On Sun, Aug 17, 2025 at 9:31 AM Ethan Ferguson <ethan.ferguson@xxxxxxxxxx> 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@xxxxxxxxxx>
>
> ---
> 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 */
>
> 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);
The iocharset specified by the mount option should be used instead of always using utf8.
> + 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)
> + 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);
If the new volume label contains invalid characters, an error should be returned.
Invalid characters are defined at
https://learn.microsoft.com/en-us/windows/win32/fileio/exfat-specification#table-35-invalid-filename-characters
> + 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;
> + }
> +
When formatting a partition, exfatprogs's mkfs will create a label directory
entry regardless of whether the user specifies a label.
However, on Windows or when using other mkfs, no label directory entry
may be created. In this case, if we want to set a volume label, should we
create it with an empty directory entry (TYPE_DELETED or TYPE_UNUSED)?
Should we even allocate a new cluster if there's no empty directory entry?
> + 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);
> + 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
