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Message-ID: <YQoX62zRERGX9BGB@B-P7TQMD6M-0146.local>
Date: Wed, 4 Aug 2021 12:30:35 +0800
From: Gao Xiang <hsiangkao@...ux.alibaba.com>
To: Chao Yu <chao@...nel.org>
Cc: linux-erofs@...ts.ozlabs.org, linux-fsdevel@...r.kernel.org,
nvdimm@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>,
"Darrick J. Wong" <djwong@...nel.org>,
Liu Bo <bo.liu@...ux.alibaba.com>,
Joseph Qi <joseph.qi@...ux.alibaba.com>,
Liu Jiang <gerry@...ux.alibaba.com>,
Huang Jianan <huangjianan@...o.com>,
Tao Ma <boyu.mt@...bao.com>
Subject: Re: [PATCH v2 1/3] erofs: iomap support for non-tailpacking DIO
Hi Chao,
On Wed, Aug 04, 2021 at 10:57:08AM +0800, Chao Yu wrote:
> On 2021/7/31 3:46, Gao Xiang wrote:
...
> > }
> > +static int erofs_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
> > + unsigned int flags, struct iomap *iomap, struct iomap *srcmap)
> > +{
> > + int ret;
> > + struct erofs_map_blocks map;
> > +
> > + map.m_la = offset;
> > + map.m_llen = length;
> > +
> > + ret = erofs_map_blocks_flatmode(inode, &map, EROFS_GET_BLOCKS_RAW);
> > + if (ret < 0)
> > + return ret;
> > +
> > + iomap->bdev = inode->i_sb->s_bdev;
> > + iomap->offset = map.m_la;
> > + iomap->length = map.m_llen;
> > + iomap->flags = 0;
> > +
> > + if (!(map.m_flags & EROFS_MAP_MAPPED)) {
> > + iomap->type = IOMAP_HOLE;
> > + iomap->addr = IOMAP_NULL_ADDR;
> > + if (!iomap->length)
> > + iomap->length = length;
>
> This only happens for the case offset exceeds isize?
Thanks for the review.
Yeah, this is a convention (length 0 with !EROFS_MAP_MAPPED) for post-EOF
in erofs_map_blocks_flatmode(), need to follow iomap rule as well.
>
> > + return 0;
> > + }
> > +
> > + /* that shouldn't happen for now */
> > + if (map.m_flags & EROFS_MAP_META) {
> > + DBG_BUGON(1);
> > + return -ENOTBLK;
> > + }
> > + iomap->type = IOMAP_MAPPED;
> > + iomap->addr = map.m_pa;
> > + return 0;
> > +}
> > +
> > +const struct iomap_ops erofs_iomap_ops = {
> > + .iomap_begin = erofs_iomap_begin,
> > +};
> > +
> > +static int erofs_prepare_dio(struct kiocb *iocb, struct iov_iter *to)
> > +{
> > + struct inode *inode = file_inode(iocb->ki_filp);
> > + loff_t align = iocb->ki_pos | iov_iter_count(to) |
> > + iov_iter_alignment(to);
> > + struct block_device *bdev = inode->i_sb->s_bdev;
> > + unsigned int blksize_mask;
> > +
> > + if (bdev)
> > + blksize_mask = (1 << ilog2(bdev_logical_block_size(bdev))) - 1;
> > + else
> > + blksize_mask = (1 << inode->i_blkbits) - 1;
> > +
> > + if (align & blksize_mask)
> > + return -EINVAL;
> > +
> > + /*
> > + * Temporarily fall back tail-packing inline to buffered I/O instead
> > + * since tail-packing inline support relies on an iomap core update.
> > + */
> > + if (EROFS_I(inode)->datalayout == EROFS_INODE_FLAT_INLINE &&
> > + iocb->ki_pos + iov_iter_count(to) >
> > + rounddown(inode->i_size, EROFS_BLKSIZ))
> > + return 1;
> > + return 0;
> > +}
> > +
> > +static ssize_t erofs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> > +{
> > + /* no need taking (shared) inode lock since it's a ro filesystem */
> > + if (!iov_iter_count(to))
> > + return 0;
> > +
> > + if (iocb->ki_flags & IOCB_DIRECT) {
> > + int err = erofs_prepare_dio(iocb, to);
> > +
> > + if (!err)
> > + return iomap_dio_rw(iocb, to, &erofs_iomap_ops,
> > + NULL, 0);
> > + if (err < 0)
> > + return err;
> > + /*
> > + * Fallback to buffered I/O if the operation being performed on
> > + * the inode is not supported by direct I/O. The IOCB_DIRECT
> > + * flag needs to be cleared here in order to ensure that the
> > + * direct I/O path within generic_file_read_iter() is not
> > + * taken.
> > + */
> > + iocb->ki_flags &= ~IOCB_DIRECT;
> > + }
> > + return generic_file_read_iter(iocb, to);
>
> It looks it's fine to call filemap_read() directly since above codes have
> covered DIO case, then we don't need to change iocb->ki_flags flag, it's
> minor though.
Yeah, we could use filemap_read() here instead. yet IMO, it might be
better to drop IOCB_DIRECT too to keep iocb consistent with the real
semantics (even it's not used internally.)
>
> > +}
> > +
> > /* for uncompressed (aligned) files and raw access for other files */
> > const struct address_space_operations erofs_raw_access_aops = {
> > .readpage = erofs_raw_access_readpage,
> > .readahead = erofs_raw_access_readahead,
> > .bmap = erofs_bmap,
> > + .direct_IO = noop_direct_IO,
> > +};
> > +
> > +const struct file_operations erofs_file_fops = {
> > + .llseek = generic_file_llseek,
> > + .read_iter = erofs_file_read_iter,
> > + .mmap = generic_file_readonly_mmap,
> > + .splice_read = generic_file_splice_read,
> > };
> > diff --git a/fs/erofs/inode.c b/fs/erofs/inode.c
> > index aa8a0d770ba3..00edb7562fea 100644
> > --- a/fs/erofs/inode.c
> > +++ b/fs/erofs/inode.c
> > @@ -247,7 +247,10 @@ static int erofs_fill_inode(struct inode *inode, int isdir)
> > switch (inode->i_mode & S_IFMT) {
> > case S_IFREG:
> > inode->i_op = &erofs_generic_iops;
> > - inode->i_fop = &generic_ro_fops;
> > + if (!erofs_inode_is_data_compressed(vi->datalayout))
> > + inode->i_fop = &erofs_file_fops;
> > + else
> > + inode->i_fop = &generic_ro_fops;
>
> if (erofs_inode_is_data_compressed(vi->datalayout))
> inode->i_fop = &generic_ro_fops;
> else
> inode->i_fop = &erofs_file_fops;
>
> Otherwise, it looks good to me.
ok, will fix in the next version.
Thanks,
Gao Xiang
>
> Reviewed-by: Chao Yu <chao@...nel.org>
>
> Thanks
>
> > break;
> > case S_IFDIR:
> > inode->i_op = &erofs_dir_iops;
> > diff --git a/fs/erofs/internal.h b/fs/erofs/internal.h
> > index 543c2ff97d30..2669c785d548 100644
> > --- a/fs/erofs/internal.h
> > +++ b/fs/erofs/internal.h
> > @@ -371,6 +371,7 @@ static inline int z_erofs_map_blocks_iter(struct inode *inode,
> > #endif /* !CONFIG_EROFS_FS_ZIP */
> > /* data.c */
> > +extern const struct file_operations erofs_file_fops;
> > struct page *erofs_get_meta_page(struct super_block *sb, erofs_blk_t blkaddr);
> > /* inode.c */
> >
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