Re: [PATCH V5 12/12] xfs: Introduce error injection to allocate only minlen size extents for files

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Tue, Oct 06, 2020 at 09:55:03AM +0530, Chandan Babu R wrote:
> On Saturday 3 October 2020 11:26:33 AM IST Chandan Babu R wrote:
> > This commit adds XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT error tag which
> > helps userspace test programs to get xfs_bmap_btalloc() to always
> > allocate minlen sized extents.
> > 
> > This is required for test programs which need a guarantee that minlen
> > extents allocated for a file do not get merged with their existing
> > neighbours in the inode's BMBT. "Inode fork extent overflow check" for
> > Directories, Xattrs and extension of realtime inodes need this since the
> > file offset at which the extents are being allocated cannot be
> > explicitly controlled from userspace.
> > 
> > One way to use this error tag is to,
> > 1. Consume all of the free space by sequentially writing to a file.
> > 2. Punch alternate blocks of the file. This causes CNTBT to contain
> >    sufficient number of one block sized extent records.
> > 3. Inject XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT error tag.
> > After step 3, xfs_bmap_btalloc() will issue space allocation
> > requests for minlen sized extents only.
> > 
> > ENOSPC error code is returned to userspace when there aren't any "one
> > block sized" extents left in any of the AGs.
> > 
> > Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>
> > ---
> >  fs/xfs/libxfs/xfs_alloc.c    | 46 ++++++++++++++++++++++++++++++++++++
> >  fs/xfs/libxfs/xfs_alloc.h    |  1 +
> >  fs/xfs/libxfs/xfs_bmap.c     | 26 ++++++++++++++------
> >  fs/xfs/libxfs/xfs_errortag.h |  4 +++-
> >  fs/xfs/xfs_error.c           |  3 +++
> >  5 files changed, 72 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> > index 852b536551b5..d8d8ab1478db 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.c
> > +++ b/fs/xfs/libxfs/xfs_alloc.c
> > @@ -2473,6 +2473,45 @@ xfs_defer_agfl_block(
> >  	xfs_defer_add(tp, XFS_DEFER_OPS_TYPE_AGFL_FREE, &new->xefi_list);
> >  }
> >  
> > +STATIC int
> > +minlen_freespace_available(
> > +	struct xfs_alloc_arg	*args,
> > +	struct xfs_buf		*agbp,
> > +	int			*stat)
> > +{
> > +	xfs_btree_cur_t		*cnt_cur;
> > +	xfs_agblock_t		fbno;
> > +	xfs_extlen_t		flen;
> > +	int			btree_error = XFS_BTREE_NOERROR;
> > +	int			error = 0;
> > +
> > +	cnt_cur = xfs_allocbt_init_cursor(args->mp, args->tp, agbp,
> > +			args->agno, XFS_BTNUM_CNT);
> > +	error = xfs_alloc_lookup_ge(cnt_cur, 0, args->minlen, stat);
> > +	if (error) {
> > +		btree_error = XFS_BTREE_ERROR;
> > +		goto out;
> > +	}
> > +
> > +	ASSERT(*stat == 1);
> > +
> > +	error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, stat);
> > +	if (error) {
> > +		btree_error = XFS_BTREE_ERROR;
> > +		goto out;
> > +	}
> > +
> > +	if (flen == args->minlen)
> > +		*stat = 1;
> > +	else
> > +		*stat = 0;
> > +
> > +out:
> > +	xfs_btree_del_cursor(cnt_cur, btree_error);
> > +
> > +	return error;
> > +}
> > +
> >  /*
> >   * Decide whether to use this allocation group for this allocation.
> >   * If so, fix up the btree freelist's size.
> > @@ -2490,6 +2529,7 @@ xfs_alloc_fix_freelist(
> >  	struct xfs_alloc_arg	targs;	/* local allocation arguments */
> >  	xfs_agblock_t		bno;	/* freelist block */
> >  	xfs_extlen_t		need;	/* total blocks needed in freelist */
> > +	int			i;
> >  	int			error = 0;
> >  
> >  	/* deferred ops (AGFL block frees) require permanent transactions */
> > @@ -2544,6 +2584,12 @@ xfs_alloc_fix_freelist(
> >  	if (!xfs_alloc_space_available(args, need, flags))
> >  		goto out_agbp_relse;
> >  
> > +	if (args->alloc_minlen_only) {
> > +		error = minlen_freespace_available(args, agbp, &i);
> > +		if (error || !i)
> > +			goto out_agbp_relse;
> > +	}
> > +
> >  	/*
> >  	 * Make the freelist shorter if it's too long.
> >  	 *
> > diff --git a/fs/xfs/libxfs/xfs_alloc.h b/fs/xfs/libxfs/xfs_alloc.h
> > index 6c22b12176b8..1d04089b7fb4 100644
> > --- a/fs/xfs/libxfs/xfs_alloc.h
> > +++ b/fs/xfs/libxfs/xfs_alloc.h
> > @@ -75,6 +75,7 @@ typedef struct xfs_alloc_arg {
> >  	char		wasfromfl;	/* set if allocation is from freelist */
> >  	struct xfs_owner_info	oinfo;	/* owner of blocks being allocated */
> >  	enum xfs_ag_resv_type	resv;	/* block reservation to use */
> > +	bool		alloc_minlen_only;
> >  } xfs_alloc_arg_t;
> >  
> >  /*
> > diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> > index 5156cbd476f2..fab4097e7492 100644
> > --- a/fs/xfs/libxfs/xfs_bmap.c
> > +++ b/fs/xfs/libxfs/xfs_bmap.c
> > @@ -3510,12 +3510,19 @@ xfs_bmap_btalloc(
> >  		ASSERT(ap->length);
> >  	}
> >  
> > +	memset(&args, 0, sizeof(args));
> > +
> > +	args.alloc_minlen_only = XFS_TEST_ERROR(false, mp,
> > +					XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT);
> >  
> >  	nullfb = ap->tp->t_firstblock == NULLFSBLOCK;
> >  	fb_agno = nullfb ? NULLAGNUMBER : XFS_FSB_TO_AGNO(mp,
> >  							ap->tp->t_firstblock);
> >  	if (nullfb) {
> > -		if ((ap->datatype & XFS_ALLOC_USERDATA) &&
> > +		if (args.alloc_minlen_only) {
> > +			ag = 0;
> > +			ap->blkno = XFS_AGB_TO_FSB(mp, ag, 0);
> > +		} else if ((ap->datatype & XFS_ALLOC_USERDATA) &&
> >  		    xfs_inode_is_filestream(ap->ip)) {
> >  			ag = xfs_filestream_lookup_ag(ap->ip);
> >  			ag = (ag != NULLAGNUMBER) ? ag : 0;
> > @@ -3523,10 +3530,12 @@ xfs_bmap_btalloc(
> >  		} else {
> >  			ap->blkno = XFS_INO_TO_FSB(mp, ap->ip->i_ino);
> >  		}
> > -	} else
> > +	} else {
> >  		ap->blkno = ap->tp->t_firstblock;
> > +	}
> >  
> > -	xfs_bmap_adjacent(ap);
> > +	if (!args.alloc_minlen_only)
> > +		xfs_bmap_adjacent(ap);
> >  
> >  	/*
> >  	 * If allowed, use ap->blkno; otherwise must use firstblock since
> > @@ -3540,7 +3549,6 @@ xfs_bmap_btalloc(
> >  	 * Normal allocation, done through xfs_alloc_vextent.
> >  	 */
> >  	tryagain = isaligned = 0;
> > -	memset(&args, 0, sizeof(args));
> >  	args.tp = ap->tp;
> >  	args.mp = mp;
> >  	args.fsbno = ap->blkno;
> > @@ -3549,7 +3557,10 @@ xfs_bmap_btalloc(
> >  	/* Trim the allocation back to the maximum an AG can fit. */
> >  	args.maxlen = min(ap->length, mp->m_ag_max_usable);
> >  	blen = 0;
> > -	if (nullfb) {
> > +	if (args.alloc_minlen_only) {
> > +		args.type = XFS_ALLOCTYPE_START_AG;
> 
> The above should have been,
> 
> args.type = XFS_ALLOCTYPE_FIRST_AG;
> 
> In my experiments, I had introduced a new args.type value and had later
> realized that XFS_ALLOCTYPE_FIRST_AG would suffice for my requirements. I had
> tested the changed version (which was in my git stash) and forgot to apply
> that to this commit after testing was completed. Hence I ended up sending a
> slightly stale patch. I am sorry about this. I will resend the series.

Ok, but wait till I've gotten all the way through the replies (nearly
done now).

--D

> -- 
> chandan
> 
> 
>