On Thu, Oct 29, 2020 at 03:43:48PM +0530, 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.
I don't see any new ENOSPC returns in this patch. Does this comment
merely confirm that we'll return ENOSPC when we run out of space, like
all the other allocators?
Or is there another subtlety to this statement? Such as ... we'll
return ENOSPC when there are no more single-block free space extents,
even if there are still larger chunks of free space?
Also, I thought this patch made it so that we always allocate minlen,
which doesn't necessarily mean single blocks?
> Reviewed-by: Allison Henderson <allison.henderson@xxxxxxxxxx>
> Signed-off-by: Chandan Babu R <chandanrlinux@xxxxxxxxx>
> ---
> fs/xfs/libxfs/xfs_alloc.c | 50 ++++++++++++++++++
> fs/xfs/libxfs/xfs_alloc.h | 3 ++
> fs/xfs/libxfs/xfs_bmap.c | 100 +++++++++++++++++++++++++++++++----
> fs/xfs/libxfs/xfs_errortag.h | 4 +-
> fs/xfs/xfs_error.c | 3 ++
> 5 files changed, 150 insertions(+), 10 deletions(-)
>
> diff --git a/fs/xfs/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
> index 852b536551b5..a7c4eb1d71d5 100644
> --- a/fs/xfs/libxfs/xfs_alloc.c
> +++ b/fs/xfs/libxfs/xfs_alloc.c
> @@ -2473,6 +2473,47 @@ 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.
> @@ -2544,6 +2585,15 @@ 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 88db23afc51c..74e148cc41b2 100644
> --- a/fs/xfs/libxfs/xfs_bmap.c
> +++ b/fs/xfs/libxfs/xfs_bmap.c
> @@ -3474,11 +3474,13 @@ xfs_bmap_compute_alignments(
> int error;
>
> /* stripe alignment for allocation is determined by mount parameters */
> - *stripe_align = 0;
> - if (mp->m_swidth && (mp->m_flags & XFS_MOUNT_SWALLOC))
> - *stripe_align = mp->m_swidth;
> - else if (mp->m_dalign)
> - *stripe_align = mp->m_dalign;
> + if (stripe_align) {
> + *stripe_align = 0;
> + if (mp->m_swidth && (mp->m_flags & XFS_MOUNT_SWALLOC))
> + *stripe_align = mp->m_swidth;
> + else if (mp->m_dalign)
> + *stripe_align = mp->m_dalign;
> + }
>
> if (ap->flags & XFS_BMAPI_COWFORK)
> align = xfs_get_cowextsz_hint(ap->ip);
> @@ -3551,6 +3553,71 @@ xfs_bmap_process_allocated_extent(
> xfs_bmap_btalloc_accounting(ap, args);
> }
>
> +#ifdef DEBUG
> +static int
> +xfs_bmap_exact_minlen_extent_alloc(
> + struct xfs_bmalloca *ap)
> +{
> + struct xfs_alloc_arg args;
> + struct xfs_mount *mp = ap->ip->i_mount;
> + xfs_fileoff_t orig_offset;
> + xfs_extlen_t orig_length;
> + int error;
> +
> + ASSERT(ap->length);
> + orig_offset = ap->offset;
> + orig_length = ap->length;
> +
> + memset(&args, 0, sizeof(args));
> + args.alloc_minlen_only = 1;
> + args.tp = ap->tp;
> + args.mp = mp;
> +
> + xfs_bmap_compute_alignments(ap, &args, NULL);
> +
> + 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;
> +}
> +#endif
Urgh, I don't like how the else bodies below are split by the
prepreprocessor directives. Could you add an #else clause here to
#define xfs_bmap_exact_minlen_extent_alloc(bma) (-EFSCORRUPTED)
so that we don't need to do that splitting below?
The rest looks ok though.
--D
> +
> STATIC int
> xfs_bmap_btalloc(
> struct xfs_bmalloca *ap) /* bmap alloc argument struct */
> @@ -4112,7 +4179,13 @@ xfs_bmap_alloc_userdata(
> return xfs_bmap_rtalloc(bma);
> }
>
> - return xfs_bmap_btalloc(bma);
> +#ifdef DEBUG
> + if (unlikely(XFS_TEST_ERROR(false, mp,
> + XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT)))
> + return xfs_bmap_exact_minlen_extent_alloc(bma);
> + else
> +#endif
> + return xfs_bmap_btalloc(bma);
> }
>
> static int
> @@ -4148,10 +4221,19 @@ 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) {
> +#ifdef DEBUG
> + if (unlikely(XFS_TEST_ERROR(false, mp,
> + XFS_ERRTAG_BMAP_ALLOC_MINLEN_EXTENT)))
> + error = xfs_bmap_exact_minlen_extent_alloc(bma);
> + else
> +#endif
> + 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,
> };
>
> --
> 2.28.0
>
