ext4: introduce a mount option for iomap buffered I/O path Since the iomap buffered I/O path does not yet support all existing ext4 features, it cannot be enabled by default. Introduce the 'buffered_iomap' and 'nobuffered_iomap' mount options to explicitly enable or disable the iomap buffered I/O path for regular files. Toggling this option via remount is allowed. The change of I/O path will not take effect immediately. It will be deferred. The new setting will only take effect after the inode is re-initialized (i.e., after the last reference is dropped and the inode is re-read from disk). Signed-off-by: Zhang Yi <yi.zhang@huawei.com> Tested-by: syzbot@syzkaller.appspotmail.com Link: https://patch.msgid.link/20261009103831.2978767-3-yi.zhang@huaweicloud.com Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h index 64eaf6c..8d3af06 100644 --- a/fs/ext4/ext4.h +++ b/fs/ext4/ext4.h
@@ -1321,6 +1321,7 @@ struct ext4_inode_info { * scanning in mballoc */ #define EXT4_MOUNT2_ABORT 0x00000100 /* Abort filesystem */ +#define EXT4_MOUNT2_BUFFERED_IOMAP 0x00000200 /* Use iomap for buffered I/O */ #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 12106bc..6ede364 100644 --- a/fs/ext4/inode.c +++ b/fs/ext4/inode.c
@@ -6125,11 +6125,17 @@ static int check_igot_inode(struct inode *inode, ext4_iget_flags flags, * For extent-to-indirect block migration (via EXT4_IOC_SETFLAGS * clearing EXT4_EXTENTS_FL), this operation is directly rejected for * inodes using the iomap path. + * + * When remounting to toggle the buffered_iomap mount option, the change + * of I/O path is deferred as well, it will be available after the inode + * is re-initialized. */ void ext4_enable_buffered_iomap(struct inode *inode) { struct super_block *sb = inode->i_sb; + if (!test_opt2(sb, BUFFERED_IOMAP)) + return; if (!S_ISREG(inode->i_mode)) return; if (ext4_test_inode_flag(inode, EXT4_INODE_EA_INODE))
diff --git a/fs/ext4/super.c b/fs/ext4/super.c index 56bde3e..7d8aedf 100644 --- a/fs/ext4/super.c +++ b/fs/ext4/super.c
@@ -1747,6 +1747,7 @@ enum { 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_buffered_iomap, Opt_nobuffered_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 @@ -1885,6 +1886,8 @@ 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_flag ("nobuffered_iomap", Opt_nobuffered_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 */ @@ -1978,6 +1981,10 @@ 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}, + {Opt_nobuffered_iomap, EXT4_MOUNT2_BUFFERED_IOMAP, + MOPT_CLEAR | 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},