[PATCH v2 2/2] xfs: add FS_IOC_GETFSUUID ioctl

[Catherine Hoang <catherine.hoang@oracle.com>]

Add a new ioctl to retrieve the UUID of a mounted xfs filesystem. This is a
precursor to adding the SETFSUUID ioctl.

Signed-off-by: Catherine Hoang <catherine.hoang@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
---
 fs/xfs/xfs_ioctl.c | 36 ++++++++++++++++++++++++++++++++++++
 1 file changed, 36 insertions(+)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 1f783e979629..cf77715afe9e 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -1865,6 +1865,39 @@ 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->fsu_len, &fsuuid.fsu_len,
+					sizeof(fsuuid.fsu_len)))
+			return -EFAULT;
+		return 0;
+	}
+
+	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);
+
+	fsuuid.fsu_len = UUID_SIZE;
+	if (copy_to_user(ufsuuid, &fsuuid, sizeof(fsuuid)) ||
+	    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 +2186,9 @@ xfs_file_ioctl(
 		return error;
 	}
 
+	case FS_IOC_GETFSUUID:
+		return xfs_ioctl_getuuid(mp, arg);
+
 	default:
 		return -ENOTTY;
 	}
-- 
2.25.1