr.count;

This value of end is unused (end is immediately reassigned further down
in the function).

Brian

> -	for (i = 0; i < end; sfe = XFS_ATTR_SF_NEXTENTRY(sfe),
> -					base += size, i++) {
> -		size = XFS_ATTR_SF_ENTSIZE(sfe);
> -		if (sfe->namelen != args->name.len)
> -			continue;
> -		if (memcmp(sfe->nameval, args->name.name, args->name.len) != 0)
> -			continue;
> -		if (!xfs_attr_namesp_match(args->name.type, sfe->flags))
> -			continue;
> -		break;
> -	}
> -	if (i == end)
> -		return -ENOATTR;
> +
> +	error = xfs_shortform_has_attr(args, &sfe, &base);
> +	if (error == -ENOATTR)
> +		return error;
> +	size = XFS_ATTR_SF_ENTSIZE(sfe);
>  
>  	/*
>  	 * Fix up the attribute fork data, covering the hole
> diff --git a/fs/xfs/libxfs/xfs_attr_leaf.h b/fs/xfs/libxfs/xfs_attr_leaf.h
> index 536a290..58e9327 100644
> --- a/fs/xfs/libxfs/xfs_attr_leaf.h
> +++ b/fs/xfs/libxfs/xfs_attr_leaf.h
> @@ -42,6 +42,8 @@ int	xfs_attr_shortform_getvalue(struct xfs_da_args *args);
>  int	xfs_attr_shortform_to_leaf(struct xfs_da_args *args,
>  			struct xfs_buf **leaf_bp);
>  int	xfs_attr_shortform_remove(struct xfs_da_args *args);
> +int	xfs_shortform_has_attr(struct xfs_da_args *args,
> +			       struct xfs_attr_sf_entry **sfep, int *basep);
>  int	xfs_attr_shortform_allfit(struct xfs_buf *bp, struct xfs_inode *dp);
>  int	xfs_attr_shortform_bytesfit(struct xfs_inode *dp, int bytes);
>  xfs_failaddr_t xfs_attr_shortform_verify(struct xfs_inode *ip);
> -- 
> 2.7.4
>