[PATCH v3 1/5] btrfs: add compat_flags to btrfs_inode_item

Boris Burkov
2021-04-08T18:34:01Z

The tree checker currently rejects unrecognized flags when it reads
btrfs_inode_item. Practically, this means that adding a new flag makes
the change backwards incompatible if the flag is ever set on a file.

Take up one of the 4 reserved u64 fields in the btrfs_inode_item as a
new "compat_flags". These flags are zero on inode creation in btrfs and
mkfs and are ignored by an older kernel, so it should be safe to use
them in this way.

Signed-off-by: Boris Burkov <boris@bur.io>
---
fs/btrfs/btrfs_inode.h | 1 +
fs/btrfs/ctree.h | 2 ++
fs/btrfs/delayed-inode.c | 2 ++
fs/btrfs/inode.c | 3 +++
fs/btrfs/ioctl.c | 7 ++++---
fs/btrfs/tree-log.c | 1 +
include/uapi/linux/btrfs_tree.h | 7 ++++++-
7 files changed, 19 insertions(+), 4 deletions(-)

diff --git a/fs/btrfs/btrfs_inode.h b/fs/btrfs/btrfs_inode.h
index c652e19ad74e..e8dbc8e848ce 100644
--- a/fs/btrfs/btrfs_inode.h
+++ b/fs/btrfs/btrfs_inode.h
@@ -191,6 +191,7 @@ struct btrfs_inode {

/* flags field from the on disk inode */
u32 flags;
+ u64 compat_flags;

/*
* Counters to keep track of the number of extent item's we may use due
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index f2fd73e58ee6..d633c563164b 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -1754,6 +1754,7 @@ BTRFS_SETGET_FUNCS(inode_gid, struct btrfs_inode_item, gid, 32);
BTRFS_SETGET_FUNCS(inode_mode, struct btrfs_inode_item, mode, 32);
BTRFS_SETGET_FUNCS(inode_rdev, struct btrfs_inode_item, rdev, 64);
BTRFS_SETGET_FUNCS(inode_flags, struct btrfs_inode_item, flags, 64);
+BTRFS_SETGET_FUNCS(inode_compat_flags, struct btrfs_inode_item, compat_flags, 64);
BTRFS_SETGET_STACK_FUNCS(stack_inode_generation, struct btrfs_inode_item,
generation, 64);
BTRFS_SETGET_STACK_FUNCS(stack_inode_sequence, struct btrfs_inode_item,
@@ -1771,6 +1772,7 @@ BTRFS_SETGET_STACK_FUNCS(stack_inode_gid, struct btrfs_inode_item, gid, 32);
BTRFS_SETGET_STACK_FUNCS(stack_inode_mode, struct btrfs_inode_item, mode, 32);
BTRFS_SETGET_STACK_FUNCS(stack_inode_rdev, struct btrfs_inode_item, rdev, 64);
BTRFS_SETGET_STACK_FUNCS(stack_inode_flags, struct btrfs_inode_item, flags, 64);
+BTRFS_SETGET_STACK_FUNCS(stack_inode_compat_flags, struct btrfs_inode_item, compat_flags, 64);
BTRFS_SETGET_FUNCS(timespec_sec, struct btrfs_timespec, sec, 64);
BTRFS_SETGET_FUNCS(timespec_nsec, struct btrfs_timespec, nsec, 32);
BTRFS_SETGET_STACK_FUNCS(stack_timespec_sec, struct btrfs_timespec, sec, 64);
diff --git a/fs/btrfs/delayed-inode.c b/fs/btrfs/delayed-inode.c
index 1a88f6214ebc..ef4e0265dbe3 100644
--- a/fs/btrfs/delayed-inode.c
+++ b/fs/btrfs/delayed-inode.c
@@ -1718,6 +1718,7 @@ static void fill_stack_inode_item(struct btrfs_trans_handle *trans,
btrfs_set_stack_inode_transid(inode_item, trans->transid);
btrfs_set_stack_inode_rdev(inode_item, inode->i_rdev);
btrfs_set_stack_inode_flags(inode_item, BTRFS_I(inode)->flags);
+ btrfs_set_stack_inode_compat_flags(inode_item, BTRFS_I(inode)->compat_flags);
btrfs_set_stack_inode_block_group(inode_item, 0);

btrfs_set_stack_timespec_sec(&inode_item->atime,
@@ -1776,6 +1777,7 @@ int btrfs_fill_inode(struct inode *inode, u32 *rdev)
inode->i_rdev = 0;
*rdev = btrfs_stack_inode_rdev(inode_item);
BTRFS_I(inode)->flags = btrfs_stack_inode_flags(inode_item);
+ BTRFS_I(inode)->compat_flags = btrfs_stack_inode_compat_flags(inode_item);

inode->i_atime.tv_sec = btrfs_stack_timespec_sec(&inode_item->atime);
inode->i_atime.tv_nsec = btrfs_stack_timespec_nsec(&inode_item->atime);
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 1e0e20ad25e4..3aa96ec27045 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -3627,6 +3627,7 @@ static int btrfs_read_locked_inode(struct inode *inode,

BTRFS_I(inode)->index_cnt = (u64)-1;
BTRFS_I(inode)->flags = btrfs_inode_flags(leaf, inode_item);
+ BTRFS_I(inode)->compat_flags = btrfs_inode_compat_flags(leaf, inode_item);

cache_index:
/*
@@ -3793,6 +3794,7 @@ static void fill_inode_item(struct btrfs_trans_handle *trans,
btrfs_set_token_inode_transid(&token, item, trans->transid);
btrfs_set_token_inode_rdev(&token, item, inode->i_rdev);
btrfs_set_token_inode_flags(&token, item, BTRFS_I(inode)->flags);
+ btrfs_set_token_inode_compat_flags(&token, item, BTRFS_I(inode)->compat_flags);
btrfs_set_token_inode_block_group(&token, item, 0);
}

@@ -8859,6 +8861,7 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
ei->defrag_bytes = 0;
ei->disk_i_size = 0;
ei->flags = 0;
+ ei->compat_flags = 0;
ei->csum_bytes = 0;
ei->index_cnt = (u64)-1;
ei->dir_index = 0;
diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3415a9f06c81..2c9cbd2642b1 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -102,8 +102,9 @@ static unsigned int btrfs_mask_fsflags_for_type(struct inode *inode,
* Export internal inode flags to the format expected by the FS_IOC_GETFLAGS
* ioctl.
*/
-static unsigned int btrfs_inode_flags_to_fsflags(unsigned int flags)
+static unsigned int btrfs_inode_flags_to_fsflags(struct btrfs_inode *binode)
{
+ unsigned int flags = binode->flags;
unsigned int iflags = 0;

if (flags & BTRFS_INODE_SYNC)
@@ -156,7 +157,7 @@ void btrfs_sync_inode_flags_to_i_flags(struct inode *inode)
static int btrfs_ioctl_getflags(struct file *file, void __user *arg)
{
struct btrfs_inode *binode = BTRFS_I(file_inode(file));
- unsigned int flags = btrfs_inode_flags_to_fsflags(binode->flags);
+ unsigned int flags = btrfs_inode_flags_to_fsflags(binode);

if (copy_to_user(arg, &flags, sizeof(flags)))
return -EFAULT;
@@ -228,7 +229,7 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)

btrfs_inode_lock(inode, 0);
fsflags = btrfs_mask_fsflags_for_type(inode, fsflags);
- old_fsflags = btrfs_inode_flags_to_fsflags(binode->flags);
+ old_fsflags = btrfs_inode_flags_to_fsflags(binode);

ret = vfs_ioc_setflags_prepare(inode, old_fsflags, fsflags);
if (ret)
diff --git a/fs/btrfs/tree-log.c b/fs/btrfs/tree-log.c
index 72c4b66ed516..fed638f995ba 100644
--- a/fs/btrfs/tree-log.c
+++ b/fs/btrfs/tree-log.c
@@ -3944,6 +3944,7 @@ static void fill_inode_item(struct btrfs_trans_handle *trans,
btrfs_set_token_inode_transid(&token, item, trans->transid);
btrfs_set_token_inode_rdev(&token, item, inode->i_rdev);
btrfs_set_token_inode_flags(&token, item, BTRFS_I(inode)->flags);
+ btrfs_set_token_inode_compat_flags(&token, item, BTRFS_I(inode)->compat_flags);
btrfs_set_token_inode_block_group(&token, item, 0);
}

diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
index 58d7cff9afb1..ae25280316bd 100644
--- a/include/uapi/linux/btrfs_tree.h
+++ b/include/uapi/linux/btrfs_tree.h
@@ -574,11 +574,16 @@ struct btrfs_inode_item {
/* modification sequence number for NFS */
__le64 sequence;

+ /*
+ * flags which aren't checked for corruption at mount
+ * and can be added in a backwards compatible way
+ */
+ __le64 compat_flags;
/*
* a little future expansion, for more than this we can
* just grow the inode item and version it
*/
- __le64 reserved[4];
+ __le64 reserved[3];
struct btrfs_timespec atime;
struct btrfs_timespec ctime;
struct btrfs_timespec mtime;
--
2.30.2