On 8/18/25 21:45, Namjae Jeon wrote:
> 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 */
> 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@xxxxxxxx, 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
>>
