btrfs: add ioctls to query/change feature bits online

There are some feature bits that require no offline setup and can
be enabled online. I've only reviewed extended irefs, but there will
probably be more.

We introduce three new ioctls:
- BTRFS_IOC_GET_SUPPORTED_FEATURES: query the kernel for supported features.
- BTRFS_IOC_GET_FEATURES: query the kernel for enabled features on a per-fs
  basis, as well as querying for which features are changeable with mounted.
- BTRFS_IOC_SET_FEATURES: change features on a per-fs basis.

We introduce two new masks per feature set (_SAFE_SET and _SAFE_CLEAR) that
allow us to define which features are safe to change at runtime.

The failure modes for BTRFS_IOC_SET_FEATURES are as follows:
- Enabling a completely unsupported feature: warns and returns -ENOTSUPP
- Enabling a feature that can only be done offline: warns and returns -EPERM

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>

1 files changed, 142 insertions, 0 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 21da5762b0b1..d4e105b54091 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -4480,6 +4480,142 @@ out_unlock:
         return ret;
 }
 
+#define INIT_FEATURE_FLAGS(suffix) \
+        { .compat_flags = BTRFS_FEATURE_COMPAT_##suffix, \
+          .compat_ro_flags = BTRFS_FEATURE_COMPAT_RO_##suffix, \
+          .incompat_flags = BTRFS_FEATURE_INCOMPAT_##suffix }
+
+static int btrfs_ioctl_get_supported_features(struct file *file,
+                                              void __user *arg)
+{
+        static struct btrfs_ioctl_feature_flags features[3] = {
+                INIT_FEATURE_FLAGS(SUPP),
+                INIT_FEATURE_FLAGS(SAFE_SET),
+                INIT_FEATURE_FLAGS(SAFE_CLEAR)
+        };
+
+        if (copy_to_user(arg, &features, sizeof(features)))
+                return -EFAULT;
+
+        return 0;
+}
+
+static int btrfs_ioctl_get_features(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(file_inode(file))->root;
+        struct btrfs_super_block *super_block = root->fs_info->super_copy;
+        struct btrfs_ioctl_feature_flags features;
+
+        features.compat_flags = btrfs_super_compat_flags(super_block);
+        features.compat_ro_flags = btrfs_super_compat_ro_flags(super_block);
+        features.incompat_flags = btrfs_super_incompat_flags(super_block);
+
+        if (copy_to_user(arg, &features, sizeof(features)))
+                return -EFAULT;
+
+        return 0;
+}
+
+static int check_feature_bits(struct btrfs_root *root, const char *type,
+                              u64 change_mask, u64 flags, u64 supported_flags,
+                              u64 safe_set, u64 safe_clear)
+{
+        u64 disallowed, unsupported;
+        u64 set_mask = flags & change_mask;
+        u64 clear_mask = ~flags & change_mask;
+
+        unsupported = set_mask & ~supported_flags;
+        if (unsupported) {
+                btrfs_warn(root->fs_info,
+                           "this kernel does not support %s bits 0x%llx",
+                           type, unsupported);
+                return -EOPNOTSUPP;
+        }
+
+        disallowed = set_mask & ~safe_set;
+        if (disallowed) {
+                btrfs_warn(root->fs_info,
+                           "can't set %s bits 0x%llx while mounted",
+                           type, disallowed);
+                return -EPERM;
+        }
+
+        disallowed = clear_mask & ~safe_clear;
+        if (disallowed) {
+                btrfs_warn(root->fs_info,
+                           "can't clear %s bits 0x%llx while mounted",
+                           type, disallowed);
+                return -EPERM;
+        }
+
+        return 0;
+}
+
+#define check_feature(root, change_mask, flags, mask_base)      \
+check_feature_bits(root, # mask_base, change_mask, flags,       \
+                   BTRFS_FEATURE_ ## mask_base ## _SUPP,        \
+                   BTRFS_FEATURE_ ## mask_base ## _SAFE_SET,    \
+                   BTRFS_FEATURE_ ## mask_base ## _SAFE_CLEAR)
+
+static int btrfs_ioctl_set_features(struct file *file, void __user *arg)
+{
+        struct btrfs_root *root = BTRFS_I(file_inode(file))->root;
+        struct btrfs_super_block *super_block = root->fs_info->super_copy;
+        struct btrfs_ioctl_feature_flags flags[2];
+        struct btrfs_trans_handle *trans;
+        u64 newflags;
+        int ret;
+
+        if (!capable(CAP_SYS_ADMIN))
+                return -EPERM;
+
+        if (copy_from_user(flags, arg, sizeof(flags)))
+                return -EFAULT;
+
+        /* Nothing to do */
+        if (!flags[0].compat_flags && !flags[0].compat_ro_flags &&
+            !flags[0].incompat_flags)
+                return 0;
+
+        ret = check_feature(root, flags[0].compat_flags,
+                            flags[1].compat_flags, COMPAT);
+        if (ret)
+                return ret;
+
+        ret = check_feature(root, flags[0].compat_ro_flags,
+                            flags[1].compat_ro_flags, COMPAT_RO);
+        if (ret)
+                return ret;
+
+        ret = check_feature(root, flags[0].incompat_flags,
+                            flags[1].incompat_flags, INCOMPAT);
+        if (ret)
+                return ret;
+
+        trans = btrfs_start_transaction(root, 1);
+        if (IS_ERR(trans))
+                return PTR_ERR(trans);
+
+        spin_lock(&root->fs_info->super_lock);
+        newflags = btrfs_super_compat_flags(super_block);
+        newflags |= flags[0].compat_flags & flags[1].compat_flags;
+        newflags &= ~(flags[0].compat_flags & ~flags[1].compat_flags);
+        btrfs_set_super_compat_flags(super_block, newflags);
+
+        newflags = btrfs_super_compat_ro_flags(super_block);
+        newflags |= flags[0].compat_ro_flags & flags[1].compat_ro_flags;
+        newflags &= ~(flags[0].compat_ro_flags & ~flags[1].compat_ro_flags);
+        btrfs_set_super_compat_ro_flags(super_block, newflags);
+
+        newflags = btrfs_super_incompat_flags(super_block);
+        newflags |= flags[0].incompat_flags & flags[1].incompat_flags;
+        newflags &= ~(flags[0].incompat_flags & ~flags[1].incompat_flags);
+        btrfs_set_super_incompat_flags(super_block, newflags);
+        spin_unlock(&root->fs_info->super_lock);
+
+        return btrfs_end_transaction(trans, root);
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
                 cmd, unsigned long arg)
 {
@@ -4598,6 +4734,12 @@ long btrfs_ioctl(struct file *file, unsigned int
                 return btrfs_ioctl_set_fslabel(file, argp);
         case BTRFS_IOC_FILE_EXTENT_SAME:
                 return btrfs_ioctl_file_extent_same(file, argp);
+        case BTRFS_IOC_GET_SUPPORTED_FEATURES:
+                return btrfs_ioctl_get_supported_features(file, argp);
+        case BTRFS_IOC_GET_FEATURES:
+                return btrfs_ioctl_get_features(file, argp);
+        case BTRFS_IOC_SET_FEATURES:
+                return btrfs_ioctl_set_features(file, argp);
         }
 
         return -ENOTTY;