[RFC PATCH v4 34/34] ext4: add mount option for buffered IO iomap path

[Zhang Yi <yi.zhang@xxxxxxxxxxxxxxx>]

From: Zhang Yi <yi.zhang@xxxxxxxxxx>

Add buffered_io_iomap mount option to enable buffered IO iomap path for
regular file, this option is disabled by default now.

Signed-off-by: Zhang Yi <yi.zhang@xxxxxxxxxx>
---
 fs/ext4/ext4.h  |  1 +
 fs/ext4/inode.c |  2 ++
 fs/ext4/super.c | 16 +++++++++++++++-
 3 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 4e7667b21c2f..fef609e6ba7d 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1254,6 +1254,7 @@ struct ext4_inode_info {
 						    * scanning in mballoc
 						    */
 #define EXT4_MOUNT2_ABORT		0x00000100 /* Abort filesystem */
+#define EXT4_MOUNT2_BUFFERED_IOMAP	0x00000200 /* Use iomap for buffered IO */
 
 #define clear_opt(sb, opt)		EXT4_SB(sb)->s_mount_opt &= \
 						~EXT4_MOUNT_##opt
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 269503749ef5..c930108f11dd 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5120,6 +5120,8 @@ bool ext4_should_use_buffered_iomap(struct inode *inode)
 {
 	struct super_block *sb = inode->i_sb;
 
+	if (!test_opt2(sb, BUFFERED_IOMAP))
+		return false;
 	if (ext4_has_feature_inline_data(sb))
 		return false;
 	if (ext4_has_feature_verity(sb))
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 6410918161a0..c8b691e605f1 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1685,7 +1685,7 @@ enum {
 	Opt_dioread_nolock, Opt_dioread_lock,
 	Opt_discard, Opt_nodiscard, Opt_init_itable, Opt_noinit_itable,
 	Opt_max_dir_size_kb, Opt_nojournal_checksum, Opt_nombcache,
-	Opt_no_prefetch_block_bitmaps, Opt_mb_optimize_scan,
+	Opt_no_prefetch_block_bitmaps, Opt_mb_optimize_scan, Opt_buffered_iomap,
 	Opt_errors, Opt_data, Opt_data_err, Opt_jqfmt, Opt_dax_type,
 #ifdef CONFIG_EXT4_DEBUG
 	Opt_fc_debug_max_replay, Opt_fc_debug_force
@@ -1828,6 +1828,7 @@ static const struct fs_parameter_spec ext4_param_specs[] = {
 	fsparam_flag	("no_prefetch_block_bitmaps",
 						Opt_no_prefetch_block_bitmaps),
 	fsparam_s32	("mb_optimize_scan",	Opt_mb_optimize_scan),
+	fsparam_flag	("buffered_iomap",	Opt_buffered_iomap),
 	fsparam_string	("check",		Opt_removed),	/* mount option from ext2/3 */
 	fsparam_flag	("nocheck",		Opt_removed),	/* mount option from ext2/3 */
 	fsparam_flag	("reservation",		Opt_removed),	/* mount option from ext2/3 */
@@ -1922,6 +1923,8 @@ static const struct mount_opts {
 	{Opt_nombcache, EXT4_MOUNT_NO_MBCACHE, MOPT_SET},
 	{Opt_no_prefetch_block_bitmaps, EXT4_MOUNT_NO_PREFETCH_BLOCK_BITMAPS,
 	 MOPT_SET},
+	{Opt_buffered_iomap, EXT4_MOUNT2_BUFFERED_IOMAP,
+	 MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
 #ifdef CONFIG_EXT4_DEBUG
 	{Opt_fc_debug_force, EXT4_MOUNT2_JOURNAL_FAST_COMMIT,
 	 MOPT_SET | MOPT_2 | MOPT_EXT4_ONLY},
@@ -2408,6 +2411,11 @@ static int ext4_parse_param(struct fs_context *fc, struct fs_parameter *param)
 			return -EINVAL;
 		}
 		return 0;
+	case Opt_buffered_iomap:
+		ext4_msg(NULL, KERN_WARNING,
+			 "iomap for buffered enabled. Warning: EXPERIMENTAL, use at your own risk");
+		ctx_set_mount_opt2(ctx, EXT4_MOUNT2_BUFFERED_IOMAP);
+		return 0;
 	}
 
 	/*
@@ -2838,6 +2846,12 @@ static int ext4_check_opt_consistency(struct fs_context *fc,
 			    !(sbi->s_mount_opt2 & EXT4_MOUNT2_DAX_INODE))) {
 			goto fail_dax_change_remount;
 		}
+
+		if (ctx_test_mount_opt2(ctx, EXT4_MOUNT2_BUFFERED_IOMAP) &&
+		    !test_opt2(sb, BUFFERED_IOMAP)) {
+			ext4_msg(NULL, KERN_ERR, "can't enable iomap for buffered IO on remount");
+			return -EINVAL;
+		}
 	}
 
 	return ext4_check_quota_consistency(fc, sb);
-- 
2.39.2