Re: [PATCH v6 05/24] erofs: add inode operations

Gao Xiang
2019-09-01T09:34:21Z

Hi Christoph,

Here are redo-ed comments of your suggestions...

On Thu, Aug 29, 2019 at 03:24:26AM -0700, Christoph Hellwig wrote:
> On Fri, Aug 02, 2019 at 08:53:28PM +0800, Gao Xiang wrote:
> > This adds core functions to get, read an inode.
> > It adds statx support as well.
> >
> > Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
> > ---
> > fs/erofs/inode.c | 291 +++++++++++++++++++++++++++++++++++++++++++++++
> > 1 file changed, 291 insertions(+)
> > create mode 100644 fs/erofs/inode.c
> >
> > diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> > new file mode 100644
> > index 000000000000..b6ea997bc4ae
> > --- /dev/null
> > +++ b/fs/erofs/inode.c
> > @@ -0,0 +1,291 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * linux/fs/erofs/inode.c
> > + *
> > + * Copyright (C) 2017-2018 HUAWEI, Inc.
> > + * http://www.huawei.com/
> > + * Created by Gao Xiang <gaoxiang25@huawei.com>
> > + */
> > +#include "internal.h"
> > +
> > +#include <trace/events/erofs.h>
> > +
> > +/* no locking */
> > +static int read_inode(struct inode *inode, void *data)
> > +{
> > + struct erofs_vnode *vi = EROFS_V(inode);
> > + struct erofs_inode_v1 *v1 = data;
> > + const unsigned int advise = le16_to_cpu(v1->i_advise);
> > + erofs_blk_t nblks = 0;
> > +
> > + vi->datamode = __inode_data_mapping(advise);
>
> What is the deal with these magic underscores here and various
> other similar helpers?

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-17-hsiangkao@aol.com/

underscores means 'internal' in my thought, it seems somewhat
some common practice of Linux kernel, or some recent discussions
about it?... I didn't notice these discussions...

>
> > + /* fast symlink (following ext4) */
>
> This actually originates in FFS. But it is so common that the comment
> seems a little pointless.

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-9-hsiangkao@aol.com/

>
> > + if (S_ISLNK(inode->i_mode) && inode->i_size < PAGE_SIZE) {
> > + char *lnk = erofs_kmalloc(sbi, inode->i_size + 1, GFP_KERNEL);
>
> Please just use plain kmalloc everywhere and let the normal kernel
> error injection code take care of injeting any errors.

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-20-hsiangkao@aol.com/

>
> > + /* inline symlink data shouldn't across page boundary as well */
>
> ... should not cross ..

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-9-hsiangkao@aol.com/

>
> > + if (unlikely(m_pofs + inode->i_size > PAGE_SIZE)) {
> > + DBG_BUGON(1);
> > + kfree(lnk);
> > + return -EIO;
> > + }
> > +
> > + /* get in-page inline data */
>
> s/get/copy/, but the comment seems rather pointless.

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-9-hsiangkao@aol.com/

>
> > + memcpy(lnk, data + m_pofs, inode->i_size);
> > + lnk[inode->i_size] = '\0';
> > +
> > + inode->i_link = lnk;
> > + set_inode_fast_symlink(inode);
>
> Please just set the ops directly instead of obsfucating that in a single
> caller, single line inline function. And please set it instead of the
> normal symlink iops in the same place where you also set those.:w

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-10-hsiangkao@aol.com/

>
> > + err = read_inode(inode, data + ofs);
> > + if (!err) {
>
> if (err)
> goto out_unlock;
>
> .. and save one level of indentation.

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-22-hsiangkao@aol.com/

>
> > + if (is_inode_layout_compression(inode)) {
>
> The name of this helper is a little odd. But I think just
> opencoding it seems generally cleaner anyway.

Fixed in
https://lore.kernel.org/linux-fsdevel/20190901055130.30572-11-hsiangkao@aol.com/

>
>
> > + err = -ENOTSUPP;
> > + goto out_unlock;
> > + }
> > +
> > + inode->i_mapping->a_ops = &erofs_raw_access_aops;
> > +
> > + /* fill last page if inline data is available */
> > + err = fill_inline_data(inode, data, ofs);
>
> Well, I think you should move the is_inode_flat_inline and
> (S_ISLNK(inode->i_mode) && inode->i_size < PAGE_SIZE) checks from that
> helper here, as otherwise you make everyone wonder why you'd always
> fill out the inline data.

fill_inline_data is killed, and the similar function turns into
erofs_fill_symlink which is called at erofs_fill_inode():

case S_IFLNK:
- /* by default, page_get_link is used for symlink */
- inode->i_op = &erofs_symlink_iops;
+ err = erofs_fill_symlink(inode, data, ofs);
+ if (err)
+ goto out_unlock;
inode_nohighmem(inode);
break;

>
> > +static inline struct inode *erofs_iget_locked(struct super_block *sb,
> > + erofs_nid_t nid)
> > +{
> > + const unsigned long hashval = erofs_inode_hash(nid);
> > +
> > +#if BITS_PER_LONG >= 64
> > + /* it is safe to use iget_locked for >= 64-bit platform */
> > + return iget_locked(sb, hashval);
> > +#else
> > + return iget5_locked(sb, hashval, erofs_ilookup_test_actor,
> > + erofs_iget_set_actor, &nid);
> > +#endif
>
> Just use the slightly more complicated 32-bit version everywhere so that
> you have a single actually tested code path. And then remove this
> helper.

As I said before, 64-bit platforms is common currently,
I think iget_locked is enough.
https://lore.kernel.org/r/20190830184606.GA175612@architecture4/

Thanks,
Gao Xiang