[PATCH RFC 4/5] btrfs: add readmirror pid mount option

[Anand Jain <anand.jain@xxxxxxxxxx>]

This patch adds mount option -o readmirror, which provides a transient
readmirror feature, which can be used in a readonly mount as well.

For example..
  mount -o readmirror=pid

Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
---
 fs/btrfs/super.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index e01fc68af6c1..9d25a01bcecb 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -343,6 +343,7 @@ enum {
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	Opt_ref_verify,
 #endif
+	Opt_readmirror_policy,
 	Opt_err,
 };
 
@@ -413,6 +414,7 @@ enum {
 #ifdef CONFIG_BTRFS_FS_REF_VERIFY
 	{Opt_ref_verify, "ref_verify"},
 #endif
+	{Opt_readmirror_policy, "readmirror=%s"},
 	{Opt_err, NULL},
 };
 
@@ -850,6 +852,14 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 			btrfs_set_opt(info->mount_opt, REF_VERIFY);
 			break;
 #endif
+		case Opt_readmirror_policy:
+			if (strcmp(args[0].from, "pid") == 0) {
+				info->fs_devices->readmirror_policy =
+							BTRFS_READMIRROR_PID;
+				break;
+			}
+			ret = -EINVAL;
+			goto out;
 		case Opt_err:
 			btrfs_info(info, "unrecognized mount option '%s'", p);
 			ret = -EINVAL;
-- 
1.8.3.1