[PATCH 4/5] btrfs: introduce rescue=ignoredatacsums

[Josef Bacik <josef@toxicpanda.com>]

There are cases where you can end up with bad data csums because of
misbehaving applications.  This happens when an application modifies a
buffer in-flight when doing an O_DIRECT write.  In order to recover the
file we need a way to turn off data checksums so you can copy the file
off, and then you can delete the file and restore it properly later.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
---
 fs/btrfs/ctree.h   |  1 +
 fs/btrfs/disk-io.c | 21 ++++++++++++---------
 fs/btrfs/super.c   | 11 ++++++++++-
 3 files changed, 23 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index fb3cfd0aaf1e..397f5f6b88a4 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1296,6 +1296,7 @@ static inline u32 BTRFS_MAX_XATTR_SIZE(const struct btrfs_fs_info *info)
 #define BTRFS_MOUNT_REF_VERIFY		(1 << 28)
 #define BTRFS_MOUNT_DISCARD_ASYNC	(1 << 29)
 #define BTRFS_MOUNT_IGNOREBADROOTS	(1 << 30)
+#define BTRFS_MOUNT_IGNOREDATACSUMS	(1 << 31)
 
 #define BTRFS_DEFAULT_COMMIT_INTERVAL	(30)
 #define BTRFS_DEFAULT_MAX_INLINE	(2048)
diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 5deedfb0e5c7..6f9d37567a10 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2269,16 +2269,19 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
 		btrfs_init_devices_late(fs_info);
 	}
 
-	location.objectid = BTRFS_CSUM_TREE_OBJECTID;
-	root = btrfs_read_tree_root(tree_root, &location);
-	if (IS_ERR(root)) {
-		if (!btrfs_test_opt(fs_info, IGNOREBADROOTS)) {
-			ret = PTR_ERR(root);
-			goto out;
+	/* If IGNOREDATASCUMS is set don't bother reading the csum root. */
+	if (!btrfs_test_opt(fs_info, IGNOREDATACSUMS)) {
+		location.objectid = BTRFS_CSUM_TREE_OBJECTID;
+		root = btrfs_read_tree_root(tree_root, &location);
+		if (IS_ERR(root)) {
+			if (!btrfs_test_opt(fs_info, IGNOREBADROOTS)) {
+				ret = PTR_ERR(root);
+				goto out;
+			}
+		} else {
+			set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
+			fs_info->csum_root = root;
 		}
-	} else {
-		set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
-		fs_info->csum_root = root;
 	}
 
 	/*
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 7cc7a9233f5e..2282f0240c1d 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -361,6 +361,7 @@ enum {
 	Opt_usebackuproot,
 	Opt_nologreplay,
 	Opt_ignorebadroots,
+	Opt_ignoredatacsums,
 
 	/* Deprecated options */
 	Opt_recovery,
@@ -457,6 +458,7 @@ static const match_table_t rescue_tokens = {
 	{Opt_usebackuproot, "usebackuproot"},
 	{Opt_nologreplay, "nologreplay"},
 	{Opt_ignorebadroots, "ignorebadroots"},
+	{Opt_ignoredatacsums, "ignoredatacsums"},
 	{Opt_err, NULL},
 };
 
@@ -504,6 +506,10 @@ static int parse_rescue_options(struct btrfs_fs_info *info, const char *options)
 			btrfs_set_and_info(info, IGNOREBADROOTS,
 					   "ignoring bad roots");
 			break;
+		case Opt_ignoredatacsums:
+			btrfs_set_and_info(info, IGNOREDATACSUMS,
+					   "ignoring data csums");
+			break;
 		case Opt_err:
 			btrfs_info(info, "unrecognized rescue option '%s'", p);
 			ret = -EINVAL;
@@ -990,7 +996,10 @@ int btrfs_parse_options(struct btrfs_fs_info *info, char *options,
 		goto out;
 
 	if (check_ro_option(info, BTRFS_MOUNT_NOLOGREPLAY, "nologreplay") ||
-	    check_ro_option(info, BTRFS_MOUNT_IGNOREBADROOTS, "ignorebadroots"))
+	    check_ro_option(info, BTRFS_MOUNT_IGNOREBADROOTS,
+			    "ignorebadroots") ||
+	    check_ro_option(info, BTRFS_MOUNT_IGNOREDATACSUMS,
+			    "ignoredatacsums"))
 		ret = -EINVAL;
 out:
 	if (btrfs_fs_compat_ro(info, FREE_SPACE_TREE) &&
-- 
2.26.2