On Mon, Aug 28, 2017 at 02:20:24PM -0700, Darrick J. Wong wrote:
> On Mon, Aug 28, 2017 at 05:06:12PM +0200, Christoph Hellwig wrote:
> > Currently getbmap uses xfs_bmapi_read to query the extent map, and then
> > fixes up various bits that are eventually reported to userspace.
> >
> > This patch instead rewrites it to use xfs_iext_lookup_extent and
> > xfs_iext_get_extent to iteratively process the extent map. This not
> > only avoids the need to allocate a map for the returned xfs_bmbt_irec
> > structures but also greatly simplified the code.
> >
> > There are two intentional behavior changes compared to the old code:
> >
> > - the current code reports unwritten extents that don't directly border
> > a written one as unwritten even when not passing the BMV_IF_PREALLOC
> > option, contrary to the documentation. The new code requires the
> > BMV_IF_PREALLOC flag to report the unwrittent extent bit.
> > - The new code does never merges consecutive extents, unlike the old
> > code that sometimes does it based on the boundaries of the
> > xfs_bmapi_read calls. Note that the extent merging behavior was
> > entirely undocumented.
> >
> > Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> > ---
> > fs/xfs/xfs_bmap_util.c | 499 ++++++++++++++++++-------------------------------
> > 1 file changed, 185 insertions(+), 314 deletions(-)
> >
> > diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
> > index 93e955262d07..5962f119d4ff 100644
> > --- a/fs/xfs/xfs_bmap_util.c
> > +++ b/fs/xfs/xfs_bmap_util.c
> > @@ -404,125 +404,69 @@ xfs_bmap_count_blocks(
> > return 0;
> > }
> >
> > -/*
> > - * returns 1 for success, 0 if we failed to map the extent.
> > - */
> > -STATIC int
> > -xfs_getbmapx_fix_eof_hole(
> > - xfs_inode_t *ip, /* xfs incore inode pointer */
> > - int whichfork,
> > - struct getbmapx *out, /* output structure */
> > - int prealloced, /* this is a file with
> > - * preallocated data space */
> > - int64_t end, /* last block requested */
> > - xfs_fsblock_t startblock,
> > - bool moretocome)
> > +static void
> > +xfs_getbmap_report_one(
> > + struct xfs_inode *ip,
> > + struct getbmapx *bmv,
> > + int64_t bmv_end,
> > + struct xfs_bmbt_irec *got,
> > + struct getbmapx *p)
> > {
> > - int64_t fixlen;
> > - xfs_mount_t *mp; /* file system mount point */
> > - xfs_ifork_t *ifp; /* inode fork pointer */
> > - xfs_extnum_t lastx; /* last extent pointer */
> > - xfs_fileoff_t fileblock;
> > -
> > - if (startblock == HOLESTARTBLOCK) {
> > - mp = ip->i_mount;
> > - out->bmv_block = -1;
> > - fixlen = XFS_FSB_TO_BB(mp, XFS_B_TO_FSB(mp, XFS_ISIZE(ip)));
> > - fixlen -= out->bmv_offset;
> > - if (prealloced && out->bmv_offset + out->bmv_length == end) {
> > - /* Came to hole at EOF. Trim it. */
> > - if (fixlen <= 0)
> > - return 0;
> > - out->bmv_length = fixlen;
> > - }
> > + if (isnullstartblock(got->br_startblock) ||
> > + got->br_startblock == DELAYSTARTBLOCK) {
> > + /*
> > + * Delalloc extents that start beyond EOF can occur due to
> > + * speculative EOF allocation when the delalloc extent is larger
> > + * than the largest freespace extent at conversion time. These
> > + * extents cannot be converted by data writeback, so can exist
> > + * here even if we are not supposed to be finding delalloc
> > + * extents.
> > + */
> > + if (got->br_startoff < XFS_B_TO_FSB(ip->i_mount, XFS_ISIZE(ip)))
> > + ASSERT((bmv->bmv_iflags & BMV_IF_DELALLOC) != 0);
> > +
> > + p->bmv_oflags |= BMV_OF_DELALLOC;
> > + p->bmv_block = -2;
> > } else {
> > - if (startblock == DELAYSTARTBLOCK)
> > - out->bmv_block = -2;
> > - else
> > - out->bmv_block = xfs_fsb_to_db(ip, startblock);
> > - fileblock = XFS_BB_TO_FSB(ip->i_mount, out->bmv_offset);
> > - ifp = XFS_IFORK_PTR(ip, whichfork);
> > - if (!moretocome &&
> > - xfs_iext_bno_to_ext(ifp, fileblock, &lastx) &&
> > - (lastx == xfs_iext_count(ifp) - 1))
> > - out->bmv_oflags |= BMV_OF_LAST;
> > + p->bmv_block = xfs_fsb_to_db(ip, got->br_startblock);
> > }
> >
> > - return 1;
> > + if (got->br_state == XFS_EXT_UNWRITTEN &&
> > + (bmv->bmv_iflags & BMV_IF_PREALLOC))
> > + p->bmv_oflags |= BMV_OF_PREALLOC;
> > +
> > + p->bmv_offset = XFS_FSB_TO_BB(ip->i_mount, got->br_startoff);
> > + p->bmv_length = XFS_FSB_TO_BB(ip->i_mount, got->br_blockcount);
> > +
> > + bmv->bmv_offset = p->bmv_offset + p->bmv_length;
> > + bmv->bmv_length = max(0LL, bmv_end - bmv->bmv_offset);
> > + bmv->bmv_entries++;
> > }
> >
> > -/* Adjust the reported bmap around shared/unshared extent transitions. */
> > -STATIC int
> > -xfs_getbmap_adjust_shared(
> > +static void
> > +xfs_getbmap_report_hole(
> > struct xfs_inode *ip,
> > - int whichfork,
> > - struct xfs_bmbt_irec *map,
> > - struct getbmapx *out,
> > - struct xfs_bmbt_irec *next_map)
> > + struct getbmapx *bmv,
> > + int64_t bmv_end,
> > + xfs_fileoff_t bno,
> > + xfs_fileoff_t end,
> > + struct getbmapx *p)
> > {
> > - struct xfs_mount *mp = ip->i_mount;
> > - xfs_agnumber_t agno;
> > - xfs_agblock_t agbno;
> > - xfs_agblock_t ebno;
> > - xfs_extlen_t elen;
> > - xfs_extlen_t nlen;
> > - int error;
> > + if (bmv->bmv_iflags & BMV_IF_NO_HOLES)
> > + return;
> >
> > - next_map->br_startblock = NULLFSBLOCK;
> > - next_map->br_startoff = NULLFILEOFF;
> > - next_map->br_blockcount = 0;
> > + p->bmv_block = -1;
> > + p->bmv_offset = XFS_FSB_TO_BB(ip->i_mount, bno);
> > + p->bmv_length = XFS_FSB_TO_BB(ip->i_mount, end - bno);
> >
> > - /* Only written data blocks can be shared. */
> > - if (!xfs_is_reflink_inode(ip) ||
> > - whichfork != XFS_DATA_FORK ||
> > - !xfs_bmap_is_real_extent(map))
> > - return 0;
> > -
> > - agno = XFS_FSB_TO_AGNO(mp, map->br_startblock);
> > - agbno = XFS_FSB_TO_AGBNO(mp, map->br_startblock);
> > - error = xfs_reflink_find_shared(mp, NULL, agno, agbno,
> > - map->br_blockcount, &ebno, &elen, true);
> > - if (error)
> > - return error;
> > -
> > - if (ebno == NULLAGBLOCK) {
> > - /* No shared blocks at all. */
> > - return 0;
> > - } else if (agbno == ebno) {
> > - /*
> > - * Shared extent at (agbno, elen). Shrink the reported
> > - * extent length and prepare to move the start of map[i]
> > - * to agbno+elen, with the aim of (re)formatting the new
> > - * map[i] the next time through the inner loop.
> > - */
> > - out->bmv_length = XFS_FSB_TO_BB(mp, elen);
> > - out->bmv_oflags |= BMV_OF_SHARED;
> > - if (elen != map->br_blockcount) {
> > - *next_map = *map;
> > - next_map->br_startblock += elen;
> > - next_map->br_startoff += elen;
> > - next_map->br_blockcount -= elen;
> > - }
> > - map->br_blockcount -= elen;
> > - } else {
> > - /*
> > - * There's an unshared extent (agbno, ebno - agbno)
> > - * followed by shared extent at (ebno, elen). Shrink
> > - * the reported extent length to cover only the unshared
> > - * extent and prepare to move up the start of map[i] to
> > - * ebno, with the aim of (re)formatting the new map[i]
> > - * the next time through the inner loop.
> > - */
> > - *next_map = *map;
> > - nlen = ebno - agbno;
> > - out->bmv_length = XFS_FSB_TO_BB(mp, nlen);
> > - next_map->br_startblock += nlen;
> > - next_map->br_startoff += nlen;
> > - next_map->br_blockcount -= nlen;
> > - map->br_blockcount -= nlen;
> > - }
> > + bmv->bmv_offset = p->bmv_offset + p->bmv_length;
> > + bmv->bmv_length = max(0LL, bmv_end - bmv->bmv_offset);
> > + bmv->bmv_entries++;
> > +}
> >
> > - return 0;
> > +static inline bool xfs_getbmap_full(struct getbmapx *bmv, int nr_entries)
> > +{
> > + return bmv->bmv_length == 0 || nr_entries >= bmv->bmv_count - 1;
> > }
> >
> > /*
> > @@ -539,119 +483,72 @@ xfs_getbmap(
> > xfs_bmap_format_t formatter, /* format to user */
> > void *arg) /* formatter arg */
> > {
> > - int64_t bmvend; /* last block requested */
> > - int error = 0; /* return value */
> > - int64_t fixlen; /* length for -1 case */
> > - int i; /* extent number */
> > - int lock; /* lock state */
> > - xfs_bmbt_irec_t *map; /* buffer for user's data */
> > - xfs_mount_t *mp; /* file system mount point */
> > - int nex; /* # of user extents can do */
> > - int subnex; /* # of bmapi's can do */
> > - int nmap; /* number of map entries */
> > - struct getbmapx *out; /* output structure */
> > - int whichfork; /* data or attr fork */
> > - int prealloced; /* this is a file with
> > - * preallocated data space */
> > - int iflags; /* interface flags */
> > - int bmapi_flags; /* flags for xfs_bmapi */
> > - int cur_ext = 0;
> > - struct xfs_bmbt_irec inject_map;
> > -
> > - mp = ip->i_mount;
> > - iflags = bmv->bmv_iflags;
> > + struct xfs_mount *mp = ip->i_mount;
> > + int iflags = bmv->bmv_iflags;
> > + int whichfork, lock, i, nr_entries = 0, error = 0;
> > + int64_t bmv_end, max_len;
> > + xfs_fileoff_t bno, first_bno;
> > + struct xfs_ifork *ifp;
> > + struct getbmapx *out;
> > + struct xfs_bmbt_irec got, rec;
> > + xfs_filblks_t len;
> > + xfs_extnum_t idx;
> >
> > #ifndef DEBUG
> > /* Only allow CoW fork queries if we're debugging. */
> > if (iflags & BMV_IF_COWFORK)
> > return -EINVAL;
> > #endif
> > +
> > if ((iflags & BMV_IF_ATTRFORK) && (iflags & BMV_IF_COWFORK))
> > return -EINVAL;
> >
> > + if (bmv->bmv_count <= 1)
> > + return -EINVAL;
> > + if (bmv->bmv_count > ULONG_MAX / sizeof(struct getbmapx))
> > + return -ENOMEM;
> > +
> > + if (bmv->bmv_length < -1)
> > + return -EINVAL;
> > +
> > + bmv->bmv_entries = 0;
> > + if (bmv->bmv_length == 0)
> > + return 0;
> > +
> > + out = kmem_zalloc_large(bmv->bmv_count * sizeof(struct getbmapx), 0);
> > + if (!out)
> > + return -ENOMEM;
> > +
> > if (iflags & BMV_IF_ATTRFORK)
> > whichfork = XFS_ATTR_FORK;
> > else if (iflags & BMV_IF_COWFORK)
> > whichfork = XFS_COW_FORK;
> > else
> > whichfork = XFS_DATA_FORK;
> > + ifp = XFS_IFORK_PTR(ip, whichfork);
> >
> > + xfs_ilock(ip, XFS_IOLOCK_SHARED);
> > switch (whichfork) {
> > case XFS_ATTR_FORK:
> > - if (XFS_IFORK_Q(ip)) {
> > - if (ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS &&
> > - ip->i_d.di_aformat != XFS_DINODE_FMT_BTREE &&
> > - ip->i_d.di_aformat != XFS_DINODE_FMT_LOCAL)
> > - return -EINVAL;
> > - } else if (unlikely(
> > - ip->i_d.di_aformat != 0 &&
> > - ip->i_d.di_aformat != XFS_DINODE_FMT_EXTENTS)) {
> > - XFS_ERROR_REPORT("xfs_getbmap", XFS_ERRLEVEL_LOW,
> > - ip->i_mount);
> > - return -EFSCORRUPTED;
> > - }
> > + if (!XFS_IFORK_Q(ip))
> > + goto out_unlock_iolock;
> >
> > - prealloced = 0;
> > - fixlen = 1LL << 32;
> > + max_len = 1LL << 32;
> > + lock = xfs_ilock_attr_map_shared(ip);
> > break;
> > case XFS_COW_FORK:
> > - if (ip->i_cformat != XFS_DINODE_FMT_EXTENTS)
> > - return -EINVAL;
> > + /* No CoW fork? Just return */
> > + if (!ifp)
> > + goto out_unlock_iolock;
> >
> > - if (xfs_get_cowextsz_hint(ip)) {
> > - prealloced = 1;
> > - fixlen = mp->m_super->s_maxbytes;
> > - } else {
> > - prealloced = 0;
> > - fixlen = XFS_ISIZE(ip);
> > - }
> > - break;
> > - default:
> > - /* Local format data forks report no extents. */
> > - if (ip->i_d.di_format == XFS_DINODE_FMT_LOCAL) {
> > - bmv->bmv_entries = 0;
> > - return 0;
> > - }
> > - if (ip->i_d.di_format != XFS_DINODE_FMT_EXTENTS &&
> > - ip->i_d.di_format != XFS_DINODE_FMT_BTREE)
> > - return -EINVAL;
> > + if (xfs_get_cowextsz_hint(ip))
> > + max_len = mp->m_super->s_maxbytes;
> > + else
> > + max_len = XFS_ISIZE(ip);
> >
> > - if (xfs_get_extsz_hint(ip) ||
> > - ip->i_d.di_flags & (XFS_DIFLAG_PREALLOC|XFS_DIFLAG_APPEND)){
> > - prealloced = 1;
> > - fixlen = mp->m_super->s_maxbytes;
> > - } else {
> > - prealloced = 0;
> > - fixlen = XFS_ISIZE(ip);
> > - }
> > + lock = XFS_ILOCK_SHARED;
> > + xfs_ilock(ip, lock);
> > break;
> > - }
> > -
> > - if (bmv->bmv_length == -1) {
> > - fixlen = XFS_FSB_TO_BB(mp, XFS_B_TO_FSB(mp, fixlen));
> > - bmv->bmv_length =
> > - max_t(int64_t, fixlen - bmv->bmv_offset, 0);
> > - } else if (bmv->bmv_length == 0) {
> > - bmv->bmv_entries = 0;
> > - return 0;
> > - } else if (bmv->bmv_length < 0) {
> > - return -EINVAL;
> > - }
> > -
> > - nex = bmv->bmv_count - 1;
> > - if (nex <= 0)
> > - return -EINVAL;
> > - bmvend = bmv->bmv_offset + bmv->bmv_length;
> > -
> > -
> > - if (bmv->bmv_count > ULONG_MAX / sizeof(struct getbmapx))
> > - return -ENOMEM;
> > - out = kmem_zalloc_large(bmv->bmv_count * sizeof(struct getbmapx), 0);
> > - if (!out)
> > - return -ENOMEM;
> > -
> > - xfs_ilock(ip, XFS_IOLOCK_SHARED);
> > - switch (whichfork) {
> > case XFS_DATA_FORK:
> > if (!(iflags & BMV_IF_DELALLOC) &&
> > (ip->i_delayed_blks || XFS_ISIZE(ip) > ip->i_d.di_size)) {
> > @@ -669,147 +566,121 @@ xfs_getbmap(
> > */
> > }
> >
> > + if (xfs_get_extsz_hint(ip) ||
> > + (ip->i_d.di_flags &
> > + (XFS_DIFLAG_PREALLOC | XFS_DIFLAG_APPEND)))
> > + max_len = mp->m_super->s_maxbytes;
> > + else
> > + max_len = XFS_ISIZE(ip);
> > +
> > lock = xfs_ilock_data_map_shared(ip);
> > break;
> > - case XFS_COW_FORK:
> > - lock = XFS_ILOCK_SHARED;
> > - xfs_ilock(ip, lock);
> > - break;
> > - case XFS_ATTR_FORK:
> > - lock = xfs_ilock_attr_map_shared(ip);
> > + }
> > +
> > + switch (XFS_IFORK_FORMAT(ip, whichfork)) {
> > + case XFS_DINODE_FMT_EXTENTS:
> > + case XFS_DINODE_FMT_BTREE:
> > break;
> > + case XFS_DINODE_FMT_LOCAL:
> > + /* Local format inode forks report no extents. */
> > + goto out_unlock_ilock;
> > + default:
> > + error = -EINVAL;
> > + goto out_unlock_ilock;
> > }
> >
> > - /*
> > - * Don't let nex be bigger than the number of extents
> > - * we can have assuming alternating holes and real extents.
> > - */
> > - if (nex > XFS_IFORK_NEXTENTS(ip, whichfork) * 2 + 1)
> > - nex = XFS_IFORK_NEXTENTS(ip, whichfork) * 2 + 1;
> > + if (bmv->bmv_length == -1) {
> > + max_len = XFS_FSB_TO_BB(mp, XFS_B_TO_FSB(mp, max_len));
> > + bmv->bmv_length = max(0LL, max_len - bmv->bmv_offset);
> > + }
> >
> > - bmapi_flags = xfs_bmapi_aflag(whichfork);
> > - if (!(iflags & BMV_IF_PREALLOC))
> > - bmapi_flags |= XFS_BMAPI_IGSTATE;
> > + bmv_end = bmv->bmv_offset + bmv->bmv_length;
> >
> > - /*
> > - * Allocate enough space to handle "subnex" maps at a time.
> > - */
> > - error = -ENOMEM;
> > - subnex = 16;
> > - map = kmem_alloc(subnex * sizeof(*map), KM_MAYFAIL | KM_NOFS);
> > - if (!map)
> > + first_bno = bno = XFS_BB_TO_FSBT(mp, bmv->bmv_offset);
> > + len = XFS_BB_TO_FSB(mp, bmv->bmv_length);
> > +
> > + if (!(ifp->if_flags & XFS_IFEXTENTS)) {
> > + error = xfs_iread_extents(NULL, ip, whichfork);
> > + if (error)
> > + goto out_unlock_ilock;
> > + }
> > +
> > + if (!xfs_iext_lookup_extent(ip, ifp, bno, &idx, &got))
> > goto out_unlock_ilock;
> >
> > - bmv->bmv_entries = 0;
> > + while (!xfs_getbmap_full(bmv, nr_entries)) {
> > + struct getbmapx *p = &out[nr_entries];
> >
> > - if (XFS_IFORK_NEXTENTS(ip, whichfork) == 0 &&
> > - (whichfork == XFS_ATTR_FORK || !(iflags & BMV_IF_DELALLOC))) {
> > - error = 0;
> > - goto out_free_map;
> > - }
> > + xfs_trim_extent(&got, first_bno, len);
> >
> > - do {
> > - nmap = (nex> subnex) ? subnex : nex;
> > - error = xfs_bmapi_read(ip, XFS_BB_TO_FSBT(mp, bmv->bmv_offset),
> > - XFS_BB_TO_FSB(mp, bmv->bmv_length),
> > - map, &nmap, bmapi_flags);
> > - if (error)
> > - goto out_free_map;
> > - ASSERT(nmap <= subnex);
> > -
> > - for (i = 0; i < nmap && bmv->bmv_length &&
> > - cur_ext < bmv->bmv_count - 1; i++) {
> > - out[cur_ext].bmv_oflags = 0;
> > - if (map[i].br_state == XFS_EXT_UNWRITTEN)
> > - out[cur_ext].bmv_oflags |= BMV_OF_PREALLOC;
> > - else if (map[i].br_startblock == DELAYSTARTBLOCK)
> > - out[cur_ext].bmv_oflags |= BMV_OF_DELALLOC;
> > - out[cur_ext].bmv_offset =
> > - XFS_FSB_TO_BB(mp, map[i].br_startoff);
> > - out[cur_ext].bmv_length =
> > - XFS_FSB_TO_BB(mp, map[i].br_blockcount);
> > - out[cur_ext].bmv_unused1 = 0;
> > - out[cur_ext].bmv_unused2 = 0;
> > + /*
> > + * Report an entry for a hole if this extent doesn't directly
> > + * follow the previous one.
> > + */
> > + if (got.br_startoff > bno) {
> > + xfs_getbmap_report_hole(ip, bmv, bmv_end, bno,
> > + got.br_startoff, p++);
> > + if (xfs_getbmap_full(bmv, ++nr_entries))
> > + break;
> > + }
> >
> > - /*
> > - * delayed allocation extents that start beyond EOF can
> > - * occur due to speculative EOF allocation when the
> > - * delalloc extent is larger than the largest freespace
> > - * extent at conversion time. These extents cannot be
> > - * converted by data writeback, so can exist here even
> > - * if we are not supposed to be finding delalloc
> > - * extents.
> > - */
> > - if (map[i].br_startblock == DELAYSTARTBLOCK &&
> > - map[i].br_startoff < XFS_B_TO_FSB(mp, XFS_ISIZE(ip)))
> > - ASSERT((iflags & BMV_IF_DELALLOC) != 0);
> > -
> > - if (map[i].br_startblock == HOLESTARTBLOCK &&
> > - whichfork == XFS_ATTR_FORK) {
> > - /* came to the end of attribute fork */
> > - out[cur_ext].bmv_oflags |= BMV_OF_LAST;
> > - goto out_free_map;
> > - }
> > + /*
> > + * In order to report shared extents accurately, we report each
> > + * distinct shared / unshared part of a single bmbt record with
> > + * an individual getbmapx record.
> > + */
> > + rec = got;
> > + for (;;) {
>
> while (!xfs_getbmap_full()) ?
Yeah.
> > - if (!xfs_getbmapx_fix_eof_hole(ip, whichfork,
> > - &out[cur_ext], prealloced, bmvend,
> > - map[i].br_startblock,
> > - inject_map.br_startblock != NULLFSBLOCK))
> > - goto out_free_map;
> > + xfs_getbmap_report_one(ip, bmv, bmv_end, &rec, p);
> > + if (shared)
> > + p->bmv_oflags |= BMV_OF_SHARED;
>
> Shouldn't we advance p/nr_entries? What if we have a single partially
> shared extent? Also, what's the difference between nr_entries and
> bmv->bmv_entries? They both track the number of bmv entries we've
> filled out, right?
We should, but I messed it up. And no test caught it..
> > + if (!xfs_iext_get_extent(ifp, ++idx, &got)) {
> > + xfs_fileoff_t end = XFS_B_TO_FSB(mp, XFS_ISIZE(ip));
> > +
> > + p->bmv_oflags |= BMV_OF_LAST;
>
> Isn't BMV_OF_LAST supposed to be set only on the last extent of the
> dataset returned? If I ask for the mappings for blocks 100-200 and
> there's a hole from 190-200, shouldn't OF_LAST be set on the 190-200
> extent?
BMV_OF_LAST doesn't seem to be document, and isn't checked by any
any userspace I could find. But my interpretation was that it's
supposed to be set on the last extent of a file, based on:
#define BMV_OF_LAST 0x4 /* segment is the last in the file */
now of course we could argue of a hole is an extent in a file;
by any normal defintion it isn't, but in terms of getbmap it
could be considered one.
The old code did this to set it:
if (startblock == HOLESTARTBLOCK) {
...
} else {
....
if (!moretocome &&
xfs_iext_bno_to_ext(ifp, fileblock, &lastx) &&
(lastx == xfs_iext_count(ifp) - 1))
out->bmv_oflags |= BMV_OF_LAST;
}
which means it sets it on the last actually allocated extent in a file
for the general ase.
But it also does a weird thing for holes in attr forks where it sets
BMV_OF_LAST on an entry that is beyond bmv_entries and this should
not even be considered valid by the caller.
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