On Sat, Oct 03, 2020 at 11:26:33AM +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.
Is step #2 required? What happens if I only turn the knob?
> 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@xxxxxxxxx>
> ---
> 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(
This ought to have an 'xfs_' prefix.
Also, what does this function do? Does it decide if there's even enough
space to go ahead with a minlen allocation?
> + struct xfs_alloc_arg *args,
> + struct xfs_buf *agbp,
> + int *stat)
> +{
> + xfs_btree_cur_t *cnt_cur;
struct xfs_btree_cur *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);
Is it ok to keep going with stat==0? Or should we just ... I don't
know? Bail out with -EFSCORRUPTED?
> +
> + 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);
Note that due to a sloppy quirk of error handling, you can pass @error
to this function, no need for a separate 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);
Can we just set maxlen = minlen here?
Also, should this debug knob also be applied to rt file allocations?
>
> 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;
Hm, so setting this magic knob also makes everyone fight for space in 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;
> + args.total = args.minlen = args.maxlen = ap->minlen;
> + } else if (nullfb) {
> /*
> * Search for an allocation group with a single extent large
> * enough for the request. If one isn't found, then adjust
> @@ -3595,7 +3606,8 @@ xfs_bmap_btalloc(
> * is only set if the allocation length is >= the stripe unit and the
> * allocation offset is at the end of file.
> */
> - if (!(ap->tp->t_flags & XFS_TRANS_LOWMODE) && ap->aeof) {
> + if (!(ap->tp->t_flags & XFS_TRANS_LOWMODE) && ap->aeof &&
> + !args.alloc_minlen_only) {
> if (!ap->offset) {
Yikes, the conditional lines up with the body!
--D
> args.alignment = stripe_align;
> atype = args.type;
> @@ -3681,7 +3693,7 @@ xfs_bmap_btalloc(
> if ((error = xfs_alloc_vextent(&args)))
> return error;
> }
> - if (args.fsbno == NULLFSBLOCK && nullfb) {
> + if (args.fsbno == NULLFSBLOCK && nullfb && !args.alloc_minlen_only) {
> args.fsbno = 0;
> args.type = XFS_ALLOCTYPE_FIRST_AG;
> args.total = ap->minlen;
> 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..028560bb596a 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
>
