[PATCH] exfat: Add support for FS_IOC_{GET,SET}FSLABEL

[Ethan Ferguson <ethan.ferguson@zetier.com>]

On 8/18/25 21:45, Namjae Jeon wrote:
> On Sun, Aug 17, 2025 at 9:31 AM Ethan Ferguson
> <ethan.ferguson@zetier.com> wrote:
>>
>> Add support for reading / writing to the exfat volume label from the
>> FS_IOC_GETFSLABEL and FS_IOC_SETFSLABEL ioctls
>>
>> Signed-off-by: Ethan Ferguson <ethan.ferguson@zetier.com>
>>
>> ---
>>  fs/exfat/exfat_fs.h  |  2 +
>>  fs/exfat/exfat_raw.h |  6 +++
>>  fs/exfat/file.c      | 56 +++++++++++++++++++++++++
>>  fs/exfat/super.c     | 99 ++++++++++++++++++++++++++++++++++++++++++++
>>  4 files changed, 163 insertions(+)
>>
>> diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
>> index f8ead4d47ef0..a764e6362172 100644
>> --- a/fs/exfat/exfat_fs.h
>> +++ b/fs/exfat/exfat_fs.h
>> @@ -267,6 +267,7 @@ struct exfat_sb_info {
>>         struct buffer_head **vol_amap; /* allocation bitmap */
>>
>>         unsigned short *vol_utbl; /* upcase table */
>> +       unsigned short volume_label[EXFAT_VOLUME_LABEL_LEN]; /* volume name */
> There's no reason to have this in sbi. I think it's better to read the
> volume name in ioctl fslabel and return it.
>
That's fair. I wrote it this way because the volume label is stored in
the sbi in btrfs, but there it's (as far as I understand) part of the
fs header on disk, and not (as is the case in exfat) a directory entry
that could be arbitrarily far from the start of the disk. Maybe we could
cache it in the sbi after the first read? I'm open to either.

>>
>>         unsigned int clu_srch_ptr; /* cluster search pointer */
>>         unsigned int used_clusters; /* number of used clusters */
>> @@ -431,6 +432,7 @@ static inline loff_t exfat_ondisk_size(const struct inode *inode)
>>  /* super.c */
>>  int exfat_set_volume_dirty(struct super_block *sb);
>>  int exfat_clear_volume_dirty(struct super_block *sb);
>> +int exfat_write_volume_label(struct super_block *sb);
>>
>>  /* fatent.c */
>>  #define exfat_get_next_cluster(sb, pclu) exfat_ent_get(sb, *(pclu), pclu)
>> diff --git a/fs/exfat/exfat_raw.h b/fs/exfat/exfat_raw.h
>> index 971a1ccd0e89..af04cef81c0c 100644
>> --- a/fs/exfat/exfat_raw.h
>> +++ b/fs/exfat/exfat_raw.h
>> @@ -80,6 +80,7 @@
>>  #define BOOTSEC_OLDBPB_LEN             53
>>
>>  #define EXFAT_FILE_NAME_LEN            15
>> +#define EXFAT_VOLUME_LABEL_LEN         11
>>
>>  #define EXFAT_MIN_SECT_SIZE_BITS               9
>>  #define EXFAT_MAX_SECT_SIZE_BITS               12
>> @@ -159,6 +160,11 @@ struct exfat_dentry {
>>                         __le32 start_clu;
>>                         __le64 size;
>>                 } __packed upcase; /* up-case table directory entry */
>> +               struct {
>> +                       __u8 char_count;
>> +                       __le16 volume_label[EXFAT_VOLUME_LABEL_LEN];
>> +                       __u8 reserved[8];
>> +               } __packed volume_label;
>>                 struct {
>>                         __u8 flags;
>>                         __u8 vendor_guid[16];
>> diff --git a/fs/exfat/file.c b/fs/exfat/file.c
>> index 538d2b6ac2ec..c57d266aae3d 100644
>> --- a/fs/exfat/file.c
>> +++ b/fs/exfat/file.c
>> @@ -12,6 +12,7 @@
>>  #include <linux/security.h>
>>  #include <linux/msdos_fs.h>
>>  #include <linux/writeback.h>
>> +#include "../nls/nls_ucs2_utils.h"
>>
>>  #include "exfat_raw.h"
>>  #include "exfat_fs.h"
>> @@ -486,6 +487,57 @@ static int exfat_ioctl_shutdown(struct super_block *sb, unsigned long arg)
>>         return exfat_force_shutdown(sb, flags);
>>  }
>>
>> +static int exfat_ioctl_get_volume_label(struct super_block *sb, unsigned long arg)
>> +{
>> +       int ret;
>> +       char utf8[FSLABEL_MAX] = {0};
>> +       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>> +       size_t len = UniStrnlen(sbi->volume_label, EXFAT_VOLUME_LABEL_LEN);
>> +
>> +       mutex_lock(&sbi->s_lock);
>> +       ret = utf16s_to_utf8s(sbi->volume_label, len,
>> +                               UTF16_HOST_ENDIAN, utf8, FSLABEL_MAX);
>> +       mutex_unlock(&sbi->s_lock);
>> +
>> +       if (ret < 0)
>> +               return ret;
>> +
>> +       if (copy_to_user((char __user *)arg, utf8, FSLABEL_MAX))
>> +               return -EFAULT;
>> +
>> +       return 0;
>> +}
>> +
>> +static int exfat_ioctl_set_volume_label(struct super_block *sb, unsigned long arg)
>> +{
>> +       int ret = 0;
>> +       char utf8[FSLABEL_MAX];
>> +       size_t len;
>> +       unsigned short utf16[EXFAT_VOLUME_LABEL_LEN] = {0};
>> +       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>> +
>> +       if (!capable(CAP_SYS_ADMIN))
>> +               return -EPERM;
>> +
>> +       if (copy_from_user(utf8, (char __user *)arg, FSLABEL_MAX))
>> +               return -EFAULT;
>> +
>> +       len = strnlen(utf8, FSLABEL_MAX);
>> +       if (len > EXFAT_VOLUME_LABEL_LEN)
> Is FSLABEL_MAX in bytes or the number of characters ?
>
the definition mentions chars, and everywhere else it's used it's in
terms of chars, so I'd say it's in terms of bytes. The
FS_IOC_{GET,SET}FSLABEL ioctls are in terms of char[FSLABEL_MAX], so
I think it's reasonable to use it as a number of bytes.

>> +               exfat_info(sb, "Volume label length too long, truncating");
>> +
>> +       mutex_lock(&sbi->s_lock);
>> +       ret = utf8s_to_utf16s(utf8, len, UTF16_HOST_ENDIAN, utf16, EXFAT_VOLUME_LABEL_LEN);
>> +       mutex_unlock(&sbi->s_lock);
>> +
>> +       if (ret < 0)
>> +               return ret;
>> +
>> +       memcpy(sbi->volume_label, utf16, sizeof(sbi->volume_label));
>> +
>> +       return exfat_write_volume_label(sb);
>> +}
>> +
>>  long exfat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>  {
>>         struct inode *inode = file_inode(filp);
>> @@ -500,6 +552,10 @@ long exfat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
>>                 return exfat_ioctl_shutdown(inode->i_sb, arg);
>>         case FITRIM:
>>                 return exfat_ioctl_fitrim(inode, arg);
>> +       case FS_IOC_GETFSLABEL:
>> +               return exfat_ioctl_get_volume_label(inode->i_sb, arg);
>> +       case FS_IOC_SETFSLABEL:
>> +               return exfat_ioctl_set_volume_label(inode->i_sb, arg);
>>         default:
>>                 return -ENOTTY;
>>         }
>> diff --git a/fs/exfat/super.c b/fs/exfat/super.c
>> index 8926e63f5bb7..96cd4bb7cb19 100644
>> --- a/fs/exfat/super.c
>> +++ b/fs/exfat/super.c
>> @@ -18,6 +18,7 @@
>>  #include <linux/nls.h>
>>  #include <linux/buffer_head.h>
>>  #include <linux/magic.h>
>> +#include "../nls/nls_ucs2_utils.h"
>>
>>  #include "exfat_raw.h"
>>  #include "exfat_fs.h"
>> @@ -573,6 +574,98 @@ static int exfat_verify_boot_region(struct super_block *sb)
>>         return 0;
>>  }
>>
>> +static int exfat_get_volume_label_ptrs(struct super_block *sb,
>> +                                      struct buffer_head **out_bh,
>> +                                      struct exfat_dentry **out_dentry)
>> +{
>> +       int i;
>> +       unsigned int type;
>> +       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>> +       struct exfat_chain clu;
>> +       struct exfat_dentry *ep;
>> +       struct buffer_head *bh;
>> +
>> +       clu.dir = sbi->root_dir;
>> +       clu.flags = ALLOC_FAT_CHAIN;
>> +
>> +       while (clu.dir != EXFAT_EOF_CLUSTER) {
>> +               for (i = 0; i < sbi->dentries_per_clu; i++) {
>> +                       ep = exfat_get_dentry(sb, &clu, i, &bh);
>> +
>> +                       if (!ep)
>> +                               return -EIO;
>> +
>> +                       type = exfat_get_entry_type(ep);
>> +                       if (type == TYPE_UNUSED) {
>> +                               brelse(bh);
>> +                               return -EIO;
>> +                       }
>> +
>> +                       if (type == TYPE_VOLUME) {
>> +                               *out_bh = bh;
>> +                               *out_dentry = ep;
>> +                               return 0;
>> +                       }
>> +
>> +                       brelse(bh);
>> +               }
>> +
>> +               if (exfat_get_next_cluster(sb, &(clu.dir)))
>> +                       return -EIO;
>> +       }
>> +
>> +       return -EIO;
>> +}
>> +
>> +static int exfat_read_volume_label(struct super_block *sb)
>> +{
>> +       int ret, i;
>> +       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>> +       struct buffer_head *bh;
>> +       struct exfat_dentry *ep;
>> +
>> +       ret = exfat_get_volume_label_ptrs(sb, &bh, &ep);
>> +       if (ret < 0)
>> +               goto cleanup;
>> +
>> +       for (i = 0; i < EXFAT_VOLUME_LABEL_LEN; i++)
>> +               sbi->volume_label[i] = le16_to_cpu(ep->dentry.volume_label.volume_label[i]);
>> +
>> +cleanup:
>> +       if (bh)
>> +               brelse(bh);
>> +
>> +       return ret;
>> +}
>> +
>> +int exfat_write_volume_label(struct super_block *sb)
>> +{
>> +       int ret, i;
>> +       struct exfat_sb_info *sbi = EXFAT_SB(sb);
>> +       struct buffer_head *bh;
>> +       struct exfat_dentry *ep;
>> +
>> +       ret = exfat_get_volume_label_ptrs(sb, &bh, &ep);
>> +       if (ret < 0)
>> +               goto cleanup;
>> +
>> +       mutex_lock(&sbi->s_lock);
>> +       for (i = 0; i < EXFAT_VOLUME_LABEL_LEN; i++)
>> +               ep->dentry.volume_label.volume_label[i] = cpu_to_le16(sbi->volume_label[i]);
>> +
>> +       ep->dentry.volume_label.char_count =
>> +               UniStrnlen(sbi->volume_label, EXFAT_VOLUME_LABEL_LEN);
>> +       mutex_unlock(&sbi->s_lock);
>> +
>> +cleanup:
>> +       if (bh) {
>> +               exfat_update_bh(bh, true);
>> +               brelse(bh);
>> +       }
>> +
>> +       return ret;
>> +}
>> +
>>  /* mount the file system volume */
>>  static int __exfat_fill_super(struct super_block *sb,
>>                 struct exfat_chain *root_clu)
>> @@ -616,6 +709,12 @@ static int __exfat_fill_super(struct super_block *sb,
>>                 goto free_bh;
>>         }
>>
>> +       ret = exfat_read_volume_label(sb);
> It will affect mount time if volume label entry is located at the end.
> So, we can read it in ioctl fslabel as I said above.
Sounds good. I'll incorporate your changes, and those of
yuezhang.mo@sony.com, and submit version 3 of the patch soon.

>> +       if (ret) {
>> +               exfat_err(sb, "failed to read volume label");
>> +               goto free_bh;
>> +       }
>> +
>>         ret = exfat_count_used_clusters(sb, &sbi->used_clusters);
>>         if (ret) {
>>                 exfat_err(sb, "failed to scan clusters");
>> --
>> 2.50.1
>>