Re: [PATCH v7 03/19] xfs: Add xfs_has_attr and subroutines

Amir Goldstein
2020-02-25T06:44:06Z

On Tue, Feb 25, 2020 at 8:26 AM Dave Chinner <david@fromorbit.com> wrote:
>
> On Sun, Feb 23, 2020 at 02:20:32PM +0200, Amir Goldstein wrote:
> > On Sun, Feb 23, 2020 at 4:07 AM Allison Collins
> > <allison.henderson@oracle.com> 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 appearance of duplicated code. We will need these
> > > routines later for delayed attributes since delayed operations cannot return error
> > > codes.
> > >
> > > Signed-off-by: Allison Collins <allison.henderson@oracle.com>
> > > ---
> > > fs/xfs/libxfs/xfs_attr.c | 171 ++++++++++++++++++++++++++++--------------
> > > fs/xfs/libxfs/xfs_attr.h | 1 +
> > > fs/xfs/libxfs/xfs_attr_leaf.c | 111 +++++++++++++++++----------
> > > fs/xfs/libxfs/xfs_attr_leaf.h | 3 +
> > > 4 files changed, 188 insertions(+), 98 deletions(-)
> > >
> > > diff --git a/fs/xfs/libxfs/xfs_attr.c b/fs/xfs/libxfs/xfs_attr.c
> > > index 9acdb23..2255060 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_attr_leaf_hasname(struct xfs_da_args *args, struct xfs_buf **bp);
> > >
> > > /*
> > > * 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);
> > >
> > > @@ -310,6 +313,37 @@ xfs_attr_set_args(
> > > }
> > >
> > > /*
> > > + * Return EEXIST if attr is found, or ENOATTR if not
> >
> > This is a very silly return value for a function named has_attr in my taste.
> > I realize you inherited this interface from xfs_attr3_leaf_lookup_int(), but
> > IMO this change looks like a very good opportunity to change that internal
> > API:
>
> tl;dr Cleaning up this API is work for another patchset.
>
> >
> > xfs_has_attr?
> >
> > 0: NO
> > 1: YES (or stay with the syscall standard of -ENOATTR)
> > <0: error
>
> While I agree with your sentiment, Amir, the API you suggest is an
> anti-pattern. We've been removing ternary return value APIs like
> this from XFS and replacing them with an explicit error return value
> and an operational return parameter like so:
>
> error = xfs_has_attr(&exists)
> if (error)
> return error;
>

That would be neat and tidy.

One of the outcomes of new reviewers is comments on code unrelated
to the changes... I have no problem of keeping API as is for Allison's
change, but I did want to point out that the API became worse to read
due to the helper name change from _lookup_attr to _has_attr, which
really asks for a yes or no answer.

Thanks,
Amir.