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Date: Wed, 4 Aug 2021 10:57:08 +0800
From: Chao Yu <chao@...nel.org>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>,
linux-erofs@...ts.ozlabs.org
Cc: 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
On 2021/7/31 3:46, Gao Xiang wrote:
> From: Huang Jianan <huangjianan@...o.com>
>
> Add iomap support for non-tailpacking uncompressed data in order to
> support DIO and DAX.
>
> Direct I/O is useful in certain scenarios for uncompressed files.
> For example, double pagecache can be avoid by direct I/O when
> loop device is used for uncompressed files containing upper layer
> compressed filesystem.
>
> This adds iomap DIO support for non-tailpacking cases first and
> tail-packing inline files are handled in the follow-up patch.
>
> Cc: linux-fsdevel@...r.kernel.org
> Signed-off-by: Huang Jianan <huangjianan@...o.com>
> Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> ---
> fs/erofs/Kconfig | 1 +
> fs/erofs/data.c | 102 ++++++++++++++++++++++++++++++++++++++++++++
> fs/erofs/inode.c | 5 ++-
> fs/erofs/internal.h | 1 +
> 4 files changed, 108 insertions(+), 1 deletion(-)
>
> diff --git a/fs/erofs/Kconfig b/fs/erofs/Kconfig
> index 906af0c1998c..14b747026742 100644
> --- a/fs/erofs/Kconfig
> +++ b/fs/erofs/Kconfig
> @@ -3,6 +3,7 @@
> config EROFS_FS
> tristate "EROFS filesystem support"
> depends on BLOCK
> + select FS_IOMAP
> select LIBCRC32C
> help
> EROFS (Enhanced Read-Only File System) is a lightweight
> diff --git a/fs/erofs/data.c b/fs/erofs/data.c
> index 3787a5fb0a42..1f97151a9f90 100644
> --- a/fs/erofs/data.c
> +++ b/fs/erofs/data.c
> @@ -5,6 +5,7 @@
> */
> #include "internal.h"
> #include <linux/prefetch.h>
> +#include <linux/iomap.h>
>
> #include <trace/events/erofs.h>
>
> @@ -308,9 +309,110 @@ static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
> return 0;
> }
>
> +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?
> + 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.
> +}
> +
> /* 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.
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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