f2fs: add nowait aio support

This patch adds nowait aio support[1].

Return EAGAIN if any of the following checks fail for direct I/O:
  - i_rwsem is not lockable
  - Blocks are not allocated at the write location

And xfstests generic/471 is passed.

 [1]: 6be96d "Introduce RWF_NOWAIT and FMODE_AIO_NOWAIT"

Signed-off-by: Hyunchul Lee <cheol.lee@lge.com>
Reviewed-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -837,13 +837,6 @@ alloc:
 	return 0;
 }
 
-static inline bool __force_buffered_io(struct inode *inode, int rw)
-{
-	return (f2fs_encrypted_file(inode) ||
-			(rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
-			F2FS_I_SB(inode)->s_ndevs);
-}
-
 int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
@@ -875,7 +868,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 
 	if (direct_io) {
 		map.m_seg_type = rw_hint_to_seg_type(iocb->ki_hint);
-		flag = __force_buffered_io(inode, WRITE) ?
+		flag = f2fs_force_buffered_io(inode, WRITE) ?
 					F2FS_GET_BLOCK_PRE_AIO :
 					F2FS_GET_BLOCK_PRE_DIO;
 		goto map_blocks;
@@ -1119,6 +1112,31 @@ out:
 	return err;
 }
 
+bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+{
+	struct f2fs_map_blocks map;
+	block_t last_lblk;
+	int err;
+
+	if (pos + len > i_size_read(inode))
+		return false;
+
+	map.m_lblk = F2FS_BYTES_TO_BLK(pos);
+	map.m_next_pgofs = NULL;
+	map.m_next_extent = NULL;
+	map.m_seg_type = NO_CHECK_TYPE;
+	last_lblk = F2FS_BLK_ALIGN(pos + len);
+
+	while (map.m_lblk < last_lblk) {
+		map.m_len = last_lblk - map.m_lblk;
+		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_DEFAULT);
+		if (err || map.m_len == 0)
+			return false;
+		map.m_lblk += map.m_len;
+	}
+	return true;
+}
+
 static int __get_data_block(struct inode *inode, sector_t iblock,
 			struct buffer_head *bh, int create, int flag,
 			pgoff_t *next_pgofs, int seg_type)
@@ -2308,7 +2326,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	if (err)
 		return err;
 
-	if (__force_buffered_io(inode, rw))
+	if (f2fs_force_buffered_io(inode, rw))
 		return 0;
 
 	trace_f2fs_direct_IO_enter(inode, offset, count, rw);
@@ -2316,7 +2334,15 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	if (rw == WRITE && whint_mode == WHINT_MODE_OFF)
 		iocb->ki_hint = WRITE_LIFE_NOT_SET;
 
-	down_read(&F2FS_I(inode)->dio_rwsem[rw]);
+	if (!down_read_trylock(&F2FS_I(inode)->dio_rwsem[rw])) {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			iocb->ki_hint = hint;
+			err = -EAGAIN;
+			goto out;
+		}
+		down_read(&F2FS_I(inode)->dio_rwsem[rw]);
+	}
+
 	err = blockdev_direct_IO(iocb, inode, iter, offset, get_data_block_dio);
 	up_read(&F2FS_I(inode)->dio_rwsem[rw]);
 
@@ -2332,6 +2358,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 		}
 	}
 
+out:
 	trace_f2fs_direct_IO_exit(inode, offset, count, rw, err);
 
 	return err;

fs/f2fs/f2fs.h

@@ -2961,6 +2961,7 @@ int f2fs_release_page(struct page *page, gfp_t wait);
 int f2fs_migrate_page(struct address_space *mapping, struct page *newpage,
 			struct page *page, enum migrate_mode mode);
 #endif
+bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len);
 
 /*
  * gc.c
@@ -3345,4 +3346,11 @@ static inline bool f2fs_may_encrypt(struct inode *inode)
 #endif
 }
 
+static inline bool f2fs_force_buffered_io(struct inode *inode, int rw)
+{
+	return (f2fs_encrypted_file(inode) ||
+			(rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
+			F2FS_I_SB(inode)->s_ndevs);
+}
+
 #endif

fs/f2fs/file.c

@@ -482,6 +482,9 @@ static int f2fs_file_open(struct inode *inode, struct file *filp)
 
 	if (err)
 		return err;
+
+	filp->f_mode |= FMODE_NOWAIT;
+
 	return dquot_file_open(inode, filp);
 }
 
@@ -2696,7 +2699,15 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (unlikely(f2fs_cp_error(F2FS_I_SB(inode))))
 		return -EIO;
 
-	inode_lock(inode);
+	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+		return -EINVAL;
+
+	if (!inode_trylock(inode)) {
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			return -EAGAIN;
+		inode_lock(inode);
+	}
+
 	ret = generic_write_checks(iocb, from);
 	if (ret > 0) {
 		int err;
@@ -2704,11 +2715,23 @@ static ssize_t f2fs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		if (iov_iter_fault_in_readable(from, iov_iter_count(from)))
 			set_inode_flag(inode, FI_NO_PREALLOC);
 
-		err = f2fs_preallocate_blocks(iocb, from);
-		if (err) {
-			clear_inode_flag(inode, FI_NO_PREALLOC);
-			inode_unlock(inode);
-			return err;
+		if ((iocb->ki_flags & IOCB_NOWAIT) &&
+			(iocb->ki_flags & IOCB_DIRECT)) {
+				if (!f2fs_overwrite_io(inode, iocb->ki_pos,
+						iov_iter_count(from)) ||
+					f2fs_has_inline_data(inode) ||
+					f2fs_force_buffered_io(inode, WRITE)) {
+						inode_unlock(inode);
+						return -EAGAIN;
+				}
+
+		} else {
+			err = f2fs_preallocate_blocks(iocb, from);
+			if (err) {
+				clear_inode_flag(inode, FI_NO_PREALLOC);
+				inode_unlock(inode);
+				return err;
+			}
 		}
 		blk_start_plug(&plug);
 		ret = __generic_file_write_iter(iocb, from);

include/linux/fs.h

@@ -144,6 +144,9 @@ typedef void (dax_iodone_t)(struct buffer_head *bh_map, int uptodate);
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY		((__force fmode_t)0x4000000)
 
+/* File is capable of returning -EAGAIN if I/O will block */
+#define FMODE_NOWAIT		((__force fmode_t)0x8000000)
+
 /*
  * Flag for rw_copy_check_uvector and compat_rw_copy_check_uvector
  * that indicates that they should check the contents of the iovec are
@@ -334,6 +337,7 @@ enum rw_hint {
 #define IOCB_EVENTFD		(1 << 0)
 #define IOCB_APPEND		(1 << 1)
 #define IOCB_DIRECT		(1 << 2)
+#define IOCB_NOWAIT		(1 << 7)
 
 struct kiocb {
 	struct file		*ki_filp;