On Tue, May 01, 2018 at 06:04:09PM -0500, Eric Sandeen wrote:
> The GET ioctl is trivial, just return the current label.
>
> The SET ioctl is more involved:
> It transactionally modifies the superblock to write a new filesystem
> label to the primary super.
>
> A new variant of xfs_sync_sb then writes the superblock buffer
> immediately to disk so that the change is visible from userspace.
>
> It then invalidates any page cache that userspace might have previously
> read on the block device so that i.e. blkid can see the change
> immediately, and updates all secondary superblocks as userspace relable
> does.
>
> Signed-off-by: Eric Sandeen <sandeen@xxxxxxxxxx>
> ---
>
> V2: rework the force-sb-to-disk approach, invalidate the whole block
> device, and block waiting for the growfs lock. Also remove too-long-label
> printk.
>
> Thanks to dchinner for the xfs_sync_sb_buf suggestion & framework.
>
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index d9b94bd..54992e8 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -888,6 +888,37 @@ struct xfs_perag *
> return xfs_trans_commit(tp);
> }
>
> +/*
> + * Same behavior as xfs_sync_sb, except that it is always synchronous and it
> + * also writes the superblock buffer to disk sector 0 immediately.
> + */
> +int
> +xfs_sync_sb_buf(
> + struct xfs_mount *mp)
> +{
> + struct xfs_trans *tp;
> + int error;
> +
> + error = xfs_trans_alloc(mp, &M_RES(mp)->tr_sb, 0, 0,
> + XFS_TRANS_NO_WRITECOUNT, &tp);
I suppose this is a straight clone of xfs_sync_sb, but do we need
NO_WRITECOUNT here? Will this get called while the fs is frozen?
> + if (error)
> + return error;
> +
> + xfs_log_sb(tp);
> + xfs_trans_bhold(tp, mp->m_sb_bp);
> + xfs_trans_set_sync(tp);
> + error = xfs_trans_commit(tp);
> + if (error)
> + goto out;
> + /*
> + * write out the sb buffer to get the changes to disk
> + */
> + error = xfs_bwrite(mp->m_sb_bp);
> +out:
> + xfs_buf_relse(mp->m_sb_bp);
> + return error;
> +}
> +
> int
> xfs_fs_geometry(
> struct xfs_sb *sbp,
> diff --git a/fs/xfs/libxfs/xfs_sb.h b/fs/xfs/libxfs/xfs_sb.h
> index 63dcd2a..2268272 100644
> --- a/fs/xfs/libxfs/xfs_sb.h
> +++ b/fs/xfs/libxfs/xfs_sb.h
> @@ -29,6 +29,7 @@ extern struct xfs_perag *xfs_perag_get_tag(struct xfs_mount *, xfs_agnumber_t,
>
> extern void xfs_log_sb(struct xfs_trans *tp);
> extern int xfs_sync_sb(struct xfs_mount *mp, bool wait);
> +extern int xfs_sync_sb_buf(struct xfs_mount *mp);
> extern void xfs_sb_mount_common(struct xfs_mount *mp, struct xfs_sb *sbp);
> extern void xfs_sb_from_disk(struct xfs_sb *to, struct xfs_dsb *from);
> extern void xfs_sb_to_disk(struct xfs_dsb *to, struct xfs_sb *from);
> diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
> index 89fb1eb..effb23a 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1811,6 +1811,72 @@ struct getfsmap_info {
> return error;
> }
>
> +static int
> +xfs_ioc_getlabel(
> + struct xfs_mount *mp,
> + char __user *label)
> +{
> + struct xfs_sb *sbp = &mp->m_sb;
> +
> + /* Paranoia */
> + BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
> +
> + if (copy_to_user(label, sbp->sb_fname, sizeof(sbp->sb_fname)))
Needs to ensure that a null is set at the end of the (userspace) buffer
just in case the label is "123456789012".
There's nothing in the documentation for this ioctl <cough> that says
the passed in buffer must already be zeroed.
> + return -EFAULT;
> + return 0;
> +}
> +
> +static int
> +xfs_ioc_setlabel(
> + struct file *filp,
> + struct xfs_mount *mp,
> + char __user *newlabel)
> +{
> + struct xfs_sb *sbp = &mp->m_sb;
> + char label[FSLABEL_MAX];
> + size_t len;
> + int error;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> +
> + if (copy_from_user(label, newlabel, FSLABEL_MAX))
> + return -EFAULT;
> + /*
> + * The generic ioctl allows up to FSLABEL_MAX chars, but XFS is much
> + * smaller, at 12 bytes.
> + * NB: The on disk label doesn't need to be null terminated.
> + */
> + len = strnlen(label, FSLABEL_MAX);
> + if (len > sizeof(sbp->sb_fname))
> + return -EINVAL;
> +
> + error = mnt_want_write_file(filp);
> + if (error)
> + return error;
> +
> + spin_lock(&mp->m_sb_lock);
> + memset(sbp->sb_fname, 0, sizeof(sbp->sb_fname));
> + strncpy(sbp->sb_fname, label, sizeof(sbp->sb_fname));
> + spin_unlock(&mp->m_sb_lock);
> +
> + /* Log primary superblock label changes & force to disk. */
> + error = xfs_sync_sb_buf(mp);
> + if (error)
> + goto out;
> +
> + /* Invalidate any cached bdev page for userspace visibility. */
> + invalidate_bdev(mp->m_ddev_targp->bt_bdev);
> +
> + /* Update the backup superblocks like userspace does. */
> + mutex_lock(&mp->m_growlock);
> + error = xfs_update_secondary_supers(mp, mp->m_sb.sb_agcount, 0);
> + mutex_unlock(&mp->m_growlock);
> +out:
> + mnt_drop_write_file(filp);
> + return error;
Looks ok enough to start testing.
--D
> +}
> +
> /*
> * Note: some of the ioctl's return positive numbers as a
> * byte count indicating success, such as readlink_by_handle.
> @@ -1834,6 +1900,10 @@ struct getfsmap_info {
> 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:
> --
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