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Subject[RFC PATCH 1/2] erofs: iomap support for non-tailpacking DIO
Date
From: Huang Jianan <huangjianan@oppo.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 can be handled later.

Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.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..38e9439c2510 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;
+
+ if (!(map.m_flags & EROFS_MAP_MAPPED)) {
+ iomap->type = IOMAP_HOLE;
+ iomap->addr = IOMAP_NULL_ADDR;
+ if (!iomap->length)
+ iomap->length = length;
+ 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;
+ iomap->flags = 0;
+ 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);
+ unsigned int blksize_mask = (1 << inode->i_blkbits) - 1;
+ loff_t align = iocb->ki_pos | iov_iter_count(to) |
+ iov_iter_alignment(to);
+ struct block_device *bdev = inode->i_sb->s_bdev;
+
+ 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;
+
+ /*
+ * Tail-packing inline data is not supported for iomap for now.
+ * Temporarily fall back this to buffered I/O instead.
+ */
+ 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);
+}
+
/* 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;
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 */
--
2.24.4
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