On Mon, Sep 08, 2025 at 11:15:50PM -0400, Theodore Ts'o via B4 Relay wrote:
> From: Theodore Ts'o <tytso@xxxxxxx>
>
> Implement the EXT4_IOC_GET_TUNE_SB_PARAM and
> EXT4_IOC_SET_TUNE_SB_PARAM ioctls, which allow certains superblock
> parameters to be set while the file system is mounted, without needing
> write access to the block device.
>
> Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
> ---
> fs/ext4/ioctl.c | 256 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++---
> include/uapi/linux/ext4.h | 75 ++++++++++++++++++++++
> 2 files changed, 324 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ext4/ioctl.c b/fs/ext4/ioctl.c
> index 84e3c73952d72e436429489f5fc8b7ae1c01c7a1..569c98c962af63130c0119f60788a26a2807bd86 100644
> --- a/fs/ext4/ioctl.c
> +++ b/fs/ext4/ioctl.c
> @@ -27,14 +27,16 @@
> #include "fsmap.h"
> #include <trace/events/ext4.h>
>
> -typedef void ext4_update_sb_callback(struct ext4_super_block *es,
> - const void *arg);
> +typedef void ext4_update_sb_callback(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es,
> + const void *arg);
>
> /*
> * Superblock modification callback function for changing file system
> * label
> */
> -static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setlabel(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> /* Sanity check, this should never happen */
> BUILD_BUG_ON(sizeof(es->s_volume_name) < EXT4_LABEL_MAX);
> @@ -46,7 +48,8 @@ static void ext4_sb_setlabel(struct ext4_super_block *es, const void *arg)
> * Superblock modification callback function for changing file system
> * UUID.
> */
> -static void ext4_sb_setuuid(struct ext4_super_block *es, const void *arg)
> +static void ext4_sb_setuuid(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> memcpy(es->s_uuid, (__u8 *)arg, UUID_SIZE);
> }
> @@ -71,7 +74,7 @@ int ext4_update_primary_sb(struct super_block *sb, handle_t *handle,
> goto out_err;
>
> lock_buffer(bh);
> - func(es, arg);
> + func(sbi, es, arg);
> ext4_superblock_csum_set(sb);
> unlock_buffer(bh);
>
> @@ -149,7 +152,7 @@ static int ext4_update_backup_sb(struct super_block *sb,
> unlock_buffer(bh);
> goto out_bh;
> }
> - func(es, arg);
> + func(EXT4_SB(sb), es, arg);
> if (ext4_has_feature_metadata_csum(sb))
> es->s_checksum = ext4_superblock_csum(es);
> set_buffer_uptodate(bh);
> @@ -1230,6 +1233,239 @@ static int ext4_ioctl_setuuid(struct file *filp,
> return ret;
> }
>
> +
> +#define TUNE_OPS_SUPPORTED (EXT4_TUNE_FL_ERRORS_BEHAVIOR | \
> + EXT4_TUNE_FL_MNT_COUNT | EXT4_TUNE_FL_MAX_MNT_COUNT | \
> + EXT4_TUNE_FL_CHECKINTRVAL | EXT4_TUNE_FL_LAST_CHECK_TIME | \
> + EXT4_TUNE_FL_RESERVED_BLOCKS | EXT4_TUNE_FL_RESERVED_UID | \
> + EXT4_TUNE_FL_RESERVED_GID | EXT4_TUNE_FL_DEFAULT_MNT_OPTS | \
> + EXT4_TUNE_FL_DEF_HASH_ALG | EXT4_TUNE_FL_RAID_STRIDE | \
> + EXT4_TUNE_FL_RAID_STRIPE_WIDTH | EXT4_TUNE_FL_MOUNT_OPTS | \
> + EXT4_TUNE_FL_FEATURES | EXT4_TUNE_FL_EDIT_FEATURES | \
> + EXT4_TUNE_FL_FORCE_FSCK)
> +
> +static int ext4_ioctl_get_tune_sb(struct ext4_sb_info *sbi,
> + struct ext4_tune_sb_params __user *params)
> +{
> + struct ext4_tune_sb_params ret;
> + struct ext4_super_block *es = sbi->s_es;
> +
> + memset(&ret, 0, sizeof(ret));
> + ret.set_flags = TUNE_OPS_SUPPORTED;
> + ret.errors_behavior = es->s_errors;
> + ret.mnt_count = le16_to_cpu(es->s_mnt_count);
> + ret.max_mnt_count = le16_to_cpu(es->s_max_mnt_count);
> + ret.checkinterval = le32_to_cpu(es->s_checkinterval);
> + ret.last_check_time = le32_to_cpu(es->s_lastcheck);
> + ret.reserved_blocks = ext4_r_blocks_count(es);
> + ret.blocks_count = ext4_blocks_count(es);
> + ret.reserved_uid = ext4_get_resuid(es);
> + ret.reserved_gid = ext4_get_resgid(es);
> + ret.default_mnt_opts = le32_to_cpu(es->s_default_mount_opts);
> + ret.def_hash_alg = es->s_def_hash_version;
> + ret.raid_stride = le16_to_cpu(es->s_raid_stride);
> + ret.raid_stripe_width = le16_to_cpu(es->s_raid_stripe_width);
> + strscpy_pad(ret.mount_opts, es->s_mount_opts);
> + ret.feature_compat = le32_to_cpu(es->s_feature_compat);
> + ret.feature_incompat = le32_to_cpu(es->s_feature_incompat);
> + ret.feature_ro_compat = le32_to_cpu(es->s_feature_ro_compat);
> + ret.set_feature_compat_mask = EXT4_TUNE_SET_COMPAT_SUPP;
> + ret.set_feature_incompat_mask = EXT4_TUNE_SET_INCOMPAT_SUPP;
> + ret.set_feature_ro_compat_mask = EXT4_TUNE_SET_RO_COMPAT_SUPP;
> + ret.clear_feature_compat_mask = EXT4_TUNE_CLEAR_COMPAT_SUPP;
> + ret.clear_feature_incompat_mask = EXT4_TUNE_CLEAR_INCOMPAT_SUPP;
> + ret.clear_feature_ro_compat_mask = EXT4_TUNE_CLEAR_RO_COMPAT_SUPP;
> + if (copy_to_user(params, &ret, sizeof(ret)))
> + return -EFAULT;
> + return 0;
> +}
> +
> +static void ext4_sb_setparams(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> +{
> + const struct ext4_tune_sb_params *params = arg;
> +
> + if (params->set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR)
> + es->s_errors = cpu_to_le16(params->errors_behavior);
> + if (params->set_flags & EXT4_TUNE_FL_MNT_COUNT)
> + es->s_mnt_count = cpu_to_le16(params->mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_MAX_MNT_COUNT)
> + es->s_max_mnt_count = cpu_to_le16(params->max_mnt_count);
> + if (params->set_flags & EXT4_TUNE_FL_CHECKINTRVAL)
> + es->s_checkinterval = cpu_to_le32(params->checkinterval);
> + if (params->set_flags & EXT4_TUNE_FL_LAST_CHECK_TIME)
> + es->s_lastcheck = cpu_to_le32(params->last_check_time);
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) {
> + ext4_fsblk_t blk = params->reserved_blocks;
> +
> + es->s_r_blocks_count_lo = cpu_to_le32((u32)blk);
> + es->s_r_blocks_count_hi = cpu_to_le32(blk >> 32);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_UID) {
> + int uid = params->reserved_uid;
> +
> + es->s_def_resuid = cpu_to_le16(uid & 0xFFFF);
> + es->s_def_resuid_hi = cpu_to_le16(uid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_RESERVED_GID) {
> + int gid = params->reserved_gid;
> +
> + es->s_def_resgid = cpu_to_le16(gid & 0xFFFF);
> + es->s_def_resgid_hi = cpu_to_le16(gid >> 16);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_DEFAULT_MNT_OPTS)
> + es->s_default_mount_opts = cpu_to_le32(params->default_mnt_opts);
> + if (params->set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + es->s_def_hash_version = params->def_hash_alg;
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIDE)
> + es->s_raid_stride = cpu_to_le16(params->raid_stride);
> + if (params->set_flags & EXT4_TUNE_FL_RAID_STRIPE_WIDTH)
> + es->s_raid_stripe_width =
> + cpu_to_le16(params->raid_stripe_width);
> + strscpy_pad(es->s_mount_opts, params->mount_opts);
> + if (params->set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + es->s_feature_compat |=
> + cpu_to_le32(params->set_feature_compat_mask);
> + es->s_feature_incompat |=
> + cpu_to_le32(params->set_feature_incompat_mask);
> + es->s_feature_ro_compat |=
> + cpu_to_le32(params->set_feature_ro_compat_mask);
> + es->s_feature_compat &=
> + ~cpu_to_le32(params->clear_feature_compat_mask);
> + es->s_feature_incompat &=
> + ~cpu_to_le32(params->clear_feature_incompat_mask);
> + es->s_feature_ro_compat &=
> + ~cpu_to_le32(params->clear_feature_ro_compat_mask);
> + if (params->set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX)
> + es->s_def_hash_version = sbi->s_def_hash_version;
> + if (params->set_feature_incompat_mask &
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED)
> + es->s_checksum_seed = cpu_to_le32(sbi->s_csum_seed);
> + }
> + if (params->set_flags & EXT4_TUNE_FL_FORCE_FSCK)
> + es->s_state |= cpu_to_le16(EXT4_ERROR_FS);
> +}
> +
> +static int ext4_ioctl_set_tune_sb(struct file *filp,
> + struct ext4_tune_sb_params __user *in)
> +{
> + struct ext4_tune_sb_params params;
> + struct super_block *sb = file_inode(filp)->i_sb;
> + struct ext4_sb_info *sbi = EXT4_SB(sb);
> + struct ext4_super_block *es = sbi->s_es;
> + int ret;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (copy_from_user(¶ms, in, sizeof(params)))
> + return -EFAULT;
> +
> + if ((params.set_flags & ~TUNE_OPS_SUPPORTED) != 0)
> + return -EOPNOTSUPP;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_ERRORS_BEHAVIOR) &&
> + (params.errors_behavior > EXT4_ERRORS_PANIC))
> + return -EINVAL;
> +
> + if ((params.set_flags & EXT4_TUNE_FL_RESERVED_BLOCKS) &&
> + (params.reserved_blocks > ext4_blocks_count(sbi->s_es) / 2))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG) &&
> + ((params.def_hash_alg > DX_HASH_LAST) ||
> + (params.def_hash_alg == DX_HASH_SIPHASH)))
> + return -EINVAL;
> + if ((params.set_flags & EXT4_TUNE_FL_FEATURES) &&
> + (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES))
> + return -EINVAL;
What's the difference between _FL_FEATURES and _FL_EDIT_FEATURES?
> +
> + if (params.set_flags & EXT4_TUNE_FL_FEATURES) {
> + params.set_feature_compat_mask =
> + params.feature_compat &
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask =
> + params.feature_incompat &
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask =
> + params.feature_ro_compat &
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + params.clear_feature_compat_mask =
> + ~params.feature_compat &
> + le32_to_cpu(es->s_feature_compat);
> + params.clear_feature_incompat_mask =
> + ~params.feature_incompat &
> + le32_to_cpu(es->s_feature_incompat);
> + params.clear_feature_ro_compat_mask =
> + ~params.feature_ro_compat &
> + le32_to_cpu(es->s_feature_ro_compat);
> + params.set_flags |= EXT4_TUNE_FL_EDIT_FEATURES;
> + }
> + if (params.set_flags & EXT4_TUNE_FL_EDIT_FEATURES) {
> + if ((params.set_feature_compat_mask &
> + ~EXT4_TUNE_SET_COMPAT_SUPP) ||
> + (params.set_feature_incompat_mask &
> + ~EXT4_TUNE_SET_INCOMPAT_SUPP) ||
> + (params.set_feature_ro_compat_mask &
> + ~EXT4_TUNE_SET_RO_COMPAT_SUPP) ||
> + (params.clear_feature_compat_mask &
> + ~EXT4_TUNE_CLEAR_COMPAT_SUPP) ||
> + (params.clear_feature_incompat_mask &
> + ~EXT4_TUNE_CLEAR_INCOMPAT_SUPP) ||
> + (params.clear_feature_ro_compat_mask &
> + ~EXT4_TUNE_CLEAR_RO_COMPAT_SUPP))
> + return -EOPNOTSUPP;
> +
> + /*
> + * Filter out the features that are already set from
> + * the set_mask.
> + */
> + params.set_feature_compat_mask &=
> + ~le32_to_cpu(es->s_feature_compat);
> + params.set_feature_incompat_mask &=
> + ~le32_to_cpu(es->s_feature_incompat);
> + params.set_feature_ro_compat_mask &=
> + ~le32_to_cpu(es->s_feature_ro_compat);
> + if ((params.set_feature_compat_mask &
> + EXT4_FEATURE_COMPAT_DIR_INDEX) &&
> + !ext4_has_feature_dir_index(sb)) {
> + uuid_t uu;
> +
> + memcpy(&uu, sbi->s_hash_seed, UUID_SIZE);
> + if (uuid_is_null(&uu))
> + generate_random_uuid((char *)
> + &sbi->s_hash_seed);
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> + else if (sbi->s_def_hash_version == 0)
> + sbi->s_def_hash_version = DX_HASH_HALF_MD4;
> + if (!(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_UNSIGNED_HASH)) &&
> + !(es->s_flags &
> + cpu_to_le32(EXT2_FLAGS_SIGNED_HASH))) {
> +#ifdef __CHAR_UNSIGNED__
> + sbi->s_hash_unsigned = 3;
> +#else
> + sbi->s_hash_unsigned = 0;
> +#endif
> + }
> + }
> + }
> +
> +
> + ret = mnt_want_write_file(filp);
> + if (ret)
> + return ret;
> +
> + ret = ext4_update_superblocks_fn(sb, ext4_sb_setparams, ¶ms);
> + mnt_drop_write_file(filp);
> +
> + if (params.set_flags & EXT4_TUNE_FL_DEF_HASH_ALG)
> + sbi->s_def_hash_version = params.def_hash_alg;
> +
> + return ret;
> +}
> +
> static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> {
> struct inode *inode = file_inode(filp);
> @@ -1616,6 +1852,11 @@ static long __ext4_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
> return ext4_ioctl_getuuid(EXT4_SB(sb), (void __user *)arg);
> case EXT4_IOC_SETFSUUID:
> return ext4_ioctl_setuuid(filp, (const void __user *)arg);
> + case EXT4_IOC_GET_TUNE_SB_PARAM:
> + return ext4_ioctl_get_tune_sb(EXT4_SB(sb),
> + (void __user *)arg);
> + case EXT4_IOC_SET_TUNE_SB_PARAM:
> + return ext4_ioctl_set_tune_sb(filp, (void __user *)arg);
> default:
> return -ENOTTY;
> }
> @@ -1703,7 +1944,8 @@ long ext4_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> }
> #endif
>
> -static void set_overhead(struct ext4_super_block *es, const void *arg)
> +static void set_overhead(struct ext4_sb_info *sbi,
> + struct ext4_super_block *es, const void *arg)
> {
> es->s_overhead_clusters = cpu_to_le32(*((unsigned long *) arg));
> }
> diff --git a/include/uapi/linux/ext4.h b/include/uapi/linux/ext4.h
> index 1c4c2dd29112cda9f7dc91d917492cffc33ee524..145875fd633772e76ce7fd8bc0fef136ff620d2d 100644
> --- a/include/uapi/linux/ext4.h
> +++ b/include/uapi/linux/ext4.h
> @@ -33,6 +33,8 @@
> #define EXT4_IOC_CHECKPOINT _IOW('f', 43, __u32)
> #define EXT4_IOC_GETFSUUID _IOR('f', 44, struct fsuuid)
> #define EXT4_IOC_SETFSUUID _IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GET_TUNE_SB_PARAM _IOR('f', 45, struct ext4_tune_sb_params)
> +#define EXT4_IOC_SET_TUNE_SB_PARAM _IOW('f', 46, struct ext4_tune_sb_params)
>
> #define EXT4_IOC_SHUTDOWN _IOR('X', 125, __u32)
>
> @@ -108,6 +110,79 @@ struct ext4_new_group_input {
> __u16 unused;
> };
>
> +struct ext4_tune_sb_params {
> + __u32 set_flags;
> + __u32 checkinterval;
> + __u16 errors_behavior;
> + __u16 mnt_count;
> + __u16 max_mnt_count;
> + __u16 raid_stride;
> + __u64 last_check_time;
> + __u64 reserved_blocks;
> + __u64 blocks_count;
> + __u32 default_mnt_opts;
> + __u32 reserved_uid;
> + __u32 reserved_gid;
> + __u32 raid_stripe_width;
> + __u8 def_hash_alg;
> + __u8 pad_1;
> + __u16 pad_2;
> + __u32 feature_compat;
> + __u32 feature_incompat;
> + __u32 feature_ro_compat;
> + __u32 set_feature_compat_mask;
> + __u32 set_feature_incompat_mask;
> + __u32 set_feature_ro_compat_mask;
> + __u32 clear_feature_compat_mask;
> + __u32 clear_feature_incompat_mask;
> + __u32 clear_feature_ro_compat_mask;
> + __u8 mount_opts[64];
> + __u8 pad[64];
> +};
> +
> +#define EXT4_TUNE_FL_ERRORS_BEHAVIOR 0x00000001
> +#define EXT4_TUNE_FL_MNT_COUNT 0x00000002
> +#define EXT4_TUNE_FL_MAX_MNT_COUNT 0x00000004
> +#define EXT4_TUNE_FL_CHECKINTRVAL 0x00000008
> +#define EXT4_TUNE_FL_LAST_CHECK_TIME 0x00000010
> +#define EXT4_TUNE_FL_RESERVED_BLOCKS 0x00000020
> +#define EXT4_TUNE_FL_RESERVED_UID 0x00000040
> +#define EXT4_TUNE_FL_RESERVED_GID 0x00000080
> +#define EXT4_TUNE_FL_DEFAULT_MNT_OPTS 0x00000100
> +#define EXT4_TUNE_FL_DEF_HASH_ALG 0x00000200
> +#define EXT4_TUNE_FL_RAID_STRIDE 0x00000400
> +#define EXT4_TUNE_FL_RAID_STRIPE_WIDTH 0x00000800
> +#define EXT4_TUNE_FL_MOUNT_OPTS 0x00001000
> +#define EXT4_TUNE_FL_FEATURES 0x00002000
> +#define EXT4_TUNE_FL_EDIT_FEATURES 0x00004000
> +#define EXT4_TUNE_FL_FORCE_FSCK 0x00008000
> +
> +#define EXT4_TUNE_SET_COMPAT_SUPP \
> + (EXT4_FEATURE_COMPAT_DIR_INDEX | \
> + EXT4_FEATURE_COMPAT_STABLE_INODES)
> +#define EXT4_TUNE_SET_INCOMPAT_SUPP \
> + (EXT4_FEATURE_INCOMPAT_EXTENTS | \
> + EXT4_FEATURE_INCOMPAT_EA_INODE | \
> + EXT4_FEATURE_INCOMPAT_ENCRYPT | \
> + EXT4_FEATURE_INCOMPAT_CSUM_SEED | \
> + EXT4_FEATURE_INCOMPAT_LARGEDIR | \
> + EXT4_FEATURE_INCOMPAT_CASEFOLD)
> +#define EXT4_TUNE_SET_RO_COMPAT_SUPP \
> + (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
> + EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
> + EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
> + EXT4_FEATURE_RO_COMPAT_READONLY | \
> + EXT4_FEATURE_RO_COMPAT_PROJECT | \
> + EXT4_FEATURE_RO_COMPAT_VERITY)
> +
> +#define EXT4_TUNE_CLEAR_COMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_INCOMPAT_SUPP (0)
> +#define EXT4_TUNE_CLEAR_RO_COMPAT_SUPP \
> + (EXT4_FEATURE_RO_COMPAT_LARGE_FILE | \
> + EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
> + EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
> + EXT4_FEATURE_RO_COMPAT_PROJECT)
Is it actually safe to clear these without scanning the filesystem to
make sure nobody's using these features?
--D
> +
> /*
> * Returned by EXT4_IOC_GET_ES_CACHE as an additional possible flag.
> * It indicates that the entry in extent status cache is for a hole.
>
> --
> 2.51.0
>
>
>
