[PATCH v1 0/2] porting the GETFSUUID ioctl to xfs

[PATCH v1 0/2] porting the GETFSUUID ioctl to xfs

[Catherine Hoang]

Hi all,

This patch aims to hoist the ext4 get/set ioctls to the VFS so we have a
common interface for tools such as coreutils. The second patch adds support
for FS_IOC_GETFSUUID in xfs (with FS_IOC_SETFSUUID planned for future patches).
In addition, the new xfs_spaceman fsuuid command uses this ioctl to retrieve
the UUID of a mounted filesystem. 

Comments and feedback appreciated!

Catherine

Catherine Hoang (2):
  fs: hoist get/set UUID ioctls
  xfs: add FS_IOC_GETFSUUID ioctl

 fs/ext4/ext4.h          | 13 ++-----------
 fs/xfs/xfs_ioctl.c      | 32 ++++++++++++++++++++++++++++++++
 include/uapi/linux/fs.h | 11 +++++++++++
 3 files changed, 45 insertions(+), 11 deletions(-)

-- 
2.25.1

[PATCH v1 1/2] fs: hoist get/set UUID ioctls

[Catherine Hoang]

Hoist the EXT4_IOC_[GS]ETFSUUID ioctls so that they can be used by all
filesystems. This allows us to have a common interface for tools such as
coreutils.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
---
 fs/ext4/ext4.h          | 13 ++-----------
 include/uapi/linux/fs.h | 11 +++++++++++
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 8d5453852f98..b200302a3732 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -722,8 +722,8 @@ enum {
 #define EXT4_IOC_GETSTATE		_IOW('f', 41, __u32)
 #define EXT4_IOC_GET_ES_CACHE		_IOWR('f', 42, struct fiemap)
 #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
-#define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
-#define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
+#define EXT4_IOC_GETFSUUID		FS_IOC_GETFSUUID
+#define EXT4_IOC_SETFSUUID		FS_IOC_SETFSUUID
 
 #define EXT4_IOC_SHUTDOWN _IOR ('X', 125, __u32)
 
@@ -753,15 +753,6 @@ enum {
 						EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT | \
 						EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN)
 
-/*
- * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID
- */
-struct fsuuid {
-	__u32       fsu_len;
-	__u32       fsu_flags;
-	__u8        fsu_uuid[];
-};
-
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*
  * ioctl commands in 32 bit emulation
diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
index b7b56871029c..63b925444592 100644
--- a/include/uapi/linux/fs.h
+++ b/include/uapi/linux/fs.h
@@ -121,6 +121,15 @@ struct fsxattr {
 	unsigned char	fsx_pad[8];
 };
 
+/*
+ * Structure for FS_IOC_GETFSUUID/FS_IOC_SETFSUUID
+ */
+struct fsuuid {
+	__u32       fsu_len;
+	__u32       fsu_flags;
+	__u8        fsu_uuid[];
+};
+
 /*
  * Flags for the fsx_xflags field
  */
@@ -215,6 +224,8 @@ struct fsxattr {
 #define FS_IOC_FSSETXATTR		_IOW('X', 32, struct fsxattr)
 #define FS_IOC_GETFSLABEL		_IOR(0x94, 49, char[FSLABEL_MAX])
 #define FS_IOC_SETFSLABEL		_IOW(0x94, 50, char[FSLABEL_MAX])
+#define FS_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
+#define FS_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
 
 /*
  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
-- 
2.25.1

[PATCH v1 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Catherine Hoang]

Add a new ioctl to retrieve the UUID of a mounted xfs filesystem.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
---
 fs/xfs/xfs_ioctl.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 1f783e979629..657fe058dfba 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1865,6 +1865,35 @@ xfs_fs_eofblocks_from_user(
 	return 0;
 }
 
+static int xfs_ioctl_getuuid(
+	struct xfs_mount	*mp,
+	struct fsuuid __user	*ufsuuid)
+{
+	struct fsuuid		fsuuid;
+	__u8			uuid[UUID_SIZE];
+
+	if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
+		return -EFAULT;
+
+	if (fsuuid.fsu_len == 0) {
+		fsuuid.fsu_len = UUID_SIZE;
+		if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid.fsu_len)))
+			return -EFAULT;
+		return -EINVAL;
+	}
+
+	if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
+		return -EINVAL;
+
+	spin_lock(&mp->m_sb_lock);
+	memcpy(uuid, &mp->m_sb.sb_uuid, UUID_SIZE);
+	spin_unlock(&mp->m_sb_lock);
+
+	if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
+		return -EFAULT;
+	return 0;
+}
+
 /*
  * These long-unused ioctls were removed from the official ioctl API in 5.17,
  * but retain these definitions so that we can log warnings about them.
@@ -2153,6 +2182,9 @@ xfs_file_ioctl(
 		return error;
 	}
 
+	case FS_IOC_GETFSUUID:
+		return xfs_ioctl_getuuid(mp, arg);
+
 	default:
 		return -ENOTTY;
 	}
-- 
2.25.1

Re: [PATCH v1 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Darrick J. Wong]

On Wed, Nov 09, 2022 at 02:19:59PM -0800, Catherine Hoang wrote:
> Add a new ioctl to retrieve the UUID of a mounted xfs filesystem.

I think it's worth mentioning that this is the precursor to trying to
implement SETFSUUID... but that's something for a future series, since
changing the uuid will upset the log, and we have to figure out how to
deal with that gracefully.

> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> ---
>  fs/xfs/xfs_ioctl.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 1f783e979629..657fe058dfba 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1865,6 +1865,35 @@ xfs_fs_eofblocks_from_user(
>  	return 0;
>  }
>  
> +static int xfs_ioctl_getuuid(

Nit: function names should start on a new line.

> +	struct xfs_mount	*mp,
> +	struct fsuuid __user	*ufsuuid)
> +{
> +	struct fsuuid		fsuuid;
> +	__u8			uuid[UUID_SIZE];
> +
> +	if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
> +		return -EFAULT;
> +
> +	if (fsuuid.fsu_len == 0) {
> +		fsuuid.fsu_len = UUID_SIZE;
> +		if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid.fsu_len)))
> +			return -EFAULT;
> +		return -EINVAL;

Ted and I were looking through the ext4_ioctl_getuuid function on this
morning's ext4 concall, and we decided that copying the desired uuid
buffer length out to userspace shouldn't result in an EINVAL return
here...

> +	}
> +
> +	if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)

...and that we shouldn't reject the case where fsu_len > UUID_SIZE.
Instead, we should copy the uuid and update the caller's fsu_len to
reflect however many bytes we copied out.  I'll send patches to do that
shortly.

> +		return -EINVAL;
> +
> +	spin_lock(&mp->m_sb_lock);
> +	memcpy(uuid, &mp->m_sb.sb_uuid, UUID_SIZE);
> +	spin_unlock(&mp->m_sb_lock);
> +
> +	if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
> +		return -EFAULT;

The rest of this logic looks correct to me.  Thanks for getting this out
there.

--D

> +	return 0;
> +}
> +
>  /*
>   * These long-unused ioctls were removed from the official ioctl API in 5.17,
>   * but retain these definitions so that we can log warnings about them.
> @@ -2153,6 +2182,9 @@ xfs_file_ioctl(
>  		return error;
>  	}
>  
> +	case FS_IOC_GETFSUUID:
> +		return xfs_ioctl_getuuid(mp, arg);
> +
>  	default:
>  		return -ENOTTY;
>  	}
> -- 
> 2.25.1
> 

Re: [PATCH v1 1/2] fs: hoist get/set UUID ioctls

[Darrick J. Wong]

On Wed, Nov 09, 2022 at 02:19:58PM -0800, Catherine Hoang wrote:
> Hoist the EXT4_IOC_[GS]ETFSUUID ioctls so that they can be used by all
> filesystems. This allows us to have a common interface for tools such as
> coreutils.
> 
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>

Looks good,
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

Also, for the inevitable v2 patchset after we sort out some weird bugs
in the ext4 implementation of this, can you please cc
linux-ext4@vger.kernel.org?

--D

> ---
>  fs/ext4/ext4.h          | 13 ++-----------
>  include/uapi/linux/fs.h | 11 +++++++++++
>  2 files changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8d5453852f98..b200302a3732 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -722,8 +722,8 @@ enum {
>  #define EXT4_IOC_GETSTATE		_IOW('f', 41, __u32)
>  #define EXT4_IOC_GET_ES_CACHE		_IOWR('f', 42, struct fiemap)
>  #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
> -#define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
> -#define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GETFSUUID		FS_IOC_GETFSUUID
> +#define EXT4_IOC_SETFSUUID		FS_IOC_SETFSUUID
>  
>  #define EXT4_IOC_SHUTDOWN _IOR ('X', 125, __u32)
>  
> @@ -753,15 +753,6 @@ enum {
>  						EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT | \
>  						EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN)
>  
> -/*
> - * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID
> - */
> -struct fsuuid {
> -	__u32       fsu_len;
> -	__u32       fsu_flags;
> -	__u8        fsu_uuid[];
> -};
> -
>  #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
>  /*
>   * ioctl commands in 32 bit emulation
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index b7b56871029c..63b925444592 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -121,6 +121,15 @@ struct fsxattr {
>  	unsigned char	fsx_pad[8];
>  };
>  
> +/*
> + * Structure for FS_IOC_GETFSUUID/FS_IOC_SETFSUUID
> + */
> +struct fsuuid {
> +	__u32       fsu_len;
> +	__u32       fsu_flags;
> +	__u8        fsu_uuid[];
> +};
> +
>  /*
>   * Flags for the fsx_xflags field
>   */
> @@ -215,6 +224,8 @@ struct fsxattr {
>  #define FS_IOC_FSSETXATTR		_IOW('X', 32, struct fsxattr)
>  #define FS_IOC_GETFSLABEL		_IOR(0x94, 49, char[FSLABEL_MAX])
>  #define FS_IOC_SETFSLABEL		_IOW(0x94, 50, char[FSLABEL_MAX])
> +#define FS_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
> +#define FS_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
>  
>  /*
>   * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
> -- 
> 2.25.1
> 

Re: [PATCH v1 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Catherine Hoang]

> On Nov 10, 2022, at 12:05 PM, Darrick J. Wong <djwong@kernel.org> wrote:
> 
> On Wed, Nov 09, 2022 at 02:19:59PM -0800, Catherine Hoang wrote:
>> Add a new ioctl to retrieve the UUID of a mounted xfs filesystem.
> 
> I think it's worth mentioning that this is the precursor to trying to
> implement SETFSUUID... but that's something for a future series, since
> changing the uuid will upset the log, and we have to figure out how to
> deal with that gracefully.
> 
>> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
>> ---
>> fs/xfs/xfs_ioctl.c | 32 ++++++++++++++++++++++++++++++++
>> 1 file changed, 32 insertions(+)
>> 
>> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
>> index 1f783e979629..657fe058dfba 100644
>> --- a/fs/xfs/xfs_ioctl.c
>> +++ b/fs/xfs/xfs_ioctl.c
>> @@ -1865,6 +1865,35 @@ xfs_fs_eofblocks_from_user(
>> 	return 0;
>> }
>> 
>> +static int xfs_ioctl_getuuid(
> 
> Nit: function names should start on a new line.
> 
Ok, will fix that
>> +	struct xfs_mount	*mp,
>> +	struct fsuuid __user	*ufsuuid)
>> +{
>> +	struct fsuuid		fsuuid;
>> +	__u8			uuid[UUID_SIZE];
>> +
>> +	if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
>> +		return -EFAULT;
>> +
>> +	if (fsuuid.fsu_len == 0) {
>> +		fsuuid.fsu_len = UUID_SIZE;
>> +		if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid.fsu_len)))
>> +			return -EFAULT;
>> +		return -EINVAL;
> 
> Ted and I were looking through the ext4_ioctl_getuuid function on this
> morning's ext4 concall, and we decided that copying the desired uuid
> buffer length out to userspace shouldn't result in an EINVAL return
> here...
> 
>> +	}
>> +
>> +	if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
> 
> ...and that we shouldn't reject the case where fsu_len > UUID_SIZE.
> Instead, we should copy the uuid and update the caller's fsu_len to
> reflect however many bytes we copied out.  I'll send patches to do that
> shortly.

Ok, that makes sense. I’ll apply those changes over to xfs. Thanks!
> 
>> +		return -EINVAL;
>> +
>> +	spin_lock(&mp->m_sb_lock);
>> +	memcpy(uuid, &mp->m_sb.sb_uuid, UUID_SIZE);
>> +	spin_unlock(&mp->m_sb_lock);
>> +
>> +	if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
>> +		return -EFAULT;
> 
> The rest of this logic looks correct to me.  Thanks for getting this out
> there.
> 
> --D
> 
>> +	return 0;
>> +}
>> +
>> /*
>>  * These long-unused ioctls were removed from the official ioctl API in 5.17,
>>  * but retain these definitions so that we can log warnings about them.
>> @@ -2153,6 +2182,9 @@ xfs_file_ioctl(
>> 		return error;
>> 	}
>> 
>> +	case FS_IOC_GETFSUUID:
>> +		return xfs_ioctl_getuuid(mp, arg);
>> +
>> 	default:
>> 		return -ENOTTY;
>> 	}
>> -- 
>> 2.25.1

Re: [PATCH v1 1/2] fs: hoist get/set UUID ioctls

[Catherine Hoang]

> On Nov 10, 2022, at 12:06 PM, Darrick J. Wong <djwong@kernel.org> wrote:
> 
> On Wed, Nov 09, 2022 at 02:19:58PM -0800, Catherine Hoang wrote:
>> Hoist the EXT4_IOC_[GS]ETFSUUID ioctls so that they can be used by all
>> filesystems. This allows us to have a common interface for tools such as
>> coreutils.
>> 
>> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
> 
> Looks good,
> Reviewed-by: Darrick J. Wong <djwong@kernel.org>
> 
> Also, for the inevitable v2 patchset after we sort out some weird bugs
> in the ext4 implementation of this, can you please cc
> linux-ext4@vger.kernel.org?

Thanks for reviewing! And sure, I’ll cc them in the next version
> 
> --D
> 
>> ---
>> fs/ext4/ext4.h          | 13 ++-----------
>> include/uapi/linux/fs.h | 11 +++++++++++
>> 2 files changed, 13 insertions(+), 11 deletions(-)
>> 
>> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
>> index 8d5453852f98..b200302a3732 100644
>> --- a/fs/ext4/ext4.h
>> +++ b/fs/ext4/ext4.h
>> @@ -722,8 +722,8 @@ enum {
>> #define EXT4_IOC_GETSTATE		_IOW('f', 41, __u32)
>> #define EXT4_IOC_GET_ES_CACHE		_IOWR('f', 42, struct fiemap)
>> #define EXT4_IOC_CHECKPOINT		_IOW('f', 43, __u32)
>> -#define EXT4_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
>> -#define EXT4_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
>> +#define EXT4_IOC_GETFSUUID		FS_IOC_GETFSUUID
>> +#define EXT4_IOC_SETFSUUID		FS_IOC_SETFSUUID
>> 
>> #define EXT4_IOC_SHUTDOWN _IOR ('X', 125, __u32)
>> 
>> @@ -753,15 +753,6 @@ enum {
>> 						EXT4_IOC_CHECKPOINT_FLAG_ZEROOUT | \
>> 						EXT4_IOC_CHECKPOINT_FLAG_DRY_RUN)
>> 
>> -/*
>> - * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID
>> - */
>> -struct fsuuid {
>> -	__u32       fsu_len;
>> -	__u32       fsu_flags;
>> -	__u8        fsu_uuid[];
>> -};
>> -
>> #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
>> /*
>>  * ioctl commands in 32 bit emulation
>> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
>> index b7b56871029c..63b925444592 100644
>> --- a/include/uapi/linux/fs.h
>> +++ b/include/uapi/linux/fs.h
>> @@ -121,6 +121,15 @@ struct fsxattr {
>> 	unsigned char	fsx_pad[8];
>> };
>> 
>> +/*
>> + * Structure for FS_IOC_GETFSUUID/FS_IOC_SETFSUUID
>> + */
>> +struct fsuuid {
>> +	__u32       fsu_len;
>> +	__u32       fsu_flags;
>> +	__u8        fsu_uuid[];
>> +};
>> +
>> /*
>>  * Flags for the fsx_xflags field
>>  */
>> @@ -215,6 +224,8 @@ struct fsxattr {
>> #define FS_IOC_FSSETXATTR		_IOW('X', 32, struct fsxattr)
>> #define FS_IOC_GETFSLABEL		_IOR(0x94, 49, char[FSLABEL_MAX])
>> #define FS_IOC_SETFSLABEL		_IOW(0x94, 50, char[FSLABEL_MAX])
>> +#define FS_IOC_GETFSUUID		_IOR('f', 44, struct fsuuid)
>> +#define FS_IOC_SETFSUUID		_IOW('f', 44, struct fsuuid)
>> 
>> /*
>>  * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)
>> -- 
>> 2.25.1
>> 

Re: [PATCH v1 1/2] fs: hoist get/set UUID ioctls

[Allison Henderson]

On Wed, 2022-11-09 at 14:19 -0800, Catherine Hoang wrote:
> Hoist the EXT4_IOC_[GS]ETFSUUID ioctls so that they can be used by
> all
> filesystems. This allows us to have a common interface for tools such
> as
> coreutils.
> 
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>

Looks straight forward to me
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
> ---
>  fs/ext4/ext4.h          | 13 ++-----------
>  include/uapi/linux/fs.h | 11 +++++++++++
>  2 files changed, 13 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 8d5453852f98..b200302a3732 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -722,8 +722,8 @@ enum {
>  #define EXT4_IOC_GETSTATE              _IOW('f', 41, __u32)
>  #define EXT4_IOC_GET_ES_CACHE          _IOWR('f', 42, struct fiemap)
>  #define EXT4_IOC_CHECKPOINT            _IOW('f', 43, __u32)
> -#define EXT4_IOC_GETFSUUID             _IOR('f', 44, struct fsuuid)
> -#define EXT4_IOC_SETFSUUID             _IOW('f', 44, struct fsuuid)
> +#define EXT4_IOC_GETFSUUID             FS_IOC_GETFSUUID
> +#define EXT4_IOC_SETFSUUID             FS_IOC_SETFSUUID
>  
>  #define EXT4_IOC_SHUTDOWN _IOR ('X', 125, __u32)
>  
> @@ -753,15 +753,6 @@ enum {
>                                                 EXT4_IOC_CHECKPOINT_F
> LAG_ZEROOUT | \
>                                                 EXT4_IOC_CHECKPOINT_F
> LAG_DRY_RUN)
>  
> -/*
> - * Structure for EXT4_IOC_GETFSUUID/EXT4_IOC_SETFSUUID
> - */
> -struct fsuuid {
> -       __u32       fsu_len;
> -       __u32       fsu_flags;
> -       __u8        fsu_uuid[];
> -};
> -
>  #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
>  /*
>   * ioctl commands in 32 bit emulation
> diff --git a/include/uapi/linux/fs.h b/include/uapi/linux/fs.h
> index b7b56871029c..63b925444592 100644
> --- a/include/uapi/linux/fs.h
> +++ b/include/uapi/linux/fs.h
> @@ -121,6 +121,15 @@ struct fsxattr {
>         unsigned char   fsx_pad[8];
>  };
>  
> +/*
> + * Structure for FS_IOC_GETFSUUID/FS_IOC_SETFSUUID
> + */
> +struct fsuuid {
> +       __u32       fsu_len;
> +       __u32       fsu_flags;
> +       __u8        fsu_uuid[];
> +};
> +
>  /*
>   * Flags for the fsx_xflags field
>   */
> @@ -215,6 +224,8 @@ struct fsxattr {
>  #define FS_IOC_FSSETXATTR              _IOW('X', 32, struct fsxattr)
>  #define FS_IOC_GETFSLABEL              _IOR(0x94, 49,
> char[FSLABEL_MAX])
>  #define FS_IOC_SETFSLABEL              _IOW(0x94, 50,
> char[FSLABEL_MAX])
> +#define FS_IOC_GETFSUUID               _IOR('f', 44, struct fsuuid)
> +#define FS_IOC_SETFSUUID               _IOW('f', 44, struct fsuuid)
>  
>  /*
>   * Inode flags (FS_IOC_GETFLAGS / FS_IOC_SETFLAGS)

Re: [PATCH v1 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Allison Henderson]

On Wed, 2022-11-09 at 14:19 -0800, Catherine Hoang wrote:
> Add a new ioctl to retrieve the UUID of a mounted xfs filesystem.
> 
> Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>

With Darricks commentary addressed, I think this one looks good
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
> ---
>  fs/xfs/xfs_ioctl.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 1f783e979629..657fe058dfba 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1865,6 +1865,35 @@ xfs_fs_eofblocks_from_user(
>         return 0;
>  }
>  
> +static int xfs_ioctl_getuuid(
> +       struct xfs_mount        *mp,
> +       struct fsuuid __user    *ufsuuid)
> +{
> +       struct fsuuid           fsuuid;
> +       __u8                    uuid[UUID_SIZE];
> +
> +       if (copy_from_user(&fsuuid, ufsuuid, sizeof(fsuuid)))
> +               return -EFAULT;
> +
> +       if (fsuuid.fsu_len == 0) {
> +               fsuuid.fsu_len = UUID_SIZE;
> +               if (copy_to_user(ufsuuid, &fsuuid,
> sizeof(fsuuid.fsu_len)))
> +                       return -EFAULT;
> +               return -EINVAL;
> +       }
> +
> +       if (fsuuid.fsu_len != UUID_SIZE || fsuuid.fsu_flags != 0)
> +               return -EINVAL;
> +
> +       spin_lock(&mp->m_sb_lock);
> +       memcpy(uuid, &mp->m_sb.sb_uuid, UUID_SIZE);
> +       spin_unlock(&mp->m_sb_lock);
> +
> +       if (copy_to_user(&ufsuuid->fsu_uuid[0], uuid, UUID_SIZE))
> +               return -EFAULT;
> +       return 0;
> +}
> +
>  /*
>   * These long-unused ioctls were removed from the official ioctl API
> in 5.17,
>   * but retain these definitions so that we can log warnings about
> them.
> @@ -2153,6 +2182,9 @@ xfs_file_ioctl(
>                 return error;
>         }
>  
> +       case FS_IOC_GETFSUUID:
> +               return xfs_ioctl_getuuid(mp, arg);
> +
>         default:
>                 return -ENOTTY;
>         }