Re: [f2fs-dev] [PATCH v4] f2fs: support dynamic reserve/release for device aliasing

[Chao Yu]

On 7/22/26 01:53, Daeho Jeong wrote:
> On Sun, Jul 19, 2026 at 1:54 AM Chao Yu <chao@xxxxxxxxxx> wrote:
>>
>> On 7/14/26 00:05, Daeho Jeong wrote:
>>> From: Daeho Jeong <daehojeong@xxxxxxxxxx>
>>>
>>> This patch adds a dynamic management feature to the existing device
>>> aliasing functionality. It allows users to dynamically reserve or
>>> release specific devices from the filesystem's free pool at runtime
>>> through new ioctls.
>>>
>>> To support this, three new ioctls are introduced:
>>> - F2FS_IOC_RESERVE_DEV_ALIAS: This reclaims the space occupied by a
>>>    device aliasing file. It first performs a capacity check, resets GC
>>>    victim information for the target range, marks the segments as in-use
>>>    to prevent new allocations, and then triggers GC to migrate existing
>>>    valid data out of the range. Finally, it reserves these blocks in the
>>>    SIT to effectively exclude the device from the usable capacity.
>>>
>>> - F2FS_IOC_RELEASE_DEV_ALIAS: This releases the reserved space of a
>>>    previously reserved device aliasing file. It truncates the blocks
>>>    associated with the file, which makes them available for general
>>>    filesystem allocation again.
>>>
>>> - F2FS_IOC_GET_DEV_ALIAS_STATUS: This retrieves the current aliasing
>>>    status of a device aliasing file, returning whether the file is
>>>    released (inactive alias) or reserved (active alias, with blocks
>>>    fully allocated on the device).
>>>
>>> Signed-off-by: Daeho Jeong <daehojeong@xxxxxxxxxx>
>>> ---
>>> v4: renamed interfaces.
>>>      fixed race conditions between checkpoint=disable mount and ioctls.
>>>      refactored segment reservation part.
>>>      modified lock usage.
>>> v3: add CAP_SYS_ADMIN and checkpoint=disabled check.
>>>      remove a f2fs specific flag exposed with getflags.
>>> v2: prevent operations during checkpoint=disabled.
>>> ---
>>>   Documentation/filesystems/f2fs.rst |  35 ++++
>>>   fs/f2fs/f2fs.h                     |   9 +-
>>>   fs/f2fs/file.c                     | 289 ++++++++++++++++++++++++++++-
>>>   fs/f2fs/gc.c                       |  30 +--
>>>   fs/f2fs/namei.c                    |  14 ++
>>>   fs/f2fs/segment.c                  | 180 +++++++++++++-----
>>>   fs/f2fs/segment.h                  |  26 +++
>>>   fs/f2fs/super.c                    |  34 ++++
>>>   include/uapi/linux/f2fs.h          |   7 +
>>>   9 files changed, 562 insertions(+), 62 deletions(-)
>>>
>>> diff --git a/Documentation/filesystems/f2fs.rst b/Documentation/filesystems/f2fs.rst
>>> index 8c4a14ae444f..1a5fd4afe609 100644
>>> --- a/Documentation/filesystems/f2fs.rst
>>> +++ b/Documentation/filesystems/f2fs.rst
>>> @@ -1045,6 +1045,41 @@ So, the key idea is, user can do any file operations on /dev/vdc, and
>>>   reclaim the space after the use, while the space is counted as /data.
>>>   That doesn't require modifying partition size and filesystem format.
>>>
>>> +Dynamic Device Aliasing Management
>>> +----------------------------------
>>> +
>>> +In addition to static device aliasing by deleting the aliasing file, F2FS
>>> +supports dynamic management of device aliasing. This mechanism allows the system
>>> +to dynamically transition partition ownership between F2FS userdata and external
>>> +entities (e.g., zRAM, raw partition) based on system requirements without
>>> +deleting the master aliasing file or requiring unmount/remount.
>>> +
>>> +The master aliasing file is created during the initial format of the file system
>>> +and remains as a persistent control entity (ioctl gateway) in the root directory.
>>> +
>>> +- Partition Reservation (In-service to Aliased)
>>> +  When a specific partition needs to be dedicated to external services (e.g., zRAM),
>>> +  a user can reserve the device alias range via ioctl. The kernel resets GC victim
>>> +  information for the target range, marks segments as in-use to prevent new
>>> +  allocations, and triggers forced GC to migrate existing valid data out of the
>>> +  range. Finally, it reserves these blocks in the SIT to effectively exclude the
>>> +  device from the usable capacity.
>>> +
>>> +- Partition Release (Aliased to In-service)
>>> +  When external usage concludes, the space is reclaimed not by deleting the file,
>>> +  but through the release ioctl. The kernel truncates blocks associated with
>>> +  the file, releasing them back to general filesystem allocation.
>>> +
>>> +.. code-block::
>>> +
>>> +   # f2fs_io dev_alias release /mnt/f2fs/vdc.file
>>> +   # df -h
>>> +   /dev/vdb                            64G  753M   64G   2% /mnt/f2fs
>>> +
>>> +   # f2fs_io dev_alias reserve /mnt/f2fs/vdc.file
>>> +   # df -h
>>> +   /dev/vdb                            64G   33G   32G  52% /mnt/f2fs
>>> +
>>>   Per-file Read-Only Large Folio Support
>>>   --------------------------------------
>>>
>>> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
>>> index f1774d4e18d2..0f9b8b66cef9 100644
>>> --- a/fs/f2fs/f2fs.h
>>> +++ b/fs/f2fs/f2fs.h
>>> @@ -1404,6 +1404,8 @@ struct f2fs_dev_info {
>>>       unsigned int total_segments;
>>>       block_t start_blk;
>>>       block_t end_blk;
>>> +     bool has_alias;
>>> +     bool is_reserving;
>>>   #ifdef CONFIG_BLK_DEV_ZONED
>>>       unsigned int nr_blkz;           /* Total number of zones */
>>>       unsigned long *blkz_seq;        /* Bitmap indicating sequential zones */
>>> @@ -4009,7 +4011,10 @@ int f2fs_create_flush_cmd_control(struct f2fs_sb_info *sbi);
>>>   int f2fs_flush_device_cache(struct f2fs_sb_info *sbi);
>>>   void f2fs_destroy_flush_cmd_control(struct f2fs_sb_info *sbi, bool free);
>>>   void f2fs_invalidate_blocks(struct f2fs_sb_info *sbi, block_t addr,
>>> -                                             unsigned int len);
>>> +                             unsigned int len);
>>> +void f2fs_reserve_device_alias(struct f2fs_sb_info *sbi, block_t addr,
>>> +                             unsigned int len);
>>> +
>>>   bool f2fs_is_checkpointed_data(struct f2fs_sb_info *sbi, block_t blkaddr);
>>>   int f2fs_start_discard_thread(struct f2fs_sb_info *sbi);
>>>   void f2fs_drop_discard_cmd(struct f2fs_sb_info *sbi);
>>> @@ -4231,6 +4236,8 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi);
>>>   int f2fs_gc_range(struct f2fs_sb_info *sbi,
>>>               unsigned int start_seg, unsigned int end_seg,
>>>               bool dry_run, unsigned int dry_run_sections);
>>> +void f2fs_reset_gc_victim_resource(struct f2fs_sb_info *sbi,
>>> +             unsigned int start, unsigned int end);
>>>   int f2fs_resize_fs(struct file *filp, __u64 block_count);
>>>   int __init f2fs_create_garbage_collection_cache(void);
>>>   void f2fs_destroy_garbage_collection_cache(void);
>>> diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
>>> index 4b52c56d71f0..9077c091c2d6 100644
>>> --- a/fs/f2fs/file.c
>>> +++ b/fs/f2fs/file.c
>>> @@ -813,13 +813,19 @@ int f2fs_do_truncate_blocks(struct inode *inode, u64 from, bool lock)
>>>
>>>       if (IS_DEVICE_ALIASING(inode)) {
>>>               struct extent_tree *et = F2FS_I(inode)->extent_tree[EX_READ];
>>> -             struct extent_info ei = et->largest;
>>> +             struct extent_info ei;
>>> +
>>> +             read_lock(&et->lock);
>>> +             ei = et->largest;
>>> +             read_unlock(&et->lock);
>>>
>>>               f2fs_invalidate_blocks(sbi, ei.blk, ei.len);
>>>
>>>               dec_valid_block_count(sbi, inode, ei.len);
>>>               f2fs_update_time(sbi, REQ_TIME);
>>>
>>> +             f2fs_drop_extent_tree(inode);
>>> +
>>>               f2fs_folio_put(ifolio, true);
>>>               goto out;
>>>       }
>>> @@ -1100,8 +1106,9 @@ int f2fs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
>>>       if ((attr->ia_valid & ATTR_SIZE)) {
>>>               if (mapping_large_folio_support(inode->i_mapping))
>>>                       return -EOPNOTSUPP;
>>> -             if (!f2fs_is_compress_backend_ready(inode) ||
>>> -                             IS_DEVICE_ALIASING(inode))
>>> +             if (IS_DEVICE_ALIASING(inode))
>>> +                     return -EPERM;
>>> +             if (!f2fs_is_compress_backend_ready(inode))
>>>                       return -EOPNOTSUPP;
>>>               if (is_inode_flag_set(inode, FI_COMPRESS_RELEASED) &&
>>>                       !IS_ALIGNED(attr->ia_size,
>>> @@ -2130,6 +2137,9 @@ static int f2fs_setflags_common(struct inode *inode, u32 iflags, u32 mask)
>>>       if (IS_NOQUOTA(inode))
>>>               return -EPERM;
>>>
>>> +     if (IS_DEVICE_ALIASING(inode))
>>> +             return -EPERM;
>>> +
>>>       if ((iflags ^ masked_flags) & F2FS_CASEFOLD_FL) {
>>>               if (!f2fs_sb_has_casefold(F2FS_I_SB(inode)))
>>>                       return -EOPNOTSUPP;
>>> @@ -2678,6 +2688,17 @@ static int f2fs_ioc_get_encryption_policy(struct file *filp, unsigned long arg)
>>>       return fscrypt_ioctl_get_policy(filp, (void __user *)arg);
>>>   }
>>>
>>> +static int f2fs_ioc_get_dev_alias_status(struct file *filp, unsigned long arg)
>>> +{
>>> +     struct inode *inode = file_inode(filp);
>>> +
>>> +     if (!IS_DEVICE_ALIASING(inode))
>>> +             return -EINVAL;
>>> +
>>> +     return put_user(F2FS_HAS_BLOCKS(inode) ? F2FS_DEV_ALIAS_STATUS_RESERVED :
>>> +                             F2FS_DEV_ALIAS_STATUS_RELEASED, (u32 __user *)arg);
>>> +}
>>> +
>>>   static int f2fs_ioc_get_encryption_pwsalt(struct file *filp, unsigned long arg)
>>>   {
>>>       struct inode *inode = file_inode(filp);
>>> @@ -3616,6 +3637,259 @@ static int f2fs_ioc_get_dev_alias_file(struct file *filp, unsigned long arg)
>>>                       (u32 __user *)arg);
>>>   }
>>>
>>> +static int f2fs_ioc_reserve_dev_alias(struct file *filp)
>>> +{
>>> +     struct inode *inode = file_inode(filp);
>>> +     struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>> +     struct extent_tree *et = F2FS_I(inode)->extent_tree[EX_READ];
>>> +     struct extent_info ei;
>>> +     struct cp_control cpc = { CP_SYNC, 0, 0, 0 };
>>> +     struct f2fs_lock_context lc, glc;
>>> +     blkcnt_t count;
>>> +     unsigned int start, end, segno;
>>> +     int type, i, err;
>>> +
>>> +     if (!capable(CAP_SYS_ADMIN))
>>> +             return -EPERM;
>>> +
>>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>>> +             return -EINVAL;
>>> +
>>> +     err = mnt_want_write_file(filp);
>>> +     if (err)
>>> +             return err;
>>> +
>>> +     inode_lock(inode);
>>> +
>>> +     if (!IS_DEVICE_ALIASING(inode)) {
>>> +             err = -EINVAL;
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     if (F2FS_HAS_BLOCKS(inode)) {
>>> +             err = 0;
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     for (i = 1; i < sbi->s_ndevs; i++) {
>>> +             char *name = strrchr(FDEV(i).path, '/');
>>> +
>>> +             name = name ? name + 1 : FDEV(i).path;
>>> +             if (!strcmp(name, filp->f_path.dentry->d_name.name)) {
>>> +                     ei.blk = FDEV(i).start_blk;
>>> +                     ei.len = FDEV(i).total_segments << sbi->log_blocks_per_seg;
>>> +                     ei.fofs = 0;
>>> +                     break;
>>> +             }
>>> +     }
>>> +
>>> +     if (i == sbi->s_ndevs) {
>>> +             f2fs_warn(sbi, "device alias file (%s, ino=%llu) has no matching device",
>>> +                       filp->f_path.dentry->d_name.name, inode->i_ino);
>>> +             set_sbi_flag(sbi, SBI_NEED_FSCK);
>>> +             f2fs_handle_error(sbi, ERROR_CORRUPTED_INODE);
>>> +             err = -EFSCORRUPTED;
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     f2fs_down_write_trace(&sbi->gc_lock, &glc);
>>> +     f2fs_lock_op(sbi, &lc);
>>> +
>>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
>>> +             err = -EINVAL;
>>> +     } else {
>>> +             count = ei.len;
>>> +             err = inc_valid_block_count(sbi, inode, &count, false);
>>> +     }
>>> +     if (err) {
>>> +             f2fs_unlock_op(sbi, &lc);
>>> +             f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     spin_lock(&FREE_I(sbi)->segmap_lock);
>>> +     FDEV(f2fs_target_device_index(sbi, ei.blk)).is_reserving = true;
>>> +     spin_unlock(&FREE_I(sbi)->segmap_lock);
>>> +
>>> +     start = GET_SEGNO(sbi, ei.blk);
>>> +     end = GET_SEGNO(sbi, ei.blk + ei.len - 1);
>>> +
>>> +     /* Reset the victim information to prevent GC from targeting the range */
>>> +     f2fs_reset_gc_victim_resource(sbi, start, end);
>>> +
>>> +     /* Move out cursegs from the target range */
>>> +     for (type = CURSEG_HOT_DATA; type < NR_CURSEG_PERSIST_TYPE; type++) {
>>> +             err = f2fs_allocate_segment_for_resize(sbi, type, start, end);
>>> +             if (err) {
>>> +                     f2fs_unlock_op(sbi, &lc);
>>> +                     goto out_gc_unlock;
>>> +             }
>>> +     }
>>> +
>>> +     f2fs_unlock_op(sbi, &lc);
>>> +     f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +
>>> +     /* Write checkpoint synchronously to flush all pending writes and free space */
>>> +     err = f2fs_write_checkpoint(sbi, &cpc);
>>> +     if (err) {
>>> +             f2fs_down_write_trace(&sbi->gc_lock, &glc);
>>> +             goto out_gc_unlock;
>>> +     }

          ^^^

I meant we have reserved blocks via inc_valid_block_count(), then here we trigger
a checkpoint, if it shutdowns later, device alias file may only have reserved
blocks w/o any physical blocks? IIUC.

>>> +
>>> +     /* Re-acquire gc_lock and cp_rwsem read lock for the entire range GC */
>>> +     f2fs_down_write_trace(&sbi->gc_lock, &glc);
>>> +     f2fs_lock_op(sbi, &lc);
>>> +
>>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
>>> +             err = -EINVAL;
>>> +             f2fs_unlock_op(sbi, &lc);
>>> +             goto out_gc_unlock;
>>> +     }
>>> +
>>> +     /* do GC to move out valid blocks in the range all at once! */
>>> +     err = f2fs_gc_range(sbi, start, end, false, 0);
>>> +     if (err) {
>>> +             f2fs_unlock_op(sbi, &lc);
>>> +             goto out_gc_unlock;
>>> +     }
>>> +
>>> +     if (et) {
>>> +             write_lock(&et->lock);
>>> +             et->largest = ei;
>>> +             write_unlock(&et->lock);
>>> +     }
>>> +     clear_inode_flag(inode, FI_NO_EXTENT);
>>> +
>>> +     f2fs_reserve_device_alias(sbi, ei.blk, ei.len);
>>> +
>>> +     i_size_write(inode, (loff_t)ei.len << PAGE_SHIFT);
>>> +     f2fs_update_inode_page(inode);
>>> +
>>> +     spin_lock(&FREE_I(sbi)->segmap_lock);
>>> +     FDEV(f2fs_target_device_index(sbi, ei.blk)).is_reserving = false;
>>> +     spin_unlock(&FREE_I(sbi)->segmap_lock);
>>> +
>>> +     f2fs_unlock_op(sbi, &lc);
>>> +     f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +
>>> +     err = f2fs_write_checkpoint(sbi, &cpc);
>>> +     return err;
>>> +
>>> +out_gc_unlock:
>>> +     spin_lock(&FREE_I(sbi)->segmap_lock);
>>> +     FDEV(f2fs_target_device_index(sbi, ei.blk)).is_reserving = false;
>>> +     spin_unlock(&FREE_I(sbi)->segmap_lock);
>>> +     f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>
>> Seems, once we have reserved blocks above, and then unlock cp_rwsem and
>> gc_lock, a following CP and sudden power-cut recovery will make device alias
>> file corrupted?
> 
> 
> Could you please elaborate on the specific scenario or race condition
> you are concerned about?

Please check above comments.

> 
> In the current implementation:
>  - Both the SIT entry updates (f2fs_reserve_device_alias) and the
> inode page updates (f2fs_update_inode_page) are performed under
> cp_rwsem (f2fs_lock_op).
>  - Once cp_rwsem is unlocked, both dirty SIT entries and the dirty
> inode page will be committed together atomically by any following
> Checkpoint.
>  - If a sudden power-cut happens before the final Checkpoint
> completes, the filesystem safely recovers to the prior Checkpoint
> (where the alias file remains in the released/unreserved state with
> i_size = 0). If it happens after, it recovers to the new Checkpoint
> (where the alias file is fully reserved).
> 
> Is there a specific edge case or inconsistency during recovery that I
> might have missed?
> 
>>
>>
>> Maybe we can reserve blocks for device alias file w/ in-memory variable, something
>> like reserve_root?
>>
>>> +
>>> +     /*
>>> +      * Put successfully GC'ed segments back into PRE list so checkpoint
>>> +      * commits and frees them!
>>> +      */
>>
>> I didn't get it, why do we need to set empty segment as prefree one? You mean
>> f2fs_reserve_device_alias() has removed all prefreed segments? seems after
>> f2fs_reserve_device_alias() there is no error path.
> 
> You are completely right.
> f2fs_reserve_device_alias() is only called on the success path, so
> prefreed segments are never removed from the PRE list on the error
> path (out_gc_unlock).
> Furthermore, f2fs_gc_range() already handles tracking invalidated
> segments in the PRE list automatically through standard block
> invalidation.
> Therefore, this manual loop adding segments back to dirty_segmap[PRE]
> in out_gc_unlock is redundant. I will remove this logic in the next
> version.
> 
> Thank you for catching this!
> 
>>
>>> +     f2fs_lock_op(sbi, &lc);
>>> +     for (segno = start; segno <= end; segno++) {
>>> +             if (get_valid_blocks(sbi, segno, false) == 0) {
>>> +                     mutex_lock(&DIRTY_I(sbi)->seglist_lock);
>>> +                     if (!test_and_set_bit(segno, DIRTY_I(sbi)->dirty_segmap[PRE]))
>>> +                             DIRTY_I(sbi)->nr_dirty[PRE]++;
>>> +                     mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
>>> +             }
>>> +     }
>>> +     count = ei.len;
>>> +     dec_valid_block_count(sbi, inode, count);
>>> +     f2fs_unlock_op(sbi, &lc);
>>> +
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +
>>> +     f2fs_write_checkpoint(sbi, &cpc);
>>> +     return err;
>>> +
>>> +out_inode_unlock:
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +     return err;
>>> +}
>>> +
>>> +static int f2fs_ioc_release_dev_alias(struct file *filp)
>>> +{
>>> +     struct inode *inode = file_inode(filp);
>>> +     struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
>>> +     struct extent_tree *et = F2FS_I(inode)->extent_tree[EX_READ];
>>> +     struct extent_info ei = {0, };
>>> +     struct cp_control cpc = { CP_SYNC, 0, 0, 0 };
>>> +     struct f2fs_lock_context lc, glc;
>>> +     int err;
>>> +
>>> +     if (!capable(CAP_SYS_ADMIN))
>>> +             return -EPERM;
>>> +
>>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED)))
>>> +             return -EINVAL;
>>> +
>>> +     err = mnt_want_write_file(filp);
>>> +     if (err)
>>> +             return err;
>>> +
>>> +     inode_lock(inode);
>>> +
>>> +     if (!IS_DEVICE_ALIASING(inode)) {
>>> +             err = -EINVAL;
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     if (!F2FS_HAS_BLOCKS(inode)) {
>>> +             err = 0;
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     err = filemap_write_and_wait(inode->i_mapping);
>>> +     if (err)
>>> +             goto out_inode_unlock;
>>> +
>>> +     read_lock(&et->lock);
>>> +     ei = et->largest;
>>> +     read_unlock(&et->lock);
>>> +
>>> +     f2fs_down_write_trace(&sbi->gc_lock, &glc);
>>> +     f2fs_lock_op(sbi, &lc);
>>> +
>>> +     if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
>>> +             err = -EINVAL;
>>> +             f2fs_unlock_op(sbi, &lc);
>>> +             f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     truncate_setsize(inode, 0);
>>> +
>>> +     err = f2fs_truncate_blocks(inode, 0, false);
>>> +     if (err) {
>>> +             i_size_write(inode, (loff_t)ei.len << PAGE_SHIFT);
>>
>> If f2fs_truncate_blocks() partially truncated blocks of device alias file,
>> it will be corrupted, since a pinned file may has partial valid blocks in
>> section?
>>
>> Can fsck detect such status of device alias for repair?
>>
> 
> That's a great question, but for device alias files, block truncation
> is strictly an all-or-nothing operation.
> 
> As implemented in f2fs_truncate_blocks() (file.c:814):
> 
> For IS_DEVICE_ALIASING(inode), we do not iterate over dnodes or
> truncate blocks partially. Instead, all ei.len blocks are invalidated
> at once in a single call via f2fs_invalidate_blocks(sbi, ei.blk,
> ei.len).
> The only error paths in f2fs_truncate_blocks() occur before
> f2fs_invalidate_blocks() is called, when zero blocks have been
> invalidated.
> Once f2fs_invalidate_blocks() is reached, all blocks are invalidated
> together and the function succeeds.
> 
> Therefore, partial block truncation never happens for device alias files:
> 
> If f2fs_truncate_blocks() fails, 0 blocks have been freed, so
> restoring i_size safely preserves the fully-reserved file without any
> holes.
> If it succeeds, 100% of the blocks are freed.

Oh, that's right, thanks for the explaination.

Thanks,

> 
>> Thanks,
>>
>>> +             f2fs_unlock_op(sbi, &lc);
>>> +             f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +             goto out_inode_unlock;
>>> +     }
>>> +
>>> +     f2fs_update_inode_page(inode);
>>> +
>>> +     f2fs_unlock_op(sbi, &lc);
>>> +     f2fs_up_write_trace(&sbi->gc_lock, &glc);
>>> +
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +
>>> +     err = f2fs_write_checkpoint(sbi, &cpc);
>>> +     return err;
>>> +
>>> +out_inode_unlock:
>>> +     inode_unlock(inode);
>>> +     mnt_drop_write_file(filp);
>>> +     return err;
>>> +}
>>> +
>>>   static int f2fs_ioc_io_prio(struct file *filp, unsigned long arg)
>>>   {
>>>       struct inode *inode = file_inode(filp);
>>> @@ -4742,8 +5016,14 @@ static long __f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>>               return f2fs_ioc_compress_file(filp);
>>>       case F2FS_IOC_GET_DEV_ALIAS_FILE:
>>>               return f2fs_ioc_get_dev_alias_file(filp, arg);
>>> +     case F2FS_IOC_GET_DEV_ALIAS_STATUS:
>>> +             return f2fs_ioc_get_dev_alias_status(filp, arg);
>>>       case F2FS_IOC_IO_PRIO:
>>>               return f2fs_ioc_io_prio(filp, arg);
>>> +     case F2FS_IOC_RESERVE_DEV_ALIAS:
>>> +             return f2fs_ioc_reserve_dev_alias(filp);
>>> +     case F2FS_IOC_RELEASE_DEV_ALIAS:
>>> +             return f2fs_ioc_release_dev_alias(filp);
>>>       default:
>>>               return -ENOTTY;
>>>       }
>>> @@ -5530,7 +5810,10 @@ long f2fs_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
>>>       case F2FS_IOC_DECOMPRESS_FILE:
>>>       case F2FS_IOC_COMPRESS_FILE:
>>>       case F2FS_IOC_GET_DEV_ALIAS_FILE:
>>> +     case F2FS_IOC_GET_DEV_ALIAS_STATUS:
>>>       case F2FS_IOC_IO_PRIO:
>>> +     case F2FS_IOC_RESERVE_DEV_ALIAS:
>>> +     case F2FS_IOC_RELEASE_DEV_ALIAS:
>>>               break;
>>>       default:
>>>               return -ENOIOCTLCMD;
>>> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
>>> index ffaa7ba76a1b..93bcb35a5b5d 100644
>>> --- a/fs/f2fs/gc.c
>>> +++ b/fs/f2fs/gc.c
>>> @@ -2197,29 +2197,37 @@ int f2fs_gc_range(struct f2fs_sb_info *sbi,
>>>       return 0;
>>>   }
>>>
>>> +void f2fs_reset_gc_victim_resource(struct f2fs_sb_info *sbi,
>>> +                     unsigned int start, unsigned int end)
>>> +{
>>> +     int i;
>>> +
>>> +     mutex_lock(&DIRTY_I(sbi)->seglist_lock);
>>> +     for (i = 0; i < MAX_GC_POLICY; i++)
>>> +             if (SIT_I(sbi)->last_victim[i] >= start &&
>>> +                     SIT_I(sbi)->last_victim[i] <= end)
>>> +                     SIT_I(sbi)->last_victim[i] = 0;
>>> +
>>> +     for (i = BG_GC; i <= FG_GC; i++)
>>> +             if (sbi->next_victim_seg[i] >= start &&
>>> +                     sbi->next_victim_seg[i] <= end)
>>> +                     sbi->next_victim_seg[i] = NULL_SEGNO;
>>> +     mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
>>> +}
>>> +
>>>   static int free_segment_range(struct f2fs_sb_info *sbi,
>>>                               unsigned int secs, bool dry_run)
>>>   {
>>>       unsigned int next_inuse, start, end;
>>>       struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
>>> -     int gc_mode, gc_type;
>>>       int err = 0;
>>>       int type;
>>>
>>> -     /* Force block allocation for GC */
>>>       MAIN_SECS(sbi) -= secs;
>>>       start = MAIN_SECS(sbi) * SEGS_PER_SEC(sbi);
>>>       end = MAIN_SEGS(sbi) - 1;
>>>
>>> -     mutex_lock(&DIRTY_I(sbi)->seglist_lock);
>>> -     for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
>>> -             if (SIT_I(sbi)->last_victim[gc_mode] >= start)
>>> -                     SIT_I(sbi)->last_victim[gc_mode] = 0;
>>> -
>>> -     for (gc_type = BG_GC; gc_type <= FG_GC; gc_type++)
>>> -             if (sbi->next_victim_seg[gc_type] >= start)
>>> -                     sbi->next_victim_seg[gc_type] = NULL_SEGNO;
>>> -     mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
>>> +     f2fs_reset_gc_victim_resource(sbi, start, end);
>>>
>>>       /* Move out cursegs from the target range */
>>>       for (type = CURSEG_HOT_DATA; type < NR_CURSEG_PERSIST_TYPE; type++) {
>>> diff --git a/fs/f2fs/namei.c b/fs/f2fs/namei.c
>>> index cac03b8e91a1..8c3b57987f6c 100644
>>> --- a/fs/f2fs/namei.c
>>> +++ b/fs/f2fs/namei.c
>>> @@ -425,6 +425,9 @@ static int f2fs_link(struct dentry *old_dentry, struct inode *dir,
>>>       if (!f2fs_is_checkpoint_ready(sbi))
>>>               return -ENOSPC;
>>>
>>> +     if (IS_DEVICE_ALIASING(inode))
>>> +             return -EPERM;
>>> +
>>>       err = fscrypt_prepare_link(old_dentry, dir, dentry);
>>>       if (err)
>>>               return err;
>>> @@ -568,6 +571,9 @@ static int f2fs_unlink(struct inode *dir, struct dentry *dentry)
>>>
>>>       trace_f2fs_unlink_enter(dir, dentry);
>>>
>>> +     if (IS_DEVICE_ALIASING(inode))
>>> +             return -EPERM;
>>> +
>>>       if (unlikely(f2fs_cp_error(sbi))) {
>>>               err = -EIO;
>>>               goto out;
>>> @@ -946,6 +952,9 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
>>>       bool old_is_dir = S_ISDIR(old_inode->i_mode);
>>>       int err;
>>>
>>> +     if (IS_DEVICE_ALIASING(old_inode))
>>> +             return -EPERM;
>>> +
>>>       if (unlikely(f2fs_cp_error(sbi)))
>>>               return -EIO;
>>>       if (!f2fs_is_checkpoint_ready(sbi))
>>> @@ -1016,6 +1025,8 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
>>>       }
>>>
>>>       if (new_inode) {
>>> +             if (IS_DEVICE_ALIASING(new_inode))
>>> +                     return -EPERM;
>>>
>>>               err = -ENOTEMPTY;
>>>               if (old_is_dir && !f2fs_empty_dir(new_inode))
>>> @@ -1143,6 +1154,9 @@ static int f2fs_cross_rename(struct inode *old_dir, struct dentry *old_dentry,
>>>       int old_nlink = 0, new_nlink = 0;
>>>       int err;
>>>
>>> +     if (IS_DEVICE_ALIASING(old_inode) || IS_DEVICE_ALIASING(new_inode))
>>> +             return -EPERM;
>>> +
>>>       if (unlikely(f2fs_cp_error(sbi)))
>>>               return -EIO;
>>>       if (!f2fs_is_checkpoint_ready(sbi))
>>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>>> index d71ddb3ee918..1a986f1884f2 100644
>>> --- a/fs/f2fs/segment.c
>>> +++ b/fs/f2fs/segment.c
>>> @@ -2502,35 +2502,42 @@ static int update_sit_entry_for_alloc(struct f2fs_sb_info *sbi, struct seg_entry
>>>                               unsigned int segno, block_t blkaddr, unsigned int offset, int del)
>>>   {
>>>       bool exist;
>>> +     int del_count = del;
>>> +     int i;
>>>
>>> -     exist = f2fs_test_and_set_bit(offset, se->cur_valid_map);
>>> -     if (unlikely(exist)) {
>>> -             f2fs_err(sbi, "Bitmap was wrongly set, blk:%u", blkaddr);
>>> -             f2fs_bug_on(sbi, 1);
>>> -             se->valid_blocks--;
>>> -             del = 0;
>>> -     }
>>> +     f2fs_bug_on(sbi, GET_SEGNO(sbi, blkaddr) != GET_SEGNO(sbi, blkaddr + del_count - 1));
>>>
>>> -     if (f2fs_block_unit_discard(sbi) &&
>>> -                     !f2fs_test_and_set_bit(offset, se->discard_map))
>>> -             sbi->discard_blks--;
>>> +     for (i = 0; i < del_count; i++) {
>>> +             exist = f2fs_test_and_set_bit(offset + i, se->cur_valid_map);
>>> +             if (unlikely(exist)) {
>>> +                     f2fs_err(sbi, "Bitmap was wrongly set, blk:%u", blkaddr + i);
>>> +                     f2fs_bug_on(sbi, 1);
>>> +                     se->valid_blocks--;
>>> +                     del -= 1;
>>> +                     continue;
>>> +             }
>>>
>>> -     /*
>>> -      * SSR should never reuse block which is checkpointed
>>> -      * or newly invalidated.
>>> -      */
>>> -     if (!is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
>>> -             if (!f2fs_test_and_set_bit(offset, se->ckpt_valid_map)) {
>>> -                     se->ckpt_valid_blocks++;
>>> -                     if (__is_large_section(sbi))
>>> -                             get_sec_entry(sbi, segno)->ckpt_valid_blocks++;
>>> +             if (f2fs_block_unit_discard(sbi) &&
>>> +                             !f2fs_test_and_set_bit(offset + i, se->discard_map))
>>> +                     sbi->discard_blks--;
>>> +
>>> +             /*
>>> +              * SSR should never reuse block which is checkpointed
>>> +              * or newly invalidated.
>>> +              */
>>> +             if (!is_sbi_flag_set(sbi, SBI_CP_DISABLED)) {
>>> +                     if (!f2fs_test_and_set_bit(offset + i, se->ckpt_valid_map)) {
>>> +                             se->ckpt_valid_blocks++;
>>> +                             if (__is_large_section(sbi))
>>> +                                     get_sec_entry(sbi, segno)->ckpt_valid_blocks++;
>>> +                     }
>>>               }
>>> -     }
>>>
>>> -     if (!f2fs_test_bit(offset, se->ckpt_valid_map)) {
>>> -             se->ckpt_valid_blocks += del;
>>> -             if (__is_large_section(sbi))
>>> -                     get_sec_entry(sbi, segno)->ckpt_valid_blocks += del;
>>> +             if (!f2fs_test_bit(offset + i, se->ckpt_valid_map)) {
>>> +                     se->ckpt_valid_blocks += 1;
>>> +                     if (__is_large_section(sbi))
>>> +                             get_sec_entry(sbi, segno)->ckpt_valid_blocks += 1;
>>> +             }
>>>       }
>>>
>>>       if (__is_large_section(sbi))
>>> @@ -2585,9 +2592,14 @@ void f2fs_invalidate_blocks(struct f2fs_sb_info *sbi, block_t addr,
>>>       unsigned int segno = GET_SEGNO(sbi, addr);
>>>       struct sit_info *sit_i = SIT_I(sbi);
>>>       block_t addr_start = addr, addr_end = addr + len - 1;
>>> -     unsigned int seg_num = GET_SEGNO(sbi, addr_end) - segno + 1;
>>> +     unsigned int seg_num;
>>>       unsigned int i = 1, max_blocks = sbi->blocks_per_seg, cnt;
>>>
>>> +     if (len == 0)
>>> +             return;
>>> +
>>> +     seg_num = GET_SEGNO(sbi, addr_end) - segno + 1;
>>> +
>>>       f2fs_bug_on(sbi, addr == NULL_ADDR);
>>>       if (addr == NEW_ADDR || addr == COMPRESS_ADDR)
>>>               return;
>>> @@ -2620,6 +2632,52 @@ void f2fs_invalidate_blocks(struct f2fs_sb_info *sbi, block_t addr,
>>>       up_write(&sit_i->sentry_lock);
>>>   }
>>>
>>> +void f2fs_reserve_device_alias(struct f2fs_sb_info *sbi, block_t addr,
>>> +                             unsigned int len)
>>> +{
>>> +     unsigned int segno = GET_SEGNO(sbi, addr);
>>> +     struct sit_info *sit_i = SIT_I(sbi);
>>> +     block_t addr_start = addr, addr_end = addr + len - 1;
>>> +     unsigned int seg_num;
>>> +     unsigned int i = 1, max_blocks = sbi->blocks_per_seg, cnt;
>>> +
>>> +     if (len == 0)
>>> +             return;
>>> +
>>> +     seg_num = GET_SEGNO(sbi, addr_end) - segno + 1;
>>> +
>>> +     down_write(&sit_i->sentry_lock);
>>> +
>>> +     if (seg_num == 1)
>>> +             cnt = len;
>>> +     else
>>> +             cnt = max_blocks - GET_BLKOFF_FROM_SEG0(sbi, addr);
>>> +
>>> +     do {
>>> +             update_segment_mtime(sbi, addr_start, 0);
>>> +             update_sit_entry(sbi, addr_start, cnt);
>>> +             __set_test_and_inuse(sbi, segno);
>>> +
>>> +             /* Remove the segment from PRE (prefree) to prevent checkpoint from freeing it! */
>>> +             mutex_lock(&DIRTY_I(sbi)->seglist_lock);
>>> +             if (test_and_clear_bit(segno, DIRTY_I(sbi)->dirty_segmap[PRE]))
>>> +                     DIRTY_I(sbi)->nr_dirty[PRE]--;
>>> +             mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
>>> +
>>> +             /* add it into dirty seglist */
>>> +             locate_dirty_segment(sbi, segno);
>>> +
>>> +             /* update @addr_start and @cnt and @segno */
>>> +             addr_start = START_BLOCK(sbi, ++segno);
>>> +             if (++i == seg_num)
>>> +                     cnt = GET_BLKOFF_FROM_SEG0(sbi, addr_end) + 1;
>>> +             else
>>> +                     cnt = max_blocks;
>>> +     } while (i <= seg_num);
>>> +
>>> +     up_write(&sit_i->sentry_lock);
>>> +}
>>> +
>>>   bool f2fs_is_checkpointed_data(struct f2fs_sb_info *sbi, block_t blkaddr)
>>>   {
>>>       struct sit_info *sit_i = SIT_I(sbi);
>>> @@ -2758,8 +2816,13 @@ static int is_next_segment_free(struct f2fs_sb_info *sbi,
>>>       unsigned int segno = curseg->segno + 1;
>>>       struct free_segmap_info *free_i = FREE_I(sbi);
>>>
>>> -     if (segno < MAIN_SEGS(sbi) && segno % SEGS_PER_SEC(sbi))
>>> +     if (segno < MAIN_SEGS(sbi) && segno % SEGS_PER_SEC(sbi)) {
>>> +             int devi = f2fs_target_device_index(sbi, START_BLOCK(sbi, segno));
>>> +
>>> +             if (f2fs_dev_is_reserving(sbi, devi))
>>> +                     return 0;
>>>               return !test_bit(segno, free_i->free_segmap);
>>> +     }
>>>       return 0;
>>>   }
>>>
>>> @@ -2778,6 +2841,7 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
>>>       unsigned int alloc_policy = sbi->allocate_section_policy;
>>>       unsigned int alloc_hint = sbi->allocate_section_hint;
>>>       bool init = true;
>>> +     bool looped = false;
>>>       int i;
>>>       int ret = 0;
>>>
>>> @@ -2791,8 +2855,13 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
>>>       if (!new_sec && ((*newseg + 1) % SEGS_PER_SEC(sbi))) {
>>>               segno = find_next_zero_bit(free_i->free_segmap,
>>>                       GET_SEG_FROM_SEC(sbi, hint + 1), *newseg + 1);
>>> -             if (segno < GET_SEG_FROM_SEC(sbi, hint + 1))
>>> +             if (segno < GET_SEG_FROM_SEC(sbi, hint + 1)) {
>>> +                     int devi = f2fs_target_device_index(sbi, START_BLOCK(sbi, segno));
>>> +
>>> +                     if (f2fs_dev_is_alloc_blocked(sbi, devi, pinning))
>>> +                             goto find_other_zone;
>>>                       goto got_it;
>>> +             }
>>>       }
>>>
>>>   #ifdef CONFIG_BLK_DEV_ZONED
>>> @@ -2828,33 +2897,50 @@ static int get_new_segment(struct f2fs_sb_info *sbi,
>>>   find_other_zone:
>>>       secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
>>>
>>> -#ifdef CONFIG_BLK_DEV_ZONED
>>> -     if (secno >= MAIN_SECS(sbi) && f2fs_sb_has_blkzoned(sbi)) {
>>> -             /* Write only to sequential zones */
>>> -             if (sbi->blkzone_alloc_policy == BLKZONE_ALLOC_ONLY_SEQ) {
>>> -                     hint = GET_SEC_FROM_SEG(sbi, sbi->first_seq_zone_segno);
>>> -                     secno = find_next_zero_bit(free_i->free_secmap, MAIN_SECS(sbi), hint);
>>> -             } else
>>> -                     secno = find_first_zero_bit(free_i->free_secmap,
>>> -                                                             MAIN_SECS(sbi));
>>> -             if (secno >= MAIN_SECS(sbi)) {
>>> -                     ret = -ENOSPC;
>>> -                     f2fs_bug_on(sbi, 1);
>>> -                     goto out_unlock;
>>> -             }
>>> -     }
>>> -#endif
>>> -
>>>       if (secno >= MAIN_SECS(sbi)) {
>>> -             secno = find_first_zero_bit(free_i->free_secmap,
>>> -                                                     MAIN_SECS(sbi));
>>> -             if (secno >= MAIN_SECS(sbi)) {
>>> +             if (looped) {
>>>                       ret = -ENOSPC;
>>>                       f2fs_bug_on(sbi, !pinning);
>>>                       goto out_unlock;
>>>               }
>>> +#ifdef CONFIG_BLK_DEV_ZONED
>>> +             /* Write only to sequential zones */
>>> +             if (f2fs_sb_has_blkzoned(sbi) &&
>>> +                     sbi->blkzone_alloc_policy == BLKZONE_ALLOC_ONLY_SEQ)
>>> +                     hint = GET_SEC_FROM_SEG(sbi, sbi->first_seq_zone_segno);
>>> +             else
>>> +#endif
>>> +                     hint = 0;
>>> +             looped = true;
>>> +             goto find_other_zone;
>>>       }
>>> +
>>>       segno = GET_SEG_FROM_SEC(sbi, secno);
>>> +
>>> +     if (f2fs_sb_has_device_alias(sbi) && f2fs_is_multi_device(sbi)) {
>>> +             int devi = f2fs_target_device_index(sbi, START_BLOCK(sbi, segno));
>>> +
>>> +             if (f2fs_dev_is_alloc_blocked(sbi, devi, pinning)) {
>>> +                     unsigned int end_segno;
>>> +
>>> +                     while (devi < sbi->s_ndevs &&
>>> +                             f2fs_dev_is_alloc_blocked(sbi, devi, pinning)) {
>>> +                             block_t next_blk;
>>> +
>>> +                             end_segno = GET_SEGNO(sbi, FDEV(devi).end_blk);
>>> +                             hint = GET_SEC_FROM_SEG(sbi, end_segno) + 1;
>>> +
>>> +                             if (hint >= MAIN_SECS(sbi) || ++devi >= sbi->s_ndevs)
>>> +                                     break;
>>> +
>>> +                             next_blk = START_BLOCK(sbi, GET_SEG_FROM_SEC(sbi, hint));
>>> +                             if (next_blk < FDEV(devi).start_blk ||
>>> +                                     next_blk > FDEV(devi).end_blk)
>>> +                                     break;
>>> +                     }
>>> +                     goto find_other_zone;
>>> +             }
>>> +     }
>>>       zoneno = GET_ZONE_FROM_SEC(sbi, secno);
>>>
>>>       /* give up on finding another zone */
>>> diff --git a/fs/f2fs/segment.h b/fs/f2fs/segment.h
>>> index b0c06b3580b4..259e4a29b494 100644
>>> --- a/fs/f2fs/segment.h
>>> +++ b/fs/f2fs/segment.h
>>> @@ -954,10 +954,36 @@ static inline block_t sum_blk_addr(struct f2fs_sb_info *sbi, int base, int type)
>>>                               - (base + 1) + type;
>>>   }
>>>
>>> +static inline bool f2fs_dev_is_reserving(struct f2fs_sb_info *sbi, int devi)
>>> +{
>>> +     if (!f2fs_sb_has_device_alias(sbi) || !f2fs_is_multi_device(sbi))
>>> +             return false;
>>> +     return FDEV(devi).is_reserving;
>>> +}
>>> +
>>> +static inline bool f2fs_dev_is_alloc_blocked(struct f2fs_sb_info *sbi,
>>> +                                     int devi, bool pinning)
>>> +{
>>> +     if (!f2fs_sb_has_device_alias(sbi) || !f2fs_is_multi_device(sbi))
>>> +             return false;
>>> +     return (pinning && FDEV(devi).has_alias) || FDEV(devi).is_reserving;
>>> +}
>>> +
>>>   static inline bool sec_usage_check(struct f2fs_sb_info *sbi, unsigned int secno)
>>>   {
>>>       if (is_cursec(sbi, secno) || (sbi->cur_victim_sec == secno))
>>>               return true;
>>> +     if (f2fs_sb_has_device_alias(sbi) && f2fs_is_multi_device(sbi)) {
>>> +             int i;
>>> +             block_t start_blk = START_BLOCK(sbi, GET_SEG_FROM_SEC(sbi, secno));
>>> +
>>> +             for (i = 0; i < sbi->s_ndevs; i++) {
>>> +                     if (f2fs_dev_is_reserving(sbi, i) &&
>>> +                             start_blk >= FDEV(i).start_blk &&
>>> +                             start_blk <= FDEV(i).end_blk)
>>> +                             return true;
>>> +             }
>>> +     }
>>>       return false;
>>>   }
>>>
>>> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
>>> index c448d992ff2a..8359eed903be 100644
>>> --- a/fs/f2fs/super.c
>>> +++ b/fs/f2fs/super.c
>>> @@ -5001,6 +5001,38 @@ static void f2fs_tuning_parameters(struct f2fs_sb_info *sbi)
>>>       sbi->readdir_ra = true;
>>>   }
>>>
>>> +static void f2fs_restore_device_alias(struct f2fs_sb_info *sbi)
>>> +{
>>> +     struct inode *root = d_inode(sbi->sb->s_root);
>>> +     struct f2fs_dir_entry *de;
>>> +     struct folio *folio;
>>> +     int i;
>>> +
>>> +     if (!f2fs_sb_has_device_alias(sbi))
>>> +             return;
>>> +
>>> +     for (i = 1; i < sbi->s_ndevs; i++) {
>>> +             char *name = strrchr(FDEV(i).path, '/');
>>> +             struct qstr qstr;
>>> +
>>> +             name = name ? name + 1 : FDEV(i).path;
>>> +             qstr.name = name;
>>> +             qstr.len = strlen(name);
>>> +
>>> +             de = f2fs_find_entry(root, &qstr, &folio);
>>> +             if (de) {
>>> +                     struct inode *inode = f2fs_iget(sbi->sb, le32_to_cpu(de->ino));
>>> +
>>> +                     if (!IS_ERR(inode)) {
>>> +                             if (IS_DEVICE_ALIASING(inode))
>>> +                                     FDEV(i).has_alias = true;
>>> +                             iput(inode);
>>> +                     }
>>> +                     f2fs_folio_put(folio, 0);
>>> +             }
>>> +     }
>>> +}
>>> +
>>>   static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
>>>   {
>>>       struct f2fs_fs_context *ctx = fc->fs_private;
>>> @@ -5436,6 +5468,8 @@ static int f2fs_fill_super(struct super_block *sb, struct fs_context *fc)
>>>       f2fs_update_time(sbi, REQ_TIME);
>>>       clear_sbi_flag(sbi, SBI_CP_DISABLED_QUICK);
>>>
>>> +     f2fs_restore_device_alias(sbi);
>>> +
>>>       sbi->umount_lock_holder = NULL;
>>>       return 0;
>>>
>>> diff --git a/include/uapi/linux/f2fs.h b/include/uapi/linux/f2fs.h
>>> index 795e26258355..4409ada2fecb 100644
>>> --- a/include/uapi/linux/f2fs.h
>>> +++ b/include/uapi/linux/f2fs.h
>>> @@ -45,6 +45,9 @@
>>>   #define F2FS_IOC_START_ATOMIC_REPLACE       _IO(F2FS_IOCTL_MAGIC, 25)
>>>   #define F2FS_IOC_GET_DEV_ALIAS_FILE _IOR(F2FS_IOCTL_MAGIC, 26, __u32)
>>>   #define F2FS_IOC_IO_PRIO            _IOW(F2FS_IOCTL_MAGIC, 27, __u32)
>>> +#define F2FS_IOC_RESERVE_DEV_ALIAS   _IO(F2FS_IOCTL_MAGIC, 28)
>>> +#define F2FS_IOC_RELEASE_DEV_ALIAS   _IO(F2FS_IOCTL_MAGIC, 29)
>>> +#define F2FS_IOC_GET_DEV_ALIAS_STATUS        _IOR(F2FS_IOCTL_MAGIC, 30, __u32)
>>>
>>>   /*
>>>    * should be same as XFS_IOC_GOINGDOWN.
>>> @@ -70,6 +73,10 @@ enum {
>>>       F2FS_IOPRIO_MAX,
>>>   };
>>>
>>> +/* for F2FS_IOC_GET_DEV_ALIAS_STATUS */
>>> +#define F2FS_DEV_ALIAS_STATUS_RELEASED       0
>>> +#define F2FS_DEV_ALIAS_STATUS_RESERVED       1
>>> +
>>>   struct f2fs_gc_range {
>>>       __u32 sync;
>>>       __u64 start;
>>