Re: [PATCH v2 1/1] exfat: Add support for FS_IOC_{GET,SET}FSLABEL

[Namjae Jeon <linkinjeon@kernel.org>]

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.

>
>         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 ?

> +               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.
> +       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
>