[PATCH] ext4: add barrier info if journal device write cache is not enabled

[Zhang Yi <yi.zhang@huawei.com>]

The block layer will check and suppress flush bio if the device write
cache is not enabled, so the journal barrier will not go into effect
even if uer specify 'barrier=1' mount option. It's dangerous if the
write cache state is false negative, and we cannot distinguish such
case easily. So just give an info and an inquire interface to let
sysadmin know the barrier is suppressed for the case of write cache is
not enabled.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
---
 fs/ext4/super.c |  3 +++
 fs/ext4/sysfs.c | 19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 7cdd2138c897..916f756ebbca 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5920,6 +5920,9 @@ static int ext4_load_journal(struct super_block *sb,
 
 	if (!(journal->j_flags & JBD2_BARRIER))
 		ext4_msg(sb, KERN_INFO, "barriers disabled");
+	else if (!bdev_write_cache(journal->j_dev))
+		ext4_msg(sb, KERN_INFO, "journal device write cache disabled, "
+					"barriers suppressed");
 
 	if (!ext4_has_feature_journal_needs_recovery(sb))
 		err = jbd2_journal_wipe(journal, !really_read_only);
diff --git a/fs/ext4/sysfs.c b/fs/ext4/sysfs.c
index d233c24ea342..67f619c1202e 100644
--- a/fs/ext4/sysfs.c
+++ b/fs/ext4/sysfs.c
@@ -37,6 +37,7 @@ typedef enum {
 	attr_pointer_string,
 	attr_pointer_atomic,
 	attr_journal_task,
+	attr_journal_barrier,
 } attr_id_t;
 
 typedef enum {
@@ -135,6 +136,20 @@ static ssize_t journal_task_show(struct ext4_sb_info *sbi, char *buf)
 			task_pid_vnr(sbi->s_journal->j_task));
 }
 
+static ssize_t journal_barrier_show(struct ext4_sb_info *sbi, char *buf)
+{
+	journal_t *journal = sbi->s_journal;
+
+	if (!journal)
+		return sysfs_emit(buf, "none\n");
+
+	if (!(journal->j_flags & JBD2_BARRIER))
+		return sysfs_emit(buf, "disabled\n");
+	if (!bdev_write_cache(sbi->s_journal->j_dev))
+		return sysfs_emit(buf, "suppressed\n");
+	return sysfs_emit(buf, "enabled\n");
+}
+
 #define EXT4_ATTR(_name,_mode,_id)					\
 static struct ext4_attr ext4_attr_##_name = {				\
 	.attr = {.name = __stringify(_name), .mode = _mode },		\
@@ -243,6 +258,7 @@ EXT4_RO_ATTR_ES_STRING(last_error_func, s_last_error_func, 32);
 EXT4_ATTR(first_error_time, 0444, first_error_time);
 EXT4_ATTR(last_error_time, 0444, last_error_time);
 EXT4_ATTR(journal_task, 0444, journal_task);
+EXT4_ATTR(journal_barrier, 0444, journal_barrier);
 EXT4_RW_ATTR_SBI_UI(mb_prefetch, s_mb_prefetch);
 EXT4_RW_ATTR_SBI_UI(mb_prefetch_limit, s_mb_prefetch_limit);
 EXT4_RW_ATTR_SBI_UL(last_trim_minblks, s_last_trim_minblks);
@@ -291,6 +307,7 @@ static struct attribute *ext4_attrs[] = {
 	ATTR_LIST(first_error_time),
 	ATTR_LIST(last_error_time),
 	ATTR_LIST(journal_task),
+	ATTR_LIST(journal_barrier),
 #ifdef CONFIG_EXT4_DEBUG
 	ATTR_LIST(simulate_fail),
 #endif
@@ -438,6 +455,8 @@ static ssize_t ext4_attr_show(struct kobject *kobj,
 		return print_tstamp(buf, sbi->s_es, s_last_error_time);
 	case attr_journal_task:
 		return journal_task_show(sbi, buf);
+	case attr_journal_barrier:
+		return journal_barrier_show(sbi, buf);
 	}
 
 	return 0;
-- 
2.31.1