On Wed, Mar 04, 2020 at 01:21:03PM -0500, Brian Foster wrote:
> 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).
Ok. I have two block comments to add.
> > 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);
> > }
Add here a new comment:
/*
* Staging Cursors and Fake Roots for Btrees
* =========================================
*
* A staging btree cursor is a special type of btree cursor that callers
* must use to construct a new btree index using the btree bulk loader
* code. The bulk loading code uses the staging btree cursor to
* abstract the details of initializing new btree blocks and filling
* them with records or key/ptr pairs. Regular btree operations (e.g.
* queries and modifications) are not supported with staging cursors,
* and callers must not invoke them.
*
* Fake root structures contain all the information about a btree that
* is under construction by the bulk loading code. Staging btree
* cursors point to fake root structures instead of the usual AG header
* or inode structure.
*
* Callers are expected to initialize a fake root structure and pass it
* into the _stage_cursor function for a specific btree type. When bulk
* loading is complete, callers should call the _commit_staged_btree
* function for that specific btree type to commit the new btree into
* the filesystem.
*/
> > +
> > +/* We don't allow staging cursors to be duplicated. */
/*
* Don't allow staging cursors to be duplicated because they're supposed
* to be kept private to a single thread.
*/
> > +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. */
/*
* Don't allow block allocation for a staging cursor. Bulk loading
* requires all the blocks to be allocated ahead of time to prevent
* ENOSPC failures.
*/
> > +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?
Correct. These functions should never be called, because doing so
implies either a bug in the btree code or a caller is misusing a staging
cursor.
I'm not sure what's a good error code for this. I hope that "Structure
needs cleaning" will cause admins to run xfs_repair like they would for
any other "structure needs cleaning" error, though that's not so helpful
if it's xfs_repair itself doing that.
I also thought about "ENOSR" (as in, "No, sir!") but whinging about
streams resources is likely to cause more confusion than it clears up.
> > +}
> > +
> > +/* Refuse to allow block freeing for a staging cursor. */
/*
* Don't allow block freeing for a staging cursor, because staging
* cursors do not support regular btree modifications.
*/
> > +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?
The only user of staging cursors is the bulk loading code, and the bulk
loader requires the caller to allocate all the blocks they'll need ahead
of time. We don't allow any of the regular btree functions on a staging
cursor, and in fact we're really only using it to abstract the details
of writing records, keys, pointers, and btree block headers.
> > +/* 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);
> > +}
Add here another block comment:
/*
* Bulk Loading for AG Btrees
* ==========================
*
* For a btree rooted in an AG header, pass a xbtree_afakeroot structure
* to the staging cursor. Callers should initialize this to zero.
*
* The _stage_cursor() function for a specific btree type should call
* xfs_btree_stage_afakeroot to set up the in-memory cursor as a staging
* cursor. The corresponding _commit_staged_btree() function should log
* the new root and call xfs_btree_commit_afakeroot() to transform the
* staging cursor into a regular btree cursor.
*/
> > +/* 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?
<shrug> It could be. I tried it and it looks like that would only
require exporting six more symbols:
xfs_btree_set_ptr_null
xfs_btree_get_buf_block
xfs_btree_init_block_cur
xfs_btree_set_sibling
xfs_btree_copy_ptrs
xfs_btree_copy_keys
> > 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.
Ok, I'll break that out.
--D
> 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
> >
>
