Re: [PATCH V15 16/16] xfs: Introduce error injection to allocate only minlen size extents for files

[Allison Henderson <allison.henderson@xxxxxxxxxx>]

On 1/25/21 11:32 PM, 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.
>
> Reviewed-by: Darrick J. Wong <darrick.wong@xxxxxxxxxx>
> Signed-off-by: Chandan Babu R <chandanrlinux@xxxxxxxxx>
Ok, looks reasonable.  Thanks!

Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> ---
>   fs/xfs/libxfs/xfs_alloc.c    |  50 ++++++++++++++
>   fs/xfs/libxfs/xfs_alloc.h    |   3 +
>   fs/xfs/libxfs/xfs_bmap.c     | 124 ++++++++++++++++++++++++++++-------
>   fs/xfs/libxfs/xfs_errortag.h |   4 +-
>   fs/xfs/xfs_error.c           |   3 +
>   5 files changed, 159 insertions(+), 25 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 7cb9f064ac64..0c623d3c1036 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2474,6 +2474,47 @@ xfs_defer_agfl_block(
>   	xfs_defer_add(tp, XFS_DEFER_OPS_TYPE_AGFL_FREE, &new->xefi_list);
>   }
>   
> +#ifdef DEBUG
> +/*
> + * Check if an AGF has a free extent record whose length is equal to
> + * args->minlen.
> + */
> +STATIC int
> +xfs_exact_minlen_extent_available(
> +	struct xfs_alloc_arg	*args,
> +	struct xfs_buf		*agbp,
> +	int			*stat)
> +{
> +	struct xfs_btree_cur	*cnt_cur;
> +	xfs_agblock_t		fbno;
> +	xfs_extlen_t		flen;
> +	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)
> +		goto out;
> +
> +	if (*stat == 0) {
> +		error = -EFSCORRUPTED;
> +		goto out;
> +	}
> +
> +	error = xfs_alloc_get_rec(cnt_cur, &fbno, &flen, stat);
> +	if (error)
> +		goto out;
> +
> +	if (*stat == 1 && flen != args->minlen)
> +		*stat = 0;
> +
> +out:
> +	xfs_btree_del_cursor(cnt_cur, error);
> +
> +	return error;
> +}
> +#endif
> +
>   /*
>    * Decide whether to use this allocation group for this allocation.
>    * If so, fix up the btree freelist's size.
> @@ -2545,6 +2586,15 @@ xfs_alloc_fix_freelist(
>   	if (!xfs_alloc_space_available(args, need, flags))
>   		goto out_agbp_relse;
>   
> +#ifdef DEBUG
> +	if (args->alloc_minlen_only) {
> +		int stat;
> +
> +		error = xfs_exact_minlen_extent_available(args, agbp, &stat);
> +		if (error || !stat)
> +			goto out_agbp_relse;
> +	}
> +#endif
>   	/*
>   	 * 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..a4427c5775c2 100644
> --- a/fs/xfs/libxfs/xfs_alloc.h
> +++ b/fs/xfs/libxfs/xfs_alloc.h
> @@ -75,6 +75,9 @@ 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 */
> +#ifdef DEBUG
> +	bool		alloc_minlen_only; /* allocate exact minlen extent */
> +#endif
>   } xfs_alloc_arg_t;
>   
>   /*
> diff --git a/fs/xfs/libxfs/xfs_bmap.c b/fs/xfs/libxfs/xfs_bmap.c
> index ee2c0a4295c6..33117aef79e5 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3552,34 +3552,101 @@ xfs_bmap_process_allocated_extent(
>   	xfs_bmap_btalloc_accounting(ap, args);
>   }
>   
> -STATIC int
> -xfs_bmap_btalloc(
> -	struct xfs_bmalloca	*ap)	/* bmap alloc argument struct */
> +#ifdef DEBUG
> +static int
> +xfs_bmap_exact_minlen_extent_alloc(
> +	struct xfs_bmalloca	*ap)
>   {
> -	xfs_mount_t	*mp;		/* mount point structure */
> -	xfs_alloctype_t	atype = 0;	/* type for allocation routines */
> -	xfs_agnumber_t	fb_agno;	/* ag number of ap->firstblock */
> -	xfs_agnumber_t	ag;
> -	xfs_alloc_arg_t	args;
> -	xfs_fileoff_t	orig_offset;
> -	xfs_extlen_t	orig_length;
> -	xfs_extlen_t	blen;
> -	xfs_extlen_t	nextminlen = 0;
> -	int		nullfb;		/* true if ap->firstblock isn't set */
> -	int		isaligned;
> -	int		tryagain;
> -	int		error;
> -	int		stripe_align;
> +	struct xfs_mount	*mp = ap->ip->i_mount;
> +	struct xfs_alloc_arg	args = { .tp = ap->tp, .mp = mp };
> +	xfs_fileoff_t		orig_offset;
> +	xfs_extlen_t		orig_length;
> +	int			error;
>   
>   	ASSERT(ap->length);
> +
> +	if (ap->minlen != 1) {
> +		ap->blkno = NULLFSBLOCK;
> +		ap->length = 0;
> +		return 0;
> +	}
> +
>   	orig_offset = ap->offset;
>   	orig_length = ap->length;
>   
> -	mp = ap->ip->i_mount;
> +	args.alloc_minlen_only = 1;
>   
> -	memset(&args, 0, sizeof(args));
> -	args.tp = ap->tp;
> -	args.mp = mp;
> +	xfs_bmap_compute_alignments(ap, &args);
> +
> +	if (ap->tp->t_firstblock == NULLFSBLOCK) {
> +		/*
> +		 * Unlike the longest extent available in an AG, we don't track
> +		 * the length of an AG's shortest extent.
> +		 * XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT is a debug only knob and
> +		 * hence we can afford to start traversing from the 0th AG since
> +		 * we need not be concerned about a drop in performance in
> +		 * "debug only" code paths.
> +		 */
> +		ap->blkno = XFS_AGB_TO_FSB(mp, 0, 0);
> +	} else {
> +		ap->blkno = ap->tp->t_firstblock;
> +	}
> +
> +	args.fsbno = ap->blkno;
> +	args.oinfo = XFS_RMAP_OINFO_SKIP_UPDATE;
> +	args.type = XFS_ALLOCTYPE_FIRST_AG;
> +	args.total = args.minlen = args.maxlen = ap->minlen;
> +
> +	args.alignment = 1;
> +	args.minalignslop = 0;
> +
> +	args.minleft = ap->minleft;
> +	args.wasdel = ap->wasdel;
> +	args.resv = XFS_AG_RESV_NONE;
> +	args.datatype = ap->datatype;
> +
> +	error = xfs_alloc_vextent(&args);
> +	if (error)
> +		return error;
> +
> +	if (args.fsbno != NULLFSBLOCK) {
> +		xfs_bmap_process_allocated_extent(ap, &args, orig_offset,
> +			orig_length);
> +	} else {
> +		ap->blkno = NULLFSBLOCK;
> +		ap->length = 0;
> +	}
> +
> +	return 0;
> +}
> +#else
> +
> +#define xfs_bmap_exact_minlen_extent_alloc(bma) (-EFSCORRUPTED)
> +
> +#endif
> +
> +STATIC int
> +xfs_bmap_btalloc(
> +	struct xfs_bmalloca	*ap)
> +{
> +	struct xfs_mount	*mp = ap->ip->i_mount;
> +	struct xfs_alloc_arg	args = { .tp = ap->tp, .mp = mp };
> +	xfs_alloctype_t		atype = 0;
> +	xfs_agnumber_t		fb_agno;	/* ag number of ap->firstblock */
> +	xfs_agnumber_t		ag;
> +	xfs_fileoff_t		orig_offset;
> +	xfs_extlen_t		orig_length;
> +	xfs_extlen_t		blen;
> +	xfs_extlen_t		nextminlen = 0;
> +	int			nullfb; /* true if ap->firstblock isn't set */
> +	int			isaligned;
> +	int			tryagain;
> +	int			error;
> +	int			stripe_align;
> +
> +	ASSERT(ap->length);
> +	orig_offset = ap->offset;
> +	orig_length = ap->length;
>   
>   	stripe_align = xfs_bmap_compute_alignments(ap, &args);
>   
> @@ -4113,6 +4180,10 @@ xfs_bmap_alloc_userdata(
>   			return xfs_bmap_rtalloc(bma);
>   	}
>   
> +	if (unlikely(XFS_TEST_ERROR(false, mp,
> +			XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT)))
> +		return xfs_bmap_exact_minlen_extent_alloc(bma);
> +
>   	return xfs_bmap_btalloc(bma);
>   }
>   
> @@ -4149,10 +4220,15 @@ xfs_bmapi_allocate(
>   	else
>   		bma->minlen = 1;
>   
> -	if (bma->flags & XFS_BMAPI_METADATA)
> -		error = xfs_bmap_btalloc(bma);
> -	else
> +	if (bma->flags & XFS_BMAPI_METADATA) {
> +		if (unlikely(XFS_TEST_ERROR(false, mp,
> +				XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT)))
> +			error = xfs_bmap_exact_minlen_extent_alloc(bma);
> +		else
> +			error = xfs_bmap_btalloc(bma);
> +	} else {
>   		error = xfs_bmap_alloc_userdata(bma);
> +	}
>   	if (error || bma->blkno == NULLFSBLOCK)
>   		return error;
>   
> diff --git a/fs/xfs/libxfs/xfs_errortag.h b/fs/xfs/libxfs/xfs_errortag.h
> index 1c56fcceeea6..6ca9084b6934 100644
> --- a/fs/xfs/libxfs/xfs_errortag.h
> +++ b/fs/xfs/libxfs/xfs_errortag.h
> @@ -57,7 +57,8 @@
>   #define XFS_ERRTAG_IUNLINK_FALLBACK			34
>   #define XFS_ERRTAG_BUF_IOERROR				35
>   #define XFS_ERRTAG_REDUCE_MAX_IEXTENTS			36
> -#define XFS_ERRTAG_MAX					37
> +#define XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT		37
> +#define XFS_ERRTAG_MAX					38
>   
>   /*
>    * Random factors for above tags, 1 means always, 2 means 1/2 time, etc.
> @@ -99,5 +100,6 @@
>   #define XFS_RANDOM_IUNLINK_FALLBACK			(XFS_RANDOM_DEFAULT/10)
>   #define XFS_RANDOM_BUF_IOERROR				XFS_RANDOM_DEFAULT
>   #define XFS_RANDOM_REDUCE_MAX_IEXTENTS			1
> +#define XFS_RANDOM_BMAP_ALLOC_MINLEN_EXTENT		1
>   
>   #endif /* __XFS_ERRORTAG_H_ */
> diff --git a/fs/xfs/xfs_error.c b/fs/xfs/xfs_error.c
> index 3780b118cc47..185b4915b7bf 100644
> --- a/fs/xfs/xfs_error.c
> +++ b/fs/xfs/xfs_error.c
> @@ -55,6 +55,7 @@ static unsigned int xfs_errortag_random_default[] = {
>   	XFS_RANDOM_IUNLINK_FALLBACK,
>   	XFS_RANDOM_BUF_IOERROR,
>   	XFS_RANDOM_REDUCE_MAX_IEXTENTS,
> +	XFS_RANDOM_BMAP_ALLOC_MINLEN_EXTENT,
>   };
>   
>   struct xfs_errortag_attr {
> @@ -166,6 +167,7 @@ XFS_ERRORTAG_ATTR_RW(bad_summary,	XFS_ERRTAG_FORCE_SUMMARY_RECALC);
>   XFS_ERRORTAG_ATTR_RW(iunlink_fallback,	XFS_ERRTAG_IUNLINK_FALLBACK);
>   XFS_ERRORTAG_ATTR_RW(buf_ioerror,	XFS_ERRTAG_BUF_IOERROR);
>   XFS_ERRORTAG_ATTR_RW(reduce_max_iextents,	XFS_ERRTAG_REDUCE_MAX_IEXTENTS);
> +XFS_ERRORTAG_ATTR_RW(bmap_alloc_minlen_extent,	XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT);
>   
>   static struct attribute *xfs_errortag_attrs[] = {
>   	XFS_ERRORTAG_ATTR_LIST(noerror),
> @@ -205,6 +207,7 @@ static struct attribute *xfs_errortag_attrs[] = {
>   	XFS_ERRORTAG_ATTR_LIST(iunlink_fallback),
>   	XFS_ERRORTAG_ATTR_LIST(buf_ioerror),
>   	XFS_ERRORTAG_ATTR_LIST(reduce_max_iextents),
> +	XFS_ERRORTAG_ATTR_LIST(bmap_alloc_minlen_extent),
>   	NULL,
>   };
>