Hi Li,
On Thursday, 09 December, 2010, Li Zefan wrote:
> Usage:
>
> Set BTRFS_SUBVOL_RDONLY of btrfs_ioctl_vol_arg_v2->flags, and call
> ioctl(BTRFS_I0CTL_SNAP_CREATE_V2).
>
> Implementation:
>
> - In disk set readonly bit of btrfs_root_item->flags, and in memory
> set btrfs_root->readonly.
>
> - Add readonly checks in btrfs_permission (inode_permission),
> btrfs_setattr, btrfs_set/remove_xattr and some ioctls.
>
> Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
> ---
> fs/btrfs/ctree.h | 3 +++
> fs/btrfs/disk-io.c | 5 +++++
> fs/btrfs/inode.c | 8 ++++++++
> fs/btrfs/ioctl.c | 40 +++++++++++++++++++++++++++++++---------
> fs/btrfs/ioctl.h | 1 +
> fs/btrfs/transaction.c | 8 ++++++++
> fs/btrfs/transaction.h | 1 +
> fs/btrfs/xattr.c | 18 ++++++++++++++++++
> 8 files changed, 75 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index af52f6d..ad37c78 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -597,6 +597,8 @@ struct btrfs_dir_item {
> u8 type;
> } __attribute__ ((__packed__));
>
> +#define BTRFS_ROOT_SNAP_RDONLY (1ULL << 0)
> +
> struct btrfs_root_item {
> struct btrfs_inode_item inode;
> __le64 generation;
> @@ -1116,6 +1118,7 @@ struct btrfs_root {
> int defrag_running;
> char *name;
> int in_sysfs;
> + bool readonly;
Does make sense to store the same information in two places ?
If we have access to root->readonly, we have also access to "root-
>root_item.flags". Because we need the latter, we can get rid of the former.
We can replace a test like
if(root->readonly)
with
if(root->root_item.flags & BTRFS_ROOT_SNAP_RDONLY)
Or better we can create a two macros like:
#define btrfs_root_readonly(x) ((x)->root_item.flags & BTRFS_ROOT_SNAP_RDONLY)
#define btrfs_root_set_readonly(x, ro) \
do{ (x)->root_item.flags = \
((x)->root_item.flags & ~BTRFS_ROOT_SNAP_RDONLY) | \
(ro ? BTRFS_ROOT_SNAP_RDONLY : 0 ); \
}while(0)
Sorry for to be too late for this kind of suggestion. But I think that this
optimization may help to avoid misalignment between the two variables (see my
reply in the next patch).
[...]
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