On Mon, May 14, 2018 at 12:39:19PM -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>
Looks ok, to me....
Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
--D
> ---
>
> V2, rework the max length handling a bit, add comments re: userspace,
> do the blkdev flush at the end, sleep for growfs lock, add locking around
> getlabel, add define for max label length ...
>
> fs/xfs/libxfs/xfs_format.h | 7 +++-
> fs/xfs/libxfs/xfs_sb.c | 30 +++++++++++++
> fs/xfs/libxfs/xfs_sb.h | 1 +
> fs/xfs/xfs_ioctl.c | 86 ++++++++++++++++++++++++++++++++++++++
> 4 files changed, 122 insertions(+), 2 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_format.h b/fs/xfs/libxfs/xfs_format.h
> index 42956d8d95ed..c1cb29a5f4f6 100644
> --- a/fs/xfs/libxfs/xfs_format.h
> +++ b/fs/xfs/libxfs/xfs_format.h
> @@ -98,6 +98,9 @@ struct xfs_ifork;
> XFS_SB_VERSION2_PROJID32BIT | \
> XFS_SB_VERSION2_FTYPE)
>
> +/* Maximum size of the xfs filesystem label, no terminating NULL */
> +#define XFSLABEL_MAX 12
> +
> /*
> * Superblock - in core version. Must match the ondisk version below.
> * Must be padded to 64 bit alignment.
> @@ -122,7 +125,7 @@ typedef struct xfs_sb {
> uint16_t sb_sectsize; /* volume sector size, bytes */
> uint16_t sb_inodesize; /* inode size, bytes */
> uint16_t sb_inopblock; /* inodes per block */
> - char sb_fname[12]; /* file system name */
> + char sb_fname[XFSLABEL_MAX]; /* file system name */
> uint8_t sb_blocklog; /* log2 of sb_blocksize */
> uint8_t sb_sectlog; /* log2 of sb_sectsize */
> uint8_t sb_inodelog; /* log2 of sb_inodesize */
> @@ -213,7 +216,7 @@ typedef struct xfs_dsb {
> __be16 sb_sectsize; /* volume sector size, bytes */
> __be16 sb_inodesize; /* inode size, bytes */
> __be16 sb_inopblock; /* inodes per block */
> - char sb_fname[12]; /* file system name */
> + char sb_fname[XFSLABEL_MAX]; /* file system name */
> __u8 sb_blocklog; /* log2 of sb_blocksize */
> __u8 sb_sectlog; /* log2 of sb_sectsize */
> __u8 sb_inodelog; /* log2 of sb_inodesize */
> diff --git a/fs/xfs/libxfs/xfs_sb.c b/fs/xfs/libxfs/xfs_sb.c
> index d9b94bd5f689..0bc0a40764e1 100644
> --- a/fs/xfs/libxfs/xfs_sb.c
> +++ b/fs/xfs/libxfs/xfs_sb.c
> @@ -888,6 +888,36 @@ xfs_sync_sb(
> 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, 0, &tp);
> + 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 63dcd2a1a657..226827281760 100644
> --- a/fs/xfs/libxfs/xfs_sb.h
> +++ b/fs/xfs/libxfs/xfs_sb.h
> @@ -29,6 +29,7 @@ extern int xfs_initialize_perag_data(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 89fb1eb80aae..5e7116ff3dd3 100644
> --- a/fs/xfs/xfs_ioctl.c
> +++ b/fs/xfs/xfs_ioctl.c
> @@ -1811,6 +1811,88 @@ xfs_ioc_swapext(
> return error;
> }
>
> +static int
> +xfs_ioc_getlabel(
> + struct xfs_mount *mp,
> + char __user *user_label)
> +{
> + struct xfs_sb *sbp = &mp->m_sb;
> + char label[XFSLABEL_MAX + 1];
> +
> + /* Paranoia */
> + BUILD_BUG_ON(sizeof(sbp->sb_fname) > FSLABEL_MAX);
> +
> + spin_lock(&mp->m_sb_lock);
> + strncpy(label, sbp->sb_fname, sizeof(sbp->sb_fname));
> + spin_unlock(&mp->m_sb_lock);
> +
> + /* xfs on-disk label is 12 chars, be sure we send a null to user */
> + label[XFSLABEL_MAX] = '\0';
> + if (copy_to_user(user_label, label, sizeof(sbp->sb_fname)))
> + 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[XFSLABEL_MAX + 1];
> + size_t len;
> + int error;
> +
> + if (!capable(CAP_SYS_ADMIN))
> + return -EPERM;
> + /*
> + * The generic ioctl allows up to FSLABEL_MAX chars, but XFS is much
> + * smaller, at 12 bytes. We copy one more to be sure we find the
> + * (required) NULL character to test the incoming label length.
> + * NB: The on disk label doesn't need to be null terminated.
> + */
> + if (copy_from_user(label, newlabel, XFSLABEL_MAX + 1))
> + return -EFAULT;
> + len = strnlen(label, XFSLABEL_MAX + 1);
> + 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);
> +
> + /*
> + * Now we do several things to satisfy userspace.
> + * In addition to normal logging of the primary superblock, we also
> + * immediately write these changes to sector zero for the primary, then
> + * update all backup supers (as xfs_db does for a label change), then
> + * invalidate the block device page cache. This is so that any prior
> + * buffered reads from userspace (i.e. from blkid) are invalidated,
> + * and userspace will see the newly-written label.
> + */
> + error = xfs_sync_sb_buf(mp);
> + if (error)
> + goto out;
> + /*
> + * growfs also updates backup supers so lock against that.
> + */
> + mutex_lock(&mp->m_growlock);
> + error = xfs_update_secondary_supers(mp);
> + mutex_unlock(&mp->m_growlock);
> +
> + invalidate_bdev(mp->m_ddev_targp->bt_bdev);
> +
> +out:
> + 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.
> @@ -1834,6 +1916,10 @@ xfs_file_ioctl(
> switch (cmd) {
> case FITRIM:
> return xfs_ioc_trim(mp, arg);
> + case FS_IOC_GETFSLABEL:
> + return xfs_ioc_getlabel(mp, arg);
> + case FS_IOC_SETFSLABEL:
> + return xfs_ioc_setlabel(filp, mp, arg);
> case XFS_IOC_ALLOCSP:
> case XFS_IOC_FREESP:
> case XFS_IOC_RESVSP:
> --
> 2.17.0
>
>
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