On Thu, Jun 09, 2016 at 11:41:07AM -0500, Eric Sandeen wrote:
> 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;
Why the trylock here? It seems like we can still block in other places
(e.g., mnt_want_write_file() above).
> + memset(sbp->sb_fname, 0, sizeof(sbp->sb_fname));
> + strncpy(sbp->sb_fname, sb_fname, sizeof(sbp->sb_fname));
> +
So m_growlock excludes grow and nothing else looks like it mucks with
sb_fname, but what about any other invocations of xfs_log_sb()? For
example, is there a risk here of somebody else logging the superblock
buffer based on a transiently zeroed mp->m_sb.sb_fname? (In fact,
xfs_log_sb() looks kind of racy to me, but maybe I'm missing something.)
Perhaps we need an xfs_trans_getsb() somewhere in here..?
Brian
> + 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
>
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