Btrfs: get/set label of a mounted file system

With the new ioctl(2) BTRFS_IOC_GET_FSLABEL we can fetch the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 
 	return -ENOTTY;

fs/btrfs/ioctl.h +2 -0

index 731e287..5b2cbef 100644
@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

With the new ioctl(2) BTRFS_IOC_SET_FSLABEL, we can set/change the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>

---
 fs/btrfs/ioctl.c |   39 +++++++++++++++++++++++++++++++++++++++
 fs/btrfs/ioctl.h |    2 ++
 2 files changed, 41 insertions(+)

fs/btrfs/ioctl.c +39 -0

index 6a2488a..99aa812 100644
@@ -3712,6 +3712,43 @@ static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
 	return ret ? -EFAULT : 0;
 }
 
+static int btrfs_ioctl_set_fslabel(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+	struct btrfs_super_block *super_block = root->fs_info->super_copy;
+	struct btrfs_trans_handle *trans;
+	char label[BTRFS_LABEL_SIZE];
+	int ret;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (copy_from_user(label, arg, sizeof(label)))
+		return -EFAULT;
+
+	if (strnlen(label, BTRFS_LABEL_SIZE) == BTRFS_LABEL_SIZE)
+		return -EINVAL;
+
+	ret = mnt_want_write_file(file);
+	if (ret)
+		return ret;
+
+	mutex_lock(&root->fs_info->volume_mutex);
+	trans = btrfs_start_transaction(root, 1);
+	if (IS_ERR(trans)) {
+		ret = PTR_ERR(trans);
+		goto out_unlock;
+	}
+
+	strcpy(super_block->label, label);
+	ret = btrfs_end_transaction(trans, root);
+
+out_unlock:
+	mutex_unlock(&root->fs_info->volume_mutex);
+	mnt_drop_write_file(file);
+	return ret;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3812,6 +3849,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_limit(root, argp);
 	case BTRFS_IOC_GET_FSLABEL:
 		return btrfs_ioctl_get_fslabel(file, argp);
+	case BTRFS_IOC_SET_FSLABEL:
+		return btrfs_ioctl_set_fslabel(file, argp);
 	}
 
 	return -ENOTTY;

fs/btrfs/ioctl.h +2 -0

index 5b2cbef..2abe239 100644
@@ -453,6 +453,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_limit_args)
 #define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
 				   char[BTRFS_LABEL_SIZE])
+#define BTRFS_IOC_SET_FSLABEL _IOW(BTRFS_IOCTL_MAGIC, 50, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

HI Jeff,

Quoted 7 lines · Jeff Liu

With the new ioctl(2) BTRFS_IOC_GET_FSLABEL we can fetch the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>

[...]

fs/btrfs/ioctl.c out: · line 3709

Quoted 8 lines

fs/btrfs/ioctl.c +8 -0

+static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+	const char *label = root->fs_info->super_copy->label;
+	int ret;
+
+	mutex_lock(&root->fs_info->volume_mutex);
+	ret = copy_to_user(arg, label, strlen(label));

Sorry for pointing out my doubt too late, but should we trust super_copy->label ?
An user could insert a usb-key with a btrfs filesystem with a label without zero. In this case strlen() could access outside super_copy->label[].

I think that it should be quite easy to alter artificially a filesystem to crash the kernel. So I not consider this as big problem. However *in case* of a further cycle of this patch I suggest to replace strlen() with strnlen().

Quoted 31 lines

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 
 	return -ENOTTY;

fs/btrfs/ioctl.h +2 -0

index 731e287..5b2cbef 100644
@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

Quoted 15 lines · Goffredo Baroncelli

fs/btrfs/ioctl.c out: · line 3709

Quoted 8 lines · Jeff Liu

fs/btrfs/ioctl.c +8 -0

+static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+	const char *label = root->fs_info->super_copy->label;
+	int ret;
+
+	mutex_lock(&root->fs_info->volume_mutex);
+	ret = copy_to_user(arg, label, strlen(label));

Sorry for pointing out my doubt too late, but should we trust super_copy->label ?
An user could insert a usb-key with a btrfs filesystem with a label without zero. In this case strlen() could access outside super_copy->label[].

Thank you for letting me be aware of this situation.

First of all, if the user set label via btrfs tools, he can not make it length exceeding BTRFS_LABLE_SIZE - 1.

If the user does that through codes wrote by himself like:
btrfslabel.c->set_label_unmounted(), he can do that.
However, it most likely he did that for evil purpose or any other reasons?

Quoted 1 line

Quoted 4 lines

I think that it should be quite easy to alter artificially a filesystem to crash the kernel. So I not consider this as big problem. However *in case* of a further cycle of this patch I suggest to replace strlen() with strnlen().

I don't think we should replace strlen() with strnlen() since it's totally wrong if the length of label is more than BTRFS_LABEL_SIZE -1, we can not just truncating the label and return it in this case. Add BUG_ON(strlen(label) > BTRFS_LABEL_SIZE - 1) is reasonable instead.

Hi Goffredo,

Quoted 11 lines · Goffredo Baroncelli

HI Jeff,

Quoted 7 lines · Jeff Liu

With the new ioctl(2) BTRFS_IOC_GET_FSLABEL we can fetch the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>

[...]

Quoted 14 lines

fs/btrfs/ioctl.c out: · line 3709

Quoted 8 lines

fs/btrfs/ioctl.c +8 -0

+static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+	const char *label = root->fs_info->super_copy->label;
+	int ret;
+
+	mutex_lock(&root->fs_info->volume_mutex);
+	ret = copy_to_user(arg, label, strlen(label));

Sorry for pointing out my doubt too late, but should we trust super_copy->label ?
An user could insert a usb-key with a btrfs filesystem with a label without zero. In this case strlen() could access outside super_copy->label[].

Thank you for letting me be aware of this situation.

First of all, if the user set label via btrfs tools, he can not make it length exceeding BTRFS_LABLE_SIZE - 1.

If the user does that through codes wrote by himself like:
btrfslabel.c->set_label_unmounted(), he can do that.
However, it most likely he did that for evil purpose or any other reasons?

Quoted 5 lines

I think that it should be quite easy to alter artificially a filesystem to crash the kernel. So I not consider this as big problem. However *in case* of a further cycle of this patch I suggest to replace strlen() with strnlen().

I don't think we should replace strlen() with strnlen() since it's totally wrong if the length of label is more than BTRFS_LABEL_SIZE -1, we can not just truncating the label and return it in this case.

Add BUG_ON(strlen(label) > BTRFS_LABEL_SIZE - 1) is reasonable instead.

Thanks,
-Jeff

Quoted 17 lines

Quoted 17 lines

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 

Quoted 16 lines

Quoted 6 lines

fs/btrfs/ioctl.c +0 -0

 	return -ENOTTY;

fs/btrfs/ioctl.h +0 -0

index 731e287..5b2cbef 100644

fs/btrfs/ioctl.h struct btrfs_ioctl_send_args { · line 458

Quoted 8 lines

fs/btrfs/ioctl.h +2 -0

@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

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Quoted 28 lines · Jeff Liu

Hi Goffredo,

Quoted 11 lines · Goffredo Baroncelli

HI Jeff,

Quoted 7 lines · Jeff Liu

With the new ioctl(2) BTRFS_IOC_GET_FSLABEL we can fetch the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>

[...]

Quoted 14 lines

fs/btrfs/ioctl.c out: · line 3709

Quoted 8 lines

fs/btrfs/ioctl.c +8 -0

+static int btrfs_ioctl_get_fslabel(struct file *file, void __user *arg)
+{
+	struct btrfs_root *root = BTRFS_I(fdentry(file)->d_inode)->root;
+	const char *label = root->fs_info->super_copy->label;
+	int ret;
+
+	mutex_lock(&root->fs_info->volume_mutex);
+	ret = copy_to_user(arg, label, strlen(label));

Sorry for pointing out my doubt too late, but should we trust super_copy->label ?
An user could insert a usb-key with a btrfs filesystem with a label without zero. In this case strlen() could access outside super_copy->label[].

Quoted 8 lines

Thank you for letting me be aware of this situation.

First of all, if the user set label via btrfs tools, he can not make it length exceeding BTRFS_LABLE_SIZE - 1.

If the user does that through codes wrote by himself like:
btrfslabel.c->set_label_unmounted(), he can do that.
However, it most likely he did that for evil purpose or any other reasons?

I think the most likely case is the "evil purpose".

Quoted 5 lines

Quoted 5 lines

I think that it should be quite easy to alter artificially a filesystem to crash the kernel. So I not consider this as big problem. However *in case* of a further cycle of this patch I suggest to replace strlen() with strnlen().

Quoted 3 lines

I don't think we should replace strlen() with strnlen() since it's totally wrong if the length of label is more than BTRFS_LABEL_SIZE -1, we can not just truncating the label and return it in this case.

This for me is sufficient, or we could copy all the label buffer, without further check:

copy_to_user(arg, label, BTRFS_LABEL_SIZE)

Quoted 3 lines

Add BUG_ON(strlen(label) > BTRFS_LABEL_SIZE - 1) is reasonable instead.

I agree with Stefan, this is not a correct use of BUG_ON; a warning is sufficient (there is un-correct data read from disk).

Quoted 43 lines

Thanks,
-Jeff

Quoted 17 lines

Quoted 17 lines

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 

Quoted 16 lines

Quoted 6 lines

fs/btrfs/ioctl.c +0 -0

 	return -ENOTTY;

fs/btrfs/ioctl.h +0 -0

index 731e287..5b2cbef 100644

fs/btrfs/ioctl.h struct btrfs_ioctl_send_args { · line 458

Quoted 8 lines

fs/btrfs/ioctl.h +2 -0

@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

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Quoted 1 line · Goffredo Baroncelli

On 12/21/2012 07:42 AM, Jeff Liu wrote:

Quoted 8 lines

Quoted 3 lines

I don't think we should replace strlen() with strnlen() since it's totally wrong if the length of label is more than BTRFS_LABEL_SIZE -1, we can not just truncating the label and return it in this case.

This for me is sufficient, or we could copy all the label buffer, without further check:

copy_to_user(arg, label, BTRFS_LABEL_SIZE)

That sounds ok to me, but it's better to limit the length to be 'BTRFS_LABEL_SIZE - 1' bytes, or else, it would copy 256 bytes back to the user space if the label length is beyond or equal to the array limits.

Quoted 6 lines

Quoted 3 lines

Add BUG_ON(strlen(label) > BTRFS_LABEL_SIZE - 1) is reasonable instead.

I agree with Stefan, this is not a correct use of BUG_ON; a warning is sufficient (there is un-correct data read from disk).

Maybe like following?

size_t len = strlen(label);

if (len > BTRFS_LABEL_SIZE - 1) {
	WARN(1, "btrfs: device label has weird length %zu bytes, "
		     "it will be truncated to %d bytes.\n",
		     len, BTRFS_LABEL_SIZE - 1);

	len = BTRFS_LABEL_SIZE - 1;
}

I'll post a new patch with those changes if no other objections.

Happy Christmas.
-Jeff

Quoted 45 lines

Quoted 43 lines

Thanks,
-Jeff

Quoted 17 lines

Quoted 17 lines

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 

Quoted 16 lines

Quoted 6 lines

fs/btrfs/ioctl.c +0 -0

 	return -ENOTTY;

fs/btrfs/ioctl.h +0 -0

index 731e287..5b2cbef 100644

fs/btrfs/ioctl.h struct btrfs_ioctl_send_args { · line 458

Quoted 8 lines

fs/btrfs/ioctl.h +2 -0

@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

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Hi Jeff,

Quoted 2 lines · Jeff Liu

Quoted 1 line · Goffredo Baroncelli

On 12/21/2012 07:42 AM, Jeff Liu wrote:

[...]

Quoted 11 lines

Quoted 8 lines

Quoted 3 lines

I don't think we should replace strlen() with strnlen() since it's totally wrong if the length of label is more than BTRFS_LABEL_SIZE -1, we can not just truncating the label and return it in this case.

This for me is sufficient, or we could copy all the label buffer, without further check:

copy_to_user(arg, label, BTRFS_LABEL_SIZE)

That sounds ok to me, but it's better to limit the length to be 'BTRFS_LABEL_SIZE - 1' bytes, or else, it would copy 256 bytes back to the user space if the label length is beyond or equal to the array limits.

Sorry I don't understand your reply. The ioctl has as argument an array of BTRFS_LABEL_SIZE characters, so it should not be any problem of page fault (with the exception of an user who passes a shorter array). So it wouldn't be any problem to copy
BTRFS_LABEL_SIZE character, or I am missing something ?

The question is another. Is a kernel responsibility to assure that the returned string is zero terminated ? If yes (and I think so) we should truncate the string before the copy:

	label[BTRFS_LABEL_SIZE-1] = 0;
	copy_to_user(arg, label, BTRFS_LABEL_SIZE);

Quoted 10 lines

Quoted 7 lines

Quoted 4 lines

Add BUG_ON(strlen(label) > BTRFS_LABEL_SIZE - 1) is reasonable instead.

I agree with Stefan, this is not a correct use of BUG_ON; a warning is sufficient (there is un-correct data read from disk).

Maybe like following?

size_t len = strlen(label);

If label (who is an array read from the disk) is not zero terminated, this would lead to a possible page fault. I suggest to use strnlen() or similar.

Quoted 7 lines

if (len > BTRFS_LABEL_SIZE - 1) {
WARN(1, "btrfs: device label has weird length %zu bytes, "
"it will be truncated to %d bytes.\n", len, BTRFS_LABEL_SIZE - 1);

Quoted 2 lines

	len = BTRFS_LABEL_SIZE - 1;
}

As message I suggest:

WARN(1, "btrfs: device label is not zero terminated, it will be truncated to %d bytes.\n",

			BTRFS_LABEL-1 );

NOTE: it is suggested to not span the string on more lines, to help searching in the source a messages with grep. It is an exception of the rule of the max 80 columns text width.

Happy Christmas you too
GB

Quoted 52 lines

I'll post a new patch with those changes if no other objections.

Happy Christmas.
-Jeff

Quoted 45 lines

Quoted 43 lines

Thanks,
-Jeff

Quoted 17 lines

Quoted 17 lines

fs/btrfs/ioctl.c +7 -0

+	mutex_unlock(&root->fs_info->volume_mutex);
+
+	return ret ? -EFAULT : 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {

@@ -3797,6 +3810,8 @@ long btrfs_ioctl(struct file *file, unsigned int
 		return btrfs_ioctl_qgroup_create(root, argp);
 	case BTRFS_IOC_QGROUP_LIMIT:
 		return btrfs_ioctl_qgroup_limit(root, argp);
+	case BTRFS_IOC_GET_FSLABEL:
+		return btrfs_ioctl_get_fslabel(file, argp);
 	}
 

Quoted 16 lines

Quoted 6 lines

fs/btrfs/ioctl.c +0 -0

 	return -ENOTTY;

fs/btrfs/ioctl.h +0 -0

index 731e287..5b2cbef 100644

fs/btrfs/ioctl.h struct btrfs_ioctl_send_args { · line 458

Quoted 8 lines

fs/btrfs/ioctl.h +2 -0

@@ -451,6 +451,8 @@ struct btrfs_ioctl_send_args {
 			       struct btrfs_ioctl_qgroup_create_args)
 #define BTRFS_IOC_QGROUP_LIMIT _IOR(BTRFS_IOCTL_MAGIC, 43, \
 			       struct btrfs_ioctl_qgroup_limit_args)
+#define BTRFS_IOC_GET_FSLABEL _IOR(BTRFS_IOCTL_MAGIC, 49, \
+				   char[BTRFS_LABEL_SIZE])
 #define BTRFS_IOC_GET_DEV_STATS _IOWR(BTRFS_IOCTL_MAGIC, 52, \
 				      struct btrfs_ioctl_get_dev_stats)
 #endif

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With the new ioctl(2) BTRFS_IOC_SET_FSLABEL, we can set/change the label of a mounted file system.

Signed-off-by Jie Liu <[email protected]>

Signed-off-by Anand Jain <[email protected]>

Cc Miao Xie <[email protected]>

Cc Goffredo Baroncelli <[email protected]>

Cc David Sterba <[email protected]>