[PATCH 3/4] xfs: implement online get/set fs label

[Eric Sandeen <sandeen@xxxxxxxxxxx>]

Wire up label ioctls for XFS.

Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
---

This is where the implementation questions come in;
is using growlock an abomination?  How can I make the
primary super change immediately visible?

 fs/xfs/xfs_ioctl.c |   62 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 files changed, 62 insertions(+), 0 deletions(-)

diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index dbca737..ab59213 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -41,6 +41,8 @@
 #include "xfs_trans.h"
 #include "xfs_pnfs.h"
 #include "xfs_acl.h"
+#include "xfs_log.h"
+#include "xfs_sb.h"
 
 #include <linux/capability.h>
 #include <linux/dcache.h>
@@ -1603,6 +1605,62 @@ xfs_ioc_swapext(
        return error;
 }
 
+static int
+xfs_ioc_getlabel(
+       struct xfs_mount        *mp,
+       char                    __user *label)
+{
+       int                     error = 0;
+       struct xfs_sb           *sbp = &mp->m_sb;
+
+       if (!mutex_trylock(&mp->m_growlock))
+               return -EWOULDBLOCK;
+       if (copy_to_user(label, sbp->sb_fname, sizeof(sbp->sb_fname)))
+               error = -EFAULT;
+       mutex_unlock(&mp->m_growlock);
+       return error;
+}
+
+static int
+xfs_ioc_setlabel(
+       struct file             *filp,
+       struct xfs_mount        *mp,
+       char                    __user *newlabel)
+{
+       int                     error;
+       struct xfs_sb           *sbp = &mp->m_sb;
+       char                    sb_fname[12];
+
+       if (!capable(CAP_SYS_ADMIN))
+               return -EPERM;
+
+       if (copy_from_user(sb_fname, newlabel, sizeof(sb_fname)))
+               return -EFAULT;
+
+       error = mnt_want_write_file(filp);
+       if (error)
+               return error;
+
+       /* growfs & label both muck w/ the super directly... */
+       if (!mutex_trylock(&mp->m_growlock))
+               return -EWOULDBLOCK;
+       memset(sbp->sb_fname, 0, sizeof(sbp->sb_fname));
+       strncpy(sbp->sb_fname, sb_fname, sizeof(sbp->sb_fname));
+
+       error = xfs_sync_sb(mp, true);
+       if (error)
+               goto out;
+       /*
+        * Most kernelspace superblock updates only update sb 0.
+        * Userspace relabel has always updated all, though, so:
+        */
+       error = xfs_update_secondary_supers(mp, sbp->sb_agcount, 0);
+out:
+       mutex_unlock(&mp->m_growlock);
+       mnt_drop_write_file(filp);
+       return error;
+}
+
 /*
  * Note: some of the ioctl's return positive numbers as a
  * byte count indicating success, such as readlink_by_handle.
@@ -1630,6 +1688,10 @@ xfs_file_ioctl(
        switch (cmd) {
        case FITRIM:
                return xfs_ioc_trim(mp, arg);
+       case FS_IOC_GET_FSLABEL:
+               return xfs_ioc_getlabel(mp, arg);
+       case FS_IOC_SET_FSLABEL:
+               return xfs_ioc_setlabel(filp, mp, arg);
        case XFS_IOC_ALLOCSP:
        case XFS_IOC_FREESP:
        case XFS_IOC_RESVSP:
-- 
1.7.1