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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * Copyright (C) 2016 Oracle.  All Rights Reserved.
  * Author: Darrick J. Wong <darrick.wong@oracle.com>
  */
 #include "xfs.h"
 #include "xfs_fs.h"
 #include "xfs_shared.h"
 #include "xfs_format.h"
 #include "xfs_log_format.h"
 #include "xfs_trans_resv.h"
 #include "xfs_mount.h"
 #include "xfs_defer.h"
 #include "xfs_inode.h"
 #include "xfs_trans.h"
 #include "xfs_bmap.h"
 #include "xfs_bmap_util.h"
 #include "xfs_trace.h"
 #include "xfs_icache.h"
 #include "xfs_btree.h"
 #include "xfs_refcount_btree.h"
 #include "xfs_refcount.h"
 #include "xfs_bmap_btree.h"
 #include "xfs_trans_space.h"
 #include "xfs_bit.h"
 #include "xfs_alloc.h"
 #include "xfs_quota.h"
 #include "xfs_reflink.h"
 #include "xfs_iomap.h"
 #include "xfs_ag.h"
 #include "xfs_ag_resv.h"
 
 /*
  * Copy on Write of Shared Blocks
  *
  * XFS must preserve "the usual" file semantics even when two files share
  * the same physical blocks.  This means that a write to one file must not
  * alter the blocks in a different file; the way that we'll do that is
  * through the use of a copy-on-write mechanism.  At a high level, that
  * means that when we want to write to a shared block, we allocate a new
  * block, write the data to the new block, and if that succeeds we map the
  * new block into the file.
  *
  * XFS provides a "delayed allocation" mechanism that defers the allocation
  * of disk blocks to dirty-but-not-yet-mapped file blocks as long as
  * possible.  This reduces fragmentation by enabling the filesystem to ask
  * for bigger chunks less often, which is exactly what we want for CoW.
  *
  * The delalloc mechanism begins when the kernel wants to make a block
  * writable (write_begin or page_mkwrite).  If the offset is not mapped, we
  * create a delalloc mapping, which is a regular in-core extent, but without
  * a real startblock.  (For delalloc mappings, the startblock encodes both
  * a flag that this is a delalloc mapping, and a worst-case estimate of how
  * many blocks might be required to put the mapping into the BMBT.)  delalloc
  * mappings are a reservation against the free space in the filesystem;
  * adjacent mappings can also be combined into fewer larger mappings.
  *
  * As an optimization, the CoW extent size hint (cowextsz) creates
  * outsized aligned delalloc reservations in the hope of landing out of
  * order nearby CoW writes in a single extent on disk, thereby reducing
  * fragmentation and improving future performance.
  *
  * D: --RRRRRRSSSRRRRRRRR--- (data fork)
  * C: ------DDDDDDD--------- (CoW fork)
  *
  * When dirty pages are being written out (typically in writepage), the
  * delalloc reservations are converted into unwritten mappings by
  * allocating blocks and replacing the delalloc mapping with real ones.
  * A delalloc mapping can be replaced by several unwritten ones if the
  * free space is fragmented.
  *
  * D: --RRRRRRSSSRRRRRRRR---
  * C: ------UUUUUUU---------
  *
  * We want to adapt the delalloc mechanism for copy-on-write, since the
  * write paths are similar.  The first two steps (creating the reservation
  * and allocating the blocks) are exactly the same as delalloc except that
  * the mappings must be stored in a separate CoW fork because we do not want
  * to disturb the mapping in the data fork until we're sure that the write
  * succeeded.  IO completion in this case is the process of removing the old
  * mapping from the data fork and moving the new mapping from the CoW fork to
  * the data fork.  This will be discussed shortly.
  *
  * For now, unaligned directio writes will be bounced back to the page cache.
  * Block-aligned directio writes will use the same mechanism as buffered
  * writes.
  *
  * Just prior to submitting the actual disk write requests, we convert
  * the extents representing the range of the file actually being written
  * (as opposed to extra pieces created for the cowextsize hint) to real
  * extents.  This will become important in the next step:
  *
  * D: --RRRRRRSSSRRRRRRRR---
  * C: ------UUrrUUU---------
  *
  * CoW remapping must be done after the data block write completes,
  * because we don't want to destroy the old data fork map until we're sure
  * the new block has been written.  Since the new mappings are kept in a
  * separate fork, we can simply iterate these mappings to find the ones
  * that cover the file blocks that we just CoW'd.  For each extent, simply
  * unmap the corresponding range in the data fork, map the new range into
  * the data fork, and remove the extent from the CoW fork.  Because of
  * the presence of the cowextsize hint, however, we must be careful
  * only to remap the blocks that we've actually written out --  we must
  * never remap delalloc reservations nor CoW staging blocks that have
  * yet to be written.  This corresponds exactly to the real extents in
  * the CoW fork:
  *
  * D: --RRRRRRrrSRRRRRRRR---
  * C: ------UU--UUU---------
  *
  * Since the remapping operation can be applied to an arbitrary file
  * range, we record the need for the remap step as a flag in the ioend
  * instead of declaring a new IO type.  This is required for direct io
  * because we only have ioend for the whole dio, and we have to be able to
  * remember the presence of unwritten blocks and CoW blocks with a single
  * ioend structure.  Better yet, the more ground we can cover with one
  * ioend, the better.
  */
 
 /*
  * Given an AG extent, find the lowest-numbered run of shared blocks
  * within that range and return the range in fbno/flen.  If
  * find_end_of_shared is true, return the longest contiguous extent of
  * shared blocks.  If there are no shared extents, fbno and flen will
  * be set to NULLAGBLOCK and 0, respectively.
  */
 static int
 xfs_reflink_find_shared(
     struct xfs_perag    *pag,
     struct xfs_trans    *tp,
     xfs_agblock_t       agbno,
     xfs_extlen_t        aglen,
     xfs_agblock_t       *fbno,
     xfs_extlen_t        *flen,
     bool            find_end_of_shared)
 {
     struct xfs_buf      *agbp;
     struct xfs_btree_cur    *cur;
     int         error;
 
     error = xfs_alloc_read_agf(pag, tp, 0, &agbp);
     if (error)
         return error;
 
     cur = xfs_refcountbt_init_cursor(pag->pag_mount, tp, agbp, pag);
 
     error = xfs_refcount_find_shared(cur, agbno, aglen, fbno, flen,
             find_end_of_shared);
 
     xfs_btree_del_cursor(cur, error);
 
     xfs_trans_brelse(tp, agbp);
     return error;
 }
 
 /*
  * Trim the mapping to the next block where there's a change in the
  * shared/unshared status.  More specifically, this means that we
  * find the lowest-numbered extent of shared blocks that coincides with
  * the given block mapping.  If the shared extent overlaps the start of
  * the mapping, trim the mapping to the end of the shared extent.  If
  * the shared region intersects the mapping, trim the mapping to the
  * start of the shared extent.  If there are no shared regions that
  * overlap, just return the original extent.
  */
 int
 xfs_reflink_trim_around_shared(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *irec,
     bool            *shared)
 {
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_perag    *pag;
     xfs_agblock_t       agbno;
     xfs_extlen_t        aglen;
     xfs_agblock_t       fbno;
     xfs_extlen_t        flen;
     int         error = 0;
 
     /* Holes, unwritten, and delalloc extents cannot be shared */
     if (!xfs_is_cow_inode(ip) || !xfs_bmap_is_written_extent(irec)) {
         *shared = false;
         return 0;
     }
 
     trace_xfs_reflink_trim_around_shared(ip, irec);
 
     pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, irec->br_startblock));
     agbno = XFS_FSB_TO_AGBNO(mp, irec->br_startblock);
     aglen = irec->br_blockcount;
 
     error = xfs_reflink_find_shared(pag, NULL, agbno, aglen, &fbno, &flen,
             true);
     xfs_perag_put(pag);
     if (error)
         return error;
 
     *shared = false;
     if (fbno == NULLAGBLOCK) {
         /* No shared blocks at all. */
         return 0;
     } else if (fbno == agbno) {
         /*
          * The start of this extent is shared.  Truncate the
          * mapping at the end of the shared region so that a
          * subsequent iteration starts at the start of the
          * unshared region.
          */
         irec->br_blockcount = flen;
         *shared = true;
         return 0;
     } else {
         /*
          * There's a shared extent midway through this extent.
          * Truncate the mapping at the start of the shared
          * extent so that a subsequent iteration starts at the
          * start of the shared region.
          */
         irec->br_blockcount = fbno - agbno;
         return 0;
     }
 }
 
 int
 xfs_bmap_trim_cow(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     bool            *shared)
 {
     /* We can't update any real extents in always COW mode. */
     if (xfs_is_always_cow_inode(ip) &&
         !isnullstartblock(imap->br_startblock)) {
         *shared = true;
         return 0;
     }
 
     /* Trim the mapping to the nearest shared extent boundary. */
     return xfs_reflink_trim_around_shared(ip, imap, shared);
 }
 
 static int
 xfs_reflink_convert_cow_locked(
     struct xfs_inode    *ip,
     xfs_fileoff_t       offset_fsb,
     xfs_filblks_t       count_fsb)
 {
     struct xfs_iext_cursor  icur;
     struct xfs_bmbt_irec    got;
     struct xfs_btree_cur    *dummy_cur = NULL;
     int         dummy_logflags;
     int         error = 0;
 
     if (!xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, &got))
         return 0;
 
     do {
         if (got.br_startoff >= offset_fsb + count_fsb)
             break;
         if (got.br_state == XFS_EXT_NORM)
             continue;
         if (WARN_ON_ONCE(isnullstartblock(got.br_startblock)))
             return -EIO;
 
         xfs_trim_extent(&got, offset_fsb, count_fsb);
         if (!got.br_blockcount)
             continue;
 
         got.br_state = XFS_EXT_NORM;
         error = xfs_bmap_add_extent_unwritten_real(NULL, ip,
                 XFS_COW_FORK, &icur, &dummy_cur, &got,
                 &dummy_logflags);
         if (error)
             return error;
     } while (xfs_iext_next_extent(ip->i_cowfp, &icur, &got));
 
     return error;
 }
 
 /* Convert all of the unwritten CoW extents in a file's range to real ones. */
 int
 xfs_reflink_convert_cow(
     struct xfs_inode    *ip,
     xfs_off_t       offset,
     xfs_off_t       count)
 {
     struct xfs_mount    *mp = ip->i_mount;
     xfs_fileoff_t       offset_fsb = XFS_B_TO_FSBT(mp, offset);
     xfs_fileoff_t       end_fsb = XFS_B_TO_FSB(mp, offset + count);
     xfs_filblks_t       count_fsb = end_fsb - offset_fsb;
     int         error;
 
     ASSERT(count != 0);
 
     xfs_ilock(ip, XFS_ILOCK_EXCL);
     error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     return error;
 }
 
 /*
  * Find the extent that maps the given range in the COW fork. Even if the extent
  * is not shared we might have a preallocation for it in the COW fork. If so we
  * use it that rather than trigger a new allocation.
  */
 static int
 xfs_find_trim_cow_extent(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     struct xfs_bmbt_irec    *cmap,
     bool            *shared,
     bool            *found)
 {
     xfs_fileoff_t       offset_fsb = imap->br_startoff;
     xfs_filblks_t       count_fsb = imap->br_blockcount;
     struct xfs_iext_cursor  icur;
 
     *found = false;
 
     /*
      * If we don't find an overlapping extent, trim the range we need to
      * allocate to fit the hole we found.
      */
     if (!xfs_iext_lookup_extent(ip, ip->i_cowfp, offset_fsb, &icur, cmap))
         cmap->br_startoff = offset_fsb + count_fsb;
     if (cmap->br_startoff > offset_fsb) {
         xfs_trim_extent(imap, imap->br_startoff,
                 cmap->br_startoff - imap->br_startoff);
         return xfs_bmap_trim_cow(ip, imap, shared);
     }
 
     *shared = true;
     if (isnullstartblock(cmap->br_startblock)) {
         xfs_trim_extent(imap, cmap->br_startoff, cmap->br_blockcount);
         return 0;
     }
 
     /* real extent found - no need to allocate */
     xfs_trim_extent(cmap, offset_fsb, count_fsb);
     *found = true;
     return 0;
 }
 
 static int
 xfs_reflink_convert_unwritten(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     struct xfs_bmbt_irec    *cmap,
     bool            convert_now)
 {
     xfs_fileoff_t       offset_fsb = imap->br_startoff;
     xfs_filblks_t       count_fsb = imap->br_blockcount;
     int         error;
 
     /*
      * cmap might larger than imap due to cowextsize hint.
      */
     xfs_trim_extent(cmap, offset_fsb, count_fsb);
 
     /*
      * COW fork extents are supposed to remain unwritten until we're ready
      * to initiate a disk write.  For direct I/O we are going to write the
      * data and need the conversion, but for buffered writes we're done.
      */
     if (!convert_now || cmap->br_state == XFS_EXT_NORM)
         return 0;
 
     trace_xfs_reflink_convert_cow(ip, cmap);
 
     error = xfs_reflink_convert_cow_locked(ip, offset_fsb, count_fsb);
     if (!error)
         cmap->br_state = XFS_EXT_NORM;
 
     return error;
 }
 
 static int
 xfs_reflink_fill_cow_hole(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     struct xfs_bmbt_irec    *cmap,
     bool            *shared,
     uint            *lockmode,
     bool            convert_now)
 {
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_trans    *tp;
     xfs_filblks_t       resaligned;
     xfs_extlen_t        resblks;
     int         nimaps;
     int         error;
     bool            found;
 
     resaligned = xfs_aligned_fsb_count(imap->br_startoff,
         imap->br_blockcount, xfs_get_cowextsz_hint(ip));
     resblks = XFS_DIOSTRAT_SPACE_RES(mp, resaligned);
 
     xfs_iunlock(ip, *lockmode);
     *lockmode = 0;
 
     error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write, resblks, 0,
             false, &tp);
     if (error)
         return error;
 
     *lockmode = XFS_ILOCK_EXCL;
 
     error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
     if (error || !*shared)
         goto out_trans_cancel;
 
     if (found) {
         xfs_trans_cancel(tp);
         goto convert;
     }
 
     ASSERT(cmap->br_startoff > imap->br_startoff);
 
     /* Allocate the entire reservation as unwritten blocks. */
     nimaps = 1;
     error = xfs_bmapi_write(tp, ip, imap->br_startoff, imap->br_blockcount,
             XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, 0, cmap,
             &nimaps);
     if (error)
         goto out_trans_cancel;
 
     xfs_inode_set_cowblocks_tag(ip);
     error = xfs_trans_commit(tp);
     if (error)
         return error;
 
     /*
      * Allocation succeeded but the requested range was not even partially
      * satisfied?  Bail out!
      */
     if (nimaps == 0)
         return -ENOSPC;
 
 convert:
     return xfs_reflink_convert_unwritten(ip, imap, cmap, convert_now);
 
 out_trans_cancel:
     xfs_trans_cancel(tp);
     return error;
 }
 
 static int
 xfs_reflink_fill_delalloc(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     struct xfs_bmbt_irec    *cmap,
     bool            *shared,
     uint            *lockmode,
     bool            convert_now)
 {
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_trans    *tp;
     int         nimaps;
     int         error;
     bool            found;
 
     do {
         xfs_iunlock(ip, *lockmode);
         *lockmode = 0;
 
         error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write, 0, 0,
                 false, &tp);
         if (error)
             return error;
 
         *lockmode = XFS_ILOCK_EXCL;
 
         error = xfs_find_trim_cow_extent(ip, imap, cmap, shared,
                 &found);
         if (error || !*shared)
             goto out_trans_cancel;
 
         if (found) {
             xfs_trans_cancel(tp);
             break;
         }
 
         ASSERT(isnullstartblock(cmap->br_startblock) ||
                cmap->br_startblock == DELAYSTARTBLOCK);
 
         /*
          * Replace delalloc reservation with an unwritten extent.
          */
         nimaps = 1;
         error = xfs_bmapi_write(tp, ip, cmap->br_startoff,
                 cmap->br_blockcount,
                 XFS_BMAPI_COWFORK | XFS_BMAPI_PREALLOC, 0,
                 cmap, &nimaps);
         if (error)
             goto out_trans_cancel;
 
         xfs_inode_set_cowblocks_tag(ip);
         error = xfs_trans_commit(tp);
         if (error)
             return error;
 
         /*
          * Allocation succeeded but the requested range was not even
          * partially satisfied?  Bail out!
          */
         if (nimaps == 0)
             return -ENOSPC;
     } while (cmap->br_startoff + cmap->br_blockcount <= imap->br_startoff);
 
     return xfs_reflink_convert_unwritten(ip, imap, cmap, convert_now);
 
 out_trans_cancel:
     xfs_trans_cancel(tp);
     return error;
 }
 
 /* Allocate all CoW reservations covering a range of blocks in a file. */
 int
 xfs_reflink_allocate_cow(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *imap,
     struct xfs_bmbt_irec    *cmap,
     bool            *shared,
     uint            *lockmode,
     bool            convert_now)
 {
     int         error;
     bool            found;
 
     ASSERT(xfs_isilocked(ip, XFS_ILOCK_EXCL));
     if (!ip->i_cowfp) {
         ASSERT(!xfs_is_reflink_inode(ip));
         xfs_ifork_init_cow(ip);
     }
 
     error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
     if (error || !*shared)
         return error;
 
     /* CoW fork has a real extent */
     if (found)
         return xfs_reflink_convert_unwritten(ip, imap, cmap,
                 convert_now);
 
     /*
      * CoW fork does not have an extent and data extent is shared.
      * Allocate a real extent in the CoW fork.
      */
     if (cmap->br_startoff > imap->br_startoff)
         return xfs_reflink_fill_cow_hole(ip, imap, cmap, shared,
                 lockmode, convert_now);
 
     /*
      * CoW fork has a delalloc reservation. Replace it with a real extent.
      * There may or may not be a data fork mapping.
      */
     if (isnullstartblock(cmap->br_startblock) ||
         cmap->br_startblock == DELAYSTARTBLOCK)
         return xfs_reflink_fill_delalloc(ip, imap, cmap, shared,
                 lockmode, convert_now);
 
     /* Shouldn't get here. */
     ASSERT(0);
     return -EFSCORRUPTED;
 }
 
 /*
  * Cancel CoW reservations for some block range of an inode.
  *
  * If cancel_real is true this function cancels all COW fork extents for the
  * inode; if cancel_real is false, real extents are not cleared.
  *
  * Caller must have already joined the inode to the current transaction. The
  * inode will be joined to the transaction returned to the caller.
  */
 int
 xfs_reflink_cancel_cow_blocks(
     struct xfs_inode        *ip,
     struct xfs_trans        **tpp,
     xfs_fileoff_t           offset_fsb,
     xfs_fileoff_t           end_fsb,
     bool                cancel_real)
 {
     struct xfs_ifork        *ifp = xfs_ifork_ptr(ip, XFS_COW_FORK);
     struct xfs_bmbt_irec        got, del;
     struct xfs_iext_cursor      icur;
     int             error = 0;
 
     if (!xfs_inode_has_cow_data(ip))
         return 0;
     if (!xfs_iext_lookup_extent_before(ip, ifp, &end_fsb, &icur, &got))
         return 0;
 
     /* Walk backwards until we're out of the I/O range... */
     while (got.br_startoff + got.br_blockcount > offset_fsb) {
         del = got;
         xfs_trim_extent(&del, offset_fsb, end_fsb - offset_fsb);
 
         /* Extent delete may have bumped ext forward */
         if (!del.br_blockcount) {
             xfs_iext_prev(ifp, &icur);
             goto next_extent;
         }
 
         trace_xfs_reflink_cancel_cow(ip, &del);
 
         if (isnullstartblock(del.br_startblock)) {
             error = xfs_bmap_del_extent_delay(ip, XFS_COW_FORK,
                     &icur, &got, &del);
             if (error)
                 break;
         } else if (del.br_state == XFS_EXT_UNWRITTEN || cancel_real) {
             ASSERT((*tpp)->t_firstblock == NULLFSBLOCK);
 
             /* Free the CoW orphan record. */
             xfs_refcount_free_cow_extent(*tpp, del.br_startblock,
                     del.br_blockcount);
 
             xfs_free_extent_later(*tpp, del.br_startblock,
                       del.br_blockcount, NULL);
 
             /* Roll the transaction */
             error = xfs_defer_finish(tpp);
             if (error)
                 break;
 
             /* Remove the mapping from the CoW fork. */
             xfs_bmap_del_extent_cow(ip, &icur, &got, &del);
 
             /* Remove the quota reservation */
             error = xfs_quota_unreserve_blkres(ip,
                     del.br_blockcount);
             if (error)
                 break;
         } else {
             /* Didn't do anything, push cursor back. */
             xfs_iext_prev(ifp, &icur);
         }
 next_extent:
         if (!xfs_iext_get_extent(ifp, &icur, &got))
             break;
     }
 
     /* clear tag if cow fork is emptied */
     if (!ifp->if_bytes)
         xfs_inode_clear_cowblocks_tag(ip);
     return error;
 }
 
 /*
  * Cancel CoW reservations for some byte range of an inode.
  *
  * If cancel_real is true this function cancels all COW fork extents for the
  * inode; if cancel_real is false, real extents are not cleared.
  */
 int
 xfs_reflink_cancel_cow_range(
     struct xfs_inode    *ip,
     xfs_off_t       offset,
     xfs_off_t       count,
     bool            cancel_real)
 {
     struct xfs_trans    *tp;
     xfs_fileoff_t       offset_fsb;
     xfs_fileoff_t       end_fsb;
     int         error;
 
     trace_xfs_reflink_cancel_cow_range(ip, offset, count);
     ASSERT(ip->i_cowfp);
 
     offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
     if (count == NULLFILEOFF)
         end_fsb = NULLFILEOFF;
     else
         end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);
 
     /* Start a rolling transaction to remove the mappings */
     error = xfs_trans_alloc(ip->i_mount, &M_RES(ip->i_mount)->tr_write,
             0, 0, 0, &tp);
     if (error)
         goto out;
 
     xfs_ilock(ip, XFS_ILOCK_EXCL);
     xfs_trans_ijoin(tp, ip, 0);
 
     /* Scrape out the old CoW reservations */
     error = xfs_reflink_cancel_cow_blocks(ip, &tp, offset_fsb, end_fsb,
             cancel_real);
     if (error)
         goto out_cancel;
 
     error = xfs_trans_commit(tp);
 
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     return error;
 
 out_cancel:
     xfs_trans_cancel(tp);
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
 out:
     trace_xfs_reflink_cancel_cow_range_error(ip, error, _RET_IP_);
     return error;
 }
 
 /*
  * Remap part of the CoW fork into the data fork.
  *
  * We aim to remap the range starting at @offset_fsb and ending at @end_fsb
  * into the data fork; this function will remap what it can (at the end of the
  * range) and update @end_fsb appropriately.  Each remap gets its own
  * transaction because we can end up merging and splitting bmbt blocks for
  * every remap operation and we'd like to keep the block reservation
  * requirements as low as possible.
  */
 STATIC int
 xfs_reflink_end_cow_extent(
     struct xfs_inode    *ip,
     xfs_fileoff_t       *offset_fsb,
     xfs_fileoff_t       end_fsb)
 {
     struct xfs_iext_cursor  icur;
     struct xfs_bmbt_irec    got, del, data;
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_trans    *tp;
     struct xfs_ifork    *ifp = xfs_ifork_ptr(ip, XFS_COW_FORK);
     unsigned int        resblks;
     int         nmaps;
     int         error;
 
     /* No COW extents?  That's easy! */
     if (ifp->if_bytes == 0) {
         *offset_fsb = end_fsb;
         return 0;
     }
 
     resblks = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
     error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0,
             XFS_TRANS_RESERVE, &tp);
     if (error)
         return error;
 
     /*
      * Lock the inode.  We have to ijoin without automatic unlock because
      * the lead transaction is the refcountbt record deletion; the data
      * fork update follows as a deferred log item.
      */
     xfs_ilock(ip, XFS_ILOCK_EXCL);
     xfs_trans_ijoin(tp, ip, 0);
 
     error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK,
             XFS_IEXT_REFLINK_END_COW_CNT);
     if (error == -EFBIG)
         error = xfs_iext_count_upgrade(tp, ip,
                 XFS_IEXT_REFLINK_END_COW_CNT);
     if (error)
         goto out_cancel;
 
     /*
      * In case of racing, overlapping AIO writes no COW extents might be
      * left by the time I/O completes for the loser of the race.  In that
      * case we are done.
      */
     if (!xfs_iext_lookup_extent(ip, ifp, *offset_fsb, &icur, &got) ||
         got.br_startoff >= end_fsb) {
         *offset_fsb = end_fsb;
         goto out_cancel;
     }
 
     /*
      * Only remap real extents that contain data.  With AIO, speculative
      * preallocations can leak into the range we are called upon, and we
      * need to skip them.  Preserve @got for the eventual CoW fork
      * deletion; from now on @del represents the mapping that we're
      * actually remapping.
      */
     while (!xfs_bmap_is_written_extent(&got)) {
         if (!xfs_iext_next_extent(ifp, &icur, &got) ||
             got.br_startoff >= end_fsb) {
             *offset_fsb = end_fsb;
             goto out_cancel;
         }
     }
     del = got;
 
     /* Grab the corresponding mapping in the data fork. */
     nmaps = 1;
     error = xfs_bmapi_read(ip, del.br_startoff, del.br_blockcount, &data,
             &nmaps, 0);
     if (error)
         goto out_cancel;
 
     /* We can only remap the smaller of the two extent sizes. */
     data.br_blockcount = min(data.br_blockcount, del.br_blockcount);
     del.br_blockcount = data.br_blockcount;
 
     trace_xfs_reflink_cow_remap_from(ip, &del);
     trace_xfs_reflink_cow_remap_to(ip, &data);
 
     if (xfs_bmap_is_real_extent(&data)) {
         /*
          * If the extent we're remapping is backed by storage (written
          * or not), unmap the extent and drop its refcount.
          */
         xfs_bmap_unmap_extent(tp, ip, &data);
         xfs_refcount_decrease_extent(tp, &data);
         xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT,
                 -data.br_blockcount);
     } else if (data.br_startblock == DELAYSTARTBLOCK) {
         int     done;
 
         /*
          * If the extent we're remapping is a delalloc reservation,
          * we can use the regular bunmapi function to release the
          * incore state.  Dropping the delalloc reservation takes care
          * of the quota reservation for us.
          */
         error = xfs_bunmapi(NULL, ip, data.br_startoff,
                 data.br_blockcount, 0, 1, &done);
         if (error)
             goto out_cancel;
         ASSERT(done);
     }
 
     /* Free the CoW orphan record. */
     xfs_refcount_free_cow_extent(tp, del.br_startblock, del.br_blockcount);
 
     /* Map the new blocks into the data fork. */
     xfs_bmap_map_extent(tp, ip, &del);
 
     /* Charge this new data fork mapping to the on-disk quota. */
     xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_DELBCOUNT,
             (long)del.br_blockcount);
 
     /* Remove the mapping from the CoW fork. */
     xfs_bmap_del_extent_cow(ip, &icur, &got, &del);
 
     error = xfs_trans_commit(tp);
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     if (error)
         return error;
 
     /* Update the caller about how much progress we made. */
     *offset_fsb = del.br_startoff + del.br_blockcount;
     return 0;
 
 out_cancel:
     xfs_trans_cancel(tp);
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     return error;
 }
 
 /*
  * Remap parts of a file's data fork after a successful CoW.
  */
 int
 xfs_reflink_end_cow(
     struct xfs_inode        *ip,
     xfs_off_t           offset,
     xfs_off_t           count)
 {
     xfs_fileoff_t           offset_fsb;
     xfs_fileoff_t           end_fsb;
     int             error = 0;
 
     trace_xfs_reflink_end_cow(ip, offset, count);
 
     offset_fsb = XFS_B_TO_FSBT(ip->i_mount, offset);
     end_fsb = XFS_B_TO_FSB(ip->i_mount, offset + count);
 
     /*
      * Walk forwards until we've remapped the I/O range.  The loop function
      * repeatedly cycles the ILOCK to allocate one transaction per remapped
      * extent.
      *
      * If we're being called by writeback then the pages will still
      * have PageWriteback set, which prevents races with reflink remapping
      * and truncate.  Reflink remapping prevents races with writeback by
      * taking the iolock and mmaplock before flushing the pages and
      * remapping, which means there won't be any further writeback or page
      * cache dirtying until the reflink completes.
      *
      * We should never have two threads issuing writeback for the same file
      * region.  There are also have post-eof checks in the writeback
      * preparation code so that we don't bother writing out pages that are
      * about to be truncated.
      *
      * If we're being called as part of directio write completion, the dio
      * count is still elevated, which reflink and truncate will wait for.
      * Reflink remapping takes the iolock and mmaplock and waits for
      * pending dio to finish, which should prevent any directio until the
      * remap completes.  Multiple concurrent directio writes to the same
      * region are handled by end_cow processing only occurring for the
      * threads which succeed; the outcome of multiple overlapping direct
      * writes is not well defined anyway.
      *
      * It's possible that a buffered write and a direct write could collide
      * here (the buffered write stumbles in after the dio flushes and
      * invalidates the page cache and immediately queues writeback), but we
      * have never supported this 100%.  If either disk write succeeds the
      * blocks will be remapped.
      */
     while (end_fsb > offset_fsb && !error)
         error = xfs_reflink_end_cow_extent(ip, &offset_fsb, end_fsb);
 
     if (error)
         trace_xfs_reflink_end_cow_error(ip, error, _RET_IP_);
     return error;
 }
 
 /*
  * Free all CoW staging blocks that are still referenced by the ondisk refcount
  * metadata.  The ondisk metadata does not track which inode created the
  * staging extent, so callers must ensure that there are no cached inodes with
  * live CoW staging extents.
  */
 int
 xfs_reflink_recover_cow(
     struct xfs_mount    *mp)
 {
     struct xfs_perag    *pag;
     xfs_agnumber_t      agno;
     int         error = 0;
 
     if (!xfs_has_reflink(mp))
         return 0;
 
     for_each_perag(mp, agno, pag) {
         error = xfs_refcount_recover_cow_leftovers(mp, pag);
         if (error) {
             xfs_perag_put(pag);
             break;
         }
     }
 
     return error;
 }
 
 /*
  * Reflinking (Block) Ranges of Two Files Together
  *
  * First, ensure that the reflink flag is set on both inodes.  The flag is an
  * optimization to avoid unnecessary refcount btree lookups in the write path.
  *
  * Now we can iteratively remap the range of extents (and holes) in src to the
  * corresponding ranges in dest.  Let drange and srange denote the ranges of
  * logical blocks in dest and src touched by the reflink operation.
  *
  * While the length of drange is greater than zero,
  *    - Read src's bmbt at the start of srange ("imap")
  *    - If imap doesn't exist, make imap appear to start at the end of srange
  *      with zero length.
  *    - If imap starts before srange, advance imap to start at srange.
  *    - If imap goes beyond srange, truncate imap to end at the end of srange.
  *    - Punch (imap start - srange start + imap len) blocks from dest at
  *      offset (drange start).
  *    - If imap points to a real range of pblks,
  *         > Increase the refcount of the imap's pblks
  *         > Map imap's pblks into dest at the offset
  *           (drange start + imap start - srange start)
  *    - Advance drange and srange by (imap start - srange start + imap len)
  *
  * Finally, if the reflink made dest longer, update both the in-core and
  * on-disk file sizes.
  *
  * ASCII Art Demonstration:
  *
  * Let's say we want to reflink this source file:
  *
  * ----SSSSSSS-SSSSS----SSSSSS (src file)
  *   <-------------------->
  *
  * into this destination file:
  *
  * --DDDDDDDDDDDDDDDDDDD--DDD (dest file)
  *        <-------------------->
  * '-' means a hole, and 'S' and 'D' are written blocks in the src and dest.
  * Observe that the range has different logical offsets in either file.
  *
  * Consider that the first extent in the source file doesn't line up with our
  * reflink range.  Unmapping  and remapping are separate operations, so we can
  * unmap more blocks from the destination file than we remap.
  *
  * ----SSSSSSS-SSSSS----SSSSSS
  *   <------->
  * --DDDDD---------DDDDD--DDD
  *        <------->
  *
  * Now remap the source extent into the destination file:
  *
  * ----SSSSSSS-SSSSS----SSSSSS
  *   <------->
  * --DDDDD--SSSSSSSDDDDD--DDD
  *        <------->
  *
  * Do likewise with the second hole and extent in our range.  Holes in the
  * unmap range don't affect our operation.
  *
  * ----SSSSSSS-SSSSS----SSSSSS
  *            <---->
  * --DDDDD--SSSSSSS-SSSSS-DDD
  *                 <---->
  *
  * Finally, unmap and remap part of the third extent.  This will increase the
  * size of the destination file.
  *
  * ----SSSSSSS-SSSSS----SSSSSS
  *                  <----->
  * --DDDDD--SSSSSSS-SSSSS----SSS
  *                       <----->
  *
  * Once we update the destination file's i_size, we're done.
  */
 
 /*
  * Ensure the reflink bit is set in both inodes.
  */
 STATIC int
 xfs_reflink_set_inode_flag(
     struct xfs_inode    *src,
     struct xfs_inode    *dest)
 {
     struct xfs_mount    *mp = src->i_mount;
     int         error;
     struct xfs_trans    *tp;
 
     if (xfs_is_reflink_inode(src) && xfs_is_reflink_inode(dest))
         return 0;
 
     error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
     if (error)
         goto out_error;
 
     /* Lock both files against IO */
     if (src->i_ino == dest->i_ino)
         xfs_ilock(src, XFS_ILOCK_EXCL);
     else
         xfs_lock_two_inodes(src, XFS_ILOCK_EXCL, dest, XFS_ILOCK_EXCL);
 
     if (!xfs_is_reflink_inode(src)) {
         trace_xfs_reflink_set_inode_flag(src);
         xfs_trans_ijoin(tp, src, XFS_ILOCK_EXCL);
         src->i_diflags2 |= XFS_DIFLAG2_REFLINK;
         xfs_trans_log_inode(tp, src, XFS_ILOG_CORE);
         xfs_ifork_init_cow(src);
     } else
         xfs_iunlock(src, XFS_ILOCK_EXCL);
 
     if (src->i_ino == dest->i_ino)
         goto commit_flags;
 
     if (!xfs_is_reflink_inode(dest)) {
         trace_xfs_reflink_set_inode_flag(dest);
         xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
         dest->i_diflags2 |= XFS_DIFLAG2_REFLINK;
         xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
         xfs_ifork_init_cow(dest);
     } else
         xfs_iunlock(dest, XFS_ILOCK_EXCL);
 
 commit_flags:
     error = xfs_trans_commit(tp);
     if (error)
         goto out_error;
     return error;
 
 out_error:
     trace_xfs_reflink_set_inode_flag_error(dest, error, _RET_IP_);
     return error;
 }
 
 /*
  * Update destination inode size & cowextsize hint, if necessary.
  */
 int
 xfs_reflink_update_dest(
     struct xfs_inode    *dest,
     xfs_off_t       newlen,
     xfs_extlen_t        cowextsize,
     unsigned int        remap_flags)
 {
     struct xfs_mount    *mp = dest->i_mount;
     struct xfs_trans    *tp;
     int         error;
 
     if (newlen <= i_size_read(VFS_I(dest)) && cowextsize == 0)
         return 0;
 
     error = xfs_trans_alloc(mp, &M_RES(mp)->tr_ichange, 0, 0, 0, &tp);
     if (error)
         goto out_error;
 
     xfs_ilock(dest, XFS_ILOCK_EXCL);
     xfs_trans_ijoin(tp, dest, XFS_ILOCK_EXCL);
 
     if (newlen > i_size_read(VFS_I(dest))) {
         trace_xfs_reflink_update_inode_size(dest, newlen);
         i_size_write(VFS_I(dest), newlen);
         dest->i_disk_size = newlen;
     }
 
     if (cowextsize) {
         dest->i_cowextsize = cowextsize;
         dest->i_diflags2 |= XFS_DIFLAG2_COWEXTSIZE;
     }
 
     xfs_trans_log_inode(tp, dest, XFS_ILOG_CORE);
 
     error = xfs_trans_commit(tp);
     if (error)
         goto out_error;
     return error;
 
 out_error:
     trace_xfs_reflink_update_inode_size_error(dest, error, _RET_IP_);
     return error;
 }
 
 /*
  * Do we have enough reserve in this AG to handle a reflink?  The refcount
  * btree already reserved all the space it needs, but the rmap btree can grow
  * infinitely, so we won't allow more reflinks when the AG is down to the
  * btree reserves.
  */
 static int
 xfs_reflink_ag_has_free_space(
     struct xfs_mount    *mp,
     xfs_agnumber_t      agno)
 {
     struct xfs_perag    *pag;
     int         error = 0;
 
     if (!xfs_has_rmapbt(mp))
         return 0;
 
     pag = xfs_perag_get(mp, agno);
     if (xfs_ag_resv_critical(pag, XFS_AG_RESV_RMAPBT) ||
         xfs_ag_resv_critical(pag, XFS_AG_RESV_METADATA))
         error = -ENOSPC;
     xfs_perag_put(pag);
     return error;
 }
 
 /*
  * Remap the given extent into the file.  The dmap blockcount will be set to
  * the number of blocks that were actually remapped.
  */
 STATIC int
 xfs_reflink_remap_extent(
     struct xfs_inode    *ip,
     struct xfs_bmbt_irec    *dmap,
     xfs_off_t       new_isize)
 {
     struct xfs_bmbt_irec    smap;
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_trans    *tp;
     xfs_off_t       newlen;
     int64_t         qdelta = 0;
     unsigned int        resblks;
     bool            quota_reserved = true;
     bool            smap_real;
     bool            dmap_written = xfs_bmap_is_written_extent(dmap);
     int         iext_delta = 0;
     int         nimaps;
     int         error;
 
     /*
      * Start a rolling transaction to switch the mappings.
      *
      * Adding a written extent to the extent map can cause a bmbt split,
      * and removing a mapped extent from the extent can cause a bmbt split.
      * The two operations cannot both cause a split since they operate on
      * the same index in the bmap btree, so we only need a reservation for
      * one bmbt split if either thing is happening.  However, we haven't
      * locked the inode yet, so we reserve assuming this is the case.
      *
      * The first allocation call tries to reserve enough space to handle
      * mapping dmap into a sparse part of the file plus the bmbt split.  We
      * haven't locked the inode or read the existing mapping yet, so we do
      * not know for sure that we need the space.  This should succeed most
      * of the time.
      *
      * If the first attempt fails, try again but reserving only enough
      * space to handle a bmbt split.  This is the hard minimum requirement,
      * and we revisit quota reservations later when we know more about what
      * we're remapping.
      */
     resblks = XFS_EXTENTADD_SPACE_RES(mp, XFS_DATA_FORK);
     error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write,
             resblks + dmap->br_blockcount, 0, false, &tp);
     if (error == -EDQUOT || error == -ENOSPC) {
         quota_reserved = false;
         error = xfs_trans_alloc_inode(ip, &M_RES(mp)->tr_write,
                 resblks, 0, false, &tp);
     }
     if (error)
         goto out;
 
     /*
      * Read what's currently mapped in the destination file into smap.
      * If smap isn't a hole, we will have to remove it before we can add
      * dmap to the destination file.
      */
     nimaps = 1;
     error = xfs_bmapi_read(ip, dmap->br_startoff, dmap->br_blockcount,
             &smap, &nimaps, 0);
     if (error)
         goto out_cancel;
     ASSERT(nimaps == 1 && smap.br_startoff == dmap->br_startoff);
     smap_real = xfs_bmap_is_real_extent(&smap);
 
     /*
      * We can only remap as many blocks as the smaller of the two extent
      * maps, because we can only remap one extent at a time.
      */
     dmap->br_blockcount = min(dmap->br_blockcount, smap.br_blockcount);
     ASSERT(dmap->br_blockcount == smap.br_blockcount);
 
     trace_xfs_reflink_remap_extent_dest(ip, &smap);
 
     /*
      * Two extents mapped to the same physical block must not have
      * different states; that's filesystem corruption.  Move on to the next
      * extent if they're both holes or both the same physical extent.
      */
     if (dmap->br_startblock == smap.br_startblock) {
         if (dmap->br_state != smap.br_state)
             error = -EFSCORRUPTED;
         goto out_cancel;
     }
 
     /* If both extents are unwritten, leave them alone. */
     if (dmap->br_state == XFS_EXT_UNWRITTEN &&
         smap.br_state == XFS_EXT_UNWRITTEN)
         goto out_cancel;
 
     /* No reflinking if the AG of the dest mapping is low on space. */
     if (dmap_written) {
         error = xfs_reflink_ag_has_free_space(mp,
                 XFS_FSB_TO_AGNO(mp, dmap->br_startblock));
         if (error)
             goto out_cancel;
     }
 
     /*
      * Increase quota reservation if we think the quota block counter for
      * this file could increase.
      *
      * If we are mapping a written extent into the file, we need to have
      * enough quota block count reservation to handle the blocks in that
      * extent.  We log only the delta to the quota block counts, so if the
      * extent we're unmapping also has blocks allocated to it, we don't
      * need a quota reservation for the extent itself.
      *
      * Note that if we're replacing a delalloc reservation with a written
      * extent, we have to take the full quota reservation because removing
      * the delalloc reservation gives the block count back to the quota
      * count.  This is suboptimal, but the VFS flushed the dest range
      * before we started.  That should have removed all the delalloc
      * reservations, but we code defensively.
      *
      * xfs_trans_alloc_inode above already tried to grab an even larger
      * quota reservation, and kicked off a blockgc scan if it couldn't.
      * If we can't get a potentially smaller quota reservation now, we're
      * done.
      */
     if (!quota_reserved && !smap_real && dmap_written) {
         error = xfs_trans_reserve_quota_nblks(tp, ip,
                 dmap->br_blockcount, 0, false);
         if (error)
             goto out_cancel;
     }
 
     if (smap_real)
         ++iext_delta;
 
     if (dmap_written)
         ++iext_delta;
 
     error = xfs_iext_count_may_overflow(ip, XFS_DATA_FORK, iext_delta);
     if (error == -EFBIG)
         error = xfs_iext_count_upgrade(tp, ip, iext_delta);
     if (error)
         goto out_cancel;
 
     if (smap_real) {
         /*
          * If the extent we're unmapping is backed by storage (written
          * or not), unmap the extent and drop its refcount.
          */
         xfs_bmap_unmap_extent(tp, ip, &smap);
         xfs_refcount_decrease_extent(tp, &smap);
         qdelta -= smap.br_blockcount;
     } else if (smap.br_startblock == DELAYSTARTBLOCK) {
         int     done;
 
         /*
          * If the extent we're unmapping is a delalloc reservation,
          * we can use the regular bunmapi function to release the
          * incore state.  Dropping the delalloc reservation takes care
          * of the quota reservation for us.
          */
         error = xfs_bunmapi(NULL, ip, smap.br_startoff,
                 smap.br_blockcount, 0, 1, &done);
         if (error)
             goto out_cancel;
         ASSERT(done);
     }
 
     /*
      * If the extent we're sharing is backed by written storage, increase
      * its refcount and map it into the file.
      */
     if (dmap_written) {
         xfs_refcount_increase_extent(tp, dmap);
         xfs_bmap_map_extent(tp, ip, dmap);
         qdelta += dmap->br_blockcount;
     }
 
     xfs_trans_mod_dquot_byino(tp, ip, XFS_TRANS_DQ_BCOUNT, qdelta);
 
     /* Update dest isize if needed. */
     newlen = XFS_FSB_TO_B(mp, dmap->br_startoff + dmap->br_blockcount);
     newlen = min_t(xfs_off_t, newlen, new_isize);
     if (newlen > i_size_read(VFS_I(ip))) {
         trace_xfs_reflink_update_inode_size(ip, newlen);
         i_size_write(VFS_I(ip), newlen);
         ip->i_disk_size = newlen;
         xfs_trans_log_inode(tp, ip, XFS_ILOG_CORE);
     }
 
     /* Commit everything and unlock. */
     error = xfs_trans_commit(tp);
     goto out_unlock;
 
 out_cancel:
     xfs_trans_cancel(tp);
 out_unlock:
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
 out:
     if (error)
         trace_xfs_reflink_remap_extent_error(ip, error, _RET_IP_);
     return error;
 }
 
 /* Remap a range of one file to the other. */
 int
 xfs_reflink_remap_blocks(
     struct xfs_inode    *src,
     loff_t          pos_in,
     struct xfs_inode    *dest,
     loff_t          pos_out,
     loff_t          remap_len,
     loff_t          *remapped)
 {
     struct xfs_bmbt_irec    imap;
     struct xfs_mount    *mp = src->i_mount;
     xfs_fileoff_t       srcoff = XFS_B_TO_FSBT(mp, pos_in);
     xfs_fileoff_t       destoff = XFS_B_TO_FSBT(mp, pos_out);
     xfs_filblks_t       len;
     xfs_filblks_t       remapped_len = 0;
     xfs_off_t       new_isize = pos_out + remap_len;
     int         nimaps;
     int         error = 0;
 
     len = min_t(xfs_filblks_t, XFS_B_TO_FSB(mp, remap_len),
             XFS_MAX_FILEOFF);
 
     trace_xfs_reflink_remap_blocks(src, srcoff, len, dest, destoff);
 
     while (len > 0) {
         unsigned int    lock_mode;
 
         /* Read extent from the source file */
         nimaps = 1;
         lock_mode = xfs_ilock_data_map_shared(src);
         error = xfs_bmapi_read(src, srcoff, len, &imap, &nimaps, 0);
         xfs_iunlock(src, lock_mode);
         if (error)
             break;
         /*
          * The caller supposedly flushed all dirty pages in the source
          * file range, which means that writeback should have allocated
          * or deleted all delalloc reservations in that range.  If we
          * find one, that's a good sign that something is seriously
          * wrong here.
          */
         ASSERT(nimaps == 1 && imap.br_startoff == srcoff);
         if (imap.br_startblock == DELAYSTARTBLOCK) {
             ASSERT(imap.br_startblock != DELAYSTARTBLOCK);
             error = -EFSCORRUPTED;
             break;
         }
 
         trace_xfs_reflink_remap_extent_src(src, &imap);
 
         /* Remap into the destination file at the given offset. */
         imap.br_startoff = destoff;
         error = xfs_reflink_remap_extent(dest, &imap, new_isize);
         if (error)
             break;
 
         if (fatal_signal_pending(current)) {
             error = -EINTR;
             break;
         }
 
         /* Advance drange/srange */
         srcoff += imap.br_blockcount;
         destoff += imap.br_blockcount;
         len -= imap.br_blockcount;
         remapped_len += imap.br_blockcount;
     }
 
     if (error)
         trace_xfs_reflink_remap_blocks_error(dest, error, _RET_IP_);
     *remapped = min_t(loff_t, remap_len,
               XFS_FSB_TO_B(src->i_mount, remapped_len));
     return error;
 }
 
 /*
  * If we're reflinking to a point past the destination file's EOF, we must
  * zero any speculative post-EOF preallocations that sit between the old EOF
  * and the destination file offset.
  */
 static int
 xfs_reflink_zero_posteof(
     struct xfs_inode    *ip,
     loff_t          pos)
 {
     loff_t          isize = i_size_read(VFS_I(ip));
 
     if (pos <= isize)
         return 0;
 
     trace_xfs_zero_eof(ip, isize, pos - isize);
     return xfs_zero_range(ip, isize, pos - isize, NULL);
 }
 
 /*
  * Prepare two files for range cloning.  Upon a successful return both inodes
  * will have the iolock and mmaplock held, the page cache of the out file will
  * be truncated, and any leases on the out file will have been broken.  This
  * function borrows heavily from xfs_file_aio_write_checks.
  *
  * The VFS allows partial EOF blocks to "match" for dedupe even though it hasn't
  * checked that the bytes beyond EOF physically match. Hence we cannot use the
  * EOF block in the source dedupe range because it's not a complete block match,
  * hence can introduce a corruption into the file that has it's block replaced.
  *
  * In similar fashion, the VFS file cloning also allows partial EOF blocks to be
  * "block aligned" for the purposes of cloning entire files.  However, if the
  * source file range includes the EOF block and it lands within the existing EOF
  * of the destination file, then we can expose stale data from beyond the source
  * file EOF in the destination file.
  *
  * XFS doesn't support partial block sharing, so in both cases we have check
  * these cases ourselves. For dedupe, we can simply round the length to dedupe
  * down to the previous whole block and ignore the partial EOF block. While this
  * means we can't dedupe the last block of a file, this is an acceptible
  * tradeoff for simplicity on implementation.
  *
  * For cloning, we want to share the partial EOF block if it is also the new EOF
  * block of the destination file. If the partial EOF block lies inside the
  * existing destination EOF, then we have to abort the clone to avoid exposing
  * stale data in the destination file. Hence we reject these clone attempts with
  * -EINVAL in this case.
  */
 int
 xfs_reflink_remap_prep(
     struct file     *file_in,
     loff_t          pos_in,
     struct file     *file_out,
     loff_t          pos_out,
     loff_t          *len,
     unsigned int        remap_flags)
 {
     struct inode        *inode_in = file_inode(file_in);
     struct xfs_inode    *src = XFS_I(inode_in);
     struct inode        *inode_out = file_inode(file_out);
     struct xfs_inode    *dest = XFS_I(inode_out);
     int         ret;
 
     /* Lock both files against IO */
     ret = xfs_ilock2_io_mmap(src, dest);
     if (ret)
         return ret;
 
     /* Check file eligibility and prepare for block sharing. */
     ret = -EINVAL;
     /* Don't reflink realtime inodes */
     if (XFS_IS_REALTIME_INODE(src) || XFS_IS_REALTIME_INODE(dest))
         goto out_unlock;
 
     /* Don't share DAX file data with non-DAX file. */
     if (IS_DAX(inode_in) != IS_DAX(inode_out))
         goto out_unlock;
 
     if (!IS_DAX(inode_in))
         ret = generic_remap_file_range_prep(file_in, pos_in, file_out,
                 pos_out, len, remap_flags);
     else
         ret = dax_remap_file_range_prep(file_in, pos_in, file_out,
                 pos_out, len, remap_flags, &xfs_read_iomap_ops);
     if (ret || *len == 0)
         goto out_unlock;
 
     /* Attach dquots to dest inode before changing block map */
     ret = xfs_qm_dqattach(dest);
     if (ret)
         goto out_unlock;
 
     /*
      * Zero existing post-eof speculative preallocations in the destination
      * file.
      */
     ret = xfs_reflink_zero_posteof(dest, pos_out);
     if (ret)
         goto out_unlock;
 
     /* Set flags and remap blocks. */
     ret = xfs_reflink_set_inode_flag(src, dest);
     if (ret)
         goto out_unlock;
 
     /*
      * If pos_out > EOF, we may have dirtied blocks between EOF and
      * pos_out. In that case, we need to extend the flush and unmap to cover
      * from EOF to the end of the copy length.
      */
     if (pos_out > XFS_ISIZE(dest)) {
         loff_t  flen = *len + (pos_out - XFS_ISIZE(dest));
         ret = xfs_flush_unmap_range(dest, XFS_ISIZE(dest), flen);
     } else {
         ret = xfs_flush_unmap_range(dest, pos_out, *len);
     }
     if (ret)
         goto out_unlock;
 
     return 0;
 out_unlock:
     xfs_iunlock2_io_mmap(src, dest);
     return ret;
 }
 
 /* Does this inode need the reflink flag? */
 int
 xfs_reflink_inode_has_shared_extents(
     struct xfs_trans        *tp,
     struct xfs_inode        *ip,
     bool                *has_shared)
 {
     struct xfs_bmbt_irec        got;
     struct xfs_mount        *mp = ip->i_mount;
     struct xfs_ifork        *ifp;
     struct xfs_iext_cursor      icur;
     bool                found;
     int             error;
 
     ifp = xfs_ifork_ptr(ip, XFS_DATA_FORK);
     error = xfs_iread_extents(tp, ip, XFS_DATA_FORK);
     if (error)
         return error;
 
     *has_shared = false;
     found = xfs_iext_lookup_extent(ip, ifp, 0, &icur, &got);
     while (found) {
         struct xfs_perag    *pag;
         xfs_agblock_t       agbno;
         xfs_extlen_t        aglen;
         xfs_agblock_t       rbno;
         xfs_extlen_t        rlen;
 
         if (isnullstartblock(got.br_startblock) ||
             got.br_state != XFS_EXT_NORM)
             goto next;
 
         pag = xfs_perag_get(mp, XFS_FSB_TO_AGNO(mp, got.br_startblock));
         agbno = XFS_FSB_TO_AGBNO(mp, got.br_startblock);
         aglen = got.br_blockcount;
         error = xfs_reflink_find_shared(pag, tp, agbno, aglen,
                 &rbno, &rlen, false);
         xfs_perag_put(pag);
         if (error)
             return error;
 
         /* Is there still a shared block here? */
         if (rbno != NULLAGBLOCK) {
             *has_shared = true;
             return 0;
         }
 next:
         found = xfs_iext_next_extent(ifp, &icur, &got);
     }
 
     return 0;
 }
 
 /*
  * Clear the inode reflink flag if there are no shared extents.
  *
  * The caller is responsible for joining the inode to the transaction passed in.
  * The inode will be joined to the transaction that is returned to the caller.
  */
 int
 xfs_reflink_clear_inode_flag(
     struct xfs_inode    *ip,
     struct xfs_trans    **tpp)
 {
     bool            needs_flag;
     int         error = 0;
 
     ASSERT(xfs_is_reflink_inode(ip));
 
     error = xfs_reflink_inode_has_shared_extents(*tpp, ip, &needs_flag);
     if (error || needs_flag)
         return error;
 
     /*
      * We didn't find any shared blocks so turn off the reflink flag.
      * First, get rid of any leftover CoW mappings.
      */
     error = xfs_reflink_cancel_cow_blocks(ip, tpp, 0, XFS_MAX_FILEOFF,
             true);
     if (error)
         return error;
 
     /* Clear the inode flag. */
     trace_xfs_reflink_unset_inode_flag(ip);
     ip->i_diflags2 &= ~XFS_DIFLAG2_REFLINK;
     xfs_inode_clear_cowblocks_tag(ip);
     xfs_trans_log_inode(*tpp, ip, XFS_ILOG_CORE);
 
     return error;
 }
 
 /*
  * Clear the inode reflink flag if there are no shared extents and the size
  * hasn't changed.
  */
 STATIC int
 xfs_reflink_try_clear_inode_flag(
     struct xfs_inode    *ip)
 {
     struct xfs_mount    *mp = ip->i_mount;
     struct xfs_trans    *tp;
     int         error = 0;
 
     /* Start a rolling transaction to remove the mappings */
     error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, 0, 0, 0, &tp);
     if (error)
         return error;
 
     xfs_ilock(ip, XFS_ILOCK_EXCL);
     xfs_trans_ijoin(tp, ip, 0);
 
     error = xfs_reflink_clear_inode_flag(ip, &tp);
     if (error)
         goto cancel;
 
     error = xfs_trans_commit(tp);
     if (error)
         goto out;
 
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     return 0;
 cancel:
     xfs_trans_cancel(tp);
 out:
     xfs_iunlock(ip, XFS_ILOCK_EXCL);
     return error;
 }
 
 /*
  * Pre-COW all shared blocks within a given byte range of a file and turn off
  * the reflink flag if we unshare all of the file's blocks.
  */
 int
 xfs_reflink_unshare(
     struct xfs_inode    *ip,
     xfs_off_t       offset,
     xfs_off_t       len)
 {
     struct inode        *inode = VFS_I(ip);
     int         error;
 
     if (!xfs_is_reflink_inode(ip))
         return 0;
 
     trace_xfs_reflink_unshare(ip, offset, len);
 
     inode_dio_wait(inode);
 
     error = iomap_file_unshare(inode, offset, len,
             &xfs_buffered_write_iomap_ops);
     if (error)
         goto out;
 
     error = filemap_write_and_wait_range(inode->i_mapping, offset,
             offset + len - 1);
     if (error)
         goto out;
 
     /* Turn off the reflink flag if possible. */
     error = xfs_reflink_try_clear_inode_flag(ip);
     if (error)
         goto out;
     return 0;
 
 out:
     trace_xfs_reflink_unshare_error(ip, error, _RET_IP_);
     return error;
 }

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