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

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

Add the exisiting %pid based readmirror policy as an attribute

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

When read, this returns 0 or 1. 1 indicates the currently active policy.
When written with 1, it sets 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 it returns EINVAL.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/sysfs.c | 54 +++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 53 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/sysfs.c b/fs/btrfs/sysfs.c
index da5e1938e9b9..5a09cf868328 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:
+		atomic_set(&fs_devices->readmirror, BTRFS_READMIRROR_DEFAULT);
+		break;
+	case 1:
+		atomic_set(&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 (atomic_read(&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,
 };
 
@@ -1241,7 +1293,7 @@ int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info)
 		error = -ENOMEM;
 		goto failure;
 	}
-	error = sysfs_create_files(fs_info->readmirror_kobj,
+	error = sysfs_create_files(fs_devs->readmirror_kobj,
 				   btrfs_readmirror_attrs);
 	if (error)
 		goto failure;
-- 
1.8.3.1