On Tue, Mar 03, 2020 at 07:28:28PM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
>
> Create an in-core fake root for AG-rooted btree types so that callers
> can generate a whole new btree using the upcoming btree bulk load
> function without making the new tree accessible from the rest of the
> filesystem. It is up to the individual btree type to provide a function
> to create a staged cursor (presumably with the appropriate callouts to
> update the fakeroot) and then commit the staged root back into the
> filesystem.
>
> Signed-off-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> ---
The code all seems reasonable, mostly infrastructure. Just a few high
level comments..
It would be helpful if the commit log (or code comments) explained more
about the callouts that are replaced for a staging tree (and why).
> fs/xfs/libxfs/xfs_btree.c | 117 +++++++++++++++++++++++++++++++++++++++++++++
> fs/xfs/libxfs/xfs_btree.h | 42 ++++++++++++++--
> fs/xfs/xfs_trace.h | 28 +++++++++++
> 3 files changed, 182 insertions(+), 5 deletions(-)
>
>
> diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
> index e6f898bf3174..9a7c1a4d0423 100644
> --- a/fs/xfs/libxfs/xfs_btree.c
> +++ b/fs/xfs/libxfs/xfs_btree.c
> @@ -382,6 +382,8 @@ xfs_btree_del_cursor(
> /*
> * Free the cursor.
> */
> + if (unlikely(cur->bc_flags & XFS_BTREE_STAGING))
> + kmem_free((void *)cur->bc_ops);
> kmem_cache_free(xfs_btree_cur_zone, cur);
> }
>
> @@ -4908,3 +4910,118 @@ xfs_btree_has_more_records(
> else
> return block->bb_u.s.bb_rightsib != cpu_to_be32(NULLAGBLOCK);
> }
> +
> +/* We don't allow staging cursors to be duplicated. */
> +STATIC struct xfs_btree_cur *
> +xfs_btree_fakeroot_dup_cursor(
> + struct xfs_btree_cur *cur)
> +{
> + ASSERT(0);
> + return NULL;
> +}
> +
> +/* Refuse to allow regular block allocation for a staging cursor. */
> +STATIC int
> +xfs_btree_fakeroot_alloc_block(
> + struct xfs_btree_cur *cur,
> + union xfs_btree_ptr *start_bno,
> + union xfs_btree_ptr *new_bno,
> + int *stat)
> +{
> + ASSERT(0);
> + return -EFSCORRUPTED;
Calling these is a runtime bug as opposed to corruption, right?
> +}
> +
> +/* Refuse to allow block freeing for a staging cursor. */
> +STATIC int
> +xfs_btree_fakeroot_free_block(
> + struct xfs_btree_cur *cur,
> + struct xfs_buf *bp)
> +{
> + ASSERT(0);
> + return -EFSCORRUPTED;
> +}
> +
For example, why do we not allow alloc/frees of blocks into a staging
tree? Is this something related to how staging trees will be constructed
vs. normal trees, or is this just stubbed in and to be implemented
later?
> +/* Initialize a pointer to the root block from the fakeroot. */
> +STATIC void
> +xfs_btree_fakeroot_init_ptr_from_cur(
> + struct xfs_btree_cur *cur,
> + union xfs_btree_ptr *ptr)
> +{
> + struct xbtree_afakeroot *afake;
> +
> + ASSERT(cur->bc_flags & XFS_BTREE_STAGING);
> +
> + afake = cur->bc_private.a.afake;
> + ptr->s = cpu_to_be32(afake->af_root);
> +}
> +
> +/* Set the root block when our tree has a fakeroot. */
> +STATIC void
> +xfs_btree_afakeroot_set_root(
> + struct xfs_btree_cur *cur,
> + union xfs_btree_ptr *ptr,
> + int inc)
> +{
> + struct xbtree_afakeroot *afake = cur->bc_private.a.afake;
> +
> + ASSERT(cur->bc_flags & XFS_BTREE_STAGING);
> + afake->af_root = be32_to_cpu(ptr->s);
> + afake->af_levels += inc;
> +}
> +
> +/*
> + * Initialize a AG-rooted btree cursor with the given AG btree fake root. The
> + * btree cursor's @bc_ops will be overridden as needed to make the staging
> + * functionality work. If @new_ops is not NULL, these new ops will be passed
> + * out to the caller for further overriding.
> + */
> +void
> +xfs_btree_stage_afakeroot(
> + struct xfs_btree_cur *cur,
> + struct xbtree_afakeroot *afake,
> + struct xfs_btree_ops **new_ops)
> +{
> + struct xfs_btree_ops *nops;
> +
> + ASSERT(!(cur->bc_flags & XFS_BTREE_STAGING));
> + ASSERT(!(cur->bc_flags & XFS_BTREE_ROOT_IN_INODE));
> +
> + nops = kmem_alloc(sizeof(struct xfs_btree_ops), KM_NOFS);
> + memcpy(nops, cur->bc_ops, sizeof(struct xfs_btree_ops));
> + nops->alloc_block = xfs_btree_fakeroot_alloc_block;
> + nops->free_block = xfs_btree_fakeroot_free_block;
> + nops->init_ptr_from_cur = xfs_btree_fakeroot_init_ptr_from_cur;
> + nops->set_root = xfs_btree_afakeroot_set_root;
> + nops->dup_cursor = xfs_btree_fakeroot_dup_cursor;
> +
> + cur->bc_private.a.afake = afake;
> + cur->bc_nlevels = afake->af_levels;
> + cur->bc_ops = nops;
> + cur->bc_flags |= XFS_BTREE_STAGING;
> +
> + if (new_ops)
> + *new_ops = nops;
> +}
> +
> +/*
> + * Transform an AG-rooted staging btree cursor back into a regular cursor by
> + * substituting a real btree root for the fake one and restoring normal btree
> + * cursor ops. The caller must log the btree root change prior to calling
> + * this.
> + */
> +void
> +xfs_btree_commit_afakeroot(
> + struct xfs_btree_cur *cur,
> + struct xfs_buf *agbp,
> + const struct xfs_btree_ops *ops)
> +{
> + ASSERT(cur->bc_flags & XFS_BTREE_STAGING);
> +
> + trace_xfs_btree_commit_afakeroot(cur);
> +
> + kmem_free((void *)cur->bc_ops);
> + cur->bc_private.a.agbp = agbp;
> + cur->bc_ops = ops;
> + cur->bc_flags &= ~XFS_BTREE_STAGING;
> +}
Any reason this new code isn't off in a new xfs_staging_btree.c or some
such instead of xfs_btree.c?
> diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
> index 3eff7c321d43..3ada085609a8 100644
> --- a/fs/xfs/libxfs/xfs_btree.h
> +++ b/fs/xfs/libxfs/xfs_btree.h
> @@ -188,6 +188,16 @@ union xfs_btree_cur_private {
> } abt;
> };
>
> +/* Private information for a AG-rooted btree. */
> +struct xfs_btree_priv_ag { /* needed for BNO, CNT, INO */
> + union {
> + struct xfs_buf *agbp; /* agf/agi buffer pointer */
> + struct xbtree_afakeroot *afake; /* fake ag header root */
> + };
> + xfs_agnumber_t agno; /* ag number */
> + union xfs_btree_cur_private priv;
> +};
> +
Ideally refactoring this would be a separate patch from adding a new
field.
Brian
> /*
> * Btree cursor structure.
> * This collects all information needed by the btree code in one place.
> @@ -209,11 +219,7 @@ typedef struct xfs_btree_cur
> xfs_btnum_t bc_btnum; /* identifies which btree type */
> int bc_statoff; /* offset of btre stats array */
> union {
> - struct { /* needed for BNO, CNT, INO */
> - struct xfs_buf *agbp; /* agf/agi buffer pointer */
> - xfs_agnumber_t agno; /* ag number */
> - union xfs_btree_cur_private priv;
> - } a;
> + struct xfs_btree_priv_ag a;
> struct { /* needed for BMAP */
> struct xfs_inode *ip; /* pointer to our inode */
> int allocated; /* count of alloced */
> @@ -232,6 +238,12 @@ typedef struct xfs_btree_cur
> #define XFS_BTREE_LASTREC_UPDATE (1<<2) /* track last rec externally */
> #define XFS_BTREE_CRC_BLOCKS (1<<3) /* uses extended btree blocks */
> #define XFS_BTREE_OVERLAPPING (1<<4) /* overlapping intervals */
> +/*
> + * The root of this btree is a fakeroot structure so that we can stage a btree
> + * rebuild without leaving it accessible via primary metadata. The ops struct
> + * is dynamically allocated and must be freed when the cursor is deleted.
> + */
> +#define XFS_BTREE_STAGING (1<<5)
>
>
> #define XFS_BTREE_NOERROR 0
> @@ -512,4 +524,24 @@ xfs_btree_islastblock(
> return block->bb_u.s.bb_rightsib == cpu_to_be32(NULLAGBLOCK);
> }
>
> +/* Fake root for an AG-rooted btree. */
> +struct xbtree_afakeroot {
> + /* AG block number of the new btree root. */
> + xfs_agblock_t af_root;
> +
> + /* Height of the new btree. */
> + unsigned int af_levels;
> +
> + /* Number of blocks used by the btree. */
> + unsigned int af_blocks;
> +};
> +
> +/* Cursor interactions with with fake roots for AG-rooted btrees. */
> +void xfs_btree_stage_afakeroot(struct xfs_btree_cur *cur,
> + struct xbtree_afakeroot *afake,
> + struct xfs_btree_ops **new_ops);
> +void xfs_btree_commit_afakeroot(struct xfs_btree_cur *cur,
> + struct xfs_buf *agbp,
> + const struct xfs_btree_ops *ops);
> +
> #endif /* __XFS_BTREE_H__ */
> diff --git a/fs/xfs/xfs_trace.h b/fs/xfs/xfs_trace.h
> index e242988f57fb..57ff9f583b5f 100644
> --- a/fs/xfs/xfs_trace.h
> +++ b/fs/xfs/xfs_trace.h
> @@ -3594,6 +3594,34 @@ TRACE_EVENT(xfs_check_new_dalign,
> __entry->calc_rootino)
> )
>
> +TRACE_EVENT(xfs_btree_commit_afakeroot,
> + TP_PROTO(struct xfs_btree_cur *cur),
> + TP_ARGS(cur),
> + TP_STRUCT__entry(
> + __field(dev_t, dev)
> + __field(xfs_btnum_t, btnum)
> + __field(xfs_agnumber_t, agno)
> + __field(xfs_agblock_t, agbno)
> + __field(unsigned int, levels)
> + __field(unsigned int, blocks)
> + ),
> + TP_fast_assign(
> + __entry->dev = cur->bc_mp->m_super->s_dev;
> + __entry->btnum = cur->bc_btnum;
> + __entry->agno = cur->bc_private.a.agno;
> + __entry->agbno = cur->bc_private.a.afake->af_root;
> + __entry->levels = cur->bc_private.a.afake->af_levels;
> + __entry->blocks = cur->bc_private.a.afake->af_blocks;
> + ),
> + TP_printk("dev %d:%d btree %s ag %u levels %u blocks %u root %u",
> + MAJOR(__entry->dev), MINOR(__entry->dev),
> + __print_symbolic(__entry->btnum, XFS_BTNUM_STRINGS),
> + __entry->agno,
> + __entry->levels,
> + __entry->blocks,
> + __entry->agbno)
> +)
> +
> #endif /* _TRACE_XFS_H */
>
> #undef TRACE_INCLUDE_PATH
>
