On 06/16/2017 12:49 AM, David Sterba wrote:
Add per-filesystem tunable to switch on/off the device barriers,
regardless of the actual device support. This is a debugging feature.
The path to the sysfs file is /sys/fs/btrfs/UUID/force_dev_flush,
allowed values are 0 and 1. Default is 0.
Anyway the flush command won't touch the device if its write through.
So unless I am missing something, IMO we don't need something
like this.
-------------------
generic_make_request_checks(struct bio *bio)
::
/*
* Filter flush bio's early so that make_request based
* drivers without flush support don't have to worry
* about them.
*/
if (op_is_flush(bio->bi_opf) &&
!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
if (!nr_sectors) {
err = 0;
goto end_io;
}
}
-------------------
Thanks, Anand
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
---
fs/btrfs/sysfs.c | 47 +++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 47 insertions(+)
diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index c2d5f3580b4c..197d43911936 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -487,12 +487,59 @@ static ssize_t quota_override_store(struct kobject *kobj,
BTRFS_ATTR_RW(quota_override, quota_override_show, quota_override_store);
+static ssize_t force_dev_flush_show(struct kobject *kobj,
+ struct kobj_attribute *a, char *buf)
+{
+ struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+ int force;
+
+ if (!fs_info)
+ return -EPERM;
+
+ force = !!(test_bit(BTRFS_FS_FORCE_DEV_FLUSH, &fs_info->flags));
+ return snprintf(buf, PAGE_SIZE, "%d\n", force);
+}
+
+static ssize_t force_dev_flush_store(struct kobject *kobj,
+ struct kobj_attribute *a,
+ const char *buf, size_t len)
+{
+ struct btrfs_fs_info *fs_info = to_fs_info(kobj);
+ unsigned long force;
+ int err;
+
+ if (!fs_info)
+ return -EPERM;
+
+ if (!capable(CAP_SYS_ADMIN))
+ return -EPERM;
+
+ err = kstrtoul(buf, 10, &force);
+ if (err)
+ return err;
+ if (force > 1)
+ return -EINVAL;
+
+ if (force) {
+ set_bit(BTRFS_FS_FORCE_DEV_FLUSH, &fs_info->flags);
+ btrfs_info(fs_info, "Forced device flushes enabled");
+ } else {
+ clear_bit(BTRFS_FS_FORCE_DEV_FLUSH, &fs_info->flags);
+ btrfs_info(fs_info, "Forced device flushes disabled");
+ }
+
+ return len;
+}
+
+BTRFS_ATTR_RW(force_dev_flush, force_dev_flush_show, force_dev_flush_store);
+
static const struct attribute *btrfs_attrs[] = {
BTRFS_ATTR_PTR(label),
BTRFS_ATTR_PTR(nodesize),
BTRFS_ATTR_PTR(sectorsize),
BTRFS_ATTR_PTR(clone_alignment),
BTRFS_ATTR_PTR(quota_override),
+ BTRFS_ATTR_PTR(force_dev_flush),
NULL,
};
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