Message-Id: <20250821150926.1025302-2-ethan.ferguson@zetier.com>
Date: Thu, 21 Aug 2025 11:09:26 -0400
From: Ethan Ferguson <ethan.ferguson@...ier.com>
To: linkinjeon@...nel.org,
	sj1557.seo@...sung.com,
	yuezhang.mo@...y.com
Cc: linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Ethan Ferguson <ethan.ferguson@...ier.com>
Subject: [PATCH v3 1/1] exfat: Add support for FS_IOC_{GET,SET}FSLABEL

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@...ier.com>

Lazy label loading, better char conversion
---
 fs/exfat/exfat_fs.h  |   3 +
 fs/exfat/exfat_raw.h |   6 ++
 fs/exfat/file.c      |  78 ++++++++++++++++++
 fs/exfat/super.c     | 190 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 277 insertions(+)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index f8ead4d47ef0..19b8524e5b7d 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; /* volume name */
 
 	unsigned int clu_srch_ptr; /* cluster search pointer */
 	unsigned int used_clusters; /* number of used clusters */
@@ -431,6 +432,8 @@ 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_read_volume_label(struct super_block *sb);
+int exfat_write_volume_label(struct super_block *sb, struct exfat_uni_name *uniname);
 
 /* 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..4082fa7b8c14 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; /* volume label directory entry */
 		struct {
 			__u8 flags;
 			__u8 vendor_guid[16];
diff --git a/fs/exfat/file.c b/fs/exfat/file.c
index 538d2b6ac2ec..12c8ae450193 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 +487,79 @@ 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_uni_name *uniname;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+
+	uniname = kmalloc(sizeof(struct exfat_uni_name), GFP_KERNEL);
+	if (!uniname)
+		return -ENOMEM;
+
+	ret = exfat_read_volume_label(sb);
+	if (ret < 0)
+		goto cleanup;
+
+	memcpy(uniname->name, sbi->volume_label,
+	       EXFAT_VOLUME_LABEL_LEN * sizeof(short));
+	uniname->name[EXFAT_VOLUME_LABEL_LEN] = 0x0000;
+	uniname->name_len = UniStrnlen(uniname->name, EXFAT_VOLUME_LABEL_LEN);
+
+	ret = exfat_utf16_to_nls(sb, uniname, utf8, FSLABEL_MAX);
+
+	if (copy_to_user((char __user *)arg, utf8, FSLABEL_MAX)) {
+		ret = -EFAULT;
+		goto cleanup;
+	}
+
+cleanup:
+	kfree(uniname);
+	return 0;
+}
+
+static int exfat_ioctl_set_volume_label(struct super_block *sb, unsigned long arg)
+{
+	int ret, lossy;
+	char utf8[FSLABEL_MAX];
+	struct exfat_uni_name *uniname;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	uniname = kmalloc(sizeof(struct exfat_uni_name), GFP_KERNEL);
+	if (!uniname)
+		return -ENOMEM;
+
+	if (copy_from_user(utf8, (char __user *)arg, FSLABEL_MAX)) {
+		ret = -EFAULT;
+		goto cleanup;
+	}
+
+	if (utf8[0]) {
+		exfat_nls_to_utf16(sb, utf8, strnlen(utf8, FSLABEL_MAX), uniname, &lossy);
+		if (lossy & NLS_NAME_LOSSY) {
+			ret = -EINVAL;
+			goto cleanup;
+		}
+	} else {
+		uniname->name[0] = 0x0000;
+		uniname->name_len = 0;
+	}
+
+	if (uniname->name_len > EXFAT_VOLUME_LABEL_LEN) {
+		exfat_info(sb, "Volume label length too long, truncating");
+		uniname->name_len = EXFAT_VOLUME_LABEL_LEN;
+	}
+
+	ret = exfat_write_volume_label(sb, uniname);
+
+cleanup:
+	kfree(uniname);
+	return ret;
+}
+
 long exfat_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -500,6 +574,10 @@ 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..7aee6ea594d8 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 +574,194 @@ 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,
+				       bool find_new)
+{
+	int i, ret;
+	unsigned int type;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct exfat_chain clu;
+	struct exfat_dentry *ep, *deleted_ep = NULL;
+	struct buffer_head *bh, *deleted_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) {
+				ret = -EIO;
+				goto end;
+			}
+
+			type = exfat_get_entry_type(ep);
+			if (type == TYPE_DELETED && !deleted_ep && find_new) {
+				deleted_ep = ep;
+				deleted_bh = bh;
+				continue;
+			}
+
+			if (type == TYPE_UNUSED) {
+				if (find_new) {
+					brelse(bh);
+					ret = -ENOENT;
+					goto end;
+				}
+
+				if (deleted_ep) {
+					brelse(bh);
+					goto end;
+				}
+
+				// Last dentry in cluster
+				if (i == sbi->dentries_per_clu - 1) {
+					// TODO allocate new cluster
+					brelse(bh);
+					ret = -ENOSPC;
+					goto end;
+				}
+
+				deleted_ep = ep;
+				deleted_bh = bh;
+
+				ep = exfat_get_dentry(sb, &clu, i + 1, &bh);
+				memset(ep, 0, sizeof(struct exfat_dentry));
+				ep->type = EXFAT_UNUSED;
+				exfat_update_bh(bh, true);
+				brelse(bh);
+
+				goto end;
+			}
+
+			if (type == TYPE_VOLUME) {
+				*out_bh = bh;
+				*out_dentry = ep;
+
+				if (deleted_ep)
+					brelse(deleted_bh);
+
+				return 0;
+			}
+
+			brelse(bh);
+		}
+
+		if (exfat_get_next_cluster(sb, &(clu.dir))) {
+			ret = -EIO;
+			goto end;
+		}
+	}
+
+end:
+	if (deleted_ep) {
+		*out_bh = deleted_bh;
+		*out_dentry = deleted_ep;
+		memset((*out_dentry), 0, sizeof(struct exfat_dentry));
+		(*out_dentry)->type = EXFAT_VOLUME;
+		return 0;
+	}
+
+	*out_bh = NULL;
+	*out_dentry = NULL;
+	return ret;
+}
+
+static int exfat_alloc_volume_label(struct super_block *sb)
+{
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+
+	if (sbi->volume_label)
+		return 0;
+
+	sbi->volume_label = kcalloc(EXFAT_VOLUME_LABEL_LEN,
+						     sizeof(short), GFP_KERNEL);
+	if (!sbi->volume_label)
+		return -ENOMEM;
+
+	return 0;
+}
+
+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, false);
+	// ENOENT signifies that a volume label dentry, doesn't exist
+	// We will treat this as an empty volume label and not fail.
+	if (ret < 0 && ret != -ENOENT)
+		goto cleanup;
+
+	ret = exfat_alloc_volume_label(sb);
+	if (ret < 0)
+		goto cleanup;
+
+	mutex_lock(&sbi->s_lock);
+	for (i = 0; i < EXFAT_VOLUME_LABEL_LEN; i++)
+		sbi->volume_label[i] = le16_to_cpu(ep->dentry.volume_label.volume_label[i]);
+	mutex_unlock(&sbi->s_lock);
+
+	ret = 0;
+
+cleanup:
+	if (bh)
+		brelse(bh);
+
+	return ret;
+}
+
+int exfat_write_volume_label(struct super_block *sb,
+			     struct exfat_uni_name *uniname)
+{
+	int ret, i;
+	struct exfat_sb_info *sbi = EXFAT_SB(sb);
+	struct buffer_head *bh;
+	struct exfat_dentry *ep;
+
+	if (uniname->name_len > EXFAT_VOLUME_LABEL_LEN) {
+		ret = -EINVAL;
+		goto cleanup;
+	}
+
+	ret = exfat_get_volume_label_ptrs(sb, &bh, &ep, true);
+	if (ret < 0)
+		goto cleanup;
+
+	ret = exfat_alloc_volume_label(sb);
+	if (ret < 0)
+		goto cleanup;
+
+	memcpy(sbi->volume_label, uniname->name,
+	       uniname->name_len * sizeof(short));
+
+	mutex_lock(&sbi->s_lock);
+	for (i = 0; i < uniname->name_len; i++)
+		ep->dentry.volume_label.volume_label[i] =
+			cpu_to_le16(sbi->volume_label[i]);
+	// Fill the rest of the str with 0x0000
+	for (; i < EXFAT_VOLUME_LABEL_LEN; i++)
+		ep->dentry.volume_label.volume_label[i] = 0x0000;
+
+	ep->dentry.volume_label.char_count = uniname->name_len;
+	mutex_unlock(&sbi->s_lock);
+
+	ret = 0;
+
+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)
@@ -791,6 +980,7 @@ static void delayed_free(struct rcu_head *p)
 
 	unload_nls(sbi->nls_io);
 	exfat_free_upcase_table(sbi);
+	kfree(sbi->volume_label);
 	exfat_free_sbi(sbi);
 }
 
-- 
2.34.1

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