[PATCH v2 3/3] btrfs: sysfs, create by_pid readmirror attribute

[Anand Jain <anand.jain@oracle.com>]

Add existing %pid based readmirror policy as an attribute

 /sys/fs/btrfs/UUID/readmirror/by_pid

When read, this returns 0 or 1. 1 indicates currently active policy.
When written with 1, it sets by_pid as the current active policy and
when written 0 it resets to the default readmirror policy, which as
of now is pid as well. For any other value returns EINVAL.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
v2: fs_devs::readmirror is no more atomic_t so update accordingly.

 fs/btrfs/sysfs.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index e604f292b42b..123d1ef72059 100644
--- a/fs/btrfs/sysfs.c
+++ b/fs/btrfs/sysfs.c
@@ -355,7 +355,59 @@ static ssize_t supported_checksums_show(struct kobject *kobj,
 
 #endif
 
+#define readmirror_to_fs_devices(_kobj)	to_fs_devs((_kobj)->parent)
+/*
+ * Set the readmirror type to BTRFS_READMIRROR_BY_PID
+ */
+static ssize_t btrfs_sysfs_readmirror_by_pid_store(struct kobject *kobj,
+						   struct kobj_attribute *a,
+						   const char *buf, size_t count)
+{
+	int ret;
+	unsigned long val;
+	struct btrfs_fs_devices *fs_devices;
+
+	fs_devices = readmirror_to_fs_devices(kobj);
+
+	ret = kstrtoul(skip_spaces(buf), 0, &val);
+	if (ret)
+		return ret;
+
+	switch (val) {
+	case 0:
+		fs_devices->readmirror = BTRFS_READMIRROR_DEFAULT;
+		break;
+	case 1:
+		fs_devices->readmirror = BTRFS_READMIRROR_BY_PID;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	return count;
+}
+
+static ssize_t btrfs_sysfs_readmirror_by_pid_show(struct kobject *kobj,
+						  struct kobj_attribute *a,
+						  char *buf)
+{
+	int val;
+	struct btrfs_fs_devices *fs_devices;
+
+	fs_devices = readmirror_to_fs_devices(kobj);
+
+	if (fs_devices->readmirror == BTRFS_READMIRROR_BY_PID)
+		val = 1;
+	else
+		val = 0;
+
+	return snprintf(buf, PAGE_SIZE, "%d\n", val);
+}
+BTRFS_ATTR_RW(readmirror, by_pid, btrfs_sysfs_readmirror_by_pid_show,
+	      btrfs_sysfs_readmirror_by_pid_store);
+
 static const struct attribute *btrfs_readmirror_attrs[] = {
+	BTRFS_ATTR_PTR(readmirror, by_pid),
 	NULL,
 };
 
-- 
1.8.3.1